A complement C3 inhibitor specifically targeted to sites of complement activation effectively ameliorates collagen-induced arthritis in DBA/1J mice.

Collagen-induced arthritis (CIA) represents an animal model of autoimmune polyarthritis with similarities to human rheumatoid arthritis, and therapy with various systemic complement-inhibitory proteins has been investigated in this model with varying results. We investigated the use of complement receptor 2 (CR2)-Crry, a complement inhibitor with the ability to target C3 breakdown products deposited in a rheumatic joint. Following induction of CIA in DBA/1J mice, animals were treated with either PBS or CR2-Crry (every other day, every 4 days, or with a single injection). The severity of clinical disease was significantly reduced in all CR2-Crry-treated groups compared with controls. Joints from mice receiving multiple doses of CR2-Crry showed significantly decreased inflammatory cell infiltrate, cartilage damage, pannus formation, and bone damage. CR2-Crry treatment also significantly decreased production of anti-collagen IgG and the inflammatory cytokines TNF-alpha and IL-1beta. IL-10 and IL-1Ra levels were increased in CR2-Crry-treated mice. CR2-Crry localized preferentially in the joints of mice with CIA. Analysis of IgG and C3 deposition in the joints of treated animals indicated that both complement regulation and the modulation of anti-collagen Ab production contributed to the protective effects of CR2-Crry. Of interest, a previous study reported that Crry-Ig, an untargeted counterpart of CR2-Crry, had minimal effect on disease, even when administered at a sufficiently high dose to maintain chronic complement inhibition.