Age-related changes in graft-versus-host reactivity of spleen cells from male, virgin, or multiparous female Long-Evans rats.

Spleen cell graft-versus-host (GVH) reactivity was determined in male and female, either virgin or breeder, Long-Evans (LE) rats from 3 to 24 months of age. The tests of a regional (popliteal lymph node enlargement index) and a systemic (splenomegaly index, mortality assay) GVH reaction was used. Although the GVH reactivity declined with age in both sexes, the onset of this decline was significantly delayed in 18-month-old virgin females in comparison with 12-month-old males. Moreover, 6 or 7 consecutive pregnancies resulted in significantly enhanced GVH reactivity of 18-24-month-old females. This long-lasting effect of multiparity was observed in females mated either syngeneically or allogeneically. The possible role of neuroendocrine factors in delaying the age-related process of thymic involution in multiparous females is suggested.