Autologous mixed lymphocyte reaction in man. IX. Autologous mixed lymphocyte reaction and lymphocyte subsets in aging humans.

Peripheral blood from 15 young (20-30 years) and 15 aging (65-80 years) subjects was analysed for the proliferative response of T cells upon stimulation with non-T cells in the autologous mixed culture reaction (AMLR) and allogeneic MLR, and for the proportion of monoclonal antibody-defined lymphocyte subsets and monocytes. No significant difference was observed in the AMLR or allogeneic MLR between T and non-T cells in aging and young subjects. However, when non-T cells were further fractionated into adherent monocytes and non-adherent B cells (B cells and null cells), the AMLR between macrophages and T cells was significantly (P less than 0.05) higher in young subjects than in simultaneously studied aging subjects. In contrast, the AMLR between T cells and B cells was significantly (P less than 0.05) higher in the aging subjects than in the young group. In the T-T AMLR (using phytohaemagglutinin-stimulated T cells as stimulators), aging subjects had a significantly (P less than 0.05) lower proliferative response than simultaneously studied young subjects. In vitro addition of purified interleukin 2 reconstituted the T-T AMLR to the base-line T-T AMLR in young humans. No significant difference was observed in the allogeneic MLR and lymphocyte subsets between the two groups. The significance of these observations is discussed.