Mouse FcγRII is a negative regulator of FcγRIII in IgG immune complex-triggered inflammation but not in autoantibody-induced hemolysis

Abstract

Murine low-affinity receptors for IgG, FcgammaRII and FcgammaRIII, differ by their distinct capacities in mediating down-regulation or activation of cellular effector functions, respectively. In this study, antibodies detecting the mouse Ly-17.1 / 2 alloantigen system are demonstrated to be specific for FcgammaRII with no cross-reactivities to other FcgammaR, including FcgammaRIII. Using these FcgammaRII-specific monoclonal antibodies (mAb), the significance of FcgammaRII inhibition of FcgammaRIII was examined in two models of autoantibody [autoimmune hemolytic anemia (AIHA)]- and IgG immune complex-induced (Arthus reaction) inflammation in C57BL / 6 mice in comparison with FcgammaRII(- / -) and FcgammaRIII(- / -) mice. Our results demonstrate that both FcgammaRIII and FcgammaRII contributed to the binding of erythrocytes opsonized with the pathogenic IgG1 autoreactive anti-murine red blood cell antibody 105-2H. However, the functional blocking with anti-FcgammaRII mAb in C57BL / 6 mice and the lack of FcgammaRII expression in FcgammaRII(- / -) mice, which both lowered the threshold level of FcgammaRIII-triggered phagocytosis in vitro, did not results in enhanced disease development of 105-2H mAb-induced AIHA in vivo. This was in sharp contrast to cutaneous Arthus reaction, where FcgammaRIII-mediated activation was inhibited by FcgammaRII. Together these results show that murine AIHA is markedly different from other FcgammaR-dependent inflammatory diseases where FcgammaRIII is normally counterregulated by FcgammaRII.

Opposite Regulation of Type II and III Receptors for Immunoglobulin G in Mouse Glomerular Mesangial Cells and in the Induction of Anti-glomerular Basement Membrane (GBM) Nephritis

“…In contrast to the attenuated phenotype in Fc␥RIII-deficient mice, the genetic deletion of the inhibitory Fc␥RII augmented anti-GBM nephritis (20). These results are very similar to that obtained in other models of IC inflammation (17,18), indicating that Fc␥RIII-mediated activation responses are regulated by the inhibitory Fc␥RII when co-expressed on the same effector cells. In this report, we now tested the concept that resident kidney cells express and function via activating and inhibitory Fc␥Rs, thus providing a pos- sible regulatory pathway for renal infiltration in IC-mediated nephritis.…”

“…To analyze the expression of individual Fc␥Rs within the glomerulus, kidney tissue of Fc␥R-deficient and C57BL/6 mice treated or not with increasing doses (50 -500 ng) of intraperitoneal Escherichia coli LPS (Sigma) were processed for histological examination by immunocytochemical techniques as described (18,32). Fc␥R-positive staining was determined by incubating cryostat sections for 30 min with the antiFc␥RII/III mAb 2.4G2 followed by incubation with the bridging antibody (Z0494) and the rat-APAAP antibody complex (D0488) for 30 min.…”

“…The following FcR-recognizing antibodies were used: anti-Fc␥RII/III (clone 2.4G2, rat anti-mouse IgG) (BD PharMingen, Heidelberg, Germany) and anti-Ly17.2 (clone K9.361, mouse anti-mouse IgG; kindly provided by Dr. U. Hä mmerling, Sloan-Kettering Institute, New York), the latter specifically binding the Fc␥RII antigen (18). Isotype control mAbs with irrelevant specificities were obtained from Immunotech (Hamburg, Germany).…”

“…showed by FACS analysis that antibodies detecting the mouse Ly-17.1/2 alloantigen system are specific for Fc␥RII with no cross-reactivity to Fc␥RIII (18). Now, we used the Fc␥RII(Ly17.2)-specific mAb, K9.361 (42), to examine Fc␥RII surface expression of mouse MC kept under proliferating conditions and stimulated cells with either IFN-␥ or a combination of TNF␣ and IL-1␤.…”

“…In contrast, the two major isoforms of Fc␥RII, Fc␥RIIb1 and Fc␥RIIb2, apparently lack such activating capacity but can inhibit FcR␥-dependent activation signals when co-expressed on the same effector cell (16). This balance between activating/inhibitory Fc␥Rs has been established in various murine models and is highlighted by an increased susceptibility of Fc␥RII (Ϫ/Ϫ) mice to the pathogenic effects of antibodies in IC-triggered inflammation and autoimmune disease (17)(18)(19)(20).…”