Phosphorylation and coupling of ζ-chains to activated T-cell receptor (TCR)/CD3 complexes from peripheral blood T-cells of elderly humans

Abstract

Aging is often accompanied by altered T-cell signaling and functions. Signals mediated through the T-cell receptor (TCR)/CD3 complex are associated with tyrosine phosphorylations of ζ-chains by the regulated activities of protein tyrosine kinases p56 lck and p59 fyn as well as protein tyrosine phosphatases. In the present investigation, the coupling and phosphorylation of ζ-chains to TCR/CD3 immunocomplexes were examined in peripheral blood T-cells from 13 elderly and young humans stimulated by ligation of the TCR/CD3 with cross-linked anti-CD3 ϵ monoclonal antibody OKT3. Western blots analyzing the non-covalent coupling of ζ-chains to TCR/CD3 immunocomplexes from Brij-96 detergent lysates of anti-CD3 ligated T-cells showed that the levels of ζ-chains within TCR/CD3 immunocomplexes from T-cells of elderly and young subjects did not significantly differ. By contrast, the levels of phosphorylated ζ-chains generated during in vitro phosphorylations of TCR/CD3 immunocomplexes from elderly subjects were significantly reduced and averaged 44% of those observed for anti-CD3 ϵ ligated T-cells from young subjects. Analyses of the levels of ζ-chain coupling and phosphorylations in T-cells from each of the 13 elderly individuals also showed that the reductions in ζ-chain phosphorylations were heterogeneous and unrelated to modest reductions in coupling. Furthermore, the age-related decreases in ζ-chain phosphorylations were not due to diminished frequencies of CD3 ϵ + cells or densities of CD3 ϵ surface receptors and could be observed without reductions in ϵ-chain phosphorylations. These results suggest that aberrancies of ζ-chain phosphorylations can occur in T-cells of elderly humans independent from any uncoupling of ζ-chains to activated TCR/CD3 complexes.