Major histocompatibility complex class II binding site for streptococcal pyrogenic (erythrogenic) toxin A.

Streptococcal pyrogenic exotoxin A (SPEA) is an important pathogenicity factor of group A streptococci. It is a member of the family of "superantigens" produced by Staphylococcus aureus and Streptococcus pyogenes and its T lymphocyte stimulating activity is involved into the pathogenesis of certain diseases caused by pyogenic streptococci. In this study we have produced and characterized recombinant SPEA molecules in Escherichia coli. These molecules are indistinguishable from natural SPEA in both T cell stimulatory and HLA class II binding activities. Human class II molecules are more efficient than mouse class II molecules in presenting SPEA to T cells. In binding tests to major histocompatibility complex class II-positive cells SPEA competes with staphylococcal enterotoxin B and A but not with toxic shock syndrome toxin-1.