HEMOLYTICALLY ACTIVE (ACYLATED) ALPHA-HEMOLYSIN ELICITS INTERLEUKIN-1-BETA (IL-1-BETA) BUT AUGMENTS THE LETHALITY OF ESCHERICHIA-COLI BY ANIL-1-INDEPENDENT AND TUMOR NECROSIS FACTOR-INDEPENDENT MECHANISM

Many pathogenic Escherichia coli produce the toxin alpha-hemolysin (Hl y), and lipopolysaccharide (LPS), interleukin-l (IL-1), and tumor necr osis factor (TNF) have all been recognized as important effector molec ules during infections by gram-negative organisms. Despite the charact erization of many in vitro effects of hemolysin, no direct relationshi p has been established between hemolysin, LPS, proinflammatory cytokin e production, and E. coli-induced mortality. Previously,,ve have shown in vivo that hemolysin elicits a distinct IL-1 alpha spike by 4 h int o a lethal hemolytic E. coli infection. Using three transformed E. col i strains, WAF108, WAF270, and WAH540 (which produce no Hly [Hly(null) ], acylated Hly [Hly(active)], or nonacylated Hly [Hly(inactive)], res pectively), we sought to determine the specific roles of hemolysin acy lation, LPS, IL-l, and TNF in mediating the lethality of E. coli infec tion in mice. WAF270) was 100% lethal in BALB/c, C3H/HeJ, and C57BL/6 mice; in mice pretreated with antibody to the type 1 IL-I receptor; in type 1 IL-1 receptor-deficient mice; and in dual (type 1 IL-1 recepto r-type 1 TNF receptor)-deficient mice at doses which were nonlethal (0 %) with both WAF108 and WAH540. At lethal doses, WAF270 kilted by 6 +/ - 2.3 h while WAF108 and WAH540 killed at 36 +/- 9.4 and 36 +/- 13.8 h , respectively. These differences in mortality were not due to IL-1 or TNF release, and the enhanced expression of LPS, which corresponded t o Hly expression, was not likely the primary factor causing mortality. We demonstrate that bacterial fatty acid acylation of hemolysin is re quired in order for it to elicit IL-1 release by monocytes and to conf er its virulence on E. coli.