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CORRESPONDENCE To the editor:HIV-associated dysfunction of in vitro IL-12 production depends on the nature of the stimulus and on the CD4 T-cell count of the patientA recent paper by Marshall et al suggests that decreased production of interleukin-12 (IL-12) is crucial in human immunodeficiency virus (HIV)-associated immune deficiency.1 According to these authors, peripheral blood mononuclear cells (PBMC) from HIV-positive subjects produce lower levels of IL-12 in response to a wide range of stimuli, irrespective of the disease stage. Interferon-gamma (IFN- ) production was decreased in response to
IL-12, and upregulation of the IL-12 receptor  2 chain, critical for
signal transmission, was impaired. The latter defect could be reversed
by rIL-12 pretreatment. The authors logically conclude: "A primary
IL-12 defect may lead to secondary deficiencies in expression of the
genes for IL-12R2 and IFN-, thus amplifying immune deficiency
during HIV infection." These data are in line with the "type-1 to
type-2 shift" paradigm of HIV pathogenesis.2-4 Because
addition of IL-12 to PBMC cultures from HIV-positive subjects was shown
to partly restore responses to antigen stimulation,5 rIL-12
seems a good candidate for immunotherapy in acquired immunodeficiency
syndrome (AIDS).
Other authors, including our group, observed HIV-associated
cytokine imbalances, which are partly inconsistent with a type-1 to -2
shift.6-8 Increased levels of various cytokines, including
IFN-
In view of the discrepancies between various studies, we decided to
compare IL-12 p70 production in blood cells from HIV-negative and
HIV-positive patients, using the following conditions: (1) RPMI only,
(2) A broadly mitogenic combination of phytohemagglutinin (PHA) and
LPS, (3) T-cell receptor V One hundred microliters of heparinized blood, diluted 1:10 in RPMI (GIBCO BRL, Paisley, Scotland), were cultured 4-fold in round-bottom polystyrene tubes (Falcon 2054, Becton Dickinson, Erembodegem, Belgium). Optimum concentrations of stimuli were determined in preliminary experiments: PHA (Difco, Detroit, IL) was used at 5 µg/mL plus LPS (Difco) at 25 µg/mL; SEB (Sigma, St Louis, Missouri) at 1 µg/mL and SAC (Pansorbin, Calbiochem, La Jolla, CA) at 0.016 vol percent. After an incubation of 24 hours at 37°C in a 5% CO2 incubator, the supernatants were harvested and stored at –70°C. IL-12 concentrations were measured using the p70 ELISA (R&D Systems, Abingdon, UK). IL-12 could not be measured in any supernatant of medium control cultures (not shown). Stimulated IL-12 levels (median and CI) are depicted in the figure. The Mann-Whitney U test was used to calculate the significance of differences between the controls and the patient groups, stratified according CD4 T count. In general, IL-12 production was highly variable, but several tendencies are obvious. In blood cultures of HIV-negative subjects, SAC was the strongest IL-12 inducer, followed by PHA/LPS, whereas SEB was relatively weak. The IL-12 response to LPS/PHA was not statistically different between patients and controls. The response to SAC was unaltered in patients with more than 500 CD4 T cells, slightly (not significant) decreased in patients with intermediate CD4 T counts, and significantly (p < .01) reduced in AIDS patients. Interestingly, SEB induced slightly (but n.s.) more IL-12 in the cultures from patients with more than 200 CD4 T cells/µL, whereas in AIDS patients SEB-stimulated IL-12 production was significantly (p < .05) decreased. The latter results are similar to those we previously obtained with CD40L in peripheral blood mononuclear cells (PBMC) cultures.8
The same data were reanalyzed after stratifying the patients according to VL (fewer than and more than 400 copies, respectively). This analysis showed IL-12 concentrations of 21.1 ± 9.9 and 9.4 ± 10.6 pg/mL (p = .07) after PHA/LPS stimulation, 9.3 ± 6.4 and 4.6 ± 5.6 pg/mL (n.s.) after SEB stimulation, and 18 ± 14.5 and 13.3 ± 19.4 pg/ml (n.s.) after SAC. Clearly, there is a tendency of lowered IL-12 production in subjects with a measurable VL, regardless of the stimulus used. Nevertheless, among the latter patients no correlation was found between the IL-12 production and VL (Spearman rank test). In summary, our present data indicate that the influence of in vivo HIV infection on in vitro IL-12 production is more complex than Marshall et al suggested. Both the nature of the stimulus and the stage of the disease determine the IL-12 p70 output in culture. The IL-12 response to SAC decreased according to CD4 T counts. Other stimuli, including SEB and CD40L, had a double-edged effect: a relative overproduction of IL-12 in non-AIDS patients and a defective IL-12 production in AIDS patients. Unfortunately, the effects of viral load itself and of viral load reduction by highly active antiretroviral therapy (HAART) on IL-12 production remain unclear, even in our present study. Together with earlier observations, the present data indicate that both immune overactivation and immune deficiency are reflected in IL-12 production during HIV infection. Although IL-12 could be useful to enhance deficient cell-mediated immunity, it also has potential proinflammatory and HIV-enhancing effects. Therefore, more studies are needed to unravel the role of dysregulated IL-12 production in HIV pathogenesis before immunotherapy with IL-12 itself or IL-12 inducers can be considered.
This work was supported by a grant
from the Janssen Research Foundation.
References
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| Copyright © 2000 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
), 12 HIV-positive
subjects with CD4 T-cell counts higher than 500/µL (
), 16 subjects
with CD4 T counts 200-500/µL (
), and 10 subjects with CD4 T counts
lower than 200/µL (
