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. All of these cells circulate within the bloodstream. The mast cell does not circulate but is instead found within the tissues of the body. This cell is also involved in defense against parasites, but like the basophil, the mast cell participates in induction of allergic reactions.