Analysis of the uterine microbiome in patients with recurrent implantation failure and its potential impact on the uterine immune microenvironment

ZHANG Lihong; HUANG Guoning; PEI Li; LIU Dongyun; CHEN Xingyu; YE Hong

doi:10.13431/j.cnki.immunol.j.20260009

Abstract：Objective To investigate the structural and functional characteristics of the endometrial microbiome in patients with recurrent implantation failure(RIF)and to investigate their potential mechanism influencing the local immune microenvironment of the uterine cavity.Method Endometrial fluid samples were collected from a total of 299 women undergoing in vitro fertilization between January 2024 and January 2025,including 203 from the non-RIF group and 96 from the RIF group.The V3-V4 region of the 16S rRNA gene was amplified and sequenced on the Illumina NovaSeq 6000 platform.Bioinformatic analyses were performed using QIIME2,including ASV clustering,taxonomic annotation,and α-and β-diversity analyses.Differentially abundant genera between groups were identified by LEfSe.Functional profiles were predicted with PICRUSt2 and combined with the KEGG/COG databases for immune-related pathways.Results Sequencing revealed a significant difference in community structure between the RIF and non-RIF groups.At the phylum level,both sets of samples were dominated by Firmicutes,Actinobacteriota and Proteobacteria.At the genus level,the relative abundance of Streptococcus was markedly higher in the RIF group than in the non-RIF group[(3.92±1.56)%vs(2.34±0.87)%,P<0.05],whereas Gardnerella showed the opposite pattern[(4.97±12.9)%vs(2.26±8.20)%,P<0.05].α-diversity analysis further indicated that the Shannon index was lower in the RIF group than in the non-RIF group,showing no significant difference(P>0.05).β-diversity analysis demonstrated that the microbial community structure of the RIF group was more heterogeneous.Functional prediction indicated significant up-regulation of"glycolysis/gluconeogenesis"and"starch and sucrose metabolism"pathways in the RIF group,together with enrichment of pathways related to Staphylococcus aureus infection,while the activity of multiple amino acid metabolic pathways in the microbiota of the RIF group was reduced relative to that of the non-RIF group.Conclusion The endometrial microbiota of the RIF group exhibited reduced diversity,enhanced carbohydrate metabolism,a higher detection rate of opportunistic pathogens,and reduced amino acid metabolic activity-features potentially linked to endometrial microenvironmental inflammation and diminished immune tolerance in RIF patients.