The effects of transplacental cell (antigen) traffic.

The feto-placental unit is a successful natural graft without the direct vascularization from the host seen in contrived surgical grafts. Our concept of the mechanisms whereby immunological rejection between mother and fetus is avoided, has changed from emphasizing single features such as the suppression of immunological properties or the vascular separation of the two participants. It is now clear that the interposed tissues of the placenta are vital filters with species differences and temporal morphological changes of probable relevance within each species, and that a number of adaptations of what is regarded as normal immunity occur in the mother and in the developing fetus. Much remains to be learned about transplacental traffic and about the adaptations of immunity found in normal pregnancy as well as those peculiar to abnormalities such as haemolytic disease, spontaneous abortion and pre-eclampsia. The development of a reproducible in-vitro system which reliably reflects the status of the graft rejection response is likely to lead to enlightening findings.