No abstract

Study question What is the immune cell profile of the human fallopian tube in health and in benign pathological conditions? Summary answer The fallopian tubes have a distinct population of immune cells from the innate and adaptive subsystems. Variations have been observed in several tubal pathologies. What is known already The fallopian tubes play a key role in fertility; up to 30% of infertility cases have been reported due to tubal pathologies, which have been neglected due to the success of in vitro fertilisation (IVF). The fallopian tubes have been shown to harbour immune cell populations with the involvement of both the innate and adaptive arms of the immune system that provide surveillance against several pathogens. Therefore, characterisation of this population is vital in promoting a better understanding of tubal pathogenesis, and its influence on infertility, leading to improvements in the sexual and reproductive health of women. Study design, size, duration This systematic review was conducted on the 1st November 2021 and reported in accordance to PRISMA statement, and preceded by a prospectively written protocol registered with PROSPERO (registration number: CRD42021288257). CINAHL, EMBASE and EMCARE, Scopus and PubMed databases were searched for relevant published material. All studies that concerning the immune cells of human fallopian tubes in health or benign pathology of pre-menopausal, pregnant and/or post-menopausal women that published in English language were included. Participants/materials, setting, methods The predefined search strategy identified 3767 publications. Following screening, a total of 42 studies were included and data was extracted. The findings are thematically reported based on: (1) menopausal status and/or cycle phase; (2) pathophysiology; (3) immune cell types. A risk of bias assessment was performed using Newcastle-Ottawa scale (NOS) and a modified version for case studies. Main results and the role of chance T lymphocytes, predominantly CD8+ cytotoxic T cells, represent the most abundant immune cell population within the healthy fallopian tube. B lymphocytes, macrophages, natural killer (NK) cells and dendritic cells have also been identified. The number of macrophages demonstrated a consistent and significant increase during the progesterone-dominant secretory phase compared to the proliferative phase. A similar distribution of lymphocytes was reported in tubal ectopic pregnancies to that in healthy tubes. Macrophages, dendritic cells, and natural killer (NK) cells were observed in tubal pregnancies with a significant increase in the number of CD56+ and CD3+ cells in cases of tubal rupture. Salpingitis, hydrosalpinx and endometriosis are all characterised by an increased population of macrophages in comparison to healthy fallopian tubes. Limitations, reasons for caution Some studies scored poorly on the NOS, suggesting their findings to be treated with caution. The deficiency in published research into common tubal pathologies and inconsistent findings presented between studies only allowed limited conclusions to be formulated regarding these immune cell populations. Wider implications of the findings Comprehensive knowledge of the immune cell profile of the human fallopian tubes will provide greater understanding into the pathophysiology of common tubal disorders, potentially leading to innovative treatments in the future. Trial registration number not applicable

The Fallopian tubes (FTs) are part of the female upper genital tract. The healthy FT provides the biological environment for successful fertilisation and facilitates the subsequent movement of the conceptus to the endometrial cavity. However, when the FT is damaged, as with salpingitis, pyosalpinx and hydrosalpinx, it may increase the risk of an ectopic pregnancy, a life-threatening condition. Decidualisation refers to a multifactorial process by which the endometrium changes to permit blastocyst implantation. The decidualisation reaction is vital for endometrial receptivity during the window of implantation. To date, no comprehensive review that collates evidence on decidualisation in the human FT has been conducted. Therefore, the aim of this review is to compile the current evidence on cellular decidualisation occurring in the healthy and pathological FT in women of reproductive age. A literature search was conducted using five databases and identified 746 articles, 24 of which were analysed based on inclusion and exclusion criteria. The available evidence indicates that the FT are able to undergo decidual changes under specific circumstances, however, the exact mechanism by which this occurs is poorly understood. Further research is needed to elucidate the mechanism by which decidualisation can occur in the FT.