Pregnancy Associated Cytokines for Successful Pregnancy Establishment in Bovines

The actual decrease in the production potential of dairy cattle, particularly due to the reduced reproductive efficiency, is a major concern for the farmers and field veterinarians. Therefore, enhancement of reproductive efficiency is needed to raise the production of dairy cattle. Reproductive failure in terms of infertility, subfertility and dreadful embryonic mortality are some of the major factors responsible for lowering the reproductive efficiency in dairy cattle. Such serious issues can be tackled and minimized by expanding the knowledge in the field of bovine pregnancy and unravel different mechanisms of pregnancy establishment in bovines. This will enable and motivate researchers to discover some possible and suitable interventions around these mechanisms in order to increase the pregnancy outcomes in dairy cattle. Although, there are many mechanisms which have been delineated so far for the pregnancy establishment in bovine but still many areas remain untapped which needs to be taken into limelight. Exploring different mechanisms in early bovine pregnancy may help to improve the reproductive efficiency in bovines and thereby production potential in the dairy sector. This chapter reviews immune tolerance mechanisms associated with the implantation of the blastocyst and early pregnancy establishment in bovines. During the early pregnancy period, where a majority of embryonic loss occurs, it is imperative for the conceptus not only to prevent the corpus luteal regression but also to modify the maternal immune system from immune rejection. In this regard, interferon tau (IFNτ), a conceptus secreted factor, known to have anti-luteolytic and immunomodulatory properties and is the key pregnancy recognition agent in bovines, plays a preliminary and vital role in the establishment of bovine pregnancy. Whether it is by paracrine or by endocrine manner, IFNτ modulates the maternal immune system and helps in the establishment of pregnancy. Besides IFNτ, another crucial molecule recently came into limelight is indoleamine 2, 3-dioxygenase (IDO), which is an interferon-induced tryptophan catabolic enzyme and is the first and rate-limiting enzyme of the tryptophan catabolism via the kynurenine pathway. It is known to modify the maternal immune system by altering the T cell metabolism and thereby inhibiting the allo-reactive T cell proliferation and at the same time promoting the proliferation of immunosuppressive T regulatory cells. Moreover, to achieve successful implantation, IDO favors an anti-inflammatory cytokine milieu by inducing a shift towards the Th2 cytokines. Although many mechanisms have been delineated so far for the pregnancy establishment in bovine, the focus of this chapter resides on the role of IFNτ and IDO associated Th1-Th2 shift for a successful pregnancy with major emphasis on the tolerogenic mechanism of these molecules.