Increase in the number of splenic plaque forming cells with length of gestation in untreated pregnant mice.

The number of plaque forming cells (PFC) in spleens from untreated virgin and syngeneically pregnant CBA mice has been evaluated by use of two different hemolytic plaque assays. The total number of splenic IgM- and IgG-PFC in virgin and 16 day pregnant mice was determined by protein A- sheep red blood cell (SRBC) plaque assay. The number of both IgM- and IgG-PFC was significantly increased in spleens from pregnant mice, but the total number of IgM-PFC was several times higher than that of the IgG-PFC. In the same experiment the number of splenic anti-trinitrophenyl (TNP) PFC was determined simultaneously. The values obtained for anti-TNP PFC in the different animals were found to correlate with the values for IgM-PFC in the protein A-SRBC plaque assay. Finally, the number of splenic anti-TNP PFC was determined at different occasions during pregnancy (day 4, 8, 12, and 16). It was found that the number of anti-TNP PFC was elevated as early as the 4th day of pregnancy, and that the number of PFC per spleen increased with the length of gestation.