Proliferative and cytotoxic immune functions in aging mice. III. Exogenous interleukin-2 rich supernatant only partially restores alloreactivity in vitro.

The ability of exogenous interleukin-2 (IL-2) rich supernatant to restore the defective T cell mediated immune functions of spleen cells from aged C57BL/6 mice was analyzed. Addition of IL-2 rich supernatant to allogeneic mixed lymphocyte cultures (MLC) resulted in an increase in the proliferative response of spleen cells from both young and old mice. The MLC response of cells from old mice was, however, not restored to the level of proliferation seen with splenocytes from young animals. In studying the generation of specific T cell suppressor function, it was found that IL-2 rich supernatant enhanced this function only for spleen cells from those aged animals which demonstrated a defective response in its absence. The response of these mice was thereby restored to the normal level. The response of cells from young control animals and aged mice with normal suppressor activity was not affected by the addition of IL-2 rich supernatant. We conclude that decreased IL-2 production constitutes a functionally important aspect, but is by no means the only defect in the immune response of aged mice. The results also suggest that responsiveness to IL-2 is less affected by age than lymphokine production.