Vaginal lactobacilli produce anti-inflammatory beta-carboline compounds.

The vaginal microbiome is a lactobacilli-dominant, human-adapted community consistently found in people around the world. Presence of lactobacilli-dominant vaginal microbial communities, apart from Lactobacillus iners, is associated with reduced vaginal inflammation and reduced levels of pro-inflammatory cytokines. Loss of lactobacilli-dominance is associated with inflammatory conditions such as bacterial vaginosis. It remains unclear if health-associated lactobacilli actively promote the anti-inflammatory immune homeostasis of the vaginal mucosa and if so, by which mechanisms. We have identified that Lactobacillus crispatus, a key vaginal bacterial species, secretes a family of beta-carboline compounds with anti-inflammatory activity. These compounds suppress NFkappaB and interferon signaling downstream of multiple pattern recognition receptors in human macrophages and significantly dampen type I interferon receptor activation. Topical vaginal application of an anti-inflammatory beta-carboline compound, perlolyrine, was sufficient to significantly reduce vaginal inflammation in a mouse model of genital herpes infection. Together, we identify a key family of compounds by which vaginal lactobacilli mediate host immune homeostasis and could highlight a new therapeutic avenue for vaginal inflammation. ### Competing Interest Statement C.W., M.M, S.B, J.C., K.H.K. and S.G. are co-inventors on a patent related to this work.