Necessity of the spleen for balanced secondary sex ratios following maternal immunization with male antigen.

A study testing the hypothesis of Hellstrom that the success of allogeneic matings in the mouse is due to the passive protection of antigenically dissimilar embryos by factors in the maternal serum is presented. Female mice were splenectomized and grafted with isogenic male skin 2-3 weeks later. The animals were then inoculated with male spleen cells and mated with isogenic males. Sham splenectomized animals treated in otherwise the same manner and untreated animals served as controls. The splenectomized animals had an unusually high number of male offspring (70.5%), though the sham group did not (55.2%). This result was corroborated in a repeat experiment with C57BL strain mice. The difference in sex ratios in litters born to splenectomized females (59.4%) and sham splenectomized females (49%) was highly significant (p less than .005). The increased sex ratio in litters born to females is related to the immunological status of the animals. The shorter the time it took to reject the male skin grafts, the higher was the sex ratio. It is suggested that a spleen-associated factor and maternal recognition of male antigens could be invlolved in the maintenance of a balanced sex ratio in most mice strains. Because of the splenetic activity and the higher sex ratios, the Hellstrom hypothesis is refuted.