AbstractRheumatoid arthritis (RA) is an autoimmune disease and a member of human heat shock protein (HSP) 70 protein family, Binding Immunoglobulin Protein (BiP), has been identified as an important autoantigen for T and B cells. We herein focused on Mycobacterial (Myc) HSPs and immune responses to MycHSPs in RA patients. Serum titers of antibodies against MycHSP70 were significantly elevated in RA patients and correlated with serum anti-BiP antibody titers. A MycHSP70-derived HLA-DR4 major epitope was identified using the proliferative capacity of RA PBMCs as an indicator. The major epitope, MycHSP70_287–306, was located at the corresponding position in the major epitope for human BiP_336–355 and a strong correlation was found between the proliferation of PBMCs in response to MycHSP70_287–306 and BiP_336–355. The immunization of HLA-DR4 transgenic mice with MycHSP70 induced the proliferation of T cells and development of anti-BiP antibodies. In contrast, the oral administration of MycHSP70_287–306 resulted in the amelioration of collagen-induced arthritis, serum antibody responses and T cell proliferation. In conclusion, immune responses to MycHSP70 were associated with adaptive immunity against BiP in RA and could be an important mechanism underlying the development of autoimmunity.