EFFECT OF AGE ON MITOGEN-INDUCED PROTEIN-TYROSINE PHOSPHORYLATION IN HUMAN T-CELL AND ITS SUBSETS - DOWN-REGULATION OF TYROSINE PHOSPHORYLATION OF ZAP-70

Several events of T cell activation have been reported to decline in h umans with age. Since protein tyrosine phosphorylation is an early cri tical event of T cell activation, we performed a systematic analysis o f the age-associated changes in the mitogen induced protein tyrosine p hosphorylation of human T lymphocytes using SDS-PAGE and Western blott ing techniques. Following stimulation with Con A and PHA, an identical pattern of protein tyrosine phosphorylation was observed in the lysat es of T cells prepared from seven healthy young adults and eight healt hy elderly human subjects. Five different high molecular mass proteins (75. 115, 120, 140 and 170 kDa) were consistently tyrosine phosphoryl ated in all of the donors from both age groups and peaked between 3 an d 10 min. Tyrosine phosphorylation of the above substrates was observe d in both CD4 and CD8 subsets. When compared for individual donors fro m both age groups, variations in the T cell response with regard to ne t tyrosine phosphorylation for all the substrates was observed. Howeve r, the mitogen induced level of tyrosine phosphorylation of only p75 w as found to be significantly lower in unfractionated T cells as well a s CD4 and CD8 subsets of older subjects than that of young subjects. U sing immunoblotting, p75 was identified as ZAP-70, a member of the syk family of protein tyrosine kinases. Understanding of the biochemical basis of the reduced level of tyrosine phosphorylation of ZAP-70 will be helpful in delineating the molecular basis of age-associated impair ment of T cell activation. (C) 1998 Published by Elsevier Science Irel and Ltd. All rights reserved.