Your gut’s microbiome — i.e., the particular collection of bacteria living in your intestines — is prone to constant influence and change. For years, the medical community has been espousing that you are what you eat, but a recent study from the University of Colorado’s Medical Center has found that in addition to the food you put in your stomach, your sexual behavior can also influence your immune system.
“The microbiome, a community of microbes in the gut, play a major role in driving and shaping the human immune system,” reports Science Daily. “But recent studies have shown that men who have sex with men (MSM) have very distinct microbiomes compared with men who have sex with women (MSW), regardless of HIV-infection status.”
“We wanted to understand how these microbiome differences in MSM could impact their immune system,” says Brent E. Palmer, an assistant professor at the University of Colorado and lead author of the study. “To test this, they transferred feces from healthy MSW and MSM to [germ-free] mice and examined the immune system in the mice post-transplant.”
Palmer and his team found that in mice that received transfers from MSM, “there were higher frequencies of activated T cells in gut tissues, which are the primary targets of HIV,” says Palmer. His findings suggest that for men who have sex with men, their gut microbes are activated in such a way that could proliferate the activation of HIV target cells. To that end, Palmer and his team also tested cells derived from a human gut, finding that the cells derived from microbes from MSM were infected at a higher rate than those derived from MSW. “Our study shows that microbes associated with MSM sexual behavior can alter the immune system in a way that could increase risk for HIV infection, at least in mice,” Palmer reiterates.
The main reason MSM have elevated risk of HIV transmission is the fact that anal sexual intercourse causes damage to the rectum/colon, says Palmer. The HIV found in semen is then able to get in close proximity with immune cells (CD4+ T cells) that are most susceptible to infection. “In addition, the cells in these mucosal sites are generally more activated, and activation is a prerequisite for infection,” says Palmer.
Oddly, according to Palmer, women who reported having anal sex didn’t have an altered microbiome — their intestinal bacteria looked pretty much the same as the MSW. Still, Palmer says, since these experiments were done in mice and in cell culture, studies in human populations will be needed to demonstrate that the gut microbiome is indeed a risk factor for HIV infection. “Additionally, it is still not clear how sexual behaviors specifically alter the gut microbiome — understanding how this occurs could lead to the development of therapies that prevent or ‘reverse’ these microbiome alterations.”