Listeriolysin O is strongly immunogenic on multiple MHC backgrounds (78.42)

Abstract

Abstract Listeriolysin O (LLO) is a key virulence determinant of the intracellular microbial pathogen Listeria monocytogenes. Previous work has shown the ability of LLO to induce a wide range of biological effects, including cytokine secretion, MAP kinase signaling, cellular lysis and apoptosis. LLO is also the source of immunodominant antigenic determinants for both CD4 and CD8 T cell responses against L. monocytogenes on multiple MHC backgrounds. We have examined the presentation of LLO protein delivered as a soluble antigen and after bacterial infection. LLO is a powerful immunogen, eliciting T cell responses at femtomolar levels of presentation in vitro. In vivo immunization with LLO in incomplete Freund's adjuvant led to the induction of a robust CD4 and CD8 T cell response as detected by ELIspot. This effect can be shown with APC and T cells derived from C57/BL6 (H-2b), C.B-17/Balb/c (H-2d) and B6.g7/NOD (H-2g7) haplotypes. Interestingly, there is an immunogenicity cluster located in domains 2 and 3 of LLO which donates most of the MHC-II epitopes for presentation. We have engineered non-hemolytic mutants of LLO and can show that they are also presented with great efficiency to CD4 T cells. Addition of ectopic antigens derived from ovalbumin and hen-egg lysozyme to the amino-terminus of LLO allowed for robust presentation to CD4 T cells directed to these antigens. Our initial data suggests that LLOs ability to be a potent antigen is based on a very fast and efficient uptake and catabolism by APC. We detected maximal presentation to T cells within 30 minutes of giving LLO to APC. APC also internalized LLO and catabolized it completely to TCA precipitable peptides within 6 hours of treatment. We conclude that LLO is a good candidate for delivering antigenic peptides in vivo and in vitro.