Antirheumatic E. coli extract OM-89 induces T cell responses to HSP60 and 70

Oral administration of E. coli extract OM-89 is used in treating RA. It has been shown that immune reactivity to heat-shock proteins (hsp) is involved in immunomodulation of arthritis. We evaluated the postulated presence and immunogenicity of hsp's in OM-89. The effects of OM-89 in experimental arthritis were analyzed. Proliferative T cell responses to bacterial hsp60 and hsp70 were found in rats immunized with OM-89. And conversely, immunization with hsp antigens induced OM-89-specific T cell responses. Hsp70 (DnaK) was found to be a major immunogenic constituent of OM-89. Parenteral immunization with OM-89 reduces resistance to adjuvant arthritis (AA), whereas oral administration protects against AA. Given the arthritis inhibitory effect of oral OM-89 in AA our findings suggest peripheral tolerance induced by hsp-specific regulatory T cells as a mode of action for OM-89 as an arthritis suppressive oral drug.