Structure and regulation of the erythroid system at the level of progenitor cells.

Considerable ground has been covered since the first clonal assays for hemopoietic cells were described. The possibility of studying populations of progenitor cells and the regulatory factors that influence them has already thrown considerable light on our understanding of the structure and physiology of the normal erythroid system and its alterations in disease. The relative importance of humoral and short-range factors and of possible cell-to-cell interactions in the regulation of proliferation and differentiation in the erythroid cell lineage is now being studied actively in several laboratories. The possibility of analyzing possible regulatory networks involving such highly reactive cells as lymphocytes and monocytes-macrophages in defined in vitro conditions now exists. As these studies are being extended to the diseased state, concepts related to alterations in regulatory mechanisms in syndromes with abnormal cell proliferation can be tested. Clinical applications in the treatment of patients with hematological disease are being contemplated. The usefulness of Epo for the treatment of the anemia of renal disease has been demonstrated already.