DIFFERENTIATION OF HEMATOPOIETIC-CELLS - ROLE OF CYTOKINES AND EXPRESSION OF MEMBRANE MARKERS

Haematopoiesis represents all of the mechanisms ensuring continuous re placement of mature blood cells with a very limited or no capacity for proliferation and a limited life span. This regulated and continuous production is ensured by a special cell pool, termed stem cells, capab le of multiplication without differentiation (self-renewal) and prolif eration with differentiation into one or other of the Various speciali zed haematopoietic cells: erythrocytes, neutrophil, eosinophil and bas ophil polymorphonuclear cells, platelets, monocytes/macrophages, T and B lymphocytes. In addition to the bone marrow compartment correspondi ng to the most primitive stem cells, the bone marrow also contains two other compartments of more differentiated cells: the progenitor and m aturation compartments. Stem cells, which represent an extremely low f raction of the total bone marrow population, are usually quiescent and are entered into cycle under the action of certain soluble glycoprote in factors, cytokines, ensuring their survival, proliferation and diff erentiation (<< positive >> regulation), but also their interactions w ith certain cells of the microenvironment and finally the << negative >> regulation activity of haematopoiesis exerted by certain biological molecules. All of the known data concerning the filiation of the vari ous haematopoietic cells belonging to the three compartments defined a bove has been considerably enriched over recent years with the demonst ration of various membrane markers on the surface of these different c ells, allowing very precise dissection of the hierarchy of these compa rtments by means of specific antibodies.