TH1 CELLS SPECIFIC FOR A SECRETED PROTEIN OF LISTERIA-MONOCYTOGENES ARE PROTECTIVE IN-VIVO

In the present study we have investigated the role of the secreted p60 protein from Listeria monocytogenes as an Ag for CD4 T cells. The p60 protein is an abundant extracellular protein that is highly conserved within the members of the genus Listeria, Our results show that L, mo nocytogenes infection induces a potent p60-specific Th1 immune respons e. Remarkably, we found that p60-specific Th1 clones mediate significa nt protection against L, monocytogenes infection. For one p60-specific clone, the peptide epitope was defined. This clone recognized p60 301 -312 (EAAKPAPAPSTN) in the context of the H-2A(d) molecule. Despite th e fact that acquired immunity against L. monocytogenes is primarily me diated by cytotoxic CD8 T lymphocytes, our data clearly demonstrate th at secreted bacterial proteins are important CD4 T cell Ags and that T h1 clones specific for a secreted bacterial protein can contribute to the protection against an intracellular pathogen such as L. monocytoge nes.