Bacterial vaginosis (BV) affects ~29% of women in the US and increases risk of HIV acquisition by 60%. ‘Healthy’ vaginal bacteria communities are dominated by Lactobacilli, lactic acid (LA) producing bacteria that acidify vaginal secretions to pH 3.0-4.0. Women with BV have polymicrobial vaginal communities with few Lactobacilli and elevated vaginal pH (>4.5). We previously found that HIV virions were adhesively trapped in human cervicovaginal mucus (CVM) from women with Lactobacilli-dominated microbiota. However, our recent unpublished work has found that HIV virions rapidly penetrate through CVM from women with BV. We hypothesized this difference in CVM barrier properties may be due to elevated vaginal pH, and may partially explain the increased risk of HIV acquisition in women with BV.
CVM was self-collected by women ages 18-45. BV was diagnosed by meeting 3/4 of Amsel’s criteria and a Nugent score >7. Samples were serially alkalinized with 1M sodium hydroxide, and in some cases, re-acidified with hydrochloric acid (HCl) or LA. Internally fluorescently labeled mCherry-GAG HIV virions were added to CVM and movement of individual virions was assessed using a quantitative fluorescent microscopy technique.
Similar to our prior unpublished observations, HIV was highly mobile in CVM samples from women with BV. Adhesive interactions (trapping) between HIV and CVM from women with healthy microbiota were abolished when pH was increased > 5.18 ± .13. However, trapping of HIV, as measured by the % of mobile virions, was restored when neutralized CVM was re-acidified below pH 4.90 ± .37 (n = 7). The results were similar whether using HCl or LA for re-acidification. In contrast, acidification of CVM from women with BV did not lead to trapping of HIV.
Increasing the pH of CVM from women with healthy vaginal microbiota led to a reduction in adhesive interactions with HIV virions, similar to what was observed in CVM from women with BV. Re-acidification of neutralized CVM from women with healthy microbiota restored adhesive interactions with HIV virions, an effect observed using both HCl and LA as the acidifying agent. However, acidification of CVM from women with BV did not lead to trapping of HIV, suggesting that elevated pH alone is not enough to explain the reduced barrier properties of BV CVM to HIV. These findings may have important implications in the design of strategies to mitigate the increased risk of HIV infection associated with BV.