Cytokine which binds to interferon gamma receptor 1 (ifngr1) (PubMed:19577303, PubMed:20507977). Has activating effects on primary macrophages (PubMed:20507977). Induces nitric oxide production and phagocytic responses in macrophages (PubMed:20507977). Primes monocytes for production of reactive oxygen intermediates (ROI), although the effect is short-lived (PubMed:20507977). Also has inhibitory effects on monocyte priming by ifng1 (interferon gamma 1) and tnfb (TNF-alpha 2) (PubMed:20507977). Stimulates phosphorylation of the JAK/STAT signal transducer stat1, but fails to induce stat1 nuclear localization (PubMed:20507977). Promotes increased expression of a number of genes important for macrophage activity, including the interferon regulatory factors irf2 and irf9 (PubMed:20507977). Homodimer. Strongly expressed in spleen. Also detected at lower levels in gill, kidney, heart, brain and intestine. In immune cell populations, expressed at highest levels in peripheral blood leukocytes and at lower levels in splenocytes, granulocytes, monocytes and macrophages. Belongs to the type II (or gamma) interferon family.