A person is more likely to get infected by HIV through anal intercourse than vaginal, but no one knows quite why. A new study by scientists at the Gladstone Institutes shows that infection sites could affect the immune system's response to a virus and the way the virus spreads through the body.

The study, published in Mucosal Immunology, aimed to understand how the immune system responds to a virus when it enters the body through different points. The researchers focused particularly on common routes of sexual transmission of viruses, such as the lower female reproductive tract and the lower gastrointestinal tract that includes the large intestine and the anus.

These mucosal barriers -- the body's openings lined with a membrane called mucosa -- are responsible for distinguishing between harmless bacteria that normally reside in us and potentially dangerous pathogens, as well as other substances, such as food or sperm.

"Our body is constantly trying to balance between tolerating harmless elements and defending us against possible threats," said Shomyseh Sanjabi, PhD, assistant investigator at Gladstone who led the study. "We wanted to learn whether the mechanisms that allow the body to be tolerant would affect its ability to elicit a protective immune response when needed. And, whether the process was different depending on the virus's point of entry."

Sanjabi's team discovered that, in fact, the body's reaction is different based on the infection site. They showed that the vaginal and rectal cavities activate a distinct immune response to the same pathogen. Read more via Science Daily