Biochemical identification of a direct physical interaction between the CD4:p56lck and Ti(TcR)/CD3 complexes

Eur J Immunol. 1991 Jul;21(7):1663-8. doi: 10.1002/eji.1830210712.


The CD4 and CD8 antigens function in synergy with the TcR/CD3 complex in the generation of intracellular signals leading to T cell proliferation. The association of the protein-tyrosine kinase p56lck with CD4 and CD8 provides a potential mechanism in the generation of intracellular signals. Several studies have shown that CD4 can co-modulate with TcR/CD3 suggesting that these receptor complexes may associated on the surface of the T cell. Nevertheless, it has proven difficult to formally demonstrate a direct physical interaction between the CD4 and TcR/CD3 complexes using biochemical techniques. In this study, we have used the sensitivity of the in vitro kinase assay to show a direct physical linkage between the CD4:p56lck complex and various CD3 subunits. Immunoprecipitation of CD4 from cell lysates derived from the T lymphoblastoid line HPB-ALL results in the co-purification of p56lck with an additional polypeptide at 20 kDa. Re-precipitation analysis and isoelectric focusing demonstrated that this band corresponds to the CD3 epsilon chain. An alternative approach which involves the labeling of microsomal membranes with [gamma-32P]ATP revealed the presence of CD3 epsilon and zeta chains in anti-CD4 immunoprecipitates. By contrast, we were unable to demonstrate the association of the CD4:p56lck and TcR/CD3 complex in resting peripheral blood lymphocytes. These data indicate that the CD4:p56lck and TcR/CD3 complexes have the ability to form stable complexes on the surface of certain T cell lines.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antigens, Differentiation, T-Lymphocyte / analysis*
  • CD3 Complex
  • CD4 Antigens / analysis*
  • CD4 Antigens / physiology
  • Lymphocyte Activation
  • Mice
  • Phosphorylation
  • Protein-Tyrosine Kinases / analysis*
  • Receptors, Antigen, T-Cell / analysis*


  • Antigens, Differentiation, T-Lymphocyte
  • CD3 Complex
  • CD4 Antigens
  • Receptors, Antigen, T-Cell
  • Protein-Tyrosine Kinases