Importance of trophoblast genotype for survival of interspecific murine chimaeras.

Interspecific chimaeras between Mus musculus and Mus caroli were made by injection of M. musculus inner cell masses (ICMs) into M. caroli blastocysts, and by aggregation of 8-cell embryos. Both types of chimaera were transferred to M. musculus recipients: the former did not survive to term, but viable chimaeras were produced following embryo aggregation. Previous experiments have shown that chimaeras produced by injection of M. caroli ICMs into M. musculus blastocysts are viable, whereas M. caroli blastocysts cannot survive in the M. musculus uterus. There results indicate that the presence of trophoblast cells of maternal uterine genotype allows M. caroli in equilibrium M. musculus chimaeras to survive in the M. musculus uterus. It is suggested that M. musculus trophoblast components may protect the M. caroli embryonic cells from maternal immune rejection.