Strong cross-reactions were demonstrated for staphylococcal enterotoxins B (SEB) and C1 (SEC1) by antigenbinding capacity and by competitive binding ability. Both SEB and SEC1 combined completely with the heterologous antibody although requiring four times as much antiserum as the homologous enterotoxin and both displaced about one-third of the other enterotoxin from a heterologous antigen-antibody system. It is proposed that one of the three major antigenic determinants of these enterotoxins possesses a significant similarity but probably not an identity of structure.
SEB and SEC1 did not combine with antiserum to enterotoxin A nor inhibit the reaction of SEA with anti-SEA. SEA had no intrinsic binding capacity for anti-SEB or anti-SEC1 nor did it inhibit the binding of either enterotoxin to its own antibody. Affinity chromatography was employed to demonstrate that a small apparent binding of SEA to anti-SEB was due to antibody to SEA in the anti-SEB serum and that an almost complete displacement of SEC1 binding to anti-SEC1 was caused by contaminating SEC (about 0.01%) in preparations of enterotoxin A.