Interferon alpha protects against AIA in a dose-dependent manner. Female mice of strains SV129EV and Balb/c were immunized with mBSA at days 1 and 7 in Freund incomplete adjuvant mixed with 0, 100, 1,000, and 5,000 U IFN-α followed by intraarticular injection of same antigen in PBS at day 21. At day 28, mice were killed, histochemical sections of the knee joint were prepared, and arthritis was evaluated as described in "Methods". (A) Percentage of animals developing arthritis. (B) Arthritis severity (mean ± SEM). (C) Representative histochemical slides of the knee joints from each group. Severity of arthritis was evaluated by using the Mann–Whitney U test (*P < 0.05; **P < 0.01, compared with control (PBS) group; n = ≥6. The Fisher Exact test was performed to compare the arthritis frequency of interferon-treated groups and the corresponding control (PBS) group.