LACK OF COMPLETE CORRELATION BETWEEN EMETIC AND T-CELL-STIMULATORY ACTIVITIES OF STAPHYLOCOCCAL ENTEROTOXINS

This study examined the emetic activity of several staphylococcal ente rotoxin type A and B (SEA and SEB, respectively) mutants that had eith er one or two amino acid residue substitutions. New sea gene mutations were constructed by site-directed mutagenesis; gene products were obt ained with glycine residues at position 25, 47, 48, 81, 85, or 86 of m ature SEA. Culture supernatants from Staphylococcus aureus RN4220, or derivatives containing either sea or a sea mutation, were analyzed for the ability to stimulate proliferation of murine splenocytes, as dete rmined by incorporation of [H-3]thymidine. Culture supernatants contai ning SEA-N25G (a SEA mutant with a substitution of glycine for the asp aragine residue at position 25), SEA-F47G, or SEA-L48G did not stimula te T-cell proliferation, unlike supernatants containing the other subs titution mutants. Purified preparations of SEA-N25G had weak activity and those of SEA-F47G and SEA-LA8G had essentially no activity in the T-cell proliferation assay. All mutants except SEA-V85G, which was deg raded by monkey stomach lavage fluid in vitro, were tested for emetic activity. SEA-C106A and two SEB mutants, SEB-D9N/N23D and SEB-F44S (pr eviously referred to as BR-257 and BR-358, respectively), whose constr uction and altered immunological properties have been reported previou sly, were also tested in the emetic assay. Each mutant was initially a dministered intragastrically at doses of 75 to 100 mug per animal; if none of the animals responded, the dose was increased four- to fivefol d. SEA-F47G, SEA-C106A, and SEB-D9N/N23D were the only mutants that di d not induce vomiting at either dose tested; these three mutants had r educed immunological activity. However, there was not a perfect correl ation between immunological and emetic activities; SEA-L48G and SEB-F4 4S retained emetic activity, although they had essentially no T-cell-s timulatory activity. These studies suggest that these two activities c an be dissociated.