Studies on the syngeneic mixed lymphocyte reaction. II. Decline in he syngeneic mixed lymphocyte reaction with age.

The syngeneic mixed lymphocyte reaction (SMLR) is the proliferative response of T lymphocytes cultured with syngeneic non-T lymphocytes. In previous studies, we found that the SMLR reaches adult level of activity at 4 weeks of age in BALB/c mice. We now report that the SMLR declines with age in this strain. The decline was first documented at 12 months of age, when non-T spleen cells were less able to stimulate young adult T cells than were non-T cells from 2 to 3 month-old mice. Splenic T cells from 12 month old mice were as responsive as splenic T cells from 2 to 3 months old mice. By 24 months of age, mice had no significant SMLR activity. Splenic T cells from 24 month old mice did not respond and splenic non-T cells did not stimulate SMLR when cultured with cells from young adult mice. Finally, suppressor cells were demonstrated in spleen cells preparations from 24 month old mice and may explain or contribute to the impaired SMLR in these animals.