CD138 expression in the endometrium associates with endometrial timing and inflammatory status but not microbiota composition.

STUDY QUESTION: What is the relationship between constitutive CD138 expression in the endometrium and the reproductive tract microbiota composition? SUMMARY ANSWER: The presence of CD138+ cells in endometrial stroma is cycle-dependent and associated with impaired luteal phase endometrial timing but not altered vaginal or endometrial microbial composition. WHAT IS KNOWN ALREADY: CD138-diagnosed chronic endometritis (CE) is associated with adverse reproductive outcomes including recurrent pregnancy loss (RPL) in uncontrolled studies. However, CD138 is constitutively expressed in the endometrium, potentially confounding the reported associations between CE, adverse endometrial function, and early pregnancy loss. STUDY DESIGN, SIZE, DURATION: Translational cohort study of a subset of 103 samples derived from 737 women embedded within the CERM trial, a double-blinded, randomized interventional trial evaluating the impact of pre-pregnancy antibiotic treatment for CE in RPL patients. PARTICIPANTS/MATERIALS, SETTING, METHODS: Women aged ≥18 to <42 years, with a history of two or more first-trimester consecutive miscarriages were recruited from specialist RPL clinics. Endometrial biopsies, vaginal, ectocervical, and endometrial swabs were obtained 10 ± 4 days following a positive home ovulation test. Additional samples, including proliferative endometrium, were obtained from the Tommy's National Reproductive Health Biobank. Endometrial biopsies were processed for CD138 expression analysis and immunohistochemistry (IHC), histological dating based on Noyes' criteria, and molecular timing analysis. Metataxonomic profiling of microbiota was performed by sequencing of bacterial 16S ribosomal RNA genes alongside cytokine analysis. MAIN RESULTS AND THE ROLE OF CHANCE: IHC revealed three patterns of CD138 immunoreactivity: predominantly membranous punctate staining, predominantly diffuse staining, and a mixed pattern. CD138 is constitutively expressed on the basolateral membrane of glandular epithelial cells and a subset of non-immune stromal cells. Stromal expression was very high (>200 CD138-positive stromal cells/10 mm2) in 26 out of 27 proliferative endometrial samples. While CD138 immunoreactivity in the stroma declines markedly following ovulation (Mann-Whitney U-test; P < 0.005), gene expression analysis demonstrated a reduction in SDC1 expression encoding CD138/syndecan-1, across the menstrual cycle. When compared to CD138-negative samples, conspicuous diffuse staining in the stromal compartment was associated with significantly earlier endometrial histological dating (P < 0.01) and lower molecular timing ratios (P < 0.01). Poor correlation between CD138 and immunoreactivity was demonstrated. Sequencing of paired vaginal and ectocervical swabs and endometrial Tao brush samples collected from 114 patients demonstrated tightly interconnected microbial composition throughout the reproductive tract. No significant difference in vaginal, ectocervical, or endometrial community state type with CD138 expression was demonstrated. Analysis of supernatants of vaginal and ectocervical swabs and Tao Brush revealed an inverse correlation between the severity of stromal CD138 immunoreactivity in endometrial stroma and secreted levels of IL-10, TNF-α, and VEGF (q < 0.05). LARGE SCALE DATA: Microbial and Metataxonomic raw data are available in the European Nucleotide Archive (Projects PRJEB83331 and PRJEB83332). LIMITATIONS, REASONS FOR CAUTION: This study relied on patient-reported ovulation-based timing. This was, however, associated with the provision of validated ovulation tests. In addition, the study is limited by lack of collection of data on the underlying fertility-related co-morbidities due to exclusion of known contributory co-morbidities at the point of recruitment. WIDER IMPLICATIONS OF THE FINDINGS: This study challenges the purported relationship between CD138+ CE and the pathophysiology of CE-associated RPL. The findings indicate endometrial CD138 levels are non-immune and non-bacterial driven and are associated with endometrial immaturity. CD138-based CE testing and treatment should not be performed outside of a research context. STUDY FUNDING/COMPETING INTEREST(S): Funding was provided by the Efficacy and Mechanism Evaluation (EME) Programme a National Institute for Health and Care Research and Medical Research Council partnership (17/60/22). Further funding was from Tommy's National Centre for Miscarriage Research, and the Imperial National Institute for Health and Care Research Biomedical Research Centre Pregnancy and Prematurity Theme. G.D.S.C. is supported by the Genesis Research Trust. All authors report no direct conflict of interest. TRIAL REGISTRATION NUMBER: ISRCTN23947730.