CSF3R (Colony Stimulating Factor 3 Receptor) is a receptor that binds to colony-stimulating factor 3 (CSF3), a cytokine responsible for regulating the production, differentiation, and function of granulocytes. This interaction is essential for the survival and activation of neutrophils, key cells in the body’s innate immune defence. Alterations in CSF3R, such as mutations or overexpression, can disrupt granulocyte function and proliferation, contributing to conditions like chronic neutrophilic leukaemia and severe congenital neutropenias.