Major immune regulatory cytokine that acts on many cells of the immune system where it has profound anti-inflammatory functions, limiting excessive tissue disruption caused by inflammation. Mechanistically, IL10 binds to its heterotetrameric receptor comprising IL10RA and IL10RB leading to JAK1 and STAT2-mediated phosphorylation of STAT3. In turn, STAT3 translocates to the nucleus where it drives expression of anti-inflammatory mediators. Targets antigen-presenting cells (APCs) such as macrophages and monocytes and inhibits their release of pro-inflammatory cytokines including granulocyte-macrophage colony-stimulating factor /GM-CSF, granulocyte colony-stimulating factor/G-CSF, IL-1 alpha, IL-1 beta, IL-6, IL-8 and TNF-alpha. Interferes also with antigen presentation by reducing the expression of MHC-class II and co-stimulatory molecules, thereby inhibiting their ability to induce T cell activation (By similarity). In addition, controls the inflammatory response of macrophages by reprogramming essential metabolic pathways including mTOR signaling (By similarity). Homodimer. Interacts with IL10RA and IL10RB. Expressed predominantly in bursa of Fabricius and cecal tonsils with low levels in thymus, liver and lung. Expression is detected as early as embryonic day 12. Higher expression in spleen of post-hatch chickens than embryos. Gradual increase in expression in the spleen which peaks by day 7 post-hatch. By lipopolysaccharide (LPS) in white blood cells, liver and spleen 3 hours after treatment. Decreases to basal levels 8 hours after treatment. By primary infection with E.acervulina and E.tenella. Chickens susceptible to E.maxima infection show higher constitutive and post-infection levels in spleen and higher post-infection levels in small intestine than infection-resistant animals. Belongs to the IL-10 family.