Is spontaneous resorption in the DBA/2-mated CBA/J mouse due to a defect in "seed" or in "soil"?

Recurrent spontaneous resorption in DBA/2-mated CBA/J mice has been attributed to damage by NK-lineage cells and TNF-alpha beginning several days after implantation. However, some recent data have suggested CBA/J female mice have a high proportion of preimplantation embryo abnormalities resulting in defective in vitro implantation and impaired trophoblast outgrowth. Could spontaneous abortion be due to a defective embryo ("seed") rather than a hostile post-implantation uterine lining ("soil").

Mated CBA/J females were manipulated so as to have high spontaneous abortion rates and a high percent abnormal embryos, or low resorption rates and a low percent abnormal embryos. Embryos from low aborting females were transferred into high aborting female recipients that were pseudopregnant, and vice versa.

Abnormal embryos from females with high abortion rates implanted in low aborting females and did not show any greater tendency to resorb than normally developed embryos in these recipients. By contrast, normal embryos to some extent and abnormal embryos to a much greater extent, gave a high abortion rate when the recipient female was a high aborter.

Properties of the "soil" into which embryos implant determines the likelihood of success or failure (abortion). Abnormal pre-implantation embryos can be "rescued" by "good soil"; "sick soil" damages both normal and abnormal embryos. Defining the cellular and molecular mechanisms may be useful in understanding basic mechanisms leading to aborting and nonaborting pregnancy.