IMMUNOBIOLOGY Neutrophils efficiently cross-prime naive T cells in vivo

Neutrophils are professional phagocytes that migrate early, in high number, to the infection sites. Our study has analyzed how neutrophils cross-present antigens and influence CD8 T-cell responses. By using highly purified neutrophils from peritoneal exudates and bone marrow, we have shown that neutrophils cross-present ovalbumin to a CD8 T-cell hybrid-oma and to naive CD8 T cells from OT1 transgenic mice. Cross-presentation by neutrophils was TAP and proteasome de-pendent and was as efficient as in macro-phages. Moreover, it actually occurred earlier than in professional antigen-presenting cells. Peritoneal exudate neu-trophils from mice injected intraperitone-ally with ovalbumin also cross-presented ovalbumin, proving that neutrophils take up and present exogenous antigens into major histocompatibility complex I (MHC I) molecules in vivo. We then evaluated the in vivo influence of antigen cross-presentation by neutrophils on CD8 T-cell response using 2-microglobulin-deficient mice transferred with OT1 CD8 T cells and injected with ovalbumin-pulsed neutrophils. Four days after neu-trophil injection, OT1 cells proliferated and expressed effector functions (IFN- production and cytolysis). They also re-sponded efficiently to a rechallenge with ovalbumin-pulsed dendritic cells in CFA. These data are the first demonstration that neutrophils cross-prime CD8 T cells in vivo and suggest that they may consti-tute, together with professional antigen-presenting cells, an attractive target to induce cytotoxic T cells in vaccines