We will begin our specific discussion of hematopoiesis with the initial stem cell, and then discuss development of the various cells lineages. We'll talk about each of the mature cells in a moment. The stem cell initially differentiates along two basic pathways. The first pathway is called the myeloid stem cell, and the second differentiative pathway is called the lymphoid stem cell. We will examine the myeloid stem cell differentiative pathway first.
Native erythropoietin is a protein initially produced as an inactive form.
After proteolytic processing by an enzyme produced in the kidney - erythropoietin is coverted to an active molecule which signals erythoroid progenitors to develop into mature erythrocytes. Through genetic engineering however, the gene for active erythropoietin has been cloned and modified, and now such individuals receive injections of the active form of erythropoeitin. Monocytes further differentiate in tissues into macrophages. Since we all know what erythrocytes do, we will begin talking about the granulocyte, monocyte, macrophage series of cells first. Basophils play a role in defense against parasites, but also are involved in producing allergic reactions due to release of powerful pharmacologically-active substances.