Abstract
Objective
To test the effects of a novel monoclonal antibody (mAb) against human osteopontin (OPN) in the prevention and treatment of collagen‐induced arthritis (CIA) and to elucidate the underlying mechanisms of these effects.
Methods
DBA/1J mice immunized with type II collagen to induce CIA were monitored to assess the effects of anti‐OPN mAb on the clinical severity of the disease, and pathologic changes in the joints were examined histologically. The effects of anti‐OPN mAb on survival of activated T cells from arthritic mice and from the synovial fluid of patients with rheumatoid arthritis (RA) were determined by TUNEL assay or annexin V assay. The levels of apoptosis‐related proteins (Bim, Bax, and Bcl‐2) and NF‐κB were detected by immunoblot analysis.
Results
One anti‐OPN mAb, 23C3, was effective in inhibiting the development of CIA and even reversing established disease in DBA/1J mice. Monoclonal antibody 23C3 reduced the levels of serum type II collagen–specific autoantibodies and proinflammatory cytokines, and suppressed T cell recall responses to type II collagen. Mechanistic studies demonstrated that OPN prevented the death of type II collagen–activated murine T cells and synovial T cells from RA patients. Monoclonal antibody 23C3 promoted apoptosis of the activated T cells, particularly CD4+ T cells, by inhibiting activation of NF‐κB and by altering the balance among the proapoptotic proteins Bim and Bax and the antiapoptotic protein Bcl‐2. Screening of a phage display peptide library led to identification of the epitope ATWLNPDPSQKQ as being recognized by this novel antibody.
Conclusion
Because of its ability to effectively promote apoptosis of activated T cells, mAb 23C3 may be a novel therapeutic agent for the treatment of RA.