Role of T cells and adherent cells in age-related decline in murine interleukin 2 production.

Spleen and lymph node cells from young (3 to 4 months) and old (24 to 36 months) mice of two inbred lines and one hybrid stock were assessed for the effect of age on IL 2 production. The results revealed that the production of IL 2 by old spleen and lymph node cells is reduced to 42% that of young cells. Cell counting, IL 2 inhibition and absorption, and cell mixture studies were then performed to determine the basis for the reduced IL 2 production. Cell counting studies revealed that the reduced IL 2 production by old cells cannot be caused by a decrease with age in the total number of Lyt 1+ T helper cells or by an increase with age in Lyt 2+ T suppressor cells. IL 2 inhibition, IL 2 absorption, and young-old spleen cells mixture studies revealed that the decrease in the level of IL 2 activity with age is caused neither by the formation of excessive amounts of soluble IL 2 inhibitors, by the generation of excessive numbers of IL 2 responsive blast cells, nor by an increase in suppressor cells. Further cell mixture studies revealed a decrease in IL 2 production by young T cells in presence of old adherent cells, which did not approach that of the old T cell-old adherent cell mixture, and an increase in IL 2 production by old T cells in the presence of young adherent cells, which did not approach that of the young T cell-young adherent cell mixture. These results would indicate that the decline in activity of both the T cells and adherent cells involved in IL 2 production are responsible for the reduction. Finally, it was found that the reduced proliferative activity of Con A-stimulated old spleen cells can be enhanced to the same extent as that of young spleen cells by exposing them to exogenous IL 2.