Immunomodulatory activity of staphylococcal enterotoxin-B. The induction of an I-J-restricted suppressor factor

Staphylococcal enterotoxin-B (SEB), a common cause of food-borne intoxication, is a potent polyclonal T cell activator. Previous studies from this laboratory and others have shown that SEB has the capacity to nonspecifically inhibit antibody responses both in vivo and in vitro. We have shown that the inhibitory activity of SEB is mediated, in part, by the activation of a CD8⁺, CD4^-, and CD5^- suppressor cell population. The present studies show that the activity of the SEB-induced suppressor cell population is mediated by a soluble factor. This factor nonspecifically inhibits both primary and secondary in vitro antibody responses. Delayed addition analysis demonstrates that the factor must be present early in the ongoing antibody response to exhibit suppressive activity. Monoclonal anti-I-J- antisera block the activity of the factor, and eluates (but not filtrates) collected from monoclonal anti-I-J immunoaffinity columns possess suppressive activity. Furthermore, the activity is restricted at the 'I-J' gene locus, but is not restricted at the Igh locus. Finally, size-exclusion chromatographic analysis shows that the factor possesses an apparent M(r) of 26 kDa. These studies suggest that SEB induces the production of a suppressive factor with properties similar to those exhibited by Ag-induced, and typically Ag-specific, suppressor factors.