INTERACTIONS OF CD4 WITH MHC CLASS-II MOLECULES, T-CELL RECEPTORS AND P56(LCK)

CD4 and CD8 are members of the immunoglobulin supergene family of proteins, and function as coreceptors with the T cell receptor (TCR) in binding MHC class II or class I molecules, respectively. Within this multimeric complex, CD4 interacts with three distinct ligands. CD4 interacts through its D1 and D2 domains with MHC class II proteins, through its D3 and D4 domains with T cell receptors, and through its cytoplasmic tail with p56lck, a src-related, protein tyrosine kinase. Each of these interactions is important in the function of CD4 and will be discussed in turn.