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Blood, 9 July 2009, Vol. 114, No. 2, pp. 318-327.
Prepublished online as a Blood First Edition Paper on May 6, 2009; DOI 10.1182/blood-2008-10-184457.
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IMMUNOBIOLOGY
Differential signal transduction, membrane trafficking, and immune effector functions mediated by Fc RI versus Fc RIIa
Xilei Dai1,
Manikandan Jayapal2,
Hwee Kee Tay2,
Renji Reghunathan2,
Gen Lin1,
Chien Tei Too1,
Yan Ting Lim1,
Soh Ha Chan1,
D. Michael Kemeny1,
R. Andres Floto3,
Kenneth G. C. Smith3,
Alirio J. Melendez2,4, and
Paul A. MacAry1
Departments of 1 Microbiology and
2 Physiology, National University of Singapore, Singapore;
3 Department of Medicine/CIMR University of Cambridge, Cambridge, United Kingdom; and
4 Division of Immunology, Infection and Inflammation, University of Glasgow, Glasgow, United Kingdom
Receptors for the fragment crystallizable region of immunoglobulin-G (Fc Rs) play an important role in linking the humoral and cellular arms of the immune response. In this study, we present a comprehensive functional comparison of 2 human Fc-receptors, Fc RI and Fc RIIa. Activation of Fc RI results in a novel signaling cascade that links phospholipase D1 to sphingosine kinase-1 in U937 cells and primary human monocytes. This induces the expression of proinflammatory mediators and is associated with trafficking of immune complexes into human leukocyte antigen-DM positive antigen-processing compartments coupled with improved MHC class II–mediated antigen presentation to T lymphocytes. In contrast, activation of Fc RIIa elicits signaling through phospholipase C 1, resulting in increases in intracellular calcium, activation of nicotinamide adenine dinucleotide phosphate-oxidative burst, and differential membrane trafficking combined with impaired antigen presentation and proinflammatory cytokine expression. These data provide a mechanistic insight into the disparate activities associated with Fc receptors in immunity, namely, reinforcement of immune responses through stimulation of proinflammatory signaling and antigen presentation, versus the maintenance of immunologic homeostasis through the noninflammatory clearance of immune complexes.

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