Erythroid colony formation in vitro from the marrow of dogs with cyclic hematopoiesis: interrelationship of progenitor cells.

Committed erythroid progenitor cells (Colony Forming Units-Erythroid, CFU-E) have been studied in canine cyclic hematopoiesis (CH) utilizing a semi-solid methyl cellulose culture system. Erythroid colonies were stimulated by the addition of a standard volume of serum from normal dogs that had been phlebotomized and subjected to hypoxia. CFU-E fluctuated over the cycle in dogs with CH from concentrations 4--5 times normal during the periods of peripheral blood neutropenia to less than one tenth of normal during the phases of elevated peripheral blood neutrophil counts. In spite of these marked fluctuations there was no change in the proliferation rate of the CFU-E as estimated by the tritiated thymidine (3H-TdR) suicide technique. Failure to demonstrate a change in the CFU-E proliferation rate may be related to the relative maturity of these cells with the fluctuations in number resulting from a 'feed-in' from more immature cells. The results show that CFU-E fluctuate in the same phase as committed granulocytic progenitor cells (CFU-C). Our current knowledge of the interrelationships of marrow progenitor cells and events in the peripheral blood of dogs with CH is briefly reviewed and some additional questions, raised by recent studies regarding the pathogenesis of this disease, are discussed.