TNF and viral infectious disease: Cytotoxic T lymphocytes (CTLs) can play important roles in combatting infection via the secretion of cytokines such as IFN-γ and TNF-α [37], the former of which, secreted by cells in response to viral infection, can enhance natural killer (NK) cell and macrophage activity, while porcine IFN-γ has been established to reduce ASFV replication in porcine macrophages in vitro [38].