ABSTRACT
In 1978, Beer and Billingham,1 while working on immunological recognition mechanisms in mammalian pregnancy, published their view that the maternal system is aware of the presence of the early embryo, and actively responds to it. This was surprising, considering the differences in genetic make-up of the mother and fetus (semi or total), and was contrary to the prevailing opinion at that time, which considered that the trophoblast was hypoantigenic, as a protection from cellular immunity. Beer and Billingham1 suggested that unique HLA (human leukocyte antigen) molecules are presented to the maternal system, the responses to which play a role in establishing and maintaining pregnancy. A decade later, Billingham and Head2
suggested that local cell-based immunosuppressive and immunoprotective activity in the placenta was mediated by suppressor and other unknown cells. Billingham and Head2 further suggested that HLA sharing in the parents leads to lack of maternal recognition and is therefore the basis for rejection, i.e., miscarriage.
