Effects of Pregnancy on the Spleen in Mice

Abstract

Spleen size was analyzed in 2368 wild white-footed mice, Peromyscus leucopus, in Minnesota. Sex, season and type of death (chloroform or killer trap) did not affect spleen size. Females in late pregnancy showed an average increase of 50% in size of spleen. The cells in the nodules of spleens of pregnant mice were found to have large vesicular nuclei. It is suggested that this may be a reaction to an antigen produced by the embryos. Normal spleen size varied greatly (15–72 mg in animals of the same size), the S.D. being 13.6. Spleen weight versus body length is a straight line.