How do vaginal lactic acid and glycogen levels in macaques compare with those in women?

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Understanding factors that affect heterosexual HIV transmission in women is important. Lactobacilli in the lower genital tract use glycogen in vaginal epithelial cells for energy and produce lactic acid. The resulting vaginal acidity is believed to help protect against HIV infection. In contrast, bacterial vaginosis (BV) is characterized by less lactic acid and a higher pH and is associated with increased susceptibility to HIV infection.

Vaginal infection of macaques with simian immunodeficiency virus (SIV) or simian-human immunodeficiency virus (SHIV) is used as a model of sexual HIV transmission. Previous studies had found few lactobacilli in the lower genital tract of rhesus macaques. The researchers therefore compared lactic acid and glycogen levels in genital fluid from rhesus and pigtail macaques with levels in humans.

Lactic acid levels were lower in rhesus macaques (median 1.2 mol lactate/mg protein) and pigtail macaques (median 0.7 mol/mg) than in women with healthy genital microbiota (median 4.2 mol/mg). Glycogen levels were significantly lower in rhesus macaques (median 0.004 μg glycogen/μg protein) and pigtail macaques (median 0 μg/μg) than in women (median 0.2 μg/μg).

Comparisons of samples collected longitudinally from cycling pigtail macaques showed no significant differences in glycogen or lactate levels. The data indicate that the previously reported scarcity of lactobacilli in macaques correlates with low glycogen and lactic acid levels. The researchers concluded that the findings have important implications for studies of vaginal SIV or SHIV infection in macaques and advance understanding of how bacterial microbiota influence HIV infection.