Development of spontaneous multisystem autoimmune disease and hypersensitivity to antibody-induced inflammation in Fcgamma receptor IIa-transgenic mice

Induction of macrophage secretion of tumor necrosis factor alpha through Fcgamma receptor IIa engagement by rheumatoid arthritis-specific autoantibodies to citrullinated proteins complexed with fibrinogen

OBJECTIVE

Macrophage-derived tumor necrosis factor alpha (TNFalpha) is a dominant mediator of synovitis in rheumatoid arthritis (RA). This study was undertaken to assess whether and how immune complexes (ICs) formed by the interaction of disease-specific autoantibodies to citrullinated proteins (ACPAs) with their main synovial target antigen, citrullinated fibrin, contribute to TNFalpha production by macrophages.

METHODS

An in vitro human model was developed in which monocyte-derived macrophages were stimulated with ACPA-containing ICs that were generated by capturing ACPAs from RA sera on immobilized citrullinated fibrinogen. Cellular activation was evaluated by TNFalpha assay in culture supernatants. Selective blockade of IC interactions with the 3 classes of Fcgamma receptors (FcgammaR) was used to assess the contribution of each receptor to macrophage activation. In addition, 2 citrullinated fibrin-derived peptides bearing major ACPA epitopes were tested for their capacity to inhibit formation of macrophage-activating ACPA-containing ICs.

RESULTS

ACPA-containing ICs induced a dose-dependent TNFalpha secretion by macrophages from 14 of 20 healthy donors. The macrophage response was systematically higher than that of the paired monocyte precursors. TNFalpha secretion was not reduced by blockade of FcgammaRI or FcgammaRIII, but was strongly repressed when interaction of ICs with FcgammaRII was prevented. The 2 citrullinated peptides significantly inhibited ACPA reactivity to citrullinated fibrinogen and, when tested together, almost completely abolished formation of macrophage-activating ICs, thereby diminishing the secreted TNFalpha levels.

CONCLUSION

Our model demonstrates the inflammatory potential of ACPA-containing ICs via engagement of FcgammaRIIa at the surface of macrophages, strongly supporting their pathophysiologic involvement. Continuing dissection of these molecular pathways could open the way to new therapeutic approaches in patients with RA.

FcgammaRIIa genotype predicts progression of HIV infection

Polymorphisms in FcgammaR genes are associated with susceptibility to or severity of a number of autoimmune and infectious diseases. We found that HIV-infected men in the Multicenter AIDS Cohort Study with the FcgammaRIIa RR genotype progressed to a CD4(+) cell count of <200/mm(3) at a faster rate than individuals with the RH or HH genotypes (relative hazard = 1.6; p = 0.0001). However, progression to AIDS (using the broad definition of either a CD4(+) cell count <200/mm(3) or development of an AIDS-defining illness) was less impacted by FcgammaRIIa genotype, largely because HH homozygotes had an increased risk of Pneumocystis jiroveci pneumonia as an AIDS-defining illness. We also showed that chronically infected subjects develop a substantial anti-gp120-specific IgG2 response. Moreover, HIV-1 immune complexes are more efficiently internalized by monocytes from HH subjects compared with RR subjects, likely because of the presence of IgG2 in the complexes. Finally, the FcgammaRIIIa F/V gene polymorphism was not associated with progression of HIV infection, but, as demonstrated previously, did predict the risk of Kaposi's sarcoma. These results demonstrate the importance of FcgammaRs in AIDS pathogenesis and point toward a critical role for interactions between FcgammaRs and immune complexes in disease progression.

High synovial expression of the inhibitory FcgammaRIIb in rheumatoid arthritis

Activating Fc gamma receptors (FcγRs) have been identified as having important roles in the inflammatory joint reaction in rheumatoid arthritis (RA) and murine models of arthritis. However, the role of the inhibitory FcγRIIb in the regulation of the synovial inflammation in RA is less known. Here we have investigated synovial tissue from RA patients using a novel monoclonal antibody (GB3) specific for the FcγRIIb isoform. FcγRIIb was abundantly expressed in synovia of RA patients, in sharp contrast to the absence or weak staining of FcγRIIb in synovial biopsies from healthy volunteers. In addition, the expression of FcγRI, FcγRII and FcγRIII was analyzed in synovia obtained from early and late stages of RA. Compared with healthy synovia, which expressed FcγRII, FcγRIII but not FcγRI, all activating FcγRs were expressed and significantly up-regulated in RA, regardless of disease duration. Macrophages were one of the major cell types in the RA synovium expressing FcγRIIb and the activating FcγRs. Anti-inflammatory treatment with glucocorticoids reduced FcγR expression in arthritic joints, particularly that of FcγRI. This study demonstrates for the first time that RA patients do not fail to up-regulate FcγRIIb upon synovial inflammation, but suggests that the balance between expression of the inhibitory FcγRIIb and activating FcγRs may be in favour of the latter throughout the disease course. Anti-inflammatory drugs that target activating FcγRs may represent valuable therapeutics in this disease.

Pathogenic complement activation in collagen antibody-induced arthritis in mice requires amplification by the alternative pathway

Immune complex-induced inflammation can be mediated by the classical pathway of complement. However, using mice genetically deficient in factor B or C4, we have shown that the collagen Ab-induced model of arthritis requires the alternative pathway of complement and is not dependent on the classical pathway. We now demonstrate that collagen Ab-induced arthritis is not altered in mice genetically deficient in either C1q or mannose-binding lectins A and C, or in both C1q and mannose-binding lectins. These in vivo results prove the ability of the alternative pathway to carry out pathologic complement activation in the combined absence of intact classical and lectin pathways. C3 activation was also examined in vitro by adherent collagen-anti-collagen immune complexes using sera from normal or complement-deficient mice. These results confirm the ability of the alternative pathway to mediate immune complex-induced C3 activation when C4 or C1q, or both C1q and mannose-binding lectins, are absent. However, when all three activation pathways of complement are intact, initiation by immune complexes occurs primarily by the classical pathway. These results indicate that the alternative pathway amplification loop, with its ability to greatly enhance C3 activation, is necessary to mediate inflammatory arthritis induced by adherent immune complexes.

Antibody-induced arthritis: disease mechanisms and genes involved at the effector phase of arthritis

During the development of rheumatoid arthritis (RA) autoantibodies to IgG-Fc, citrullinated proteins, collagen type II (CII), glucose 6 phosphoisomerase (G6PI) and some other self-antigens appear. Of these, a pathogenic effect of the anti-CII and anti-G6PI antibodies is well demonstrated using animal models. These new antibody mediated arthritis models have proven to be very useful for studies involved in understanding the molecular pathways of the induction of arthritis in joints. Both the complement and FcgammaR systems have been found to play essential roles. Neutrophils and macrophages are important inflammatory cells and the secretion of tumour necrosis factor-alpha and IL-1beta is pathogenic. The identification of the genetic polymorphisms predisposing to arthritis is important for understanding the complexity of arthritis. Disease mechanisms and gene regions studied using the two antibody-induced arthritis mouse models (collagen antibody-induced arthritis and serum transfer-induced arthritis) are compared and discussed for their relevance in RA pathogenesis.

FcgammaRII and multi-system autoimmune disease

The FcR are a crucial link in the immune response between humoral and cellular immunity and cell-based effector systems, mediating a wide variety of physiological and biochemical responses. The FcR for IgG (FcgammaR) and in particular the most widely expressed of these, FcgammaRII, are important in regulating adaptive immunity. Disruption of their function is a key factor in the development of autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), which are characterized by chronic, multi-organ inflammation. Studies of the FcgammaRII include structure/function relationships, investigation of the associations between FcR polymorphisms and human disease and animal studies using knockout or transgenic mouse models. These investigations showed that the various forms of FcgammaRII interact with immune complexes to either initiate or inhibit inflammation. In conjunction with environmental antigens and genotype, the FcgammaRII activating and inhibitory receptors determine the nature and magnitude of response to antigens. In this review, the structure and function of the FcgammaRIIs and their role in immune complex-mediated auto-immunity are discussed.

The complex role of Fcγ receptors in the pathology of arthritis

Autoantibodies of the IgG class and the immune complexes they form are central players in the pathology of rheumatoid arthritis (RA). Receptors for the Fc part of IgG, FcgammaR constitute one of the main effector mechanisms through which IgG immune complexes exert their action. The different members of the FcgammaR family exhibit extensive structural homology leading to redundancy in ligand specificity and signal transduction. Moreover, the initiation of effector mechanisms by IgG immune complexes can also be mediated by the complement system. This strong redundancy and high degree of complexity hampers a direct in vivo analysis of antibody effector pathways. Over the last decade, mice deficient for different combinations of FcgammaR have been generated by gene targeting. These knockout mice provide excellent tools to define the specific contribution of the different FcgammaR to IgG effector pathways in well-established in vivo mouse models for arthritis. This review will discuss the results of the studies that analyze the role of the different members of the FcgammaR family in murine arthritis models and their implications for our understanding of the human disease.

Electro-acupuncture at acupoint ST36 reduces inflammation and regulates immune activity in Collagen-Induced Arthritic Mice

This study aimed to investigate the anti-inflammatory, anti-arthritic and immuno-regulatory effects of electro-acupuncture (EA) at ST36 on Collagen-induced arthritis (CIA) in mice. Male DBA/1J mice were divided into five groups: Normal, Control, NR (needle retention), EAI and EAII. All mice except those in the normal group were immunized with Collagen II for arthritis induction. Acupuncture needles were inserted into mice ST36 and electrical currents at a frequency of 2 Hz in a continuous rectangular wave form were conducted through the needles for 15 min, 3 times a week. EA treatments were administered for 5 weeks in the EAI group and for 9 weeks in the EAII group. The mice in the NR group were acupunctured in the same manner as the EA groups and the needles were retained for 15 min without electrical stimulation. CIA incidence analysis, ELISA, histological analysis and FACS analysis were performed to evaluate the effect of EA on CIA. EA at ST36 significantly reduced CIA incidence, IL-6, TNF-a, INF-γ, collagen II antibody, IgG and IgM levels in CIA mice serum and prevented knee joint destruction. EA at ST36 also reduced CD69+/CD3e+ cells and CD11a+/CD19+ cells in CIA mice lymph nodes, and CD11b+/Gr1+ cells in CIA mice knee joints. The ratios of CD3e+ cells to CD19+ cells, and CD8+ cells to CD4+ cells were maintained closer to the normal range in the EA groups as compared with the control group or the NR group. EAII was more effective than EAI throughout all the measurements. The NR was effective as well, though less effective than EA. EA at ST36 may have an anti-inflammatory, anti-arthritic and immuno-regulatory effects on CIA in mice. The effectiveness is stronger when EA starts earlier and is applied longer. Needle retention without electrical stimulation may be effective on CIA as well, however less effective than EA. Electrical stimulation and acupoint ST36 may have synergistic effects on CIA.

Surface-bound anti-type II collagen-containing immune complexes induce production of tumor necrosis factor alpha, interleukin-1beta, and interleukin-8 from peripheral blood monocytes via Fc gamma receptor IIA: a potential pathophysiologic mechanism for humoral anti-type II collagen immunity in arthritis

OBJECTIVE

Type II collagen (CII) is a major component of hyaline cartilage, and antibodies against CII are found in a subgroup of patients with rheumatoid arthritis. We undertook this study to investigate whether and how antibodies directed against CII can form solid-phase immune complexes (ICs) with cytokine-inducing properties in a model theoretically resembling the situation in the inflamed joint, in which CII is exposed for interaction with anti-CII antibodies during periods of inflammation.

METHODS

Sixty-five arthritis patients with varying levels of anti-native CII antibodies and 10 healthy controls were evaluated concerning anti-CII and cytokines induced in a solid-phase IC model. Monocytes were either depleted or enriched to define responder cells. Antibodies blocking Fc gamma receptors (Fc gammaR) were used to define the responsible T cell surface receptors.

RESULTS

ICs containing anti-CII from arthritis patients induced the production of tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and IL-8. We found a close correlation between enzyme-linked immunosorbent assay optical density values and induction of TNFalpha (r = 0.862, P < 0.0001), IL-1beta (r = 0.839, P < 0.0001), and IL-8 (r = 0.547, P < 0.0001). The anti-CII-containing IC density threshold needed for cytokine induction differed among peripheral blood mononuclear cell donors. Anti-CII-containing IC-induced cytokine production was almost totally abolished (>99%) after monocyte depletion, and receptor blocking studies showed significant decreases in the production of TNFalpha, IL-1beta, and IL-8 after blocking Fc gammaRIIa, but not after blocking Fc gammaRIII.

CONCLUSION

These findings represent a possible mechanism for perpetuation of joint inflammation in the subgroup of arthritis patients with high levels of anti-CII. Blockade of Fc gammaRIIa and suppression of synovial macrophages are conceivable treatment options in such patients.

Alteration of the Fc gamma RIIa dimer interface affects receptor signaling but not ligand binding

The aggregation of cell surface FcRs by immune complexes induces a number of important Ab-dependent effector functions. However, despite numerous studies that examine receptor function, very little is known about the molecular organization of these receptors within the cell. In this study, protein complementation, mutagenesis, and ligand binding analyses demonstrate that human FcgammaRIIa is present as a noncovalent dimer form. Protein complementation studies found that FcgammaRIIa molecules are closely associated. Mutagenesis of the dimer interface, as identified by crystallographic analyses, did not affect ligand binding yet caused significant alteration to the magnitude and kinetics of receptor phosphorylation. The data suggest that the ligand binding and the dimer interface are distinct regions within the receptor, and noncovalent dimerization of FcgammaRIIa may be an essential feature of the FcgammaRIIa signaling cascade.