Characteristics of intrauterine microecology and Lactobacillus-associated immune profiles in patients with chronic endometritis

Abstract

Chronic endometritis (CE) is a persistent inflammatory condition of the endometrium implicated in infertility and recurrent implantation failure. Microbial dysbiosis and altered immune responses are increasingly recognized as central features of its pathogenesis. This study aimed to characterize the clinical, microbial, immunologic, and hysteroscopic features of CE in infertile women and to evaluate their association with reproductive outcomes. A retrospective study was conducted on 252 infertile women who underwent diagnostic hysteroscopy and endometrial biopsy between 2020 and 2023. Based on histopathologic and hysteroscopic findings, patients were categorized into CE ( n = 98) and non-CE ( n = 154) groups. Microbial profiling was performed using 16S rRNA sequencing, and inflammatory cytokines were measured via ELISA. Clinical data, including vaginal pH, hormone levels, and reproductive outcomes, were analyzed. Compared to controls, CE patients showed a markedly higher prevalence of hysteroscopic abnormalities (micropolyps: 82.7% vs. 12.3%), CST IV microbiota (34.7% vs. 14.3%), elevated vaginal pH (> 4.5 in 73.5%), and reduced Lactobacillus dominance (21.4% vs. 76.0%) (all P < 0.001). Shannon diversity and Bray–Curtis beta-diversity analyses suggested CE-associated microbial alterations, although the global community-level difference was modest. Endometrial cytokines IL-6, TNF-α, and IL-1β were significantly elevated and correlated with CD138+ plasma cell counts. CE patients had thinner endometrium (7.1 ± 1.2 mm), lower implantation (18.4%) and pregnancy rates (25.5%), and higher miscarriage rates (42.1%). Multivariate analysis identified CST IV microbiota, elevated vaginal pH, higher IL-6 levels, and reduced endometrial thickness as factors independently associated with CE, whereas Lactobacillus-dominant microbiota was inversely associated with CE. CD138+ plasma cell count showed a strong criterion-related association with CE status because CD138 positivity formed part of the histopathological diagnosis. CE was associated with uterine microbial dysbiosis, inflammation, and adverse reproductive outcomes. Integrated diagnostic profiling may enhance early detection and management in infertility care.