FcγRIIB: a modulator of cell activation and humoral tolerance.
ABSTRACT An immune response needs to be tightly regulated to prevent excessive inflammation, which may result in the destruction of healthy tissues. At the molecular level, the strength of an immune response is determined by the integration of a multitude of positive and negative signals. This review will focus on IgG-dependent immune responses and discuss how the inhibitory receptor FcγRIIB may be involved in regulating both the afferent and efferent phases of such a response. Furthermore, we will discuss recent evidence suggesting that FcγRIIB may have important functions beyond the negative regulation of signals transduced by the B-cell receptor or activating FcγRs and could be responsible for the activity of agonistic antibodies in vivo.
- SourceAvailable from: Toshikazu Shirai[show abstract] [hide abstract]
ABSTRACT: FcgammaRIIB1 molecules serve as negative feedback regulator for B cell Ag receptor-elicited activation of B cells; thus, any impaired FcgammaRIIB1 function may possibly be related to aberrant B cell activation. We earlier found deletion polymorphism in the Fcgr2b promoter region among mouse strains in which systemic autoimmune disease-prone NZB, BXSB, MRL, and autoimmune diabetes-prone nonobese diabetic, but not NZW, BALB/c, and C57BL/6 mice have two identical deletion sites, consisting of 13 and 3 nucleotides. In this study, we established congenic C57BL/6 mice for NZB-type Fcgr2b allele and found that NZB-type allele down-regulates FcgammaRIIB1 expression levels in germinal center B cells and up-regulates IgG Ab responses. We did luciferase reporter assays to determine whether NZB-type deletion polymorphism affects transcriptional regulation of Fcgr2b gene. Although NZW- and BALB/c-derived segments from position -302 to +585 of Fcgr2b upstream region produced significant levels of luciferase activities, only a limited activity was detected in the NZB-derived sequence. EMSA and Southwestern analysis revealed that defect in transcription activity in the NZB-derived segment is likely due to absence of transactivation by AP-4, which binds to the polymorphic 13 nucleotide deletion site. Our data imply that because of the deficient AP-4 binding, the NZB-type Fcgr2b allele polymorphism results in up-regulation of IgG Ab responses through down-regulation of FcgammaRIIB1 expression levels in germinal center B cells, and that such polymorphism may possibly form the basis of autoimmune susceptibility in combination with other background contributing genes.The Journal of Immunology 11/2002; 169(8):4340-6. · 5.52 Impact Factor
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ABSTRACT: The final differentiation or maturation of dendritic cells (DCs) in response to environmental stimuli influences their ability to both initiate immunity and determine the quality of the response to antigens. Circulating immune complexes and cell-bound immunoglobulins present in normal human sera represent a potential stimulus for inadvertent DC activation in the steady state and during autoimmunity. Here, we show that selective blockade of the inhibitory Fcgamma receptor (FcgammaR) FcgammaRIIb with recently developed monoclonal antibodies leads to maturation of human monocyte-derived DCs, which depends on the presence of IgG in normal human plasma. Plasma, in the presence of an FcgammaRIIb blockade, caused the DCs to up-regulate the expression of costimulatory molecules and to produce the inflammatory mediator IL-12p70. FcgammaRIIb blockade of DCs loaded with tumor cells led to increased tumor-specific T cell immunity without the need for exogenous stimuli other than human plasma. Therefore, the activation status of DCs in the presence of normal human serum depends on the balance between activating and inhibitory FcgammaRs and can be enhanced by new antibodies that react selectively with FcgammaRIIb. These data suggest an approach for modifying this balance to enhance immunity to immune complexes and antibody-coated tumor cells and to silence DC activation by immune complexes in autoimmune states.Proceedings of the National Academy of Sciences 03/2005; 102(8):2910-5. · 9.74 Impact Factor
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ABSTRACT: By virtue of its ability to couple the BCR to an inhibitory pathway, FcgammaRIIB can potentially determine the fate of B cells upon IgG immune complex engagement. We now provide evidence for FcgammaRIIB as a component of a peripheral tolerance pathway with the observation that RIIB-/- mice develop autoantibodies and autoimmune glomerulonephritis in a strain-dependent fashion. Transfer of the autoimmune phenotype is associated with the presence of donor RIIB-/- B cells, with the RIIB+/+ myeloid cells primarily derived from the recipient. These results suggest that deficiency of RIIB on B cells leads to autoimmune disease in specific genetic backgrounds, thus identifying it as a susceptibility factor under the influence of epistatic modifiers for the development of autoimmunity.Immunity 09/2000; 13(2):277-85. · 19.80 Impact Factor