Oral dosing of rats with OM-89 results in the appearance of specific OM-89 antibodies of the IgG2a isotype: possible significance in the treatment of rheumatoid arthritis.

Abstract OM-89 is a glycoprotein-rich extract of Escherichia coli shown to be effective in the treatment of rheumatoid arthritis (RA). It has been reported that oral dosing of animals results in the appearance of specific OM-89 antibodies. In the current study we have investigated some of the immunoglobulin isotypes that may be involved. OM-89 antibodies of IgG 1 , IgG 2a and IgM isotypes were measured by ELISA in serum from rats dosed three times a week for 3 weeks at 4 or 40 mg kg −1 . The results showed a small but significant rise in IgM and a greater rise in IgG 2a . The possibility that antigens within OM-89 (e.g. hsp65) may have homology with antigens involved in RA raises the possibility that OM-89 antibodies, particularly of the IgG 2 class, may block pathogenic antigens from being recognized by T cells.