Identification of an IFN-γ-producing neutrophil early in the response to Listeria monocytogenes

IFN-γ plays a critical role during the immune response to infection with Listeria monocytogenes. Early in the innate response NK cells are thought to be a primary source of IFN-γ; however, protection can be mediated by the presence of significant numbers of primed IFN-γ-secreting CD8 ⁺ T cells. In this report, we examined the early response to Listeria and found that 18 h after infection spleens contain CD11b⁺, Gr-1^high, or Ly6G⁺ cells that produce significant IFN-γ. Morphological analysis of sorted Gr-1^highIFN- γ⁺ and Gr-1^lowIFN-γ⁺ or Ly6G ⁺IFN-γ⁺ cells confirmed that these cells were neutrophils. The importance of IFN-γ production by these cells was further tested using adoptive transfer studies. Transfer of purified neutrophils from Ifng^+/+ mice led to increased bacterial clearance in Ifng ^-/- mice. Transfer of Ifng^-/- neutrophils provided no such protection. We conclude that neutrophils are an early source of IFN-γ during Listeria infection and are important in providing immune protection.