Physical association of CD4 with the T cell receptor.
The coreceptor hypothesis postulates that physical association of CD4 with the TCR is required for effective signaling for T cell activation. A variety of studies has suggested that the coreceptor function of CD4 allows responses to 10- to 100-fold lower levels of peptide:self MHC class II ligand. We test the hypothesis of CD4 physical association with the TCR in two different ways. First, we use a panel of soluble antibodies directed at different TCR epitopes to activate a cloned T cell line, and show that activation by antibodies directed at a particular TCR epitope can be inhibited by anti-CD4 antibodies binding to a certain CD4 epitope. These effects establish that the interaction of CD4 and the TCR occurs in a specific orientation. Second, we use the same system to provide evidence that the physical association of CD4 with the TCR is required for effective tyrosine phosphorylation of the TCR zeta-chain subunit, presumably reflecting delivery of p56lck (lck) to the TCR. Only anti-TCR antibodies that induce physical association of CD4 with the TCR as monitored by cocapping can induce efficient tyrosine-phosphorylation of the TCR zeta-chain, unless second antibodies are used to force CD4 and the TCR to associate. Furthermore, the phosphorylation of the TCR zeta-chain exactly parallesl physical association in time and drug sensitivity. We conclude from these studies that stimuli that drive physical association of CD4 and the TCR strongly favor T cell activation, supporting the coreceptor hypothesis of CD4 function.
Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510.
U
U
Dianzani
A
A
Shaw
B K
BK
al-Ramadi
R T
RT
Kubo
C A
CA
Janeway
D000818:Animals; D000911:Antibodies, Monoclonal; D000938:Antigen-Presenting Cells / Q000276:immunology; D015704:CD4 Antigens / Q000737:chemistry*; D015496:CD4-Positive T-Lymphocytes / Q000502:physiology*; D002999:Clone Cells; D003432:Cross-Linking Reagents; D015638:Cytochalasin D / Q000494:pharmacology; D000939:Epitopes; D006183:H-2 Antigens / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000502:physiology; D066298:In Vitro Techniques; D008213:Lymphocyte Activation; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D046911:Macromolecular Substances; D051379:Mice; D015739:Nocodazole / Q000494:pharmacology; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011940:Receptor Aggregation; D011948:Receptors, Antigen, T-Cell / Q000737:chemistry*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D000911:Antibodies, Monoclonal; D015704:CD4 Antigens; D003432:Cross-Linking Reagents; D000939:Epitopes; D006183:H-2 Antigens; D000949:Histocompatibility Antigens Class II; D046911:Macromolecular Substances; D011948:Receptors, Antigen, T-Cell; D019000:Phosphotyrosine; D015638:Cytochalasin D; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D015739:Nocodazole