UNC researchers identify a type of vaginal bacteria that can protect women from HIV

Researchers at the University of North Carolina at Chapel Hill have identified a type of vaginal bacteria within the mucus of the female reproductive system that can protect women from HIV as well as other sexually transmitted infections.

The vaginal microbiota has long been considered healthy if it was dominated by any species of lactobacillus, said Sam Lai, senior author of the study and an assistant professor at the UNC Eshelman School of Pharmacy. His team found that a specific species of lactobacillus -- lactobacillus crispatus -- appears to play a key role in sustaining the mucus barrier against HIV and other sexually transmitted infections. The findings, he said, that could lead to the development of new strategies to protect women against HIV.

"What we discovered is that a woman's risk of being infected by HIV can be affected by the type of helpful bacteria present in vaginal mucus," said Lai. "We found that vaginal microorganisms, including specific species of lactobacillus bacteria, can directly alter the protective properties of cervicovaginal mucus."

The research team examined mucus from 31 women of reproductive age using high-resolution, time-lapse microscopy to test whether fluorescent HIV pseudovirus particles became trapped in the mucus or spread freely. The team's findings were published in mBio, the online open-access journal of the American Society for Microbiology.

The researchers observed two distinct types of mucus samples: one that was very good at trapping HIV and one that did not. Trapping of HIV did not correlate to the mucus' pH, total lactic acid, or Nugent score, which is a rough measure of vaginal health that reflects how much lactobacillus bacteria is present compared to other microbes.

However, one difference between the two groups did stand out: higher levels of D-lactic acid in the group that trapped HIV. Humans cannot make D-lactic acid, so the team suspected that bacteria living within the mucus layer were responsible for the difference.

The researchers found that mucus that trapped HIV had predominantly lactobacillus crispatus. Samples that did not trap HIV were either dominated by lactobacillus iners or had multiple bacterial species present including gardnerella vaginalis, both conditions that are frequently associated with bacterial vaginosis. The majority of women in developing countries, including those in Africa, have vaginal microbiota that are either dominated by lactobacillus iners or microbes associated with bacterial vaginosis, Lai said.

To reinforce the mucus barrier against pathogens, Lai is also working to immobilize pathogens in mucus using antibodies either delivered directly to mucosal surfaces or elicited by vaccines.

In 2014 his lab discovered that IgG antibodies can be harnessed to trap viruses in mucus with exceptional potency and that trapping viruses in mucus alone blocked vaginal herpes transmission in mouse models. His work showing how antibodies can work in tandem with mucus to block infections resulted in him receiving a Packard Fellowship in Science and Engineering and a Career Award from the National Science Foundation.