Immunodominant antigens of Streptococcus equisimilis shared by other {beta}-haemolytic streptococci

Division of Medical Microbiology, Department of Pathology, University of British Columbia, Vancouver, British Columbia, Canada * Correspondence should be sent to Dr N. Cimolai. Microbiology, Department of Pathology, British Columbia's Children's Hospital, 4480 Oak Street, Vancouver, British Columbia, Canada V6H 3V4. Received July 22, 1993 Revision received October 21, 1993. Three immunodominant antigens of Streptococcus equisimilis (Lancefield group C) with approximate mol. wts of 46, 66 and 105 kDa were recognised by human serum IgG and IgA immunoblotting. These antigens were identified consistently by various human sera but immunoblots with IgA (heavy chain) and secretory IgA (J chain) from human respiratory secretions gave more variable results. Antigens with similar migration rates were demonstrated in S. pyogenes , large colony human biotype group G streptococci, and streptococci of groups C and G from the "S. anginosus-milleri group". Polyclonal antibody which was eluted from immunoblot substrates that contained the S. equisimilis 66-kDa antigen reacted with the 66-kDa antigen of S. pyogenes. Both polyclonal and monoclonal anti-vimentin antibodies identified the 46-kDa and 66-kDa antigens of S. equisimilis. The homology of these antigens among β-haemolytic streptococci has the potential to complicate both a strategy for the utilisation of immunoblotting for diagnostic purposes and the understanding of how such antigens may be involved in the pathogenesis of post-infectious sequelae.