HIV in blood different than in semen

Scientists claim to have found evidence that HIV-1 in semen is different than HIV-1 in blood, possibly due to changes the virus undergoes in the male genital tract.

Worldwide, much of the transmission of HIV-1 is via sexual contact with mostly men being the transmitting partner.

The nature of the virus in male genital tract is of importance to understanding the transmission process and the selective pressures that may impact the transmitted virus. A vaccine must block the transmitted virus ultimately.

Now, in its research, an international team sought to better understand the process by which HIV, the virus that causes AIDS, is transmitted. They compared the gene encoding the major surface protein of HIV-1 in semen and blood.

"In some men, the virus population in semen was similar to that in the blood, suggesting that virus was being imported from the blood into the genital tract and not being generated locally in the genital tract.

"However, we found two mechanisms that significantly altered the virus population in the semen, showing that virus can grow in the seminal tract in two different ways," Ronald Swanstrom of North Carolina University, who led the team, said.

In one way, one or more viruses grow rapidly in the seminal tract over a short period such that the viral population in semen is relatively homogeneous as compared to the complex population in the blood, say the scientists.

In the other way, the virus replicates in T cells in the seminal tract over a long period, creating a separate population of virus in semen that is both complex and distinct from the virus in the blood.

"While it remains unknown how these differences change the biology of the virus or if these changes are important for the transmission process, it`s clear that the virus in blood doesn`t always represent the virus at transmission site," said team member Jeffrey Anderson.

Added another team member Li-Hua Ping: "Making molecular clones of these compartmentalised viral env genes is an important next step that will allow us to study these differences."

The scientists from the University of North Carolina in the US, the Edward Jenner Institute for Vaccine Research in the UK and the Baylor Pediatric Center of Excellence have published the findings in PLoS Pathogens journal.