Mutual Preservation: A Review of Interactions Between Cervicovaginal Mucus and Microbiota

Abstract

At mucosal surfaces throughout the body mucus and mucins regulate interactions between epithelia and both commensal and pathogenic bacteria. Although the microbes in the female genital tract have been linked to multiple reproductive health outcomes, the role of cervicovaginal mucus in regulating genital tract microbes is largely unexplored. Mucus-microbe interactions could support the predominance of specific bacterial species and, conversely, commensal bacteria can influence mucus properties and its influence on reproductive health. Herein, we discuss the current evidence for both synergistic and antagonistic interactions between cervicovaginal mucus and the female genital tract microbiome, and how an improved understanding of these relationships could significantly improve women's health.

Keywords: cervicovaginal mucus; female genital tract; microbiome; mucins; reproductive health.

Figure 1

Schematic depiction of interactions between cervicovaginal mucus (CVM) and microbiota. (A) CVM may drive the composition of the commensal vaginal microbial community. Mucin binding protein (MucBP) domains and other binding factors allowing adhesion to mucins have been found on several lactobacilli, including the common vaginal species L. crispatus and L. gasseri. In addition, mucus constituents can be used as nutrient sources by commensal bacteria. Sialidase producing bacteria are able to catabolize the sialic acid present on mucins through an internal aldolase/lyase reaction. (B) Beneficial microbes, such as L. crispatus, also drive functional changes in the CVM. L. crispatus produces both D-lactic acid (D-LA) and L-LA, and CVM from women with L. crispatus-dominance has been associated with increased entrapment of viruses, including human immunodeficiency virus (HIV). (C) Bacterial vaginosis (BV)- associated bacteria can alter CVM properties. They may express sialidase and other mucus degrading enzymes, such as mucinases or other galactosidases. Sialidase production is associated with many of the adverse health outcomes related with BV, such as preterm birth, intrauterine infection during pregnancy, or invading infection. The lower sialic acid and the high mannose abundance, that have been correlated with BV-associated bacteria populations, along with the associated impaired lectin binding further compromise that innate immune responses in the lower genital tract. The resulting inflammatory environment has been shown to increased mucin mRNA expression and abundance (Figure created with BioRender.com).