Decline, in aging mice, of the anti‐2, 4, 6‐trinitrophenyl (TNP) cytotoxic T cell response attributable to loss of Lyt‐2−, interleukin 2‐producing helper cell function

Abstract

The in vitro generation of cytotoxic T lymphocytes (CTL) specific for 2,4,6-trinitrophenyl (TNP)-modified syngeneic spleen cells is almost variably depressed in apparently healthy 18 mo. old mice of the long-lived (BALB/c .times. C57BL/6)F1 hybrid strain. Studies of CTL production from Lyt-2+ thymus cells have suggested that pre-killer cells may require, for maturation into effectors, the presence of a soluble helper factor, interleukin 2 (IL2), produced by Lyt-2- cells which are devoid of pre-CTL activity. A petri-dish adherence technique was developed for separating spleen cells into Lyt-2+ and Lyt-2- populations in order to test for helper and pre-killer activity independently. Pre-CTL function is measured by stimulating Lyt-2+ cells in the presence of exogenous IL 2. Helper cell activity is tested by adding Lyt-2-cells to indicator populations of Lyt-2+ pre-CTL. Estimation of IL2 levels in medium conditioned by unfractionated, TNP-self-stimulated splenocytes provides a 2nd measurement of helper cell function. Mice 18 mo. of age, when compared to 4 mo. old controls, retain nearly all their pre-CTL activity but have lost sufficient helper cell activity to account for the decline in unseparated spleen cell cultures. Older mice also produce lower IL2 levels.