NOS2 and neoplasm: M1 macrophages can be activated by Th1 cytokine interferon γ (IFNγ) and microbial products, and they express high levels of pro-inflammatory cytokines (e.g. TNFα, IL-1, IL-6, IL-12 and IL-23), and inducible nitric oxide synthase (iNOS), and are capable of killing pathogens and tumor cells.