Cynomolgus monkey 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 cynomolgus monkeys (Macaca fascicularis), IL-3 supports the development and expansion of myeloid lineage cells—including monocytes, macrophages, dendritic cells, basophils, eosinophils, and mast cells—thereby shaping innate immunity and inflammatory responses. In nonhuman primate health, IL-3 is relevant to immune regulation during infectious diseases, allergic inflammation, and hematologic disorders. Importantly, cynomolgus monkeys are widely used as translational models in preclinical research due to their close genetic and immunological similarity to humans, making IL-3 highly relevant for studying hematopoiesis, cytokine-driven inflammation, mast cell biology, and the safety and efficacy of therapeutics targeting IL-3 or myeloid cell pathways. As such, cynomolgus monkey IL-3 plays a critical role in both primate immunology and the development of human-targeted biologics.