Canine Interleukin-33 (IL-33) is a cytokine that plays an important role in regulating immune responses and inflammatory signaling in dogs (Canis lupus familiaris). IL-33 is a member of the IL-1 cytokine family and is produced primarily by epithelial cells, endothelial cells, and fibroblasts, particularly following tissue damage, stress, or infection. Canine IL-33 functions as an “alarmin,” being released upon cellular injury to alert and activate the immune system. It binds to the ST2 receptor (IL1RL1) in combination with the IL-1 receptor accessory protein (IL-1RAcP), activating intracellular signaling pathways such as NF-κB and MAPK that promote production of inflammatory mediators. In dogs, IL-33 is involved in the activation of type 2 immune responses by stimulating T helper 2 (Th2) cells, group 2 innate lymphoid cells (ILC2s), mast cells, and eosinophils, leading to the production of cytokines such as IL-4, IL-5, and IL-13. Through these actions, IL-33 contributes to regulation of allergic inflammation, tissue repair, and host defense against parasites. Canine IL-33 is studied in veterinary immunology and translational research, particularly in investigations of allergic and inflammatory conditions such as canine atopic dermatitis, asthma-like airway inflammation, and other immune-mediated diseases.