Investigation of cytokines in equine serum, conceptuses and endometrium in early pregnancy

Abstract

Cytokines and their receptor systems are present at the fetomaternal interface of some species and regulate trophoblast biology. The cytokine and chemokine systems are key in the communication between fetal derived trophoblast cells and the maternal tissue. However, evidence for the presence of cytokines and their receptors during early equine pregnancy is lacking. Our objective was to investigate interleukins, chemokine ligands, dendritic cells and TNFα in equine serum, conceptuses and endometrium during early pregnancy. Daily transrectal ultrasound examinations of the mares were performed when in estrus until the day (D) of ovulation (OV). An endometrial biopsy was taken from non-pregnant (NP) mares at: D11 (NP11; n=6) or D13 (NP13; n=7). Mares in the pregnant (P) group were bred by artificial insemination from a single fertile stallion, and transrectal ultrasound was performed to detect and measure conceptuses. On the day of sample collection, conceptuses were collected through a transcervical bivona catheter and uterine lavage using 0.9% NaCl, and this was followed by an endometrial biopsy. Pregnant mares’ conceptuses and endometrial biopsies were retrieved at D11 (P11; n=7), D13 (P13; n=8), or D16 (P16; n=6). A D16 sample was not obtained for NP group. A Bradford assay was performed on extracted endometrium and conceptus tissue to determine total protein concentration,followed by a bead-based equine validated multiplex assay (Luminex Corp. Austin, TX) to quantify concentration of the following equine specific inflammatory markers: IL-4, IL-17, IL-10, IL-1β, CCL2, CCL3, CCL5, CCL11, sCD-14 and TNFα. A restricted maximum likelihood model was performed to compare the protein concentration between groups and days in JMP Pro 16 (Cary, NC) with the mare as a random factor and significance set at p<0.05. Cytokine and chemokine serum concentrations were similar between groups and days of collection. Regarding the endometrium, IL-17 U/mg was higher (p<0.05) in group NP13 [median (interquartile)] [11.4 (8.2, 21.7)] than NP11 [4.1 (2.6, 5.3)]. In pregnant mares, endometrial IL-17 was higher in P13 group [6.3 (3.4, 13.9)] compared to group P16 [2.5 (2.1, 4.8)] (p<0.05). In conceptuses, D11 had significantly higher concentrations of CCL2 [1350.2 (793, 1839.5); p<0.03], CCL3 [1990.9 (998.6, 3083.8); p<0.01], CCL5 [363.2 (149.6, 480.6); p<0.006] and CCL11[3143.7 (1764.2, 5221.9); p<0.01 compared to D16 [66.7 (38.8, 644.8); 67.8 (43, 572.30); 9.1 (6.6, 96.3); 196.2 (150.9, 1436.6)], respectively. Higher chemokine concentrations in the earlier embryos may reflect the recruitment of endometrial leukocytes. Further investigation into the role of cytokines and chemokines in early equine pregnancy is warranted.