An investigation of splenic enlargement in pregnant mice

Enlargement of the spleen was found around the 12th day of gestation in CBA and NMRI mice. No clear difference was observed between spleens from mice pregnant after syngeneic or allogeneic matings. The degree of enlargement was dependent on the number of foetuses present in the uterus. The enlarged spleen was characterized histologically by 1) a remarkable change in the structure of the red pulp, with increased numbers of erythroblasts and plasma cells in different stages of maturation, and 2) an increase in size both of marginal zones and of lymphoid nodules. T- and B-cell proportions remained fairly unaffected in spleens from 12 day pregnant mice. Splenic enlargement during pregnancy is a reaction independent of foetal transplantation antigens of paternal origin, but dependent upon particular properties of growing foetal or placental tissues.