NOS2 and infection: Trauma, infection, malignancy, and aberrant inflammatory states trigger MDSC proliferation, then MDSCs are recruited to the inflammatory microenvironment, exerting immunosuppressive effects via secreting Arg‐1, inducible nitric oxide synthase (iNOS) and indolamine dioxygenase (IDO), which restrict TCR ζ‐chain production and prompt T‐cell apoptosis.10