Binding of staphylococcal enterotoxin A to purified murine MHC class II molecules in supported lipid bilayers
Lee, J.M.; Watts, T.H.
Journal of Immunology 145(10): 3360-3366
1990
ISSN/ISBN: 0022-1767 PMID: 2230121 Document Number: 365169
The staphylococcal enterotoxins are a family of bacterial toxins that are thought to exert their pathogenic effects by the massive activation of T lymphocytes to produce lymphokines. Activation of T cells by these toxins is dependent on MHC class II + APC. Recent studies from a number of laboratories have implicated MHC class II proteins as the APC surface receptor for a number of the staphylococcal enterotoxins. The present report shows that staphylococcal enterotoxin A, (SEA) binds to the purified murine MHC class II molecule I-Ed reconstituted in supported planar membranes, indicating that no other cell surface proteins are required for SEA binding. The Kd for SEA binding to I-Ed was determined to be 3.5 .+-. 1.6 .times. 10-6M. Specific binding of SEA to I-Ad was also observed, but the interaction was of significantly lower affinity. Binding of SEA to purified I-Ed was blocked by antibodies against both the .alpha.- and the .beta.-chain of the I-Ed molecule, but not by antibodies specific for an unrelated MHC class II protein. Binding of SEA to I-Ad was blocked by an A.beta.d but not by an A.alpha.d-specific antibody. Planar membranes containing only lipid and purified I-Ed molecules were sufficient for activation of a V.beta.1 expressing T hybrid by SEA. The T cell responded to as few as 180 toxin molecules per T cell.