Studies on the syngeneic mixed lymphocyte reaction. I. The ontogeny of the syngeneic mixed lymphocyte reaction in mice.

The syngeneic mixed lymphocyte reaction (SMLR) is the proliferative response of T lymphocytes cultured with syngeneic non-T lymphocytes. The ontogenic development of the SMLR has been studied in BALB/c mice. The SMLR is not demonstrable in BALB/c mice less than 3 weeks old. The SMLR attains an adult level of activity at 4 weeks of age. Splenic T cells from mice less than 3 weeks old do not respond and splenic non-T cells do not stimulate an SMLR. T-cell preparations acquire the capacity to respond in the SMLR between 2 and 3 weeks of age and non-T cells acquire the capacity to stimulate in SMLR between 3 and 4 weeks old. Spleen cells from 1 week old mice suppress the adult SMLR. Suppressor activity was eliminated by depleting either Thy-1.2 positive cells or adherent cells. When suppressor activity was eliminated, spleen cells from 1 week old donors were capable of stimulating syngeneic T cells. Spleen cells from 1 week old nude BALB/c mice do not suppress the SMLR and stimulate syngeneic T cells normally. These results suggest that the impaired SMLR in very young mice is, at least in part, due to cell-mediated suppression of the SMLR.