Active maternal immunoregulatory responses
A central creed in reproductive immunology is that there is active maternal immune recognition of pregnancy (i.e. of fetal trophoblast) that leads to cellular, antibody or cytokine responses which protect the fetal allograft. Taking antibody responses first, there has been much evidence that so-called blocking antibodies (which impair in vitro lymphocyte response assays) can be found in normal pregnancy sera and placental eluates. However, the data often are not convincing that these systemic effects can always be ascribable to specific antibody, rather than other serum factors, and that they occur in all successful pregnancies. For example, agammaglobulinemic women do not suffer undue problems of pregnancy failure other than indirectly following their susceptibility to infection. It is probable that the blocking antibody phenomenon is an effect rather than a cause of the immunologic success of outbred pregnancy.