H-2 I-E molecules isolated from Mls1a stimulatory cells do not activate Mls1a-responsive T cells but do present exogenous staphylococcal enterotoxins.

The T cell response to allogeneic murine Mls determinants is not H-2 restricted but is dependent on H-2 class II molecules on the Mls-expressing stimulator cells. We have tested planar membranes containing H-2 class II I-E molecules alone or with I-A molecules for their ability to activate a panel of Mls1a-specific T hybrids. Despite the ability of the planar membranes to activate an alloreactive T hybrid and to present staphylococcal enterotoxins or an antigenic peptide to appropriately responsive T hybrids, they failed to stimulate the Mls1a-specific T hybrids. These findings, in the light of the various controls demonstrating sufficiency of the I-E molecules in the planar membranes, indicate that Mls1a determinants are not covalently bound to I-E molecules; the two molecular species are thus either not physically associated or are linked by a relatively weak interaction. In addition, our experiments show that isolated I-E molecules but not I-A molecules present staphylococcal enterotoxins A and B to two independently derived T hybrids expressing T cell receptor V beta 1, V beta 2 and V beta 6 elements.