Monocyte Production of Colony Stimulating Factor in Familial Cyclic Neutropenia

S ummary . Granulocyte‐macrophage colony formation in agar culture of marrow is dependent on the presence of a glycoprotein colony stimulating factor (CSF). Measurement of the plasma levels of this factor in a 15‐yr‐old child with familial cyclic neutropenia revealed regular cycles with peak levels coinciding with nadirs of neutrophils and peaks of monocytes. A close correlation was observed between the incidence of monocytes and the capacity of the patient's leucocytes to elaborate CSF in culture. The frequency and amplitude of the blood monocyte cycles together with in vitro measurements of monocyte CSF‐producing capacity adequately accounted for the observed fluctuations of plasma CSF levels. A model of granulopoiesis is presented in which a positive stimulus for granulopoiesis is provided by CSF elaborated by nionocytes and a negative or neutral influence exerted by mature granulocytes.