Abstract:
The bovine fetus, like that of other species, is a semi-allograft and the regulation of
materno-fetal alloimmunity is critical to prevent its immunological rejection. In cattle, a
materno-fetal alloimmune response may be beneficial at parturition. It is hypothesized that
upregulation of major histocompatibility complex (MHC) class I on the fetal membranes
toward the end of gestation induces a maternal alloimmune response that activates innate
immune effector mechanisms, aiding in the loss of the adherence between the fetal membranes
and the uterus. Loss of fetal–maternal adherence is pivotal for the timely expulsion
of the fetal membranes and the absence (or reduction) of the maternal immune response
may lead to retained fetal membranes, a common reproductive disorder of cattle. Currently,
there is no effective treatment for retained fetal membranes and a better understanding of
materno-fetal alloimmune-assisted separation of the fetal membranes may lead to novel
targets for the treatment of retained fetal membranes. In this review, the regulation of
materno-fetal alloimmunity during pregnancy in cattle, with a focus on placental MHC
class I expression, and the importance of maternal alloimmunity for the timely separation
of the fetal membranes, are discussed.
