Note that the 2 2 mice in pair 4 had undetectable arthritis in the measured joint but unambiguous arthritis in the other paws, resulting in discrepancies between the switch in ankle thickness and the clinical score. induction, and the cartilage of these arthritic mice contained deposits of C3. == Conclusion == In a mouse model in which the option pathway of match activation is critical to the induction of arthritis by autoantibodies, circulating C3 was necessary and sufficient for arthritis induction. The match cascade is essential for the induction of inflammatory arthritis by autoantibodies in at least 2 mouse models (13). The role of match in human rheumatoid arthritis (RA) has been more difficult to assess, but a contribution of this pathway is suggested by several findings. First, match components are depleted (4,5) and match degradation products are generated (6,7) in the synovial fluid in RA but not other types of inflammatory arthritis. Second, C3 is usually deposited on the surface Lodenafil of cartilage and synovium in RA (8,9), as it is in various rodent models (1012). The details of match involvement are particularly obvious in the K/BxN mouse serum-transfer model. K/BxN mice uniformly develop severe, symmetric, inflammatory arthritis due to activation of the KRN transgene-encoded T cell receptor by a peptide from your glycolytic enzyme glucose-6-phosphate isomerase (GPI) offered by the class II major histocompatibility complex molecule Ag7(13), leading to massive production of anti-GPI antibodies. These antibodies can effectively induce arthritis upon transfer into other mice (14). Because a wide range of natural mutant and gene-disrupted mouse strains can be used as recipients, this serum-transfer model has allowed the delineation of many genes and cell types required downstream of autoantibody production (1,1518). With regard to the match cascade, factors B, D (Monach PA: unpublished observations), C3, C5, and the receptor for C5a (C5aR) are required, whereas C1q, C4, C6, and the match receptors Lodenafil CR1, CR2, and CR3 are not (1,19). Thus, induction of arthritis requires the alternative pathway of match activation, leading to production of the chemoattractant and activating mediator C5a. Recently, a similar requirement for option but not classical pathway elements was found for induction of arthritis by antibodies directed against type II collagen (20). Most studies of match in RA have not differentiated between activation of the classical and alternate pathways, but one that did so indicated that local activation of the alternative pathway in synovial fluid is particularly characteristic of RA (21). The details of C3 involvement in inflammatory arthritis are of particular interest, not only because this protein is involved in all of the major pathways of match activation and subsequent activation Lodenafil of effector mechanisms, but also because both systemic and local synthesis have been well documented. A few years ago, one might have Rabbit Polyclonal to CA12 assumed that this obligatory source of C3 and other essential match Lodenafil components would be the liver. The liver is thought to be the source of the vast majority of circulating C3, and although this protein has a relatively short half-life, its concentration in plasma is the highest of any match protein, at 1.01.4 mg/ml. However, not only has the synthesis of match proteins by leukocytes now been clearly exhibited (2224), but leukocyte-derived C3 was found to be sufficient for the generation of antibody responses to a model antigen (25) and to be both necessary and sufficient for optimal antibody responses to intradermal herpes simplex virus contamination in mice (26,27). Production of C3 by the inflamed synovium from patients with RA has also been exhibited (28), and both hematopoietic and nonhematopoietic cells were implicated as potential sources (29,30), leading to the proposal that local synthesis of C3 might be important in propagating inflammation (30). Because it is not currently possible to test this hypothesis in human RA, we did so in the K/BxN mouse serum-transfer system by using bone marrow chimeras and parabiotic mice. == MATERIALS AND METHODS == == Mice == C3/mice (31) were managed locally; C57BL/6 (B6) mice and B6 mice congenic for the CD45.1 isoform were purchased from your Jackson Laboratory (Bar Harbor, ME). Animals were managed under specific pathogenfree conditions, and all procedures were performed in accordance Lodenafil with Institutional Animal Care.