Pregnancy and gamma/delta T cells: Taking on the hard questions

Introduction Considering the allograft rejection as one of the basic features of the immune system, the mammalian pregnancy is still a puzzling situation where the semiallogeneic embryo, a mating product of non-histocompatible individuals is not rejected. How are the demands of pregnancy solved in the context of the maternal immunity? How is the competent maternal immune system modulated during pregnancy? These are hard questions to answer and an intriguing challenge for immunologists to explain. Historically, the mammalian fetus has been regarded as a successful allograft, a tumor or a parasite [1,2]. Although the mechanisms that promote the survival of the conceptus are at large still unknown, it has become increasingly clear that the maternal immune tolerance towards the fetus is the result of the interactions of a jigsaw puzzle of actors – cells, serum proteins, hormones, cytokines, enzymes and neurotransmitters.