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Problem: Although endometrial receptivity is a key factor in influencing implantation in both naturally conceived and assisted reproductive technology (ART) cycles, very little is known about the endometrium milieu around the time of implantation. Previous studies have demonstrated the presence of several cytokines in the endometrium that affect implantation. However, there is lacking data about the presence of immune cell subtypes within the endometrium and in the uterine cavity at the time of implantation., Method of Study: This study was approved by the Institutional Review Board (# 225589). The study was designed as a prospective observational cohort study between May 2021 and December 2022 at a single academic-based fertility center. All patients underwent at least one In Vitro Fertilization (IVF) cycle and have frozen embryos. Twenty-four participants were recruited for this study which was conducted during the frozen embryo transfer (FET) cycle regardless of the outcome of previous cycles. Two samples were acquired from each subject, denoted as lower and upper. A trial transfer catheter was introduced under ultrasound guidance into the lower uterine segment. Upon removal, the tip was rinsed in IMDM medium containing 10% FBS (lower uterus). A transfer catheter was then loaded with the embryo that was placed in the upper uterus under ultrasound guidance. The tip of the transfer catheter was rinsed in separate aliquot of the above media (upper uterus). After centrifugation, pelleted cells were stained for the following surface markers: CD45, CD3, CD19, CD4, CD8, gamma delta TCR, CD25, CD127, CD66b, CD14, CD16, CD56 and acquired on Sony SP6800 Spectral Analyzer., Results: Upon staining the pelleted cells, we were able to identify viable leukocytes from samples obtained from both, upper and lower uterus (0.125 × 10 6 cells ± SD 0.32), (0.123 × 10 6 cells ± SD 0.12), respectively. Among total viable cells, there was no significant difference in both percent and number of CD45+ cells between the upper and lower uterus (9.88% ± 6.98 SD, 13.67% ± 9.79 SD, p = .198) respectively. However, there was significantly higher expression of CD3+ (p = .006), CD19+ (p = .032) and CD14+ (p = .019) cells in samples collected from upper compared to lower uterus. Within all CD3+ cells, we found that gamma delta T cells (GDT) were the major population of T cells in both upper and lower uterus. In contrast, CD8+ T cells were significantly higher in the lower uterus when compared to the upper uterus (p = .009). There was no statistically significant difference in the expression of CD4+ T cells, T regulatory cells (CD4+CD25+CD127-), NK cells (CD56+), neutrophils (CD66b+) and FcγRIII+ cells (CD16+) between upper and lower uterus., Conclusions: We believe the immune milieu at the time of embryo transfer will affect implantation. Understanding the composition of immune cells will guide further research in identifying optimal immune milieus that favor implantation. Comprehensive analysis of endometrium is expected to lead to new diagnostic and therapeutic approaches to improve IVF outcomes., (© 2024 The Authors. American Journal of Reproductive Immunology published by John Wiley & Sons Ltd.)

Background: Successful trophoblast invasion and transformation of the maternal spiral arteries requires that the pregnant endometrium (i.e., decidua) act in an immunologically paradoxical fashion, accepting the semi-allogenic placenta, while maintaining host defenses against an array of microbial pathogens. In contrast to the growing evidence that the immune surveillance molecules known as Toll-like receptors (TLRs) are expressed by trophoblasts and fetal membranes, to date, no studies have been conducted on the decidua., Methods: Decidual tissues and cells were obtained from women undergoing first trimester elective terminations or repeat Cesarean sections and analyzed at both the protein and mRNA level., Results: We now demonstrate for the first time that human decidua differentially express TLRs and their downstream signaling molecules as well as TLR stimulated induction of cytokine production in the first and third trimester of pregnancy., Conclusions: These findings suggest that the decidua is a critical component of the innate immune response in pregnancy. Moreover, the results have implications for the success or failure of compromised pregnancies in early or late gestation.