The CD4 antigen is involved in the recognition of the type II MHC antigen. It is also a receptor for HIV. It is present on most T helper cells and normal thymocytes. The cytoplasmic portion of CD4 is associated with p56lck tyrosine kinase. CD4 expression is commonly found in human lymph nodes and tonsils. 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; CD4; CD4 antigen (p55); CD4 antigen p55; CD4 receptor; MGC138290; T-cell surface antigen T4/Leu-3; T-cell surface glycoprotein CD4; T-cell-specific surface glycoprotein CD28; TP44