BIOLOGICAL-ACTIVITY OF TOXIC SHOCK SYNDROME TOXIN-1 AND A SITE-DIRECTED MUTANT, H135A, IN A LIPOPOLYSACCHARIDE-POTENTIATED MOUSE LETHALITY MODEL

A recombinant of toxic shock syndrome toxin 1 (TSST-1) which contains a single histidine-to-alanine mutation at residue 135 (H135A) was anal yzed for toxicity and vaccine potential in a lipopolysaccharide (LPS)- potentiated mouse lethality model. The 50% lethal dose (LD(50)) of TSS T-1 in BALB/c mice was 47.2 mu/kg, but H135A was not lethal when teste d at a dose equivalent to 10 LD(50)s of TSST-1. Levels of tumor necros is factor (TNF) and gamma interferon (IFN-gamma) in serum were, respec tively, 10- and 50 fold higher in LPS-potentiated mice injected with 1 5 LD(50)s of TSST-1 than in mice given H135A. Mice injected with only TSST-1 did not have elevated levels of TNF or IFN-gamma in serum, whil e H135A plus LPS or LPS alone elicited identical, yet very low, levels of TNF and IFN-gamma. An enzyme-linked immunosorbent assay of H135A a nd TSST-1 with anti-TSST-1 serum yielded very similar dose-response cu rves, which strongly suggests that H135A serologically and conformatio nally resembles the native toxin. Mice immunized with H135A developed anti bodies that recognized TSST-1 in an enzyme-linked immunosorbent a ssay and afforded protection against a 15-LD(50) challenge of TSST-1 p lus LPS. The pooled sera of mice immunized with either TSST-1 or H135A also prevented lymphocyte proliferation due to TSST-1.