Dolphin Interleukin-31 (IL-31) is a cytokine involved in regulation of immune responses and inflammatory signaling in dolphins (family Delphinidae). IL-31 is produced primarily by activated T helper 2 (Th2) cells and other immune cells following immune stimulation. Dolphin IL-31 binds to a heterodimeric receptor complex composed of IL-31 receptor A (IL-31RA) and oncostatin M receptor (OSMR), activating intracellular signaling pathways such as JAK–STAT, MAPK, and PI3K that regulate gene expression, inflammation, and cellular responses. Through these signaling pathways, IL-31 contributes to modulation of immune responses, communication between immune cells and epithelial tissues, and regulation of inflammatory processes in tissues such as the skin and mucosal surfaces. In dolphins, IL-31 is believed to play roles in host defense and inflammatory regulation, and it is studied in marine mammal immunology and comparative biomedical research to better understand immune system function, responses to environmental pathogens, and mechanisms of inflammation in marine mammals.