Selected Uterine Immune Events Associated With the Establishment of Pregnancy in the Dog.

Miguel Tavares Pereira,Selim Aslan,Mariusz P Kowalewski,Renata Nowaczyk,Rita Payan-Carreira,Duygu Kaya,Sonia Miranda

doi:10.3389/fvets.2020.625921

Abstract

In the dog, implantation takes place at approximately 17 days of embryonal life and, while exposed to relatively high circulating progesterone concentrations, embryos presence is required for the formation of decidua. Furthermore, a balance between pro- and anti-inflammatory responses in conceptus-maternal communication is crucial for the onset of pregnancy. Strikingly, the understanding of such immune mechanisms in canine reproduction is still elusive. Here, canine uterine samples from pre-implantation (day 10–12, E+) and corresponding non-pregnant controls (E–), implantation (day 17, Imp) and post-implantation (day 18–25, Post-Imp) stages of pregnancy were used to investigate the expression and localization of several immune-related factors. The most important findings indicate increased availability of CD4, MHCII, NCR1, IDO1, AIF1, CD25, CCR7, and IL6 in response to embryo presence (E+), while FoxP3 and CCL3 were more abundant in E– samples. Implantation was characterized by upregulated levels of FoxP3, IL12a, ENG, and CDH1, whereas CD4, CCR7, IL8, and -10 were less represented. Following implantation, decreased transcript levels of TNFR1, MHCII, NCR1, TLR4, CD206, FoxP3, and IL12a were observed concomitantly with the highest expression of IL6 and IL1β. MHCII, CD86, CD206, CD163, TNFα, IDO1, and AIF1 were immunolocalized in macrophages, CD4 and Nkp46 in lymphocytes, and some signals of IDO1, AIF1, and TNF-receptors could also be identified in endothelial cells and/or uterine glands. Cumulatively, new insights regarding uterine immunity in the peri-implantation period are provided, with apparent moderated pro-inflammatory signals prevailing during pre-implantation, while implantation and early trophoblast invasion appear to be associated with immunomodulatory and rather anti-inflammatory conditions.

Highlights

The uterine mucosal immune system plays an important role during maternal recognition and establishment of pregnancy
Both CD86 and MHCII are expressed in M1 and M2b macrophages, the latter have a lower expression of MHCII [32, 33]
The quantification of immune cells in the uterus was not within the scope of the present work, these expression patterns suggest a decreased immune activity in the uterus during this period, despite the significantly increased expression of the proinflammatory IL1β. We found it interesting that the localization of CD206, CD163, and NKp46 positive cells was predominantly associated with the superficial uterine compartments during pre-implantation, contrasting with their increased presence in deeper endometrial layers following early placentation, i.e., during the post-implantation stage

Summary

Introduction

The uterine mucosal immune system plays an important role during maternal recognition and establishment of pregnancy This is accomplished by maintaining a balance between the defense against pathogens and the tolerance toward the allogeneic sperm and semiallogeneic embryo, adapting thereby to different pregnancy-associated events (e.g., implantation, placentation, parturition) and contributing to tissue remodeling [1,2,3]. This balance relies on the complex population of resident immune cells, composed of, e.g., macrophages, natural killer (NK) cells, B and T lymphocytes, regulated by local and systemic signaling, including endocrine insults [1, 2, 4, 5], and changing during the progression of pregnancy. Despite presenting a deciduate endotheliochorial placenta, no such mechanisms are known for the dog, nor has the composition of the immune system been thoroughly studied in this species

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