Falk Nimmerjahn

Divergent Immunoglobulin G Subclass Activity Through Selective Fc Receptor Binding

Subclasses of immunoglobulin G (IgG) display substantial differences in their ability to mediate effector responses, contributing to variable activity of antibodies against microbes and tumors. We demonstrate that the mechanism underlying this long-standing observation of subclass dominance in function is provided by the differential affinities of IgG subclasses for specific activating IgG Fc receptors compared with their affinities for the inhibitory IgG Fc receptor. The significant differences in the ratios of activating-to-inhibitory receptor binding predicted the in vivo activity. We suggest that these highly predictable functions assigned by Fc binding will be an important consideration in the design of therapeutic antibodies and vaccines.

Recapitulation of IVIG Anti-Inflammatory Activity with a Recombinant IgG Fc

It is well established that high doses of monomeric immunoglobulin G (IgG) purified from pooled human plasma [intravenous immunoglobulin (IVIG)] confer anti-inflammatory activity in a variety of autoimmune settings. However, exactly how those effects are mediated is not clear because of the heterogeneity of IVIG. Recent studies have demonstrated that the anti-inflammatory activity of IgG is completely dependent on sialylation of the N-linked glycan of the IgG Fc fragment. Here we determine the precise glycan requirements for this anti-inflammatory activity, allowing us to engineer an appropriate IgG1 Fc fragment, and thus generate a fully recombinant, sialylated IgG1 Fc with greatly enhanced potency. This therapeutic molecule precisely defines the biologically active component of IVIG and helps guide development of an IVIG replacement with improved activity and availability.

The inhibitory Fcγ receptor modulates autoimmunity by limiting the accumulation of immunoglobulin G + anti-DNA plasma cells

Deletion of the gene encoding the Fc immunoglobulin G receptor IIB (FcγRIIB) results in a fulminant, lupus-like disease in C57BL/6 but not BALB/c mice. Here we have investigated this strain-specific, epistatic loss of tolerance using gene-targeted immunoglobulin variable heavy-chain (VH) alleles 3H9 or 56R, which encode DNA-specific heavy chains, expressed on the C57BL/6 or BALB/c background. The combination of C57BL/6 and VH 56R (B6.56R) resulted in a loss of tolerance; hybridoma and single-cell analysis indicated an FcγRIIB-independent difference in immunoglobulin light-chain usage, consistent with an alteration in receptor editing. FcγRIIB deficiency resulted in an increase in immunoglobulin G (IgG) antibodies to DNA in the serum, an increased frequency of anti-DNA-reactive IgG+ B cells with a plasma cell phenotype and immune complex deposition in the glomeruli and renal disease in B6.56R mice. Thus, FcγRIIB provides a distal peripheral checkpoint to limit the accumulation of autoreactive plasma cells, thereby maintaining tolerance.

Pathology and protection in nephrotoxic nephritis is determined by selective engagement of specific Fc receptors

Introduction of heterologous anti–glomerular basement membrane antiserum (nephrotoxic serum, NTS) into presensitized mice triggers the production of IgG anti-NTS antibodies that are predominantly IgG2b and the glomerular deposition of pathogenic immune complexes, leading to accelerated renal disease. The pathology observed in this model is determined by the effector cell activation threshold that is established by the coexpression on infiltrating macrophages of the IgG2a/2b restricted activation receptor FcγRIV and its inhibitory receptor counterpart, FcγRIIB. Blocking FcγRIV with a specific monoclonal antibody thereby preventing IgG2b engagement or treatment with high dose intravenous γ-globulin (IVIG) to down-regulate FcγRIV while up-regulating FcγRIIB, protects mice from fatal disease. In the absence of FcγRIIB, IVIG is not protective; this indicates that reduced FcγRIV expression alone is insufficient to protect animals from pathogenic IgG2b immune complexes. These results establish the significance of specific IgG subclasses and their cognate FcγRs in renal disease.

Endoglycosidase treatment abrogates IgG arthritogenicity: Importance of IgG glycosylation in arthritis.

The glycosylation status of IgG has been implicated in the pathology of rheumatoid arthritis. Earlier, we reported the identification of a novel secreted endo‐β‐N‐acetylglucosaminidase (EndoS), secreted by Streptococcus pyogenes that specifically hydrolyzes the β‐1,4‐di‐N‐acetylchitobiose core of the asparagine‐linked glycan of human IgG. Here, we analyzed the arthritogenicity of EndoS‐treated collagen typeu2004II (CII)‐specific mouse mAb in vivo. Endoglycosidase treatment of the antibodies inhibited the induction of arthritis in (BALB/c × B10.Q) F1 mice and induced a milder arthritis in B10.RIII mice as compared with the severe arthritis induced by non‐treated antibodies. Furthermore, EndoS treatment did not affect the binding of IgG to CII and their ability to activate complement, but it resulted in reduced IgG binding to FcγR and disturbed the formation of stable immune complexes. Hence, the asparagine‐linked glycan on IgG plays a crucial role in the development of arthritis.

Deletion of Activating Fcγ Receptors Does Not Confer Protection in Murine Cryoglobulinemia-Associated Membranoproliferative Glomerulonephritis

Many types of glomerulonephritis are initiated by the deposition of immune complexes, which induce tissue injury via either engagement of Fc receptors on effector cells or via complement activation. Four murine Fcgamma receptors (FcgammaRs) have been identified at present. Ligand binding to FcgammaRI, III, and IV induces cell activation via the immunoreceptor tyrosine-based activation motif on the common gamma chain (FcRgamma). In this study, FcRgamma chain knockout (FcRgamma(-/-)) mice were crossed with thymic stromal lymphopoietin transgenic (TSLPtg) mice, which develop cryoglobulinemic membranoproliferative glomerulonephritis (MPGN). Female mice were studied at 30 and 50 days of age, when MPGN is in early and fully developed stages, respectively. Both TSLPtg and TSLPtg/FcRgamma(-/-) mice developed MPGN with massive glomerular immune deposits, mesangial cell proliferation, extensive mesangial matrix accumulation, and macrophage influx. TSLPtg/FcRgamma(-/-) mice had more glomerular immune complex deposits and higher levels of circulating cryoglobulins, IgG2a, IgG2b, and IgM, compared with TSLPtg mice. TSLPtg and TSLPtg/FcRgamma(-/-) mice developed similar levels of proteinuria. These results demonstrated that deletion of activating FcgammaRs does not confer protection in this model of immune complex-mediated MPGN. The findings contradict accepted paradigms on the role of activating FcgammaRs in promoting features of glomerulonephritis as seen in other model systems. We speculate engagement of FcgammaRs on cells such as monocytes/macrophages may be important for the clearance of deposited immune complexes and extracellular matrix proteins.