CD28/TP44

T-cell-specific surface glycoprotein CD28 (CD28) is a single-pass typeI membrane protein which contains one Ig-likeV-type (immunoglobulin-like) domain. It belongs to the immunoglobulin (Ig) superfamily. CD28 is one of the molecules expressed on T cells that provide co-stimulatory signals, which are required for T cell activation.CD28 co-stimulation is necessary for CD4 positive T-cell proliferation and survival, interleukin-2 production, and T-helper type-2 development. Human post-thymic regulatory T cells require CD28 co-stimulation to expand and maintain potent suppressive function in vivo. Apoptosis plays a key role in the age-related decline of CD28 expression and in immunosenescence. CD28 is the receptor for CD80 (B7.1) and CD86 (B7.2) . When activated by Toll-like receptor ligands, the CD80 expression is upregulated in antigen presenting cells (APCs) . The CD86 expression on antigen presenting cells is constitutive. CD28 is the only B7 receptor constitutively expressed on naive T cells.