Objective. To establish a new murine model of polymyositis (PM) for the understanding of its pathologic mechanisms and the development of new treatment strategies.Methods. C protein-induced myositis (CIM) was induced by a single immunization of recombinant human skeletal C protein in C57BL/6 mice, as well as in CD4-depleted, CD8-depleted, and mutant mice as controls. Some mice were treated with high-dose intravenous immunoglobulin (IVIG) after disease induction. Muscle tissues were examined histologically.Results. In mice with CIM, inflammation was confined to the skeletal muscles. Polymyositis (PM) is a chronic autoimmune inflammatory myopathy affecting striated muscles (1). Damage of muscles results in varying degrees of muscle weakness. Dysphagia with choking episodes and respiratory muscle weakness can occur in acute cases of PM. Currently, the pathogenesis of PM is unknown, and patients are therefore treated with nonspecific immunosuppressants. High-dose corticosteroids are the first-line treatment but are not effective in all patients. Improvement of disease often depends on the dosage of corticosteroids, making a dosage reduction difficult and thus, in many cases, necessitating administration of methotrexate or other immunosuppressants as adjunctive treatment. Because these medications can elicit a wide variety of adverse drug reactions, new therapies to address the specific pathologic features of PM are needed.In affected muscles of patients with PM, infiltration of mononuclear cells leads to muscle fiber necrosis. These cells are found in the endomysial site, where non-necrotic muscle fibers are damaged, and also in the perimysial and perivascular sites of the muscles. Immunohistochemical studies have disclosed that CD8 T cells are most abundant in the endomysial site and invade

Adhesion molecules of the integrin family are implicated not only in leukocyte migration but also in leukocyte activation. Here we characterize the expression and function of fibronectin receptor integrins on rat mast cells. A rat basophilic leukemia cell line (RBL-2H3) and phorbol ester-stimulated rat peritoneal mast cells adhered to fibronectin (FN), vitronectin and fibrinogen. These mast cells expressed fibronectin receptor integrins, including very late antigen (VLA)-4, VLA-5 and vitronectin receptor (VNR), as estimated by immunofluorescent staining and inhibition of FN adherence by newly established mAbs reactive with the rat alpha 4 (MR alpha 4-1), alpha 5 (HM alpha 5-1) or beta 3 (HM beta 3-1) chains of the integrin molecules. The beta-hexosaminidase release, a marker for mast cell degranulation, triggered by high affinity IgE receptor (Fc epsilon RI)-mediated stimulation, was enhanced by adhesion of RBL-2H3 cells to either immobilized FN, MR alpha 4-1, HM alpha 5-1 or HM beta 3-1. This FN enhancement of beta-hexosaminidase release was inhibited by soluble MR alpha 4-1, HM alpha 5-1 and HM beta 3-1 as well as by GRGDSP and DELPQLVTLPHPNHLGPEILDVPST peptides which abrogate VLA-5/VNR and VLA-4 binding to FN respectively. In vivo, passive cutaneous anaphylaxis induced by IgE anti-DNP and DNP-BSA was inhibited by concurrent s.c. injection of MR alpha 4-1, HM alpha 5-1 and HM beta 3-1. These results demonstrate that FN receptor integrins expressed on rat mast cells play an important role in regulating mast cell activation both in vitro and in vivo.

IntroductionOsteoclastogenesis plays an important role in the bone erosion of rheumatoid arthritis (RA). Recently, Notch receptors have been implicated in the development of osteoclasts. However, the responsible Notch ligands have not been identified yet. This study was undertaken to determine the role of individual Notch receptors and ligands in osteoclastogenesis.MethodsMouse bone marrow-derived macrophages or human peripheral blood monocytes were used as osteoclast precursors and cultured with receptor activator of nuclear factor-kappaB ligand (RANKL) and macrophage-colony stimulating factor (M-CSF) to induce osteoclasts. Osteoclasts were detected by tartrate-resistant acid phosphatase (TRAP) staining. K/BxN serum-induced arthritic mice and ovariectomized mice were treated with anti-mouse Delta-like 1 (Dll1) blocking monoclonal antibody (mAb).ResultsBlockade of a Notch ligand Dll1 with mAb inhibited osteoclastogenesis and, conversely, immobilized Dll1-Fc fusion protein enhanced it in both mice and humans. In contrast, blockade of a Notch ligand Jagged1 enhanced osteoclastogenesis and immobilized Jagged1-Fc suppressed it. Enhancement of osteoclastogenesis by agonistic anti-Notch2 mAb suggested that Dll1 promoted osteoclastogenesis via Notch2, while suppression by agonistic anti-Notch1 mAb suggested that Jagged1 suppressed osteoclastogenesis via Notch1. Inhibition of Notch signaling by a gamma-secretase inhibitor suppressed osteoclastogenesis, implying that Notch2/Dll1-mediated enhancement was dominant. Actually, blockade of Dll1 ameliorated arthritis induced by K/BxN serum transfer, reduced the number of osteoclasts in the affected joints and suppressed ovariectomy-induced bone loss.ConclusionsThe differential regulation of osteoclastogenesis by Notch2/Dll1 and Notch1/Jagged1 axes may be a novel target for amelioration of bone erosion in RA patients.

Notch2 and Delta-like 1 (Dll1) have been implicated in the development of marginal zone B (MZB) cells. In the present study, we characterized the expression and function of mouse Notch receptors and ligands in the spleen by using newly generated mAbs. Although Notch2 was expressed on both B and T cells in the spleen, the highest expression was observed on precursors of marginal zone B and MZB cells. Dll1 was expressed on macrophage and erythroblasts in the red pulp, but not on B cells or marginal zone macrophage. Administration of a blocking mAb against Dll1 not only blocked the development of MZB cells in juvenile mice but also gradually depleted the pre-established MZB cells in adult mice, indicating a critical role for Dll1 in the maintenance of MZB cells in the spleen of normal mice. Interestingly, Dll1 was not necessary for the maintenance of MZB cells in lupus-prone (NZB x NZW) F1 mice particularly after the onset of the disease, suggesting that the Dll1 independence may be a feature of dysregulated MZB cells producing auto-antibodies.

Intraarticular gene transfer of cyclin-dependent kinase (CDK) inhibitors to suppress synovial cell cycling has shown efficacy in treating animal models of rheumatoid arthritis. Endogenous CDK inhibitors also modulate immune function via a CDK-independent pathway. Accordingly, systemic administration of small molecules that inhibit CDK may or may not ameliorate arthritis. To address this issue, alvocidib (flavopiridol), known to be tolerated clinically for treating cancers, and a newly synthesized CDK4/6-selective inhibitor were tested for antiarthritic effects. In vitro, they inhibited proliferation of human and mouse synovial fibroblasts without inducing apoptosis. In vivo, treatment of collagen-induced arthritis mice with alvocidib suppressed synovial hyperplasia and joint destruction, whereas serum concentrations of anti-collagen type II (CII) Abs and proliferative responses to CII were maintained. Treatment was effective even when therapeutically administered. Treated mice developed arthritis after termination of treatment. Thus, immune responses to CII were unimpaired. The same treatment ameliorated arthritis induced by K/BxN serum transfer to lymphocyte-deficient mice. Similarly, the CDK4/6-selective inhibitor suppressed collagen-induced arthritis. Both small-molecule CDK inhibitors were effective in treating animal models of rheumatoid arthritis not by suppressing lymphocyte function. Thus, the two small-molecule CDK inhibitors ameliorated arthritis models in a distinctive way, compared with other immunosuppressive drugs.