Immunoregulatory peptides in placental viviparity

Placental viviparity is a reproductive strategy usually attributed to mammals. However, it is also present in other vertebrate species, e.g. in squamate reptiles and elasmobranch fishes. Viviparity may involve the formation of a placenta, a structure formed by the apposition of extra-embryonic membranes and maternal tissues. Although the immunological mechanisms that allow the survival of the semiallogenic embryo in maternal tissues are still largely unknown, cytokines (peptides with an immunoregulatory action) seem to play an important role. The presence of cytokines has been demonstrated in the placenta of various vertebrates independently of the species or the type of placenta the species has. Many methodological approaches have been used to show the role of cytokines at the maternal-fetal interface. However, we believe that the evolutionary approach is the most physiological model to understand the importance of such factors in the establishment and maintenance of placental viviparity.