Abstract
Pig embryo transfer (ET) is burdened by high embryo mortality, with cytokines playing a significant role in recruitment of immune cells during embryo attachment and placentation. We hereby tested if their levels in endometrium and placenta from sows carrying hemi-allogeneic (artificially inseminated sows; C+ positive control) or allogeneic embryos (sows subjected to ET; ET) during peri-implantation (D18) or post-implantation (D24) are suitable mirrors of embryo rejection or tolerance after ET. Non-pregnant sows (C−) were used as negative controls. A set of cytokines was assayed in the tissues through multiplexed microsphere-based flow cytometry (Luminex xMAP, Millipore. USA). Fewer (58.7%. p < 0.003) conceptuses were recovered at D24 after ET compared to C+ (80.9%); with more than 20% of the ET conceptuses being developmentally delayed. Cytokine levels shifted during implantation. Anti-inflammatory IL-10 levels were significantly (p < 0.05) lower in ET sows compared to C+ at D24 of pregnancy. The C+ controls (carrying hemi-allogeneic embryos) consistently showed higher levels of pro-inflammatory TNF-α, IFN-γ, and IL-2 cytokines at D18 and IL-1α at D24, compared to the ET group. This clear dysregulation of pro- and anti-inflammatory cytokine levels in sows subjected to ET could be associated with an impaired maternal immune tolerance, explaining the high embryonic mortality of ET programs.
Highlights
Spontaneous conceptus loss in pigs resulting in a significant decrease in litter size is of major concern for its negative economic impact [1]
Embryo mortality after pig embryo transfer (ET) has been a topic of increased interest, the contributing causes are still not well understood, regarding the response of the maternal uterus to the stimuli produced by allogeneic embryos
This paper describes experimental work aimed to investigate whether pro- and anti-inflammatory cytokine expression and/or their ratio in endometrial and placental samples during early pregnancy (Days 18 and 24) differ in response to the presence of hemi- or allogeneic embryos, testing the hypothesis that the condition of allogeneity is substantially involved in maternal embryo rejection after pig ET
Summary
Spontaneous conceptus loss in pigs resulting in a significant decrease in litter size is of major concern for its negative economic impact [1]. Embryo mortality after pig ET has been a topic of increased interest, the contributing causes are still not well understood, regarding the response of the maternal uterus to the stimuli produced by allogeneic embryos. The cross-talk on either side of the maternal-fetal interface is crucial to achieve endometrial receptivity during the peri-implantation period of pregnancy [9]. During this period, porcine conceptuses modulate the maternal environment toward successful pregnancy [10], being responsible of establishing endometrial receptivity, and a balance between pro- and anti-inflammatory signals [11] through the secretion of different molecules such as growth factors and cytokines [12,13]
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