Abstract
M proteins are coiled-coil dimers expressed on group A streptococcal cell surfaces. They have an importantrole in host antistreptococcal immunity and in poststreptococcal autoimmune sequelae. Controversy has arisen regardingwhether type 5 M proteins are superantigenic for human T cells. To investigate this, we have produced and tested M5 inthe form of two novel recombinant proteins. We found no evidence of superantigenicity using either recombinant whole M5protein (rM5) or recombinant pep M5 protein (rpepM5) to activate peripheral blood mononuclear cells (PBMC) from healthyadult volunteers. Short-term, rM5-specific T-cell lines from different subjects were uniformly self-APC restricted andshowed no consistent pattern of TCR Vβ usage. A synthetic peptide of M5 residues 217–237 was found tocontain epitope(s) recognized by some rM5-specific human T cells. PBMC responses to rM5 and rpepM5 in 3- and 7-dayproliferation assays were characteristic of antigenic rather than superantigenic stimulation. We conclude that type5 M protein activates human T cells as a conventional antigen.
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