Molecular Associations between the T-Lymphocyte Antigen Receptor Complex and the Surface Antigens CD2, CD4, or CD8 and CD5

The T-cell antigen receptor (TCR) complex is the key structure involved in signal transduction in T cells. To analyze associations between the TCR complex and other molecules, immunoprecipitations were carried out, followed by phosphorylation of molecules in vitro by tyrosine kinases associated with the precipitated molecules. This provided a sensitive assay for molecular complexes, and associations were demonstrated between the TCR complex and the surface antigens CD2, CD4, or CD8 and CD5 in normal rat T cells. The complexes were readily seen in immunoprecipitates from Brij 96 but not Nonidet P-40 detergent extracts. The multimolecular complexes are associated with the internal tyrosine kinases p56lckand p59fyn. The presence of p56lckassociated with CD4 or CD8 was also examined in early thymocytes, natural killer cells, and macrophages. The kinase was present in all cases except that of normal macrophages.