CD8 molecule is composed of two chains termed alpha and beta. CD8 is found on a T cell subset of normal cytotoxic / suppressor cells which make up approximately 20 to 35 % of human peripheral blood lymphocytes. The CD8 antigen is also detected on natural killer cells, 80% of thymocytes, on a subpopulation of 30% of peripheral blood null cells and 15 to 30% of bone marrow cells. Human CD28 antigen is a 44 kDa disulfide linked homodimeric T cell specific surface glycoprotein. It is a cell adhesion molecule of the immunoglobulin superfamily which is constitutively expressed on most peripheral blood T lymphocytes (approximately 95% of CD4+ cells and 50% of CD8+ cells). Mature thymocytes exhibit higher levels of CD28 than the immature cells. Activation of T cells results in enhanced CD28 expression. T cell activation requires two combined signals provided by antigen presenting cells.
CD28; CD28 antigen; CD8 antigen, alpha polypeptide (p32); CD8 antigen, beta polypeptide 1 (p37); CD8a; CD8alpha; CD8b; CD8beta; Leu-2; Leu2 T-lymphocyte antigen; MGC138290; OKT8 T-cell antigen; T cell co-receptor; T lymphocyte surface glycoprotein beta chain; T-cell antigen Leu2; T-cell surface glycoprotein CD8 alpha chain; T-cell surface glycoprotein CD8 beta chain; T-cell-specific surface glycoprotein CD28; T-lymphocyte differentiation antigen T8/Leu-2; T8 T-cell antigen; TP44