Through an extrinsic mechanism, IFN-γ upregulates the expression of MHC molecules and co-stimulatory molecules, induces CD4+ T cells and macrophages to differentiate into Th1 and M1 subtypes, respectively, and ultimately promotes the cytotoxicity of CD8+ T cells and tumor cell cytolysis mediated by NK cells [36]. The gene discussed is IFNG; the disease is neoplasm.