A nonamer peptide derived from Listeria monocytogenes metalloprotease is presented to cytolytic T lymphocytes

Listeria monocytogenes is an intracellular bacterium that secretes proteins into the cytosol of infected macrophages. Major histocompatibility complex (MHC) class I molecules bind peptides that are generated by the degradation of bacterial proteins and present them to cytolytic T lymphocytes (CTL). In this study we have investigated CTL responses in L. monocytogenes- immunized mice to peptides that i) derive from the L. monocytogenes proteins phosphatidylinositol-specific phospholipase C, lecithinase (most active on phosphatidylcholine), metalloprotease (Mpl), PrfA, and the ORF-A product and (ii) conform to the binding motif of the H2-K(d) MHC class I molecule. We identified a nonamer peptide, Mpl 84-92, that is presented to L. monocytogenes-specific CTL by H2-K(d) MHC class I molecules. Unlike other motif-conforming peptides derived from the secreted Mpl of L. monocytogenes, Mpl 84-92 is bound with high affinity by H2-K(d). Mpl 84-92 is the fourth L. monocytogenes-derived peptide found to be presented to CTL by the H2-K(d) molecule during infection and demonstrates the importance of high-affinity interactions between antigenic peptides and MHC class I molecules for CTL priming.