Jamaican Fruit-eating Bat GM-CSF (Granulocyte–Macrophage Colony-Stimulating Factor, CSF2) is a hematopoietic cytokine belonging to the colony-stimulating factor family, which also includes G-CSF (CSF3) and M-CSF (CSF1) that regulate the development, differentiation, and activation of myeloid immune cells. In the Jamaican fruit-eating bat (Artibeus jamaicensis), GM-CSF is likely produced by activated T lymphocytes, macrophages, endothelial cells, and fibroblasts in response to infection, inflammatory cytokines, or immune stimulation. GM-CSF binds to the GM-CSF receptor (CSF2R) on hematopoietic progenitor cells and mature myeloid cells, activating intracellular signaling pathways such as JAK/STAT, MAPK/ERK, and PI3K–AKT, which promote the proliferation, differentiation, and activation of granulocytes, macrophages, and dendritic cells. In bats, GM-CSF likely contributes to regulation of innate immune responses and development of antigen-presenting cells, which are important for coordinating antiviral immunity and immune homeostasis. Because bats serve as natural reservoirs for several zoonotic viruses, including coronaviruses and other emerging pathogens, studying cytokines such as GM-CSF in species like the Jamaican fruit-eating bat helps researchers understand myeloid cell development, inflammatory regulation, and host–pathogen interactions in bat immune systems, providing insights into how bats tolerate viral infections while limiting excessive inflammatory damage.