Recombinant mycobacterial HSP65 in combination with incomplete Freund's adjuvant induced rat arthritis comparable with that induced by complete Freund's adjuvant

Complete Freund's adjuvant (CFA) containing the inactivated mycobacterium has been conventionally used to induce typical arthritis in rats. In comparison, incomplete Freund's adjuvant (IFA), lacking the mycobacterium, can only induce less severe arthritis. However, the key components responsible for the arthritogenic effect of the whole mycobacterium are rarely known. Although mycobacterial heat-shock protein 65 (MHSP65) specific humoral and cellular immune responses were detected in rats with arthritis induced by CFA, MHSP65 alone cannot induce arthritis. In this study, we replaced the whole mycobacterium in CFA with recombinant MHSP65 (rMHSP65), prepared rMHSP65-IFA emulsion by mixing rMHSP65 and IFA, and investigated whether rMHSP65-IFA could induce arthritis in rats as CFA did. We found that intradermal injection of the rMHSP65-IFA emulsion induced arthritic lesions in testing animals to the same degree as those induced by CFA, manifested by severe swelling in hind paws, and synovial thickening, cartilage erosion and lymphocytes infiltration in ankle joints. Notably, the rMHSP65-IFA recipe also induced the production of anti-dsDNA and -rMHSP65 antibodies in rats. These results thus demonstrate that rMHSP65 can be used to substitute the inactivated mycobacteria in CFA to induce typical arthritis in rats.