It's long been known that HIV tends to progress more rapidly in women than in men, even when viral levels between the sexes are virtually identical. Now researchers in Massachusetts might know why. A key molecule that helps regulate the immune system's responses to bacteria and viruses in the body actually could be too efficient in women.

Writing in the journal Nature Medicine, the scientists say that the molecule in women is better at recognizing HIV than in men, and it coordinates an early, aggressive response to the virus. But that response also results in a condition known as "chronic T cell activation," a known factor in rapid disease progression. So while women tend to have a stronger initial response to HIV than men, they also progress to AIDS more quickly.

The researchers hope to use their findings to develop therapeutic approaches to treating HIV by focusing on the way the immune system responds to the virus in the body.