FcγR ligation by Ag-Ab immune complexes (IC) not only mediates effective Ag uptake, but also strongly initiates dendritic cell (DC) maturation, a requirement for effective T cell activation.... Show moreFcγR ligation by Ag-Ab immune complexes (IC) not only mediates effective Ag uptake, but also strongly initiates dendritic cell (DC) maturation, a requirement for effective T cell activation. Besides the activating FcγRI, FcγRIII, and FcγRIV, the inhibitory FcγRIIb is expressed on DCs. It is unclear how the ratio between signals from the activating FcγR and the inhibitory FcγRIIb determines the outcome of FcγR ligation on DCs. By microarray analysis, we compared the transcriptomes of steady state and IC-activated bone marrow-derived wild-type (WT) DCs expressing all FcγR or DCs expressing only activating FcγR (FcγRIIb knockout [KO]) or only the inhibitory FcγRIIb (FcR γ-chain KO). In WT DCs, we observed a gene expression profile associated with effective T cell activation, which was absent in FcR γ-chain KO, but strikingly more pronounced in FcγRIIb KO bone marrow-derived DCs. These microarray results, confirmed at the protein level for many cytokines and other immunological relevant genes, demonstrate that the transcriptome of IC-activated DCs is dependent on the presence of the activating FcγR and that the modulation of the expression of the majority of the genes was strongly regulated by FcγRIIb. Our data suggest that FcγRIIb-deficient DCs have an improved capacity to activate naive T lymphocytes. This was confirmed by their enhanced FcγR-dependent Ag presentation and in vivo induction of CD8(+) T cell expansion compared with WT DCs. Our findings underscore the potency of FcγR ligation on DCs for the effective induction of T cell immunity by ICs and the strong regulatory role of FcγRIIb. Show less
FcγRIIB-deficient mice generated in 129 background (FcγRIIB(129)(-/-)) if back-crossed into C57BL/6 background exhibit a hyperactive phenotype and develop lethal lupus. Both in mice and humans, the... Show moreFcγRIIB-deficient mice generated in 129 background (FcγRIIB(129)(-/-)) if back-crossed into C57BL/6 background exhibit a hyperactive phenotype and develop lethal lupus. Both in mice and humans, the Fcγr2b gene is located within a genomic interval on chromosome 1 associated with lupus susceptibility. In mice, the 129-derived haplotype of this interval, named Sle16, causes loss of self-tolerance in the context of the B6 genome, hampering the analysis of the specific contribution of FcγRIIB deficiency to the development of lupus in FcγRIIB(129)(-/-) mice. Moreover, in humans genetic linkage studies revealed contradictory results regarding the association of "loss of function" mutations in the Fcγr2b gene and susceptibility to systemic lupus erythematosis. In this study, we demonstrate that FcγRIIB(-/-) mice generated by gene targeting in B6-derived ES cells (FcγRIIB(B6)(-/-)), lacking the 129-derived flanking Sle16 region, exhibit a hyperactive phenotype but fail to develop lupus indicating that in FcγRIIB(129)(-/-) mice, not FcγRIIB deficiency but epistatic interactions between the C57BL/6 genome and the 129-derived Fcγr2b flanking region cause loss of tolerance. The contribution to the development of autoimmune disease by the resulting autoreactive B cells is amplified by the absence of FcγRIIB, culminating in lethal lupus. In the presence of the Yaa lupus-susceptibility locus, FcγRIIB(B6)(-/-) mice do develop lethal lupus, confirming that FcγRIIB deficiency only amplifies spontaneous autoimmunity determined by other loci. Show less
Antibody-Fc receptor (FcR) interactions play an important role in the mechanism of action of most therapeutic antibodies against cancer. Effector cell activation through FcR triggering may induce... Show moreAntibody-Fc receptor (FcR) interactions play an important role in the mechanism of action of most therapeutic antibodies against cancer. Effector cell activation through FcR triggering may induce tumor cell killing via antibody-dependent cellular cytotoxicity (ADCC). Reciprocally, FcR cross-linking of antibody may lead to the induction of apoptotic signaling in tumor cells. The relative importance of these bisecting pathways to in vivo antibody activity is unknown. To unravel these roles, we developed a novel mouse model with normal FcR expression but in which FcR signaling was inactivated by mutation of the associated gamma-chain. Transgenic mice showed similar immune complex binding compared with wild-type mice. In contrast, ADCC of cells expressing frequently used cancer targets, such as CD20, epidermal growth factor receptor, Her2, and gp75, was abrogated. Using the therapeutic CD20 antibodies ofatumumab and rituximab, we show that FcR cross-linking of antibody-antigen immune complexes in the absence of gamma-chain signaling is insufficient for their therapeutic activity in vivo. ADCC therefore represents an essential mechanism of action for immunotherapy of lymphoid tumors. Cancer Res; 70(8); 3209-17. (C)2010 AACR. Show less
In this thesis the role of murine FcgammaR in autoimmune diseases is analyzed with special focus on arthritis and lupus. Series of studies performed with a variety of arthritis models established... Show moreIn this thesis the role of murine FcgammaR in autoimmune diseases is analyzed with special focus on arthritis and lupus. Series of studies performed with a variety of arthritis models established in mice deficient for one or more FcgammaR provided direct evidence for a prominent role of FcgammaR in arthritis (Chapter 2). Chapters 3 to 5 provide new insights into the role of individual FcgammaR in arthritis pathology. The precise contribution of FcgammaRIIB to the development of autoimmunity has been a matter of debate. In Chapter 6, we provide direct evidence that FcgammaRIIB on its own plays a limited role in the development of spontaneous autoimmunity in C57Bl/6 mice. Our results suggest that the role of FcgammaRIIB in the development of spontaneous autoimmunity (Systemic Lupus Erythematosus) is more restricted as originally postulated on the basis of the phenotype of FcgammaRIIB129-/- mice, whereas its role in induced autoimmunity is prominent, supporting the hypothesis that FcgammaRIIB represents a late checkpoint in B cell tolerance. In Chapter 7 we describe the generation and characterization of a novel B cell-specific inducible Cre transgenic mouse line. The results presented in this thesis provide new insights in the role of FcgammaRs in protective immunity and immuno-pathology. Show less
