Gut flora influences HIV immune response

Normal microorganisms in the intestines appear to play a pivotal role in how the HIV virus foils a successful attack from the body's immune system, according to new research.

The study builds on previous work from researchers at the Duke Human Vaccine Institute that outlined a perplexing quality about HIV: The antibodies that originally arise to fight the virus are ineffective.

These initial, ineffective antibodies target regions of the virus's outer envelope called gp41 that quickly mutates, and the virus escapes being neutralized. It turns out that the virus has an accomplice in this feat -- the natural microbiome in the gut. "Gut flora keeps us all healthy by helping the immune system develop, and by stimulating a group of immune cells that keep bacteria in check," said senior author Barton F. Haynes, M.D., director of the Duke Human Vaccine Institute. "But this research shows that antibodies that react to bacteria also cross-react to the HIV envelope."

Haynes said the body fights most new infections by deploying what are known as naïve B cells, which then imprint a memory of the pathogen so the next time it encounters the bug, it knows how to fight it.

But when the HIV virus invades and begins replicating in the gastrointestinal tract, no such naïve B cells are dispatched. Instead, a large, pre-existing pool of memory B cells respond -- the same memory B cells in the gut that fight bacterial infections such as E coli. This occurs because the region of the HIV virus that the immune system targets, the gp41 region on the virus's outer envelope, appears to be a molecular mimic of bacterial antigens that B cells are primed to target. "The B cells see the virus and take off -- they make all these antibodies, but they aren't protective, because they are targeted to non-protective regions of the virus envelope."

Haynes and colleagues said the findings were confirmed in tests of people who were not infected with HIV. Among non-infected people, the researchers isolated mutated gp41-gut flora antibodies that cross-react with intestinal bacteria.

"The hypothesis now is that the gp41 antibody response in HIV infection can be derived from a pre-infection memory B cell pool triggered by gut bacteria that cross-reacts with the HIV envelope," said lead author Ashley M. Trama. "This supports the notion that the dominant HIV antibody response is influenced by previously activated memory B cells that are present before HIV infection and are cross-reactive with intestinal bacteria."

Haynes said the finding provides compelling new information for HIV vaccine development, which is the next phase of research. "Not only can gut flora influence the development and function of the immune system, but perhaps also pre-determine our reaction to certain infections such as HIV," Haynes said.

AIDS and Seniors

HIV (short for human immunodeficiency virus) is a virus that kills cells in your immune system, the system that fights diseases. Once your immune system is weakened to the point where you get certain types of life-threatening diseases, infections, and cancers, you have what is called AIDS or acquired immunodeficiency syndrome. AIDS is the most advanced stage of HIV infection. If there's any chance that you might be infected with HIV, you should be tested because now there are drugs you can take to help your body keep the HIV in check and fight against AIDS.

Many people do not have any symptoms when they are first infected with HIV. It can take as little as a few weeks for minor flu-like symptoms to show up or as long as 10 years or more for more serious symptoms. Symptoms can include headache, chronic cough, diarrhea, swollen glands, lack of energy, loss of appetite and weight loss, frequent fevers and sweats, frequent yeast infections, skin rashes, pelvic and abdominal cramps, sores on certain parts of your body, and short-term memory loss. People age 50 and older may not recognize HIV symptoms in themselves because they think what they are feeling and experiencing is part of normal aging.

Anyone can get HIV and AIDS. Regardless of your age, and especially if you are 50 years old or older, you may be at risk for HIV if any of the following is true:

• If you are sexually active and don't use a male latex condom. You can get HIV/AIDS from having sex with someone who is infected with the HIV virus. The virus passes from the infected person to another through the exchange of body fluids such as blood, semen, and vaginal fluid. HIV can get into your body during sex through any opening, such as a tear or cut in the lining of the vagina, vulva, penis, rectum or mouth.
• If you don't know your partner's sexual and drug history. Has your partner been tested for HIV/AIDS? Has he or she had a number of different sex partners? Does your partner inject drugs?
• If you inject drugs and share needles or syringes with other people. Drug users are not the only people who might share needles. People with diabetes, for example, who inject insulin or draw blood to test glucose levels, might share needles. If you have shared needles for any reason or if you have had sex with someone who has, you should be tested for HIV/AIDS.
• If you had a blood transfusion between 1978 and 1985, or a blood transfusion or operation in a developing country at any time.
• If any one of the above is true, you should be tested for HIV/AIDS. Check your local phone directory for the number of a hospital or health center where you can get a list of test sites. In most states the tests can be confidential (you give your name) or anonymous (you don't give your name).

There are many myths about HIV/AIDS. The examples below are facts:

1. You cannot get HIV through casual contact such as shaking hands or hugging a person with HIV/AIDS.
2. You cannot get HIV from using a public telephone, drinking fountain, restroom, swimming pool, Jacuzzi, or hot tub.
3. You cannot get HIV from sharing a drink or being coughed or sneezed on by a person with HIV/AIDS.
4. You cannot get HIV from donating blood
5. You cannot get HIV from a mosquito bite.