OVERVIEW OF THE IMMUNE AND HEMATOPOIETIC SYSTEMS

Current knowledge of the immune and hematopoietic systems is reviewed. All blood cells are derived from the totipotent stem cell, also known as the pluripotent stem cell. The differentiation of pluripotent peri pheral stem cells into blood cells is controlled by a variety of biolo gic response modifiers, including colony-stimulating factors (CSFs) an d interleukins. Among the known CSFs are stem cell growth factor, gran ulocyte-macrophage CSF, multilineage CSF (interleukin-3), granulocyte CSF, macrophage CSF, and erythropoietin. CSFs are categorized as class I (those that stimulate the production of several types of blood cell s; also called pluripotent) and class II (those that stimulate only on e cell line; also called unipotent). Effects of CSFs can be studied us ing laboratory tests of colony-forming-unit activity. Pathogens enteri ng the body through damaged skin or mucous membranes are met with both a cellular response (neutrophils, macrophages, cytotoxic T lymphocyte s, and natural killer celts) and a humoral response (antibodies and co mplement). There is interplay between these two arms of the immune sys tem to defend against foreign antigens. This interplay can occur by ce ll-to-cell contact and by cytokines. Hematopoietic and immune cells of the body are produced and destroyed under precise control of many dif ferent biologic response modifiers, including the colony-stimulating f actors, interleukins, and interferons.