Factors affecting trophoblast growth in extrauterine sites.

The effect of genetical dissimilarity between the trophoblast and host on trophoblast growth was studied in extrauterine sites, where people can observe trophoblast growth without the complicating factors of the uterine environment. Trophoblast growth was estimated in this study by measuring the extent of trophoblast proliferation in the kidney and testis per body weight in the testis. The results showed that the trophoblast growth was not enhanced by genetical dissimilarity, but was probably determined by the capacity of the host to support trophoblast growth and the capacity of the trophoblast itself to grow. No hormonal influence on trophoblast growth was observed. When hosts were immunized with double skin grafts from donors, however, the success rate of attempted transplantation of the blastocyst was remarkably lowered and trophoblast growth was also suppressed in terms of the number of trophoblast cells and the extent of trophoblast proliferation. In such cases, intensive lymphocytic infiltration was seen between the trophoblast and host tissues. This suggests that some antigenicity on the trophoblast may be expressed in vivo under some conditions, e.g., in the strongly immunized host by the donor's antigen and the immunity to this antigen suppresses trophobalst growth.