– T-cell-specific surface glycoprotein CD28, contains an Ig-like V-type domain. CD28 is one of the proteins expressed on T cells that provide co-stimulatory signals, which are required for their activation. It is the receptor for CD80 and CD86. 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. It involved in T-cell activation, the induction of cell proliferation and cytokine production and promotion of T-cell survival.