Last Updated: 2002-05-28 11:00:16 -0400 (Reuters Health)

By Emma Hitt, PhD

ORLANDO, Florida (Reuters Health) - Circumcision, or removal of the foreskin of the penis, is known to reduce the risk of HIV infection, and now researchers may understand why. The findings could help in the development of new therapies to prevent the spread of the AIDS-causing virus.

According to Carlos R. Estrada from Rush-Presbyterian-St. Luke's Medical Center in Chicago, Illinois and colleagues, about 80% of HIV infections occur during sex, and the route of entry for most HIV-infected men is via the penis. Circumcision is known to reduce the risk of infection 2- to 8-fold, but the reason why has been unclear.

In their study, presented here Saturday at the American Urological Association's annual meeting, researchers evaluated 14 samples of foreskin tissue from children and adults. They also examined specimens of female cervical tissue.

To determine how susceptible the tissue might be to HIV infection, they counted the number of three types of immune system cells that are known to become infected with HIV in each specimen. The researchers counted CD4+ T-cells, macrophages and Langerhan's cells.

Compared to cervical tissue, the foreskins contained higher numbers of the three infectable cell types. Adult foreskins contained the highest proportion.

Further, when they tried to infect the samples with HIV, they found that the inner surface of the foreskin was seven times more susceptible to infection than the cervical tissue and the outer foreskin.

"During sexual intercourse, this inner layer is the area that becomes traumatized and infected," Estrada told Reuters Health. "In fact, we were not able to infect the outer layer of foreskin."

According to Estrada, adult patients that have had recent infections, whether sexually transmitted diseases or some other type of infection, also have a higher proportion of these infectable cells, and therefore may be at increased risk of HIV infection.

Estrada and colleagues also measured the numbers of HIV-specific receptors on the surface of the cells. These bind to the virus and help it to gain entry into the cells. One type, called CCR5, was especially predominant.

The researchers suggest that agents capable of blocking these HIV binding sites that could be applied topically to the penis or vagina should be developed.

"The US is one of the few countries in which circumcision is performed on a regular basis," Estrada said. "We think that in a third world country such as Africa, where AIDS is an epidemic, circumcision of children could provide a protective effect down the road."