Cyclic hematopoiesis: etiological concepts. Clinical research update.

The cellular elements of the blood are normally maintained in a remarkable steady state. However, in human patients with cyclic neutropenia and in a putative animal model--canine cyclic hematopoiesis--the formed elements oscillate with constant regularity. The clocklike precision of the cycles implies a strong regulatory control failure. Since an understanding of the pathogenesis of these events could enhance our perception of normal and abnormal regulatory mechanisms, we have undertaken briefly to review current concepts regarding the possible etiologies of cyclic hematopoiesis.