Immunological markers of human mononuclear cells.

The immune response to an antigenic challenge results from complex intercellular communications between several populations of lymphoreticular cells. Immunocompetent cells are derived from a common stem cell precursor and develop along two distinct pathways. The T-cell lineage (T-lymphocytes) originates in the thymus and mediates cellular immunity, whereas B-cells (bone marrow derived lymphocytes) mature into antibody producing cells. The maturation of B-cells into plasmacytes is under the control of two regulatory T-cell subsets. Helper T-cells (TH) induce the differentiation of B-cells into antibody producing cells. In contrast, suppressor T-cells (TS) inhibit this maturation process. Therefore, immunoregulation results from a delicate balance between inducer and suppressor T-cell subsets. The various lymphocyte populations and subsets express specific membrane glycoproteins (surface antigens and receptors) which therefore allow their identification by cell surface marker analysis. The advent of hybridoma antibodies directed against unique integral membrane proteins has provided a powerful tool for characterizing lymphocyte subsets and for understanding the antigenic changes that occur during their ontogeny. Pre-B cells produce intracytoplasmic mu chains. B cells express surface immunoglobulins, Ia antigens, Fc receptors and complement receptors. Plasmacytes contain intracytoplasmic immunoglobulins. T-cells form spontaneous rosettes with sheep erythrocytes. Helper T-cells express a specific surface antigen (T4), whereas cytotoxic/suppressor T-cells bear another membrane marker (T8). The use of such immunological markers has greatly facilitated the dissection of various human diseases, such as lymphoproliferative malignancies, autoimmune disorders and immunodeficiencies.