Evolutionarily conserved function of CD28 in alpha beta T cell activation

The functional role of the chicken homologue of CD28 was studied. It is expressed on all thymocytes, and both V beta 1- and V beta 2-family expressing peripheral alpha beta T cells. Peripheral gamma delta T cells are CD28-negative. Monoclonal antibody against CD28 had a costimulatory effect on T cells stimulated by phorbol myristate acetate (PMA), concanavalin A or MoAb against TCR. V beta 1 and V beta 2 expressing cells responded equally well to stimulation with anti-CD28 in combination with PMA. These responses were resistant to cyclosporin A, but inhibited by herbimycin A, suggesting that CD28 employs a signalling pathway at least partly distinct from that triggered by TCR/CD3. These data indicate a striking conservation of the costimulatory function of CD28 and emphasize the importance of this costimulatory pathway.