THE T-CELL SURFACE PROTEIN, CD28

The cluster of differentiation (CD) antigen CD28 is a 44-kDa, disulphi de-bonded, homodimeric glycoprotein, which is constitutively expressed on the surface of all murine T cells and the majority of human T cell s. Ligation of CD28 by its counter receptor, B7, expressed on the surf ace of antigen presenting cells, has been shown to induce signals that , in synergy with those derived from engagement of the T cell receptor by an antigen bound to a major histocompatibility complex, enhance pr oliferation and cytokine production. Manipulation of this interaction can have dramatic effects on the outcome of T cell activation. Blockin g CD28/B7 interactions may be useful in preventing unwanted activation in allergy and autoimmune diseases, whereas enhancing this interactio n can promote tumour rejection. Thus, CD28 and its signalling pathways may prove to be useful targets in the development of new therapeutic treatments. (C) 1997 Elsevier Science Ltd.