COMPLEX HIGH-AFFINITY INTERACTIONS OCCUR BETWEEN MHCI AND SUPERANTIGENS

Staphylococcal enterotoxins A and Cl (SEA or SEC1) bound to major hist ocompatibility-I (MHCI) molecules with high affinity (binding constant s ranging from 1.1 mu M to 79 nM), SEA and SEC1 directly bound MHCI mo lecules that had been captured by monoclonal antibodies specific for H -2K(k), H-2D(k), Or both. In addition, MHCI-specific antibodies inhibi ted the binding of SEC1 to LM929 cells and SEA competitively inhibited SEC1 binding; indicating that the superantigens bound to MHCI on the cell surface. The affinity and number of superantigen binding sites di ffered depending on whether MHCI was expressed in the membrane of LM92 9 cells or whether it was captured. These data support the hypothesis that MHCI molecules can serve as superantigen receptors.