Neutrophil involvement in cross-priming CD8⁺ T cell responses to bacterial antigens

Substantial CD8⁺ T cell responses are generated after infection of mice with recombinant Listeria monocytogenes strains expressing a model epitope (lymphocytic choriomeningitis virus NP_118-126) in secreted and nonsecreted forms. L. monocytogenes gains access to the cytosol of infected cells, where secreted Ags can be accessed by the endogenous MHC class I presentation pathway. However, the route of presentation of the nonsecreted Ag in vivo remains undefined. In this study we show that neutrophil-enriched peritoneal exudate cells from L. monocytogenes-infected mice can serve as substrates for in vitro cross-presentation of both nonsecreted and secreted Ag by dendritic cells as well as for in vivo cross-priming of CD8⁺ T cells. In addition, specific neutrophil depletion in vivo by low dose treatment with either of two Ly6G-specific mAb substantially decreased the relative CD8⁺ T cell response against the nonsecreted, but not the secreted, Ag compared with control Ab-treated mice. Thus, neutrophils not only provide rapid innate defense against infection, bot also contribute to shaping the specificity and breadth of the CD8⁺ T cell response. In addition, cross-presentation of bacterial Ags from neutrophils may explain how CD8 ⁺ T cell responses are generated against Ags from extracellular bacterial pathogens.