The erythroid hemopoietic microenvironments

The cells present in the blood can be divided into three classes - red cells, white cells and platelets. Within the white cell class a subdivision can be made into granulocytes (neutrophils, eosinophils and basophils), lymphocytes and monocytes. In the normal adult the production of each mature cell type is mainly achieved by proliferation and differentiation of hemopoietic progenitor cells in the bone marrow and, in case of mice, also in the spleen. When morphological and functional differentiation of these progenitor ceils has occurred the maturing cells are usually kept at the site of formation in the hemopoietic tissues for a certain period before they are released to the blood strearn. In addition to these mature cells also immature cells may circulate in the blood in smal! numbers.