Deletion of the gene encoding CD59a in mice increases disease severity in a murine model of rheumatoid arthritis

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Abstract
Objective To investigate the roles of CD59a in the protection of joint tissue in the context of murine antigen‐induced arthritis (AIA). Methods AIA was triggered in CD59a‐deficient (CD59a−/−) mice and in CD59a‐sufficient (CD59a+/+) controls; the course and severity of disease were compared between groups. The effects on arthritis of restoring CD59 to the joint in CD59a−/− mice by use of a membrane‐targeted recombinant CD59 were also explored. Results Disease, as assessed clinically by measurement of joint swelling on day 1 (P < 0.0001), day 2 (P < 0.01), and day 7 (P < 0.02) and histologically from indicators of joint damage on day 21 (P < 0.02), was significantly enhanced in CD59a−/− mice compared with CD59a+/+ wild‐type controls. Membrane attack complex (MAC) deposition in the arthritic joints of CD59a−/− mice was also increased compared with that in the joints of CD59a+/+ controls. Restitution of CD59 activity in joints of CD59a−/− mice was attempted with soluble recombinant rat CD59 (sCD59) or with a novel membrane‐targeted rat CD59 derivative (sCD59‐APT542). Strong immunohistochemical staining of the synovial membrane and subsynovial tissue was apparent in sCD59‐APT542–injected joints, but not in joints injected with untargeted sCD59. Intraarticular administration of sCD59‐APT542 markedly ameliorated disease severity in CD59a−/− mice, knee swelling was significantly reduced over the time course of the disease, and joint damage, assessed histologically, was significantly milder on day 21 (P < 0.05). Conclusion These data firmly implicate the MAC of complement as a major effector of joint damage in the murine AIA model of rheumatoid arthritis (RA), and they provide a rationale for the inhibition of MAC assembly as a therapeutic strategy for RA.

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