The effect of age, sex and breeding on graft versus host reactivity of spleen cells from C57BL mice.

Spleen cell graft versus host (GvH) reactivity was determined in male and female, either virgin or breeder, C57BL mice from 3 to 24 months of age. The GvH reaction was assessed by a local popliteal lymph node assay and by a splenomegaly test for a systemic reaction. Although the GvH reactivity declines progressively with age in both sexes the virgin female response was greater than that of males throughout the period of 6-18 months of age. Two-year-old mice of both sexes were practically unable to mount a GvH reaction. No differences were evident in aging female reactivity after one or two syngeneic pregnancies. On the other hand, 3 or more consecutive pregnancies resulted in enhanced GvH reactivity of 12-24-month-old females, which responded comparably to young virgin mice. This long-lasting immunopotentiating effect of multiparity was similar after 3-4 and 8-9 pregnancies. The possible role of developing foetuses on the maintenance of high GvH reactivity in breeder females is suggested.