
Like IL-1, IL-6 also exhibits a wide variety of effects in hematopoiesis and the immune system as an acute phase protein, whereas thymosin beta-4 regulates cell life, differentiation, proliferation/growth, migration, and motility. IL-1 plays an important role in hematopoiesis by stimulating marrow stromal cells to secrete CSFs (colony stimulating factors). GMCSF acts as an autocrine mediator of cell growth. IL-3 and SCF support the survival and stimulate the proliferation of granulocyte progenitors. The initial stages of pluripotent hematopoietic cell development is regulated by broadly acting cytokine groups/growth factors such as IL-3 (interleukin-3), SCF (stem cell factor), GMCSF (granulocyte-macrophage colony-stimulating factor), IL-1 (interleukin-1), IL-6 (interleukin-6), IL-11 (interleukin-11), IL-2 (interleukin-2), and thymosin beta-4. Hematopoietic progression-survival, proliferation, or differentiation-is well-supported by cytokines and growth factors. During blood-cell development, pluripotent HSC undergo either self-renewal or differentiation into multilineage committed progenitor cells: myeloid stem cells or lymphoid stem cells, which are CD4 (CD4 antigen), CD8 (CD8 antigen) and TCR (T-Cell antigen receptor) negative. Unipotent cells produce only one cell type, but have the property of self-renewal which distinguishes them from non-stem cells (e.g., muscle stem cells). Multipotent cells produce only cells of a closely related family of cells (e.g., hematopoietic stem cells differentiate into red blood cells, white blood cells, platelets). Multipotent stem cells are partially differentiated, so that they form a limited number of tissue types. Pluripotent cells are capable of forming virtually all of the possible tissue types found in human beings. Totipotent cells differentiate into embryonic and extraembryonic cell types, whereas pluripotent cells are defined as the descendants of totipotent cells and differentiate into cells derived from any of the three germ layers, although multipotent or unipotent progenitor cells are sometimes referred to as stem cells. In the strictest sense, depending on potency (i.e., the capacity to differentiate into specialized cell types), stem cells are either totipotent or pluripotent.

The earlier progenitor cells are multipotent, but as division and differentiation proceed, later progenitors are formed that are committed to three, two, or one cell line. Hematopoietic stem cells (HSCs) have the property of self-renewal and, through cell division and differentiation, form populations of progenitor cells which are committed to the main marrow cell lines: erythroid, granulocytic and monocytic, megakaryocytic, and lymphocytic. VEGF Family Ligands and Receptor Interactions.Tumoricidal Effects of Hepatic NK Cells.Transendothelial Migration of Leukocytes.IL-2 Gene Expression in Activated and Quiescent T-Cells.Hematopoiesis from Pluripotent Stem Cells.Hematopoiesis from Multipotent Stem Cells.Cytokine, Chemokine, Growth Factor Pathways.Killer T Cell Mediated Apoptosis Pathway.Intrinsic and Extrinsic Pathways of Apoptosis.

