Cross-linking staphylococcal enterotoxin A bound to major histocompatibility complex class I is required for TNF-alpha secretion

The mechanism of how superantigens function to activate cells has been link ed to their ability to bind and cross-link the major histocompatibility com plex class II (MHCII) molecule. Cells that lack the MHCII molecule also res pond to superantigens, however, with much less efficiency. Therefore, the p urpose of this study was to confirm that staphylococcal enterotoxin A (SEA) could bind the MHCI molecule and to test the hypothesis that cross-linking SEA bound to MHCII-deficient macrophages mould induce a more robust cytoki ne response than without cross-linking. We used a capture enzyme-linked imm unosorbent assay and an immunprecipitation assay to directly demonstrate th at MHCI molecules bind SEA. Directly cross-linking MHCI using monoclonal an tibodies or cross-linking bound SEA with an anti-SEA antibody or biotinylat ed SEA with avidin increased TNF-alpha and IL-6 secretion by MHCII-/- macro phages. The induction of a vigorous macrophage cytokine response by SEA/ant i-SEA cross-linking of MHCI offers a mechanism to explain how MHCI could pl ay an important role in superantigen-mediated pathogenesis. (C) 1999 Academ ic Press.