IgG coating of Lactobacillus crispatus is associated with cervicovaginal immune homeostasis and reduced preterm birth rates, identifying S-layer proteins as candidate antibody targets

Background Maternal host immune system responses to cervicovaginal microbiota influence the risk of microbial-driven spontaneous preterm birth (sPTB). Immunoglobulins are present in cervicovaginal fluid (CVF). There are decreased IgG concentrations in women with CST I compared to CST IV, but their role in sPTB is unclear. Here, we investigate immunoglobulin coating of vaginal bacteria in 100 women at high-risk of sPTB (48 sPTB vs 53 term). Results Lactobacillus -dominated communities, especially L. crispatus -dominated, had higher proportions of IgG coating than high diversity, Lactobacillus -depleted communities. There was a positive correlation between IgG and IgG2 coating, indicating IgG2 was the main bound subclass. The percentage of bacterial coating by IgG and IgG2 was higher in women who delivered at term compared to preterm, and IgG coating negatively correlated with concentrations of CVF pro-inflammatory immune mediators. IgG and IgG2 both bound to L. crispatus surface layer proteins (SLPs), identifying SLPs as potential targets of antibody binding associated with immune homeostasis and term birth. Conclusions Our results reveal an association between vaginal bacterial antibody coating and mucosal microbe-immune homeostasis with reduced cervicovaginal inflammation and term birth. These represent a potential component of host-microbe interactions associated with pregnancy outcome.