[Hematopoiesis regulation]

Positive and negative signals are crucial in the regulation of the hematopoietic system. In the last 30 years, more than 20 molecules (glycoproteins) with biological activity upon the hematopoietic progenitor cells and even on the mature blood cells have been purified. The best known of these biomolecules are the hematopoietic growth factors (colony stimulating factors and interleukins), which are able to stimulate bone marrow cells to give mature progeny. At present, not only the sequence of the majority of these glycoproteins and their codifying genes has been determined, but also their target cells and cellular receptors. Research studies of the interaction between the hematopoietic progenitor cells and their stimulating and inhibiting factors are very helpful in the development of clinical trials and have become important tools to explore the origin of a great number of hematological diseases. However, the mechanisms underlying growth/inhibitory factor production and progenitor cell proliferation remain poorly understood.