Tags: Protein.
CD28 (Cluster of Differentiation 28) is one of the proteins expressed on T cells that provide co-stimulatory signals which are required for their activation. 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.