The CD8 glycoprotein of cytotoxic T cells is both an adhesion protein
and a cosignalling receptor. These functions are regulated by signals
from the T-cell antigen receptor complex (TCR-CD3), and CD8 acts to co
uple TCR occupancy to second messenger pathways. Here Anne O'Rourke an
d Matthew Mescher examine the roles of CD8 in activating the adhesion
and signalling cascade initiated by antigen binding.