Canine interleukin-3 (IL-3) is a hematopoietic growth factor produced primarily by activated T lymphocytes and mast cells that regulates the proliferation, differentiation, and survival of multipotent hematopoietic progenitor cells through signaling via the IL-3 receptor complex (IL-3Rα/CD123 and the common β chain), activating JAK/STAT, MAPK, and PI3K pathways. In dogs, IL-3 plays a key role in supporting the development and expansion of myeloid lineage cells—including monocytes, macrophages, dendritic cells, basophils, eosinophils, and mast cells—thereby influencing innate immunity, inflammatory responses, and host defense against bacterial, viral, and parasitic infections. In canine health, dysregulated IL-3 activity may contribute to allergic conditions such as atopic dermatitis, eosinophilic disorders, and mast cell–associated diseases, as well as hematologic abnormalities including myeloproliferative disorders and mast cell tumors. Because dogs naturally develop spontaneous immune-mediated diseases and hematologic cancers that closely resemble human conditions, canine IL-3 is relevant both for advancing veterinary therapeutics and as a translational animal model for studying hematopoiesis, inflammatory disease, and targeted therapies directed at IL-3 signaling pathways.