Dissecting the roles of distinct dendritic cell subsets in the immune response to the intracellular bacterial pathogen, Listeria monocytogenes

Dendritic cells (DC) are vital to the development of protective immunity to many pathogens and link the innate and adaptive immune systems. While DC as a whole have been studied extensively and are widely known for their ability to prime naive T cells, there is much yet to be discovered about DC biology and function in responses to pathogens. DC are composed of several subsets that have distinct repertoires of pathogen sensing molecules and functions. Four subsets of DC have been identified in the spleen and at least two DC subsets can also be generated in vitro from mouse bone marrow using the cytokine, Fms-like tyrosine kinase 3-ligand (Flt3L). We therefore set out to determine how distinct DC subsets respond and contribute to immune response against the intracellular bacteria pathogen, Listeria monocytogenes (Lm).;We observed, in contrast to previous studies, that in Flt3L DC maturation responses were independent of cytosolic entry by Lm, and responses to vacuolar Lm were dependent on the TLR adapter protein MyD88. The CD11b+ DC population within Flt3L DC had a higher level of maturation to Lm and uptake capacity than B220+ DC within Flt3L DC. While CD11b+ DC were capable of priming naive T cells, B220+ DC were also capable of priming T cells when the level of infection was normalized to that found in the CD11b+ cells.;In contrast to Flt3L DC, CD8alpha+ DC, CD4+ DC, and pDC subsets of the spleen following infection with wt Lm increased costimulatory molecule expression but responded minimally to vacuolar Lm. The DC maturation to wild type Lm peaked at 24--48 hours post infection. We have also shown that the CD8alpha + DC subset, and to a lesser extent, CD4+ DC are capable of priming CD8 T cell responses. This was reflective of both the maturation level and bacterial load of the CD8alpha+ and CD4 + DC subsets. We also observed that wild type Lm was found clustered with CD11b+ cells in the periarteriolar lymphoid sheath while vacuolar Lm was found in the marginal zones of the spleen. With this work we have developed a model of DC responses to Lm that dissects the ability of DC to take up Lm, undergo maturation, and then prime protective T cell responses.