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

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.

Utero-Placental Immune Milieu during Normal and Aglepristone-Induced Parturition in the Dog

“…As represented in Figure 1 A, possible changes in the presence of different phenotypes of macrophages in the placenta were primarily investigated by assessing the transcriptional availability of the surface markers MHCII , CD163 and CD206 , whereas CD4 , CD8 , NCR1 , CD25 and FoxP3 were investigated for lymphocytes. These markers were used in our previous publication [ 38 ], and were selected based on current literature [ 29 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ]. No significant changes in the expression of MHCII could be observed in the utero-placental compartments during the progression and termination of pregnancy ( p > 0.05, Figure 1 B).…”

“…The differentiation between macrophages and lymphocytes expressing CD4 was performed in our previous work [ 38 ], referring to the differential staining of consecutive slides and morphological differentiation. Regarding their immunolocalization, CD4-positive cells, mainly recognized as lymphocytes, were localized in superficial layers of the endometrium during post-implantation ( Figure 2 J), while single cells could be observed in deep layers of the endometrium and myometrium during mid-gestation ( Figure 2 K).…”

“…Despite the great importance of the dog as a companion animal, there is not much information available about this species’ utero-placental immune system. Recently, the dynamic changes in the uterine immune milieu of the dog during the peri-implantation period have been reported [ 38 ]. Whereas the presence of the embryo before implantation was associated with moderate pro-inflammatory activity, implantation was associated with the presence of a local anti-inflammatory signal, possibly involving the activity of regulatory T and NK cells [ 38 ].…”

“…Recently, the dynamic changes in the uterine immune milieu of the dog during the peri-implantation period have been reported [ 38 ]. Whereas the presence of the embryo before implantation was associated with moderate pro-inflammatory activity, implantation was associated with the presence of a local anti-inflammatory signal, possibly involving the activity of regulatory T and NK cells [ 38 ]. Also the early placentation period appeared to be associated with decreased immune activity [ 38 ].…”

“…Whereas the presence of the embryo before implantation was associated with moderate pro-inflammatory activity, implantation was associated with the presence of a local anti-inflammatory signal, possibly involving the activity of regulatory T and NK cells [ 38 ]. Also the early placentation period appeared to be associated with decreased immune activity [ 38 ]. With regard to parturition, a recent transcriptional analysis from our group described an increased immune activity in the canine placenta during normal and antigestagen-induced parturition/abortion [ 39 ].…”