Chicken Interleukin-34 (IL-34) is a cytokine involved in the regulation of innate immune responses and macrophage biology in chickens (Gallus gallus). IL-34 is produced by a variety of cell types, including epithelial cells, fibroblasts, and immune cells, in response to inflammatory stimuli and infection. Chicken IL-34 functions primarily as a ligand for the colony-stimulating factor-1 receptor (CSF1R), activating intracellular signaling pathways such as ERK, JAK–STAT, and PI3K–AKT that promote survival, proliferation, and differentiation of monocytes and macrophages. Through these mechanisms, IL-34 contributes to the development and maintenance of macrophage populations and plays a role in regulating inflammatory and host defense responses in avian tissues. In chickens, IL-34 has been studied in immune responses to bacterial and viral pathogens and in the regulation of macrophage-mediated immunity. In cell culture, recombinant chicken IL-34 is commonly used to promote differentiation and survival of monocytes into macrophages and to support macrophage proliferation and functional studies in in vitro avian immune assays.