Reproductive immunology in viviparous mammals: evolutionary paradox of interactions among immune mechanisms and autologous or allogeneic gametes and semiallogeneic foetuses

Immunological uterine response to pig embryos before and during implantation

“…The ratios of anti‐/pro‐inflammatory cytokines were also analyzed as a potential precise indicator of the optimal conditions for adequate embryo survival and progression. Our findings indicated that at this period, the uterine environment is progressing or has progressed from an initial pro‐inflammatory stage towards an anti‐inflammatory stage (see Figure 2 ), which, in accordance with previous studies, appears necessary for the establishment of immunotolerant mechanisms preventing embryo rejection (Almiñana et al., 2012 ; Jalali et al., 2014 ; O’Leary et al., 2004 ; Samardzijaa et al., 2020 ). Further research is necessary to decipher the mechanisms underlying the modulatory effects of insemination components and the embryo presence on the uterine response of pig females at pre‐implantation moments.…”

“…This reaction consists of the endometrium increasing its expression of pro‐inflammatory mediators (see Figure 1 ), along with an important increase in uterine leucocyte infiltration, mainly neutrophils, macrophages, dendritic cells and T lymphocytes (Jiwakanon et al., 2011 ; O’Leary et al., 2004 ; Taylor et al., 2009 ). The main functions of this inflammatory response it to eliminate bacteria and excess sperm debris and, more importantly, to prime the maternal immune system to accept the presence of paternal antigens, facilitating embryo attachment and growth (Alvarez‐Rodriguez et al., 2019 ; Bidarimath & Tayade, 2017 ; Samardzijaa et al., 2020 ). While the infiltrated neutrophils are short‐lived (24–36 hr after insemination), the macrophages and dendritic cells remain in the uterus until Day 6 of gestation, and their effects in promoting immune tolerance status can remain until Day 13 of gestation (Robertson, 2005 ; Ziecik et al., 2011 ).…”

“…Two events determinant to reach a viable pregnancy take successively place during these days (see Figure 1 ), namely, the maternal recognition of pregnancy (Day 12) and implantation, which includes embryo attachment (Day 18) and full implantation reached around Day 25 (Lin et al., 2015 ). Both events are highly dependent on a correct cross‐talk between the developing conceptuses and the female endometrium (see reviews by Geisert et al., 2017 ; Samardzijaa et al., 2020 ; Waclawik et al., 2017 ).…”

Context is key: Maternal immune responses to pig allogeneic embryos

“…An adequate process of antigen presentation is essential for promoting an adequate immune response during pregnancy to induce trophoblast invasion, tissue remodeling, embryonic development, and placentation (Zhang et al, 2021). In response to all these altered signals, maternal immune cells can reduce or even stop the transcription of angiogenic factors, blocking vascularization of the yolk sac and particularly the allantois; leading to inhibition of conceptus development and death (Samardžija et al, 2020).…”