Glycosaminoglycans and the haemopoietic microenvironment

Mature blood cells in mammals have a limited life span. Because these cells are usually unable to multiply in th~ blood stream, a continuous production of new cells is needed. This production, located in specific organs, includes proliferation, differentiation and maturation of cells. In order to guarantee adequate production of the different kinds of blood cells in response to the demands of the organism a continuous regulation of cell production is required. Such a regulation is considered to be effected by two categories of factors, namely (1) humoral factors, and (2) microenvironmental factors. Some humoral factors have been isolated and characterised (for instance the hormone erythropoietin).