T-cell-specific surface glycoprotein CD28, also known as TP44 and CD28, is a single-pass type I membrane protein which contains one Ig-like V-type (immunoglobulin-like) domain. CD28 / TP44 can binds the B7-1 and B7-2 ligand, and together perform important functions in the T and B cell response pathways. CD28 / TP44 is thus involved in T-cell activation, the induction of cell proliferation and cytokine production and promotion of T-cell survival.
