Muscle-specific kinase (MuSK) is critical for the synaptic clustering of nicotinic acetylcholine receptors (AChRs) and plays multiple roles in the organization and maintenance of neuromuscular junctions (NMJs). MuSK is activated by agrin, which is released from motoneurons, and induces AChR clustering at the postsynaptic membrane. Although autoantibodies against the ectodomain of MuSK have been found in a proportion of patients with generalized myasthenia gravis (MG), it is unclear whether MuSK autoantibodies are the causative agent of generalized MG. In the present study, rabbits immunized with MuSK ectodomain protein manifested MG-like muscle weakness with a reduction of AChR clustering at the NMJs. The autoantibodies activated MuSK and blocked AChR clustering induced by agrin or by mediators that do not activate MuSK. Thus MuSK autoantibodies rigorously inhibit AChR clustering mediated by multiple pathways, an outcome that broadens our general comprehension of the pathogenesis of MG.
Kazuhiro Shigemoto, Sachiho Kubo, Naoki Maruyama, Naohito Hato, Hiroyuki Yamada, Chen Jie, Naoto Kobayashi, Katsumi Mominoki, Yasuhito Abe, Norifumi Ueda,, Seiji Matsuda
One approach to improving efficacy in MS therapy is to identify medications that provide additive or synergistic benefit in combination. Orally administered cholesterol-lowering HMG-CoA reductase inhibitors (known as statins), which exhibit immunomodulatory properties and are effective in treatment of the MS model EAE, are being tested in MS. As atorvastatin can enhance protective Th2 responses and has a different mechanism of action than glatiramer acetate (GA), a parenterally administered immunomodulatory agent approved for MS treatment, we tested whether the combination of these agents could be beneficial in EAE. Combination therapy using suboptimal doses of atorvastatin and GA prevented or reversed clinical and histologic EAE. Secretion of proinflammatory Th1 cytokines was reduced — and conversely Th2 cytokine secretion was increased — in these mice, but not in mice treated with each drug alone at the same doses. Monocytes treated with the combination of suboptimal doses of atorvastatin and GA secreted an antiinflammatory type II cytokine pattern and, when used as APCs, promoted Th2 differentiation of naive myelin-specific T cells. Our results demonstrate that agents with different mechanisms of immune modulation can combine in a synergistic manner for the treatment of CNS autoimmunity and provide rationale for testing the combination of atorvastatin and GA in MS.
Olaf Stüve, Sawsan Youssef, Martin S. Weber, Stefan Nessler, Hans-Christian von Büdingen, Bernhard Hemmer, Thomas Prod’homme, Raymond A. Sobel, Lawrence Steinman, Scott S. Zamvil
Antibodies against citrullinated proteins are specific and predictive markers for rheumatoid arthritis although the pathologic relevance of these antibodies remains unclear. To investigate the significance of these autoantibodies, collagen-induced arthritis (CIA) in mice was used to establish an animal model of antibody reactivity to citrullinated proteins. DBA/1J mice were immunized with bovine type II collagen (CII) at days 0 and 21, and serum was collected every 7 days for analysis. Antibodies against both CII and cyclic citrullinated peptide, one such citrullinated antigen, appeared early after immunization, before joint swelling was observed. Further, these antibodies demonstrated specific binding to citrullinated filaggrin in rat esophagus by indirect immunofluorescence and citrullinated fibrinogen by Western blot. To evaluate the role of immune responses to citrullinated proteins in CIA, mice were tolerized with a citrulline-containing peptide, followed by antigen challenge with CII. Tolerized mice demonstrated significantly reduced disease severity and incidence compared with controls. We also identified novel murine monoclonal antibodies specific to citrullinated fibrinogen that enhanced arthritis when coadministered with a submaximal dose of anti-CII antibodies and bound targets within the inflamed synovium of mice with CIA. These results demonstrate that antibodies against citrullinated proteins are centrally involved in the pathogenesis of autoimmune arthritis.
Kristine A. Kuhn, Liudmila Kulik, Beren Tomooka, Kristin J. Braschler, William P. Arend, William H. Robinson, V. Michael Holers
B cells have multiple roles in immune activation and inflammation separate from their capacity to produce antibodies. B cell depletion is currently under intense investigation as a therapeutic strategy for autoimmune diseases. The TNF family members B cell–activating factor of the TNF family (BAFF) and its homolog A proliferation-inducing ligand (APRIL) are B cell survival and differentiation factors and are therefore rational therapeutic targets. We compared the effects of BAFF receptor–Ig, which blocks only BAFF, with those of transmembrane activator and calcium modulator ligand interactor–Ig, which blocks both BAFF and APRIL, in a murine SLE model. Both reagents prolonged the life of NZB/W F1 mice when given either before or after disease onset. Many immunologic effects of the 2 reagents were similar, including B cell and B cell subset depletion and prevention of the progressive T cell activation and dendritic cell accumulation that occurs with age in NZB/W mice without substantial effects on the emergence of the IgG anti–double-stranded DNA response. Furthermore, both reagents inhibited the T cell–independent marginal zone B cell response to particulate antigen delivered i.v., but not the B1 B cell response to the same antigen delivered i.p. In contrast, blockade of both BAFF and APRIL, but not blockade of BAFF alone, reduced the serum levels of IgM antibodies, decreased the frequency of plasma cells in the spleen, and inhibited the IgM response to a T cell–dependent antigen. The differences between selective and nonselective BAFF blockade are relevant to the choice of a BAFF blocking agent for the treatment of autoimmune and malignant diseases.
Meera Ramanujam, Xiaobo Wang, Weiqing Huang, Zheng Liu, Lena Schiffer, Haiou Tao, Daniel Frank, Jeffrey Rice, Betty Diamond, Karl O.A. Yu, teven Porcelli,, Anne Davidson
Recent evidence has indicated that leptin, an adipocyte-secreted hormone belonging to the helical cytokine family, significantly influences immune and autoimmune responses. We investigate here the mechanisms by which in vivo abrogation of leptin effects protects SJL/J mice from proteolipid protein peptide PLP139–151-induced EAE, an animal model of MS. Blockade of leptin with anti-leptin Abs or with a soluble mouse leptin receptor chimera (ObR:Fc), either before or after onset of EAE, improved clinical score, slowed disease progression, reduced disease relapses, inhibited PLP139–151-specific T cell proliferation, and switched cytokine secretion toward a Th2/regulatory profile. This was also confirmed by induction of forkhead box p3 (Foxp3) expression in CD4+ T cells in leptin-neutralized mice. Importantly, anti-leptin treatment induced a failure to downmodulate the cyclin-dependent kinase inhibitor p27 (p27Kip-1) in autoreactive CD4+ T cells. These effects were associated with increased tyrosine phosphorylation of both ERK1/2 and STAT6. Taken together, our data provide what we believe is a new molecular basis for leptin antagonism in EAE and envision novel strategies of leptin-based molecular targeting in the disease.
Veronica De Rosa, Claudio Procaccini, Antonio La Cava, Paolo Chieffi, Giovanni Francesco Nicoletti, Silvia Fontana, Serafino Zappacosta, Giuseppe Matarese
We describe here a patient with a clinical and molecular diagnosis of recombinase activating gene 1–deficient (RAG1-deficient) SCID, who produced specific antibodies despite minimal B cell numbers. Memory B cells were detected and antibodies were produced not only against some vaccines and infections, but also against autoantigens. The patient had severely reduced levels of oligoclonal T cells expressing the αβ TCR but surprisingly normal numbers of T cells expressing the γδ TCR. Analysis at a clonal level and TCR complementarity-determining region–3 spectratyping for γδ T cells revealed a diversified oligoclonal repertoire with predominance of cells expressing a γ4-δ3 TCR. Several γδ T cell clones displayed reactivity against CMV-infected cells. These observations are compatible with 2 non–mutually exclusive explanations for the γδ T cell predominance: a developmental advantage and infection-triggered, antigen-driven peripheral expansion. The patient carried the homozygous hypomorphic R561H RAG1 mutation leading to reduced V(D)J recombination but lacked all clinical features characteristic of Omenn syndrome. This report describes a new phenotype of RAG deficiency and shows that the ability to form specific antibodies does not exclude the diagnosis of SCID.
Stephan Ehl, Klaus Schwarz, Anselm Enders, Ulrich Duffner, Ulrich Pannicke, Joachim Kühr, Françoise Mascart, Annette Schmitt-Graeff, Charlotte Niemeyer, Paul Fisch
Breach of B cell tolerance is central to the pathogenesis of systemic lupus erythematosus (SLE). However, how B cell tolerance is subverted in human SLE is poorly understood due to difficulties in identifying relevant autoreactive B cells and in obtaining lymphoid tissue. We have circumvented these limitations by using tonsil biopsies to study autoreactive B cells (9G4 B cells), whose regulation is abnormal in SLE. Here we show that 9G4 B cells are physiologically excluded during the early stages of the GC reaction before acquiring a centroblast phenotype. Furthermore, we provide evidence to indicate that an anergic response to B cell receptor stimulation may be responsible for such behavior. In contrast, in SLE, 9G4 B cells progressed unimpeded through this checkpoint, successfully participated in GC reactions, and expanded within the post-GC IgG memory and plasma cell compartments. The faulty regulation of 9G4 B cells was not shared by RA patients. To our knowledge, this work represents the first comparative analysis of the fate of a specific autoreactive human B cell population. The results identify a defective tolerance checkpoint that appears to be specific for human SLE.
Amedeo Cappione III, Jennifer H. Anolik, Aimee Pugh-Bernard, Jennifer Barnard, Paul Dutcher, Gregg Silverman, Iñaki Sanz
NF-κB is an important component of both autoimmunity and bone destruction in RA. NF-κB–inducing kinase (NIK) is a key mediator of the alternative arm of the NF-κB pathway, which is characterized by the nuclear translocation of RelB/p52 complexes. Mice lacking functional NIK have no peripheral lymph nodes, defective B and T cells, and impaired receptor activator of NF-κB ligand–stimulated osteoclastogenesis. We investigated the role of NIK in murine models of inflammatory arthritis using Nik–/– mice. The serum transfer arthritis model is initiated by preformed antibodies and required only intact neutrophil and complement systems in recipients. While Nik–/– mice had inflammation equivalent to that of Nik+/+ controls, they showed significantly less periarticular osteoclastogenesis and less bone erosion. In contrast, Nik–/– mice were completely resistant to antigen-induced arthritis (AIA), which requires intact antigen presentation and lymphocyte function but not lymph nodes. Additionally, transfer of Nik+/+ splenocytes or T cells to Rag2–/– mice conferred susceptibility to AIA, while transfer of Nik–/– cells did not. Nik–/– mice were also resistant to a genetic, spontaneous form of arthritis, generated in mice expressing both the KRN T cell receptor and H-2g7. Thus, NIK is important in the immune and bone-destructive components of inflammatory arthritis and represents a possible therapeutic target for these diseases.
Kunihiko Aya, Muhammad Alhawagri, Amanda Hagen-Stapleton, Hideki Kitaura, Osami Kanagawa, Deborah Veis Novack
The progression of immune responses is generally associated with an increase in the overall avidity of antigen-specific T cell populations for peptide-MHC. This is thought to result from preferential expansion of high-avidity clonotypes at the expense of their low-avidity counterparts. Since T cell antigen-receptor genes do not mutate, it is puzzling that high-avidity clonotypes do not predominate from the outset. Here we provide a developmental basis for this phenomenon in the context of autoimmunity. We have carried out comprehensive studies of the diabetogenic CD8+ T cell population that targets residues 206–214 of the β cell antigen islet-specific glucose-6-phosphatase catalytic subunit–related protein (IGRP206–214) and undergoes avidity maturation as disease progresses. We find that the succession of IGRP206–214–specific clonotypes with increasing avidities during the progression of islet inflammation to overt diabetes in nonobese diabetic mice is fueled by autoimmune inflammation but opposed by systemic tolerance. As expected, naive high-avidity IGRP206–214–specific T cells respond more efficiently to antigen and are significantly more diabetogenic than their intermediate- or low-avidity counterparts. However, central and peripheral tolerance selectively limit the contribution of these high-avidity T cells to the earliest stages of disease without abrogating their ability to progressively accumulate in inflamed islets and kill β cells. These results illustrate the way in which incomplete deletion of autoreactive T cell populations of relatively high avidity can contribute to the development of pathogenic autoimmunity in the periphery.
Bingye Han, Pau Serra, Jun Yamanouchi, Abdelaziz Amrani, John F. Elliott, Peter Dickie, Teresa P. DiLorenzo, Pere Santamaria
Osteopontin (OPN) is an extracellular matrix protein of pleiotropic properties and has been recently recognized as a potential inflammatory cytokine. In this study, we demonstrate, for the first time to our knowledge, that overexpression of OPN in synovial T cells is associated with local inflammatory milieu and that OPN acts as an important mediator in amplification and perpetuation of rheumatoid synovitis. The study revealed that mRNA expression of OPN was highly elevated in CD4+ synovial T cells derived from patients with RA, which correlated with increased OPN concentrations in synovial fluid (SF). The pattern of OPN overexpression was confined to rheumatoid synovium and correlated with coexpression of selected OPN receptors in synovial T cells, including integrins αv and β1 and CD44. RA-derived SF stimulated the expression of OPN in T cells, which was attributable to IL-10 present in SF and abrogated by anti–IL-10 antibody. Among the more than 300 autoimmune and inflammatory response genes examined, OPN selectively induced the expression of proinflammatory cytokines and chemokines known to promote migration and recruitment of inflammatory cells. Furthermore, it was evident that OPN activated transcription factor NF-κB in mononuclear cells. The study has important implications for understanding the role of OPN in rheumatoid synovitis and other inflammatory conditions.
Guangwu Xu, Hong Nie, Ningli Li, Wenxin Zheng, Dongqing Zhang, Guozhang Feng, Liqing Ni, Rong Xu, Jian Hong, Jingwu Z. Zhang
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