Neutrophils suppress mucosal‐associated invariant T cells in humans

Mucosal‐associated invariant T (MAIT) cells are innate‐like T lymphocytes that are abundant in mucosal tissues and the liver where they can respond rapidly to a broad range of riboflavin producing bacterial and fungal pathogens. Neutrophils, which are recruited early to sites of infection, play a nonredundant role in pathogen clearance and are crucial for controlling infection. The interaction of these two cell types is poorly studied. Here, we investigated both the effect of neutrophils on MAIT cell activation and the effect of activated MAIT cells on neutrophils. We show that neutrophils suppress the activation of MAIT cells by a cell‐contact and hydrogen peroxide dependent mechanism. Moreover, highly activated MAIT cells were able to produce high levels of TNF‐α that induced neutrophil death. We therefore provide evidence for a negative regulatory feedback mechanism in which neutrophils prevent overactivation of MAIT cells and, in turn, MAIT cells limit neutrophil survival. Neutrophils suppress the T‐cell receptor‐mediated activation of mucosal‐associated invariant T (MAIT) cells, in part through the production of ROS. In turn, bacterially activated MAIT cells can induce neutrophil apoptosis through TNF‐α production.