Antigen details

Specificity & Reactivity: The CD8 antigenic determinant interacts with class I major histocompatibility complex (MHC) molecules resulting in increased adhesion between the CD8 + T lymphocytes and the target cells. Binding of the CD8 antigen to class I MHC molecules enhances the activation of resting T lymphocytes. CD8 recognizes an antigen expressed on the 32-kdalton (kDa) subunit of a disulfide-linked bimolecular complex. The cytoplasmic domain of the subunit of the CD8 antigen is associated with the protein tyrosine kinase p56 lck . CD38 recognizes an antigen that is an integral membrane glycoprotein, Mr 45 kDa, with a protein core of 35 kDa.

The CD8 antigen is expressed on 19% to 48% of normal peripheral blood lymphocytes 10 and 60% to 85% of normal thymocytes. The CD38 antigen is expressed on essentially all pre-B lymphocytes, plasma cells, and thymocytes. It is also present on activated-T lymphocytes, NK lymphocytes, monocytes, myeloblasts, and erythro-blasts.

Applications: The antigen is expressed during the early stages of T- and B-lymphocyte differentiation, is lost during the intermediate stages of maturation, and then reappears during the final stages of maturation. The antigen is also expressed in some cases of T- and B-acute lymphoblastic leukemia (ALL), Burkitt's lymphoma, multiple myeloma, and acute myeloid leukemia (AML). CD8 + CD38 + T lymphocytes are involved in the immune response to viral infection. Elevated levels of CD8 + CD38 + lymphocytes are observed in human immunodeficiency virus (HIV) infection, and during the acute stages of Epstein-Barr virus (EBV) and cytomegalovirus (CMV) infection. Increased numbers of CD8 + CD38 + T lymphocytes are also present in the period immediately following bone marrow transplantation. In HIV infection, the coexpression of the CD8 and CD38 antigens, with a concomitant low percentage of CD4 + lymphocytes, is closely associated with disease progression. Beginning at seroconversion, and during the first stages of HIV infection, the number of CD8 + T lymphocytes increases while the number of CD4 + T lymphocytes decreases. When the onset of acquired immune deficiency syndrome (AIDS) occurs, there is a decline in the absolute CD3 +, CD4 + , and CD8 + lymphocyte levels along with a further decrease in the CD4 + T lymphocyte percentage, but the relative percentage of CD8 + T lymphocytes continues to rise until, in the late stages of AIDS, the majority of the remaining T lymphocytes are CD8 +.