EVIDENCE THAT LISTERIOLYSIN IS A MAJOR INDUCER OF EARLY IL-6 PRODUCTION IN LISTERIA-MONOCYTOGENES INFECTED MICE

The ability of recombinant hemolytic and non-hemolytic strains of Listeria monocytogenes and Listeria innocua to induce IL-6 and TNF-alpha in C57 BL/6 mice and naive mouse macrophages following infection was tested. Listeriolysin-negative strains were found to only transiently increase the IL-6 production to modest levels while listeriolysin-producing strains induced IL-6 production by 3-5 fold over listeriolysin-negative strains in the organs of infected mice. When peritoneal macrophages were cultured in vitro, hemolytic listeriae completely abrogated the relatively high IL-6 response of uninfected cells. This is probably due to the impairment of cellular function induced by listeriolysin, as indicated by a high release of lactate dehydrogenase from these macrophages.