T-CELL ACTIVATION IN THE ELDERLY - EVIDENCE FOR SPECIFIC DEFICIENCIES IN T-CELL ACCESSORY CELL-INTERACTIONS

We studied T cell activation in the healthy aged (> 70 years) by examining lymphocyte proliferative responses to various mitogenic stimuli in accessory cell (AC)-dependent and AC-independent systems. Results show that despite a near normal responses to the anti-CD3 monoclonal antibody (mAb) OKT3, peripheral blood mononuclear cells (PBM) from the elderly exhibit a profund reduction in phytohaemagglutinin (PHA)-responsiveness (approximately 30% of young adults). This deficit becomes even more severe at suboptimal doses of PHA. Adding exogenous interleukin-2 (IL-2) or pretreating the AC population with gamma interferon (IFN-γ) returns the level of proliferation to that seen with young adults Furthermore, replacing "old" AC with AC from young adults or with U937 (a monocytic cell lin) in T cell/AC cell-mixing experiments restores PHA-responsiveness in 70% of cases. On the other hand, AC from the aged fully support PHA responses in T cells from young adults. In AC-depleted cultures, purified T cells from the aged respond normally to the co-mitogenic stimuli, PHA + PMA. Taken together, these results suggest that the age-associated diminution in PHA-responsiveness is due, at least in part, to specific deficiencies in T cell/AC communication. © 1990.