Interferon gamma (IFN-γ) is one of the key factors of both innate and adaptive immune response that promotes differentiation of naive CD4+ cells into effector Th1 T cells producing the main mediators of cellular immunity against viral and intracellular bacterial infections, and specific cytotoxic immunity through the interaction of T cells with antigen-presenting cells and macrophage activation. The clinical importance of IFN-γ includes its medical use to treat and prevent various viral and bacterial infections. IFN-γ has a direct antiviral effect on infected cells, activates local infiltrating dendritic cells, macrophages and NK cells, modulates the differentiation and maturation of T and B cells, and enhances inflammation and antiviral functions. Immunoregulatory effect of IFN-γ plays one of the essential roles in the regulation of adaptive immune response in patients with tuberculosis infection and cancer. Producing IFN-γ by T cells increases the efficiency of infiltrated phagocytic cells, by stimulating NO and maintaining local host defense during tuberculosis infection. The direct antitumor effect of IFN-γ revealed in several experimental models has numerous mechanisms for the effect of development. IFN-γ has crucial potential for enhancing any antiviral, antimycobacterial, and specific antitumor therapies.