Amelioration of collagen-induced arthritis by human recombinant soluble FcγRIIb

Immune complex (IC) binding to Fc gamma receptors (FcγRs) is central for inflammatory reactions seen in autoimmune diseases. Consequently, a therapeutic agent with a possibility to interfere with binding of pathogenic IC to FcγRs would be valuable in autoimmune disorders such as rheumatoid arthritis (RA). Here we have explored the therapeutic effect of a recombinant soluble human FcγRIIb (sFcγRIIb) protein in collagen-induced arthritis (CIA). In vitro studies of the sFcγRIIb demonstrated binding to mouse IgG, suggesting that sFcγRIIb can absorb pathogenic IgG anti-collagen type II (CII) IC in vivo. Hence, administration of sFcγRIIb significantly reduced CIA severity compared to control treated mice. The sFcγRIIb treated mice had significantly less IgG anti-CII antibodies in serum and lower mRNA levels of inflammatory cytokines compared to control mice. In conclusion, sFcγRIIb treatment ameliorates CIA by reducing IC-stimulated inflammation and joint swelling. This suggests that recombinant sFcγRIIb may be useful as therapeutic agent in RA.