Blood IMMUNOBIOLOGY

A role for interleukin-12/23 in the maturation of human natural killer and CD56+ T cells in vivo

2008-05-08

Natural killer (NK) cells have been originally defined by their "naturally occurring" effector function. However, only a fraction of human NK cells is reactive toward a panel of prototypical tumor cell targets in vitro, both for the production of interferon- (IFN-) and for their cytotoxic response. In patients with IL12RB1 mutations that lead to a complete IL-12Rβ1 deficiency, the size of this naturally reactive NK cell subset is diminished, in particular for the IFN- production. Similar data were obtained from a patient with a complete deficit in IL-12p40. In addition, the size of the subset of effector memory T cells expressing CD56 was severely decreased in IL-12Rβ1– and IL-12p40–deficient patients. Human NK cells thus require in vivo priming with IL-12/23 to acquire their full spectrum of functional reactivity, while T cells are dependent upon IL-12/23 signals for the differentiation and/or the maintenance of CD56⁺ effector memory T cells. The susceptibility of IL-12/23 axis–deficient patients to Mycobacterium and Salmonella infections in combination with the absence of mycobacteriosis or salmonellosis in the rare cases of human NK cell deficiencies point to a role for CD56⁺ T cells in the control of these infections in humans.

The proapoptotic and antimitogenic protein p66SHC acts as a negative regulator of lymphocyte activation and autoimmunity

2008-05-08

The ShcA locus encodes 3 protein isoforms that differ in tissue specificity, subcellular localization, and function. Among these, p66Shc inhibits TCR coupling to the Ras/MAPK pathway and primes T cells to undergo apoptotic death. We have investigated the outcome of p66Shc deficiency on lymphocyte development and homeostasis. We show that p66Shc^–/– mice develop an age-related lupus-like autoimmune disease characterized by spontaneous peripheral T- and B-cell activation and proliferation, autoantibody production, and immune complex deposition in kidney and skin, resulting in autoimmune glomerulonephritis and alopecia. p66Shc^–/– lymphocytes display enhanced proliferation in response to antigen receptor engagement in vitro and more robust immune responses both to vaccination and to allergen sensitization in vivo. The data identify p66Shc as a negative regulator of lymphocyte activation and show that loss of this protein results in breaking of immunologic tolerance and development of systemic autoimmunity.

Platelet-mediated modulation of adaptive immunity: unique delivery of CD154 signal by platelet-derived membrane vesicles

2008-05-08

Although mounting evidence indicates that platelets participate in the modulation of both innate and adaptive immunity, the mechanisms by which platelets exert these effects have not been clearly defined. The study reported herein uses a previously documented adoptive transfer model to investigate the ability of platelet-derived membrane vesicles to communicate activation signals to the B-cell compartment. The findings demonstrate for the first time that platelet-derived membrane vesicles are sufficient to deliver CD154 to stimulate antigen-specific IgG production and modulate germinal center formation through cooperation with responses elicited by CD4⁺ T cells. The data are consistent with the hypothesis that platelets modulate inflammation and adaptive immunity at sites distant from the location of activation and that platelet-derived membrane vesicles are sufficient to mediate the effect.

IgG regulates the CD1 expression profile and lipid antigen-presenting function in human dendritic cells via Fc{gamma}RIIa

2008-05-08

Dendritic cells (DCs) process and present bacterial and endogenous lipid antigens in complex with CD1 molecules to T cells and invariant natural killer T (NKT) cells. However, different types of DCs, such as blood myeloid DCs and skin Langerhans cells, exhibit distinct patterns of CD1a, CD1b, CD1c, and CD1d expression. The regulation of such differences is incompletely understood. Here, we initially observed that monocyte-derived DCs cultured in an immunoglobulin-rich milieu expressed CD1d but not CD1a, CD1b, and CD1c, whereas DCs cultured in the presence of low levels of immunoglobulins had an opposite CD1 profile. Based on this, we tested the possibility that immunoglobulins play a central role in determining these differences. IgG depletion and intravenous immunoglobulin (IVIg) add-in experiments strongly supported a role for IgG in directing the CD1 expression profile. Blocking experiments indicated that this effect was mediated by FcRIIa (CD32a), and quantitative polymerase chain reaction data demonstrated that regulation of the CD1 profile occurred at the gene expression level. Finally, the ability of DCs to activate CD1-restricted NKT cells and T cells was determined by this regulatory effect of IgG. Our data demonstrate an important role for FcRIIa in regulating the CD1 antigen presentation machinery of human DCs.

High frequency of CD4+FoxP3+ cells in HTLV-1 infection: inverse correlation with HTLV-1-specific CTL response

Toulza, F., Heaps, A., Tanaka, Y., Taylor, G. P., Bangham, C. R. M. — 2008-05-08

Evidence from population genetics, gene expression microarrays, and assays of ex vivo T-cell function indicates that the cytotoxic T lymphocyte (CTL) response to human T-lymphotropic virus type 1 (HTLV-1) controls the level of HTLV-1 expression and the proviral load. The rate at which CTLs kill autologous HTLV-1–infected lymphocytes differs significantly among infected people, but the reasons for such variation are unknown. Here, we demonstrate a strong negative cor-relation between the frequency of CD4⁺FoxP3⁺ Tax^– regulatory T cells (T_regs) in the circulation and the rate of CTL-mediated lysis of autologous HTLV-1–infected cells ex vivo. We propose that the frequency of CD4⁺FoxP3⁺ Tax^– T_regs is one of the chief determinants of the efficiency of T cell–mediated immune control of HTLV-1.

Epigenetic control of MHC class II expression in tumor-associated macrophages by decoy receptor 3

2008-05-08

Decoy receptor 3 (DcR3) is a member of the TNF receptor superfamily and is up-regulated in tumors originating from a diversity of lineages. DcR3 is capable of promoting angiogenesis, inducing dendritic cell apoptosis, and modulating macrophage differentiation. Since tumor-associated macrophages (TAMs) are the major infiltrating leukocytes in most malignant tumors, we used microarray technology to investigate whether DcR3 contributes to the development of TAMs. Among the DcR3-modulated genes expressed by TAMs, those that encode proteins involved in MHC class II (MHC-II)–dependent antigen presentation were down-regulated substantially, together with the master regulator of MHC-II expression (the class II transactivator, CIITA). The ERK- and JNK-induced deacetylation of histones associated with the CIITA promoters was responsible for DcR3-mediated down-regulation of MHC-II expression. Furthermore, the expression level of DcR3 in cancer cells correlated inversely with HLA-DR levels on TAMs and with the overall survival time of pancreatic cancer patients. The role of DcR3 in the development of TAMs was further confirmed using transgenic mice overexpressing DcR3. This elucidates the molecular mechanism of impaired MHC-II–mediated antigen presentation by TAMs, and raises the possibility that subversion of TAM-induced immunosuppression via inhibition of DcR3 expression might represent a target for the design of new therapeutics.

Unprecedented diversity of genotypic revertants in lymphocytes of a patient with Wiskott-Aldrich syndrome

2008-05-08

Spontaneous somatic reversions of inherited mutations are poorly understood phenomena that are thought to occur uncommonly in a variety of genetic disorders. When molecularly characterized, revertant cells have rarely exhibited more than one revertant genotype per patient. We analyzed individual allospecific T-cell clones derived from a Wiskott-Aldrich syndrome (WAS) patient identified by flow cytometry to have 10% to 15% revertant, WAS protein–expressing lymphocytes in his blood. Genotypic analysis of the clones revealed a remarkable diversity of deletions and base substitutions resulting in at least 34 different revertant genotypes that restored expression of WASp. A large fraction of these revertant genotypes were also identified in primary T cells purified from peripheral blood. These data suggest that the use of sensitive methods may reveal the presence of wide arrays of individual genotypic revertants in WAS patients and offer opportunities for further understanding of their occurrence.

Proteasome-dependent autoregulation of Bruton tyrosine kinase (Btk) promoter via NF-{kappa}B

2008-04-25

Bruton tyrosine kinase (Btk) is critical for B-cell development. Btk regulates a plethora of signaling proteins, among them nuclear factor-[]B (NF-B). Activation of NF-B is a hallmark of B cells, and NF-B signaling is severely compromised in Btk deficiency. We here present strong evidence indicating that NF-B is required for efficient transcription of the Btk gene. First, we found that proteasome blockers and inhibitors of NF-B signaling suppress Btk transcription and intracellular expression. Similar to Btk, proteasome inhibitors also reduced the expression of other members of this family of kinases, Itk, Bmx, and Tec. Second, 2 functional NF-B–binding sites were found in the Btk promoter. Moreover, in live mice, by hydrodynamic transfection, we show that bortezomib (a blocker of proteasomes and NF-B signaling), as well as NF-B binding sequence-oligonucleotide decoys block Btk transcription. We also demonstrate that Btk induces NF-B activity in mice. Collectively, we show that Btk uses a positive autoregulatory feedback mechanism to stimulate transcription from its own promoter via NF-B.

A critical role of Rap1b in B-cell trafficking and marginal zone B-cell development

2008-04-25

B-cell development is orchestrated by complex signaling networks. Rap1 is a member of the Ras superfamily of small GTP-binding proteins and has 2 isoforms, Rap1a and Rap1b. Although Rap1 has been suggested to have an important role in a variety of cellular processes, no direct evidence demonstrates a role for Rap1 in B-cell biology. In this study, we found that Rap1b was the dominant isoform of Rap1 in B cells. We discovered that Rap1b deficiency in mice barely affected early development of B cells but markedly reduced marginal zone (MZ) B cells in the spleen and mature B cells in peripheral and mucosal lymph nodes. Rap1b-deficient B cells displayed normal survival and proliferation in vivo and in vitro. However, Rap1b-deficient B cells had impaired adhesion and reduced chemotaxis in vitro, and lessened homing to lymph nodes in vivo. Furthermore, we found that Rap1b deficiency had no marked effect on LPS-, BCR-, or SDF-1–induced activation of mitogen-activated protein kinases and AKT but clearly impaired SDF-1–mediated activation of Pyk-2, a key regulator of SDF-1–mediated B-cell migration. Thus, we have discovered a critical and distinct role of Rap1b in mature B-cell trafficking and development of MZ B cells.

Phagocytosis and intracellular killing of MD-2 opsonized Gram-negative bacteria depend on TLR4 signaling

2008-04-25

Both Toll-like receptor 4 (TLR4)– and MD-2–deficient mice succumb to otherwise nonfatal Gram-negative bacteria inocula, demonstrating the pivotal role played by these proteins in antibacterial defense in mammals. MD-2 is a soluble endogenous ligand for TLR4 and a receptor for lipopolysaccharide (LPS). LPS-bound MD-2 transmits an activating signal onto TLR4. In this report, we show that both recombinant and endogenous soluble MD-2 bind tightly to the surface of live Gram-negative bacteria. As a consequence, MD-2 enhances cellular activation, bacterial internalization, and intracellular killing, all in a TLR4-dependent manner. The enhanced internalization of MD-2–coated bacteria was not observed in macrophages expressing Lps^d, a signaling-incompetent mutant form of TLR4, suggesting that the enhanced phagocytosis observed is dependent on signal transduction. The data confirm the notion that soluble MD-2 is a genuine opsonin that enhances proinflammatory opsonophagocytosis by bridging live Gram-negative bacteria to the LPS transducing complex. The presented results extend our understanding of the role of the TLR4/MD-2 signaling axis in bacterial recognition by phagocytes.

Sphingosine 1-phosphate-dependent trafficking of peritoneal B cells requires functional NF{kappa}B-inducing kinase in stromal cells

Kunisawa, J., Gohda, M., Kurashima, Y., Ishikawa, I., Higuchi, M., Kiyono, H. — 2008-04-25

We previously reported that sphingosine 1-phosphate (S1P) regulates peritoneal B-cell trafficking and subsequent intestinal IgA production, but the underlying mechanisms remain obscure. We demonstrate here that nuclear factor B–inducing kinase (NIK) is involved in the regulation of S1P-mediated trafficking of peritoneal B cells. Although peritoneal B cells from NIK-mutated alymphoplasia (aly) mice expressed type 1 S1P receptor (S1P₁) at comparable levels and demonstrated normal migration toward S1P, aly peritoneal B cells showed decreased sensitivity to FTY720, an S1P₁ modulator. NIK-mutated stromal cells showed decreased levels of adhesion molecules (VCAM-1 and ICAM-1) and increased CXCL13 expressions, leading to impaired ability to support S1P-mediated emigration, but not immigration, of peritoneal B cells. Therefore, aly peritoneal B cells exhibited normal S1P-mediated peritoneal B-cell trafficking from peritoneum to intestine for IgA production when they were transferred into severe combined immunodeficient or wild-type mice. However, S1P-mediated emigration of wild-type B cells from the aly peritoneal cavity was impaired without affecting their immigration from the blood. Further, transfer of wild-type stromal cells into the peritoneum restored S1P-mediated trafficking of aly peritoneal B cells. These findings suggest that NIK in stromal cells has a specific role in the regulation of S1P-mediated trafficking of peritoneal B cells.

The human spleen is a major reservoir for long-lived vaccinia virus-specific memory B cells

2008-04-25

The fact that you can vaccinate a child at 5 years of age and find lymphoid B cells and antibodies specific for this vaccination 70 years later remains an immunologic enigma. It has never been determined how these long-lived memory B cells are maintained and whether they are protected by storage in a special niche. We report that, whereas blood and spleen compartments present similar frequencies of IgG⁺ cells, antismallpox memory B cells are specifically enriched in the spleen where they account for 0.24% of all IgG⁺ cells (ie, 10-20 million cells) more than 30 years after vaccination. They represent, in contrast, only 0.07% of circulating IgG⁺ B cells in blood (ie, 50-100 000 cells). An analysis of patients either splenectomized or rituximab-treated confirmed that the spleen is a major reservoir for long-lived memory B cells. No significant correlation was observed between the abundance of these cells in blood and serum titers of antivaccinia virus antibodies in this study, including in the contrasted cases of B cell– depleting treatments. Altogether, these data provide evidence that in humans, the two arms of B-cell memory—long-lived memory B cells and plasma cells—have specific anatomic distributions—spleen and bone marrow—and homeostatic regulation.

Efficient HIV-1 transmission from macrophages to T cells across transient virological synapses

Groot, F., Welsch, S., Sattentau, Q. J. — 2008-04-25

Macrophages are reservoirs of HIV-1 infection, proposed to transmit virus to CD4⁺ T cells, the primary target of the virus. Here we report that human monocyte-derived macrophages (MDMs) rapidly spread HIV-1 to autologous CD4⁺ T cells resulting in productive infection. Transmission takes place across transient adhesive contacts between T cells and MDMs, which have the features of a virological synapse including copolarization of CD4 on the T cell with HIV-1 Gag and Env on the macrophage. We propose that an infected MDM can infect at least one T cell every 6 hours. Since HIV-1–infected macrophages can survive for many weeks, these results highlight the central role played by macrophages in HIV-1 infection and pathogenesis.

PI5KI-dependent signals are critical regulators of the cytolytic secretory pathway

2008-04-08

Although membrane phospholipid phosphatidylinositol-4,5bisphosphate (PIP2) plays a key role as signaling intermediate and coordinator of actin dynamics and vesicle trafficking, it remains completely unknown its involvement in the activation of cytolytic machinery. By live confocal imaging of primary human natural killer (NK) cells expressing the chimeric protein GFP-PH, we observed, during effector-target cell interaction, the consumption of a preexisting PIP2 pool, which is critically required for the activation of cytolytic machinery. We identified type I phosphatidylinositol-4-phosphate-5-kinase (PI5KI) and isoforms as the enzymes responsible for PIP2 synthesis in NK cells. By hRNA-driven gene silencing, we observed that both enzymes are required for the proper activation of NK cytotoxicity and for inositol-1,4,5-trisphosphate (IP3) generation on receptor stimulation. In an attempt to elucidate the specific step controlled by PI5KIs, we found that lytic granule secretion but not polarization resulted in impaired PI5KI- and PI5KI-silenced cells. Our findings delineate a novel mechanism implicating PI5KI and PI5KI isoforms in the synthesis of PIP2 pools critically required for IP3-dependent Ca²⁺ response and lytic granule release.

Colocalization of the IL-12 receptor and Fc{gamma}RIIIa to natural killer cell lipid rafts leads to activation of ERK and enhanced production of interferon-{gamma}

2008-04-08

Natural killer (NK) cells express an activating receptor for the Fc portion of IgG (FcRIIIa) that mediates interferon (IFN)– production in response to antibody (Ab)–coated targets. We have previously demonstrated that NK cells activated with interleukin-12 (IL-12) in the presence of immobilized IgG secrete 10-fold or more higher levels of IFN- as compared with stimulation with either agent alone. We examined the intracellular signaling pathways responsible for this synergistic IFN- production. NK cells costimulated via the FcR and the IL-12 receptor (IL-12R) exhibited enhanced levels of activated STAT4 and Syk as compared with NK cells stimulated through either receptor alone. Extracellular signal–regulated kinase (ERK) was also synergistically activated under these conditions. Studies with specific chemical inhibitors revealed that the activation of ERK was dependent on the activation of PI3-K, whose activation was dependent on Syk, and that sequential activation of these molecules was required for NK cell IFN- production in response to FcR and IL-12 stimulation. Retroviral transfection of ERK1 into primary human NK cells substantially increased IFN- production in response to immobilized IgG and IL-12, while transfection of human NK cells with a dominant-negative ERK1 abrogated IFN- production. Confocal microscopy and cellular fractionation experiments revealed that FcRIIIa and the IL-12R colocalized to areas of lipid raft microdomains in response to costimulation with IgG and IL-12. Chemical disruption of lipid rafts inhibited ERK signaling in response to costimulation and significantly inhibited IFN- production. These data suggest that dual recruitment of FcRIIIa and the IL-12R to lipid raft microdomains allows for enhanced activation of downstream signaling events that lead to IFN- production.

Novel biphasic role for lymphocytes revealed during resolving inflammation

2008-04-08

Acute inflammation is traditionally described as the influx of polymorphonuclear leukocytes (PMNs) followed by monocyte-derived macrophages, leading to resolution. This is a classic view, and despite subpopulations of lymphocytes possessing innate immune-regulatory properties, seldom is their role in acute inflammation and its resolution discussed. To redress this we show, using lymphocyte-deficient RAG1^–/– mice, that peritoneal T/B lymphocytes control PMN trafficking by regulating cytokine synthesis. Once inflammation ensues in normal mice, lymphocytes disappear in response to DP1 receptor activation by prostaglandin D₂. However, upon resolution, lymphocytes repopulate the cavity comprising B1, natural killer (NK), / T, CD4⁺/CD25⁺, and B2 cells. Repopulating lymphocytes are dispensable for resolution, as inflammation in RAG1^–/– and wild-type mice resolve uniformly. However, repopulating lymphocytes are critical for modulating responses to superinfection. Thus, in chronic granulomatous disease using gp91phox^–/– mice, not only is resolution delayed compared with wild-type, but there is a failure of lymphocyte re-appearance predisposing to exaggerated immune responses upon secondary challenge that is rescued by resolution-phase lymphocytes. In conclusion, as lymphocyte repopulation is also evident in human peritonitis, we hereby describe a transition in T/B cells from acute inflammation to resolution, with a central role in modulating the severity of early onset and orchestrating responses to secondary infection.

Distinct roles of sphingosine kinases 1 and 2 in human mast-cell functions

2008-04-08

Sphingosine-1-phosphate (S1P) is now emerging as a potent lipid mediator produced by mast cells that contributes to inflammatory and allergic responses. In contrast to its weak effect on degranulation of murine mast cells, S1P potently induced degranulation of the human LAD2 mast-cell line and cord blood–derived human mast cells (hMCs). S1P also stimulated production and secretion of cytokines, TNF- and IL-6, and markedly enhanced secretion of a chemokine, CCL2/MCP-1, important modulators of inflammation. S1P is produced in mast cells by the 2 sphingosine kinases, SphK1 and SphK2. SphK1 but not SphK2 plays a critical role in IgE/Ag-induced degranulation, migration toward antigen, and CCL2 secretion from hMCs, as determined by specifically down-regulating their expression. However, both isoenzymes were required for efficient TNF- secretion. Taken together, our data suggest that differential formation of S1P by SphK1 and SphK2 has distinct and important actions in hMCs.

Unique subset of natural killer cells develops from progenitors in lymph node

Veinotte, L. L., Halim, T. Y. F., Takei, F. — 2008-04-08

Natural killer (NK) cells have been thought to develop from committed progenitors in the bone marrow. However, a novel pathway of thymus-dependent NK-cell development that produces a unique subset of NK cells expressing CD127 has recently been reported. We now have identified 2 populations of NK progenitors, one in the thymus and the other in the lymph node (LN). Immature double-negative 2 (CD4^–CD8^–CD44⁺CD25⁺) thymocytes have potential to produce NK cells with rearranged T-cell receptor genes (Tcr⁺) in vitro. Tcr⁺ NK cells are rare in spleen but relatively abundant in the thymus and LN. Approximately 20% of LN NK cells are Tcr⁺, and they are found at similar levels in both CD127⁺ and CD127^– subsets. Moreover, a subpopulation of LN cells resembling immature thymocytes differentiates into Tcr⁺ NK cells in vitro and also repopulates the NK compartment in lymphopenic mice. Athymic mice lack the LN NK progenitors expressing CD127 as well as Tcr⁺ NK cells. These results suggest that Tcr⁺ NK cells may be generated from unique progenitors in the thymus as well as in the LN.

Altered intracellular and extracellular signaling leads to impaired T-cell functions in ADA-SCID patients

2008-04-08

Mutations in the adenosine deaminase (ADA) gene are responsible for a form of severe combined immunodeficiency (SCID) caused by the lymphotoxic accumulation of ADA substrates, adenosine and 2'-deoxy-adenosine. The molecular mechanisms underlying T-cell dysfunction in humans remain to be elucidated. Here, we show that CD4⁺ T cells from ADA-SCID patients have severely compromised TCR/CD28-driven proliferation and cytokine production, both at the transcriptional and protein levels. Such an impairment is associated with an intrinsically reduced ZAP-70 phosphorylation, Ca²⁺ flux, and ERK1/2 signaling and to defective transcriptional events linked to CREB and NF-B. Moreover, exposure to 2'-deoxy-adenosine results in a stronger inhibition of T-cell activation, mediated by the aberrant A_2A adenosine receptor signaling engagement and PKA hyperactivation, or in a direct apoptotic effect at higher doses. Conversely, in T cells isolated from patients after gene therapy with retrovirally transduced hematopoietic stem/progenitor cells, the biochemical events after TCR triggering occur properly, leading to restored effector functions and normal sensitivity to apoptosis. Overall, our findings provide a better understanding of the pathogenesis of the immune defects associated with an altered purine metabolism and confirm that ADA gene transfer is an efficacious treatment for ADA-SCID. The trials in this study are enrolled at www.ClinicalTrials.gov as #NCT00598481 and #NCT0059978.

NSOM/QD-based nanoscale immunofluorescence imaging of antigen-specific T-cell receptor responses during an in vivo clonal V{gamma}2V{delta}2 T-cell expansion

Chen, Y., Shao, L., Ali, Z., Cai, J., Chen, Z. W. — 2008-04-08

Nanoscale imaging of an in vivo antigen-specific T-cell immune response has not been reported. Here, the combined near-field scanning optical microscopy– and fluorescent quantum dot–based nanotechnology was used to perform immunofluorescence imaging of antigen-specific T-cell receptor (TCR) response in an in vivo model of clonal T-cell expansion. The near-field scanning optical microscopy/quantum dot system provided a best-optical-resolution (<50 nm) nano-scale imaging of V2V2 TCR on the membrane of nonstimulated V2V2 T cells. Before Ag-induced clonal expansion, these nonstimulating V2V2 TCRs appeared to be distributed differently from their β TCR counterparts on the cell surface. Surprisingly, V2V2 TCR nanoclusters not only were formed but also sustained on the membrane during an in vivo clonal expansion of V2V2 T cells after phosphoantigen treatment or phosphoantigen plus mycobacterial infection. The TCR nanoclusters could array to form nanodomains or microdomains on the membrane of clonally expanded V2V2 T cells. Interestingly, expanded V2V2 T cells bearing TCR nanoclusters or nanodomains were able to rerecognize phosphoantigen and to exert better effector function. These studies provided nanoscale insight into the in vivo T-cell immune response.

Identification of discrete tumor-induced myeloid-derived suppressor cell subpopulations with distinct T cell-suppressive activity

2008-04-08

The induction of CD11b⁺Gr-1⁺ myeloid-derived suppressor cells (MDSCs) is an important immune-evading mechanism used by tumors. However, the exact nature and function of MDSCs remain elusive, especially because they constitute a heterogeneous population that has not yet been clearly defined. Here, we identified 2 distinct MDSC subfractions with clear morphologic, molecular, and functional differences. These fractions consisted of either mononuclear cells (MO-MDSCs), resembling inflammatory monocytes, or low-density polymorphonuclear cells (PMN-MDSCs), akin to immature neutrophils. Interestingly, both MO-MDSCs and PMN-MDSCs suppressed antigen-specific T-cell responses, albeit using distinct effector molecules and signaling pathways. Blocking IFN- or disrupting STAT1 partially impaired suppression by MO-MDSCs, for which nitric oxide (NO) was one of the mediators. In contrast, while IFN- was strictly required for the suppressor function of PMN-MDSCs, this did not rely on STAT1 signaling or NO production. Finally, MO-MDSCs were shown to be potential precursors of highly antiproliferative NO-producing mature macrophages. However, distinct tumors differentially regulated this inherent MO-MDSC differentiation program, indicating that this phenomenon was tumor driven. Overall, our data refine tumor-induced MDSC functions by uncovering mechanistically distinct MDSC subpopulations, potentially relevant for MDSC-targeted therapies.

Targeting DCIR on human plasmacytoid dendritic cells results in antigen presentation and inhibits IFN-{alpha} production

2008-04-08

C-type lectin receptors (CLRs) fulfill multiple functions within the immune system by recognition of carbohydrate moieties on foreign or (altered) self-structures. CLRs on myeloid dendritic cells (DCs) have been well characterized as pattern-recognition receptors (PRRs) combining ligand internalization with complex signaling events. Much less is known about CLR expression and function in human plasmacytoid DCs (pDCs), the major type I interferon (IFN) producers. In this study, we demonstrate that, next to the CLR BDCA-2, human pDCs express DC immunoreceptor (DCIR), a CLR with putative immune-inhibitory function, but not dectin-1, mannose receptor, or DC-specific ICAM-3–grabbing nonintegrin. DCIR surface levels are reduced on pDC maturation after TLR9 triggering. Interestingly, DCIR triggering inhibits TLR9-induced IFN- production while leaving up-regulation of costimulatory molecule expression unaffected. Furthermore, DCIR is readily internalized into pDCs after receptor triggering. We show that DCIR internalization is clathrin-dependent because it can be inhibited by hypertonic shock and dominant-negative dynamin. Importantly, antigens targeted to pDCs via DCIR are presented to T cells. These findings indicate that targeting DCIR on pDCs not only results in efficient antigen presentation but also affects TLR9-induced IFN- production. Collectively, the data show that targeting of DCIR can modulate human pDC function and may be applied in disease preven-tion and treatment.

Human invariant V{alpha}24+ natural killer T cells acquire regulatory functions by interacting with IL-10-treated dendritic cells

Yamaura, A., Hotta, C., Nakazawa, M., Van Kaer, L., Minami, M. — 2008-04-08

Glycolipid-reactive V24⁺ invariant natural killer T (iNKT) cells have been implicated in regulating a variety of immune responses and in the induction of immunologic tolerance. Activation of iNKT cells requires interaction with professional antigen-presenting cells, such as dendritic cells (DCs). We have investigated the capacity of distinct DC subsets to modulate iNKT cell functions. We demonstrate that tolerogenic DCs (tolDCs), generated by treatment of monocyte-derived DC with interleukin (IL)-10, induced regulatory functions in human iNKT cells. tolDCs, compared with immunogenic DCs, had reduced capacity to induce iNKT-cell proliferation, but these cells produced large amounts of IL-10 and acquired an anergic phenotype. These anergic V24⁺ iNKT cells were able to potently inhibit allogeneic CD4⁺ T-cell proliferation in vitro. Furthermore, the anergic V24⁺ iNKT cells could suppress DC maturation in vitro. We conclude that the interaction of iNKT cells with tolDCs plays an important role in the immune regulatory network, which might be exploited for therapeutic purposes.

hDectin-1 is involved in uptake and cross-presentation of cellular antigens

2008-04-08

Human Dectin-1 (hDectin-1) is a member of the C-type lectin–like receptor family that was shown to be the major receptor for fungal beta-glucans and to play an important role in the cellular responses mediated by these carbohydrates. In this study, we demonstrate that hDectin-1 is involved in the uptake and cross-presentation of cellular antigens. Furthermore, activation of monocyte-derived dendritic cells (MDCs) with toll-like receptor 3 (TLR3) ligand but not with TLR2 ligand or TLR7 ligand resulted in down-regulation of hDectin-1 expression and reduced phagocytosis of apoptotic tumor cells as well as presentation of pp65-derived T-cell epitopes upon engulfment of cytomegalovirus (CMV)–infected human foreskin fibroblasts.

Itch-/-{alpha}{beta} and {gamma}{delta} T cells independently contribute to autoimmunity in Itchy mice

Parravicini, V., Field, A.-C., Tomlinson, P. D., Albert Basson, M., Zamoyska, R. — 2008-04-08

E3 ubiquitin ligases determine which intracellular proteins are targets of the ubiquitin conjugation pathway and thus play a key role in determining the half-life, subcellular localization and/or activation status of their target proteins. Itchy mice lack the E3 ligase, Itch, and show dysregulation of T lymphocytes and the induction of a lethal autoimmune inflammatory condition. Itch is widely expressed in hematopoietic and nonhematopoietic cells, and we demonstrate that disease is transferred exclusively by hematopoietic cells. Moreover, distinct manifestations of the autoimmune inflammatory phenotype are contributed by discrete populations of lymphocytes. The presence of Itch-deficient β T cells drives expansion of peritoneal B1b cells and elevated IgM levels, which correlate with itching and pathology. In contrast, Itch^–/– interleukin-4–producing T cells, even in the absence of β T cells, are associated with elevated levels of IgE and an inflammatory condition. These data indicate that disruption of an E3 ubiquitin ligase in β T cells can subvert a B-cell subpopulation, which normally functions to control particular microbial pathogens in a T-independent manner, to contribute to autoimmunity. In addition, disruption of Itch in innate T cells can influence autoimmune pathology and might therefore require distinct therapeutic intervention.

Impact of clonal competition for peptide-MHC complexes on the CD8+ T-cell repertoire selection in a persistent viral infection

2008-04-08

CD8⁺ T-cell responses to persistent viral infections are characterized by the accumulation of an oligoclonal T-cell repertoire and a reduction in the naive T-cell pool. However, the precise mechanism for this phenomenon remains elusive. Here we show that human cytomegalovirus (HCMV)–specific CD8⁺ T cells recognizing distinct epitopes from the pp65 protein and restricted through an identical HLA class I allele (HLA B*3508) exhibited either a highly conserved public T-cell repertoire or a private, diverse T-cell response, which was uniquely altered in each donor following in vitro antigen exposure. Selection of a public T-cell receptor (TCR) was coincident with an atypical major histocompatibility complex (MHC)–peptide structure, in that the epitope adopted a helical conformation that bulged from the peptide-binding groove, while a diverse TCR profile was observed in response to the epitope that formed a flatter, more "featureless" landscape. Clonotypes with biased TCR usage demonstrated more efficient recognition of virus-infected cells, a greater CD8 dependency, and were more terminally differentiated in their phenotype when compared with the T cells expressing diverse TCR. These findings provide new insights into our understanding on how the biology of antigen presentation in addition to the structural features of the pMHC-I might shape the T-cell repertoire and its phenotype.

Antigen-specific human T-cell responses and T cell-dependent production of human antibodies in a humanized mouse model

Tonomura, N., Habiro, K., Shimizu, A., Sykes, M., Yang, Y.-G. — 2008-04-08

Humanized mice with a functional human immune system would be very useful for in vivo studies of human immunobiology. We have previously shown that cotransplantation of human fetal thymus/liver tissues and CD34⁺ fetal liver cells into immunodeficient nonobese diabetic severe combined immunodeficiency (NOD/SCID) mice leads to the development of multiple lineages of human lymphohematopoietic cells and formation of secondary lymphoid organs with normal architecture. Here, we evaluated the ability of these humanized mice to develop antigen-specific, T cell–dependent antibody responses after in vivo immunization with T-dependent antigen, 2,4-dinitrophenyl hapten-keyhole limpet hemocyanin (DNP₂₃-KLH). Human T cells from DNP₂₃-KLH–immunized mice showed strong proliferation in response to KLH in vitro. Furthermore, T cell–dependent production of DNP-specific human antibodies (mainly IgG1 and IgG2) was detected in all immunized mice. These results confirm that a functional human immune system can be established in immunodeficient mice through cotransplantation of human fetal thymus/liver tissues and CD34⁺ hematopoietic stem/progenitor cells.

Killer artificial antigen-presenting cells: a novel strategy to delete specific T cells

2008-03-24

Several cell-based immunotherapy strategies have been developed to specifically modulate T cell–mediated immune responses. These methods frequently rely on the utilization of tolerogenic cell–based antigen-presenting cells (APCs). However, APCs are highly sensitive to cytotoxic T-cell responses, thus limiting their therapeutic capacity. Here, we describe a novel bead-based approach to modulate T-cell responses in an antigen-specific fashion. We have generated killer artificial APCs (aAPCs) by coupling an apoptosis-inducing -Fas (CD95) IgM mAb together with HLA-A₂ Ig molecules onto beads. These aAPCs deplete targeted antigen-specific T cells in a Fas/Fas ligand (FasL)–dependent fashion. T-cell depletion in cocultures is rapidly initiated (30 minutes), dependent on the amount of aAPCs and independent of activation-induced cell death (AICD). aAPCs represent a novel technology that can control T cell–mediated immune responses, and therefore has potential for use in treatment of autoimmune diseases and allograft rejection.

Nuclear factor of activated T cells (NFAT) mediates CD154 expression in megakaryocytes

Crist, S. A., Sprague, D. L., Ratliff, T. L. — 2008-03-24

Platelets are an abundant source of CD40 ligand (CD154), an immunomodulatory and proinflammatory molecule implicated in the onset and progression of several inflammatory diseases, including systemic lupus erythematosus (SLE), diabetes, and cardiovascular disease. Heretofore considered largely restricted to activated T cells, we initiated studies to investigate the source and regulation of platelet-associated CD154. We found that CD154 is abundantly expressed in platelet precursor cells, megakaryocytes. We show that CD154 is expressed in primary human CD34⁺ and murine hematopoietic precursor cells only after cytokine-driven megakaryocyte differentiation. Furthermore, using several established megakaryocyte-like cells lines, we performed promoter analysis of the CD154 gene and found that NFAT, a calcium-dependent transcriptional regulator associated with activated T cells, mediated both differentiation-dependent and inducible megakaryocyte-specific CD154 expression. Overall, these data represent the first investigation of the regulation of a novel source of CD154 and suggests that platelet-associated CD154 can be biochemically modulated.

Crosstalk between the {alpha}2{beta}1 integrin and c-met/HGF-R regulates innate immunity

McCall-Culbreath, K. D., Li, Z., Zutter, M. M. — 2008-03-24

Data from several investigators suggest that the 2β1 integrin, a receptor for collagens, laminins, decorin, E-cadherin, matrix metalloproteinase-1, endorepellin, and several viruses, is required for innate immunity and regulation of autoimmune/allergic disorders. We demonstrated that the innate immune response to Listeria monocytogenes required 2β1 integrin expression by peritoneal mast cells (PMCs). Ligation of the 2β1 integrin by C1q contained in immune complexes comprised of Listeria and antibody was required for PMC activation in vitro and in vivo. However, ligation of the 2β1 integrin alone was insufficient to activate cytokine secretion, suggesting that one or more additional signals emanating from a coreceptor were required for PMC activation. Here, we demonstrate that C1q, but neither other complement proteins nor FcR, is required for early innate immune response to Listeria. The binding of Listeria's Internalin B (InlB) to hepatocyte growth factor receptor (HGF-R)/c-met provides the costimulatory function required for PMC activation. Either HGF or Listeria InlB bound to c-met and either C1q or type I collagen bound to 2β1 integrin stimulates PMC activation. These findings suggest that crosstalk between c-met and the 2β1 integrin may contribute to mast-cell activation in autoimmune and inflammatory disorders.

Sustained NKG2D engagement induces cross-tolerance of multiple distinct NK cell activation pathways

Coudert, J. D., Scarpellino, L., Gros, F., Vivier, E., Held, W. — 2008-03-24

NKG2D is a multisubunit activation receptor that allows natural killer (NK) cells to detect and eliminate stressed, infected, and transformed host cells. However, the chronic exposure of NK cells to cell-bound NKG2D ligands has been shown to impair NKG2D function both in vitro and in vivo. Here we have tested whether continuous NKG2D engagement selectively impacted NKG2D function or whether heterologous NK cell activation pathways were also affected. We found that sustained NKG2D engagement induced cross-tolerization of several unrelated NK cell activation receptors. We show that receptors that activate NK cells via the DAP12/KARAP and DAP10 signaling adaptors, such as murine NKG2D and Ly49D, cross-tolerize preferentially NK cell activation pathways that function independent of DAP10/12, such as antibody-dependent cell-mediated cytotoxicity and missing-self recognition. Conversely, DAP10/12-independent pathways are unable to cross-tolerize unrelated NK cell activation receptors such as NKG2D or Ly49D. These data define a class of NK cell activation receptors that can tolerize mature NK cells. The reversible suppression of the NK cells' cytolytic function probably reduces the NK cells' efficacy to control endogenous and exogenous stress yet may be needed to limit tissue damage.

Cognate CD4+ T-cell-dendritic cell interactions induce migration of immature dendritic cells through dissolution of their podosomes

2008-03-24

Dendritic cells (DCs) control T cell–based immunity. To do so they need to mature and migrate to sites of T-cell priming. We have previously shown that cognate interactions of human CD4⁺ T cells with DCs induce DC maturation. We show here that CC chemokines produced during antigen-specific T-DC interactions also induce strong morphologic modifications and migration of immature DCs. These modifications are required for efficient T-cell activation. Moreover, we show that CC chemokines produced during antigen-specific DC–T-cell interactions induce the dissolution of structures involved in cell motility and present on immature DCs (ie, podosomes). We thus propose a model in which chemokines secreted during Ag-specific contact between T cells and DCs induce disassembly of interacting and neighboring immature DC podosomes, leading to recruitment of more immature DCs toward sites of antigenic stimulation and to amplification of T-cell responses.

Neutrophil-selective CD18 silencing using RNA interference in vivo

Cullere, X., Lauterbach, M., Tsuboi, N., Mayadas, T. N. — 2008-03-24

Tissue-specific silencing of genes may be used for genetic engineering in mice and has possible therapeutic applications in humans. Current strategies in mice rely on Cre/loxP technology requiring the generation of multiple transgenic lines and breeding strategies. Here, we describe the selective silencing of CD18, a leukocyte-specific integrin in neutrophils using a micro RNA (miRNA) strategy that requires the generation of one transgenic line. CD18-specific miRNA hairpin driven by the myeloid specific human MRP8 promoter resulted in the generation of transgenic lines with 75% to 95% reduction in CD18 protein levels in neutrophils and monocytes. Minimal decreases in T cells and a partial diminution in macrophages were observed. Neutrophil CD18 silencing resulted in neutrophilia, splenomegaly, and significant defects in neutrophil trafficking with the degree of alterations correlating with the extent of CD18 silencing. Thus, our data demonstrate the utility of using miRNA approaches to silence genes in neutrophils, which are terminally differentiated cells with a short half-life that largely precludes their genetic manipulation in vitro. Furthermore, the mouse models provide a valuable tool to examine the contribution of CD18 on neutrophils to leukocyte adhesion deficiency type I (LAD-I), a complex inherited disorder in which reduced or absent CD18 expression in multiple leukocyte subsets leads to impaired innate and adaptive immune responses.

FoxP3 maintains Treg unresponsiveness by selectively inhibiting the promoter DNA-binding activity of AP-1

Lee, S.-M., Gao, B., Fang, D. — 2008-03-24

Regulatory T cells (Tregs) have been shown to play a crucial role in maintaining self-tolerance and suppressing autoimmunity. The forkhead transcription factor, FoxP3, is a key molecule necessary and sufficient for Tregs development and function. However, the molecular mechanisms by which FoxP3 regulates the phenotypic (anergic) and the functional (suppressive) characteristics of Tregs are not well defined. Here we found that the promoter DNA-binding activity of AP-1 transcription factors is selectively inhibited in the naturally occurring CD4⁺ CD25⁺ Tregs from mice. The impaired AP-1 DNA binding is not the result of the decreased nuclear translocation of AP-1 family transcription factors, including c-Jun, JunB, and c-Fos. FoxP3 significantly suppresses both the transcriptional activity and promoter DNA-binding of AP-1 by interacting with c-Jun. The N-terminus of FoxP3, but not its C-terminus forkhead domain, specifically interacts with phosphorylated c-Jun and alters c-Jun subnuclear distribution. This N-terminus of FoxP3 with nuclear localization signals (FoxP3N/NLS) is able to suppress AP-1 transcriptional activity. Ectopic expression of FoxP3N/NLS sufficiently induces the unresponsiveness of mouse primary CD4⁺ CD25^– T cells, whereas the full-length FoxP3 is required for the suppressive functions of Tregs. These findings uncover one of the mechanisms underlying how FoxP3 maintains the unresponsiveness of Tregs.

Regulation of LFA-1-dependent inflammatory cell recruitment by Cbl-b and 14-3-3 proteins

2008-03-24

Inside-out signaling regulation of the β2-integrin leukocyte function–associated antigen-1 (LFA-1) by different cytoplasmic proteins, including 14-3-3 proteins, is essential for adhesion and migration of immune cells. Here, we identify a new pathway for the regulation of LFA-1 activity by Cbl-b, an adapter molecule and ubiquitin ligase that modulates several signaling pathways. Cbl-b^–/– mice displayed increased macrophage recruitment in thioglycollate-induced peritonitis, which was attributed to Cbl-b deficiency in macrophages, as assessed by bone marrow chimera experiments. In vitro, Cbl-b^–/– bone marrow–derived mononuclear phagocytes (BMDMs) displayed increased adhesion to endothelial cells. Activation of LFA-1 in Cbl-b–deficient cells was responsible for their increased endothelial adhesion in vitro and peritoneal recruitment in vivo, as the phenotype of Cbl-b deficiency was reversed in Cbl-b^–/–LFA-1^–/– mice. Consistently, LFA-1–mediated adhesion of BMDM to ICAM-1 but not VLA-4–mediated adhesion to VCAM-1 was enhanced by Cbl-b deficiency. Cbl-b deficiency resulted in increased phosphorylation of T758 in the β2-chain of LFA-1 and thereby in enhanced association of 14-3-3β protein with the β2-chain, leading to activation of LFA-1. Consistently, disruption of the 14-3-3/β2-integrin interaction abrogated the enhanced ICAM-1 adhesion of Cbl-b^–/– BMDMs. In conclusion, Cbl-b deficiency activates LFA-1 and LFA-1–mediated inflammatory cell recruitment by stimulating the interaction between the LFA-1 β-chain and 14-3-3 proteins.

Shedded neuronal ICAM-5 suppresses T-cell activation

2008-03-24

Intercellular adhesion molecules (ICAMs) bind to leukocyte β2 integrins, which, among other functions, provide costimulatory signals for T-cell activation. ICAM-5 (telencephalin) is expressed in the somadendritic region of neurons of the mammalian brain. The receptor for ICAM-5 is the integrin LFA-1, a major leukocyte integ-rin expressed in lymphocytes and microglia. In conditions of brain ischemia, epilepsy, and encephalitis, the soluble form of ICAM-5 (sICAM-5) has been detected in physiologic fluids. Here, we report that sICAM-5 attenuates the T-cell receptor-mediated activation of T cells as demonstrated by the decreased expression of the activation markers CD69, CD40L, and CD25 (IL-2R). This effect is most clearly seen in CD45RO^Low (naive), and not in CD45RO^High (memory) T cells, and is most effective early in priming, but not in the presence of strong costimulatory signals. Furthermore, sICAM-5 promotes the mRNA expression of the cytokines TGF-β1 and IFN-, but not TNF. The formation of sICAM-5 is promoted by activated T cells through the cleavage of ICAM-5 from neurons. This suggests that ICAM-5 is involved in immune privilege of the brain and acts as an anti-inflammatory agent.

CCL3 and CXCL12 regulate trafficking of mouse bone marrow NK cell subsets

Bernardini, G., Sciume, G., Bosisio, D., Morrone, S., Sozzani, S., Santoni, A. — 2008-03-24

Herein we have analyzed chemokine involvement in the trafficking of developing and mature mouse natural killer (NK) cells in the bone marrow (BM). We observed drastic changes of CCR1, CXCR3, and CXCR4 expression and function during progression from precursor NK (pNK) cells to immature DX5^– NK (iNK) and mature DX5⁺ NK (mNK) cells. pNK and mNK cells expressed the 3 receptors, while only CXCR4 was detected on iNK cells. Correspondingly, mNK cells migrated to CXCL12, CXCL10, and CCL3, and pNK and iNK cells to CXCL12, whereas pNK cells migrated to CCL3 and CXCL10 only after CXCL12 stimulation. Comparison of BM, peripheral blood, and spleen mNK cell populations revealed that CXCL12, CXCL10, and CCL3 preferentially affected BM mNK cell migration. Administration of the CXCR4 antagonist, AMD-3100, to C57BL/6 mice induced strong reduction of mNK and iNK cells in the BM and increased their number in blood and spleen. Conversely, CCL3 administration selectively mobilized mNK cells from the BM and this effect correlated with its ability to inhibit CXCL12-mediated mNK cell responses in vitro. Our results suggest that the combined action of chemokines selectively regulates localization of NK cell subsets in the BM and direct their maturation and migration to the periphery.

B7-H1 is a ubiquitous antiapoptotic receptor on cancer cells

Azuma, T., Yao, S., Zhu, G., Flies, A. S., Flies, S. J., Chen, L. — 2008-03-24

B7-H1 is an immunoglobulin-like immune suppressive molecule broadly detectable on the majority of human and rodent cancers, and its functions have been attributed to delivering an inhibitory signal to its counter-receptor programmed death-1 (PD-1) on T cells. Here we report that B7-H1 on cancer cells receives a signal from PD-1 to rapidly induce resistance against T cell–mediated killing because crippling signaling capacity of B7-H1 but not PD-1 ablates this resistance. Importantly, loss of B7-H1 signaling is accompanied by increased susceptibility to immune-mediated tumoricidal activity. In addition to resistance against T-cell destruction, B7-H1⁺ cancer cells also become refractory to apoptosis induced by Fas ligation or the protein kinase inhibitor Staurosporine. Our study reveals a new mechanism by which cancer cells use a receptor on immune cells as a ligand to induce resistance to therapy.

CD38 induces differentiation of immature transitional 2 B lymphocytes in the spleen

2008-03-24

CD38 is a surface receptor able to induce activation, proliferation, and survival of human and mouse lymphocytes; this molecule is expressed on the surface of both mature and immature B cells. In this work, the function of CD38 in the maturation of murine B lymphocytes in the spleen was analyzed. The results showed that CD38 is highly expressed on Transitional 2 (T2) B lymphocytes with an intermediate expression on Transitional 1 (T1) and mature follicular B cells (M). Correlating with a high expression of CD38, T2 cells are also larger and more granular than T1 or M B cells. T2 cells also showed high levels of other molecules, which indicate an activated phenotype. CD38 crosslinking induced proliferation and maturation of T2 B lymphocytes; in contrast, T1 subset died by apoptosis. Finally, CD38 stimulation of T2 B lymphocytes obtained from Btk-, Lyn-, or Fyn-deficient mice showed a defective differentiation; similarly, drugs interfering with PI3K or ERK decreased the proliferation or differentiation of this subset. This suggests that these molecules participate in the CD38 signaling pathway. As a whole, the results indicate that CD38 plays an important role in the regulation of B-cell maturation in the spleen.

Antigen-induced clustering of surface CD38 and recruitment of intracellular CD38 to the immunologic synapse

2008-03-24

During immunologic synapse (IS) formation, human CD38 redistributes to the contact area of T cell–antigen-presenting cell (APC) conjugates in an antigen-dependent manner. Confocal microscopy showed that CD38 preferentially accumulated along the contact zone, whereas CD3- redistributed toward the central zone of the IS. APC conjugates with human T cells or B cells transiently expressing CD38–green fluorescent protein revealed the presence of 2 distinct pools of CD38, one localized at the cell membrane and the other in recycling endosomes. Both pools were recruited to the T/APC contact sites and required antigen-pulsed APCs. The process appeared more efficient in T cells than in APCs. CD38 was actively recruited at the IS of T cells by means of Lck-mediated signals. Overexpression of CD38 in T cells increased the levels of antigen-induced intracellular calcium release. Opposite results were obtained by down-regulating surface CD38 expression by means of CD38 siRNA. CD38 blockade in influenza HA-specific T cells inhibited IL-2 and IFN- production, PKC phosphorylation at Thr538, and PKC recruitment to the IS induced by antigen-pulsed APCs. These results reveal a new role for CD38 in modulating antigen-mediated T-cell responses during IS formation.

VAMP-8 segregates mast cell-preformed mediator exocytosis from cytokine trafficking pathways

2008-03-24

Inflammatory responses by mast cells are characterized by massive exocytosis of prestored granular mediators followed by cytokine/chemokine release. The vesicular trafficking mechanisms involved remain poorly understood. Vesicular-associated membrane protein-8 (VAMP-8), a member of the soluble N-ethylmaleimide–sensitive factor (NSF) attachment protein receptor (SNARE) family of fusion proteins initially characterized in endosomal and endosomal-lysosomal fusion, may also function in regulated exocytosis. Here we show that in bone marrow–derived mast cells (BMMCs) VAMP-8 partially colocalized with secretory granules and redistributed upon stimulation. This was associated with increased SNARE complex formation with the target t-SNAREs, SNAP-23 and syntaxin-4. VAMP-8–deficient BMMCs exhibited a markedly reduced degranulation response after IgE⁺ antigen-, thapsigargin-, or ionomycin-induced stimulation. VAMP-8–deficient mice also showed reduced plasma histamine levels in passive systemic anaphylaxis experiments, while cytokine/chemokine release was not affected. Unprocessed TNF accumulated at the plasma membrane where it colocalized with a VAMP-3–positive vesicular compartment but not with VAMP-8. The findings demonstrate that VAMP-8 segregates secretory lysosomal granule exocytosis in mast cells from cytokine/chemokine molecular trafficking pathways.

Rabbit ATG but not horse ATG promotes expansion of functional CD4+CD25highFOXP3+ regulatory T cells in vitro

2008-03-24

Regulatory T cells (Treg) play important roles in suppressing immune responses and maintaining tolerance. Rabbit antithymocyte globulin (rATG) and horse ATG (hATG) are widely used in the treatment of immune-mediated syndromes, but their effects on Treg are unknown. We show here that in vitro culture of normal human peripheral blood mononuclear cells (PBMCs) with a low-dose rATG resulted in marked expansion of functional Treg by converting CD4⁺CD25^– T cells to CD4⁺CD25⁺ T cells. hATG did not expand but rather decreased Treg. Immuno-blot showed increased expression of FOXP3 and NFAT1 in CD4⁺CD25^– and CD4⁺CD25⁺ T cells exposed to rATG. PBMCs treated with rATG displayed increased interleukin-10 in culture supernatants than those treated with hATG. Furthermore, rATG and hATG showed differences in their potential to stimulate CD4⁺ T cells as examined using different activation markers. Microarray revealed that rATG induced markedly different gene-expression patterns in PBMCs, compared with hATG-treated or untreated PBMCs. Our findings indicate that rATG expanded Treg, probably through transcriptional regulation by enhanced NFAT1 expression, in turn conferring CD4⁺CD25^– T cell FOXP3 expression and regulatory activity. The therapeutic effects of rATG may occur not only because of lymphocyte depletion but also enhanced Treg cell number and function.

Platelet-derived CD154 enables T-cell priming and protection against Listeria monocytogenes challenge

2008-03-24

Collagen exposure in tissue activates platelets, initiates wound healing, and modulates adaptive immunity. In this report, data are presented to demonstrate a requirement for platelet-derived CD154 for both collagen-induced augmentation of T-cell immunity and induction of pro-tective immunity to Listeria challenge. Specifically, we demonstrate that Ad5 encoding the membrane-bound form of ovalbumin (Ad5-mOVA) delivered in collagen induces higher ovalbumin-specific cytotoxic T lymphocyte (CTL) activity in a dose-dependent manner compared with Ad5-mOVA delivered in PBS. Increased CTL activity was dependent on the ability of platelets to respond to collagen and to express CD154. Furthermore, mice immunized with low-dose Ad5-mOVA in collagen were able to control a challenge of Listeria monocytogenes recombinant for ovalbumin expression (Lm-OVA), whereas mice immunized with low-dose Ad5-mOVA in PBS were not. These data indicate that in a physiologic setting that mimics wounding, platelets perform a sentinel function when antigen dose is too low to provoke an efficient immune response, and can enhance the generation of antigen-specific CD8 T cells that are functionally relevant to the host.