Marker of T lymphocyte

In addition to CD3 and z proteins, T cells express several other proteins that assist the TCR complex in functional responses. These include CD4, CD8, CD28, and integrins. CD4 and CD8 are expressed on two mutually exclusive subsets of ab T cells. Approximately 60% of mature T cells are CD4+ and about 30% are CD8+. Most CD4+ T cells function as cytokine-secreting helper cells that assist macrophages and B lymphocytes to combat infections. Most CD8+ cells function as cytotoxic (killer) T lymphocytes (CTLs) to destroy host cells harboring microbes. During antigen recognition, CD4 molecules bind to class II MHC molecules that are displaying antigen and CD8 molecules bind to class I MHC molecules, and the CD4 or CD8 coreceptor initiates signals that are necessary for activation of the T cells.Reference: Robbins and Cotran Pathologic Basis of Disease; 9th edition; Chapter 6; 191The normal immune response