COMPARATIVE-ANALYSIS OF PHOSPHOTYROSYL POLYPEPTIDES IN NORMAL AND LEUKEMIC HUMAN T-LYMPHOCYTES ACTIVATED VIA CD3 OR CD2

Phosphotyrosyl polypeptides induced following CD3- or CD2- specific antibody stimulation were analysed in different human T cell lines by immunoblotting or by immunoprecipitation of P-32-labelled cell lysates using a phosphotyrosine-specific monoclonal antibody. In Jurkat cells, resting peripheral T lymphocytes, T lymphoblasts, CD8+ T lymphoblasts and a CD4+ T cell clone, CD3 stimulation induced a strong but transient tyrosine phosphorylation of at least 15 polypeptides. However, in peripheral T cells and T blasts, the kinetics of phosphorylation were considerably slower than in Jurkat cells. The pattern of phosphotyrosyl polypeptides induced by CD3 stimulation was similar, although some differences were noted between normal T cells and Jurkat, especially at the level of the extent of phosphorylation. As had been previously reported for Jurkat T cells, a qualitatively similar tyrosine phosphorylation response was induced upon CD2 or CD3 stimulation in each of the analysed T cell populations, suggesting.that CD3 and CD2 share a common pathway of protein tyrosine kinase (PTK) activation. In HPB.ALL leukemia T cells (which express very low levels of CD45), both CD3 and CD2 stimulation induced only very weak protein tyrosyl phosphorylation. However, a 50 kDa polypeptide, which was part of an inducible doublet in Jurkat or normal T lymphocytes, was constitutively tyrosyl-phosphorylated in the HPB.ALL line. These results suggest that there is a common pathway of early PTK activation following CD3- or CD2-mediated stimulation in mature T cells, whether they express surface CD4 or CD8, and also that the PTK may be differently regulated in different T cell populations leading to different kinetics or intensity of tyrosyl phosphorylation.