 HIV is the virus that causes AIDS, for which there is currently no cure. The HIV virus gets into cells of our immune system and kills them. Because our immune system protects us from harmful agents, individuals with HIV have a weakened immune system and eventually develop AIDS. AIDS occurs when the body's weakened defenses allow pathogens such as bacteria or viruses to infect the body, or diseases such as cancer to develop, and this can be lethal. We don't yet know all of the factors that influence progression to AIDS, but inflammation is thought to play a role. Inflammation is the body's way of protecting itself from harmful agents, or heal itself from injury. But, when inflammation is sustained, it can irritate the body and be harmful, in this case by supporting the progression to AIDS. So where could this inflammation come from? One interesting theory points to the gut. The wall of our intestine protects us by preventing harmful substances in our intestine from entering the bloodstream. A sea of immune cells prevents this from happening. Some of the things that reside in our intestine are actually bacteria. In fact, you may be surprised to hear that our bodies are actually made up of more bacterial cells than human cells. All of the bacteria that live in our intestine are part of the gut microbiome, which plays very important roles in maintaining our health. So this immune barrier keeps the bacteria in the intestine, where they have beneficial roles in our health. But upon HIV infection, this barrier is weakened and harmful substances as well as bacteria of the gut microbiome can enter the blood. Once the bacteria leave the gut and enter the bloodstream, they can travel throughout the body and cause body-wide inflammation, which can be harmful. Scientists think this may be a major cause of body-wide inflammation that is characteristic of HIV and that contributes to AIDS. But we're not really sure exactly how this barrier gets damaged in HIV. The types of bacteria that live in our gut influence how healthy the immune barrier is. So the scientists of this paper were interested in seeing if there were any differences in the types of bacteria that reside in the gut of patients with and without HIV. Their findings are published in Science Transitional Medicine in July 2013. In their article titled, Disbiosis of the Gut Microbiota is associated with HIV disease progression and tryptophan catabolism. It was published by the McEwen and Lynch Labs at the University of California in San Francisco. The scientists took patients that had HIV but were never treated with antiviral drugs and patients that were HIV negative and examined their gut microbiome. What the scientists found was that everyone had the same overall number of bacteria, but the types of bacteria that were present in both groups were very different. Some species of bacteria were increased while some were depleted upon HIV infection. As overall, the gut microbiome from HIV positive patients contained many of the bacterial species that have been shown in other contexts to cause disease on their own. I pictured them in red here. They further went on to show that some of these bacteria may be directly weakening the gut barrier. By weakening the gut barrier, these bacteria may be allowing all kinds of other bacteria to go through and travel in the body and cause inflammation. However, this evidence is not direct and needs to be confirmed in this context. Interestingly, the scientists also studied one individual that had HIV for over 21 years and was never treated but never progressed to AIDS. This is very rare and when scientists looked at the gut microbiome of that individual, it looked just like the gut microbiome of a person without HIV. This again provides evidence that the composition of the gut microbiome may be linked to the likelihood of disease progression to AIDS. So what did this study show? This study showed the gut microbiome or the community of bacteria that live in the intestines of HIV patients is very different from that of uninfected patients. And individuals with a more disease associated microbiome had more inflammation and more advanced disease. This can be explained by the fact that the microbiome from HIV patients could mean lots of species here in red that may, along with other factors, weaken the gut barrier. This could then open the door for a whole range of other bacteria to cross into the bloodstream and cause body-wide inflammation. So what does this mean for you? This article provides a very interesting theory that the composition of the gut microbiome could be linked to the development of AIDS from HIV infection by being a major contributor to the inflammation. But important questions remain. Is the disease-associated bacterial community actually damaging the immune barrier in HIV individuals in this context, in humans, with HIV infection, and in the intestine? And how does this community grow out in an HIV-infected person? Nevertheless, this study leaves much to fantasize about. We can envision a scenario where instead of killing the HIV virus, we could slow the development of AIDS simply by changing the bacterial community in the gut to that of an HIV-free person in order to prevent body-wide inflammation. This will likely be difficult, but it's an interesting way of approaching the problem. This video has been provided to you by Eureka Science. 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