Study Finds Sperm Responsible For HIV Transmission

By Nora Proops

Published: Nov 1, 2009 11:12 pm





A study accepted by the Journal of Experimental Medicine on September 28 shows that sperm are responsible for the transmission of HIV viruses during sexual intercourse. The results suggest that sperm play a central role in the sexual transmission of HIV, the most common mode of spreading infection.


Sperm’s role in viral transmission has been a matter of debate. HIV is known to infect the semen, but it is also present as a free-floating virus and as infected white blood cells. This study suggests that the actual sperm, and not just the fluid it bathes in, are the culprit.


Having a vasectomy may reduce transmission of HIV from HIV-positive men, since this procedure blocks sperm from entering the seminal fluid.


For the first time, scientists in Argentina and France have identified a molecule involved in the connection between sperm cells and HIV. Previous studies have only shown an association between molecules and HIV protein, but have not done so with cells and the entire HIV virus.


Researchers found that heparan sulfate, a carbohydrate present on the surface of sperm, is required for HIV attachment. Heparan sulfate could potentially provide a target for drugs to prevent sexual transmission of HIV.


HIV and sperm binding is an insufficient explanation for how HIV infects the body. After semen is deposited, HIV must cross the first layer of cells that cover the internal surface of the vagina and anus to come into contact with dendritic cells (DCs). The authors of the study show that sperm are able to transmit HIV to DCs.


Infected DCs then travel to lymph nodes and introduce the virus to CD4 T cells, which become the center of viral reproduction.


These researchers propose that infected sperm may come into contact with DCs in the body either directly or by traveling through the small tears in the vagina or anus caused by friction during sexual contact.


This seems plausible, since these small tears are detected in 60 percent of healthy women after consensual sexual intercourse.


In support of this idea, their results also show that an acidic environment similar to that of the vagina increased sperm-HIV binding and infection of DCs.


This study raises questions about preventing HIV infection in couples wishing to conceive. Sperm donation remains the first choice of fertility treatment for men who are HIV positive.


Sperm can be “washed” of HIV, but scientists disagree about the safety of the procedure. Sperm washing separates and concentrates sperm from the infectious seminal fluid, which is then used to artificially inseminate a woman during ovulation.


This study suggests that sperm cells are the infectious agent in semen, which casts doubt on the practice of sperm washing. A fertility clinic in Milan, where the technique was developed, reports that of the 2000 procedures performed, no woman or child has become infected.


For more information, please see the study in the Journal of Experimental Medicine (abstract) as well as the related editorial.