The interplay between microbiota, metabolites, immunity during BV

The surface of the female lower genital tract is covered with squamous epithelium, and some bacteria and fungi reside in the cavity. Among them, the dominant Lactobacillus maintain the acidic environment of the vagina. The acidic environment, squamous epithelium barrier, mucus and innate immune response together resist the invasion of pathogens and local homeostasis. Bacterial vaginosis (BV) is a disorder of the vaginal microbiota, which is characterized by a shift in the vaginal flora from the dominant Lactobacillus to a polymicrobial anaerobic flora accompanied by an increase in pH ​> ​4.5. Its high recurrence rate, obvious clinical symptoms, and possible adverse pregnancy outcome seriously disturb women's healthy life. However, its pathogenesis is still elusive. The vaginal microenvironment includes not only microbiota, but also microbially and host-produced metabolites, and vaginal local immunity. Given the inseparable relationship between the microbiota and its metabolites and the immune response, it is important to study how these interactions regulate vaginal local immunity to resist pathogens. In this review, we will discuss the main theories of BV etiology, which eventually involves the interaction between BV-related pathogens, small molecular metabolites, and host immune responses in the vagina.