INTERACTIONS OF CD4 WITH MHC CLASS-II MOLECULES, T-CELL RECEPTORS ANDP56(LCK)

CD4 and CD8 are members of the immunoglobulin supergene family of prot eins, and function as coreceptors with the T cell receptor (TCR) in bi nding MHC class II or class I molecules, respectively. Within this mul timeric complex, CD4 interacts with three distinct ligands. CD4 intera cts through its D1 and D2 domains with MHC class II proteins, through its D3 and D4 domains with T cell receptors, and through its cytoplasm ic tail with p56lck, a src-related, protein tyrosine kinase. Each of t hese interactions is important in the function of CD4 and will be disc ussed in turn.