Immunopathology of Early Pregnancy

One of the important discoveries in reproduction is that the reproductive process uses for its own purpose lymphokines and cytokines which were initially defined as being of immunologic nature, first traced within the immune system. This is not very surprising, since most of these molecules are more signaling factors and communication molecules between cells of various lineages than molecules strictly restricted to the immune system, such as immunoglobulins (Ig) and T-cell receptors. The field has now evolved from the idea of a host-graft relationship to the concept of an integrated dialogue between the mother and the conceptus, more akin, for some, to a host-tumour relationship. Yet, in fact, the paradigm of acceptance and/or rejection of the foetus by its mother is still heavily embedded in the thinking of many reproductive immunologists. This is not surprising, since the trend of research that led to modern reproductive immunology was initiated by Sir Peter Medawar’s disquisition on "the riddle of the foetal allograft. ’’1 It is therefore not all disconcerting that, in 1997, one of Medawar’s colleagues, Leslie Brent, in his recent book A History of Transplantation Immunology, still depicts the materno-fetal relationship as "Nature’s (almost) perfect allograft, ’’z nor that pioneering work in the field is due to another collaborator of Leslie Brent and Peter Medawar, Rupert E. Billingham. However, the paradigms have evolved. As you will see in this brief presentation, there is still room for discussing, and re-envisaging, with the use of murine models and data in humans, the concept and mechanisms of "rejection" of the foetal allograft. But the question of the tolerance of the conceptus has evolved. First, we have known for a long time that we can and must dissociate local and systemic events, but this idea has not yet fully penetrated the thinking of the general public. It is possible to observe rejection of paternal strain tissues after preimmunisation of the mother without compromising pregnancy (in fact, the babies born in such situations are in most circum-