Oct. 26 (HealthDay News) -- New research suggests that sperm, not just semen, can transmit the virus that causes AIDS to immune cells in the body and, in fact, sperm may play a major role in transmission.

Scientists already know that men infected with HIV, the virus that causes AIDS, can spread the disease through their semen, the fluid that carries sperm. But it hasn't been clear what role sperm itself plays, especially considering that men who don't produce sperm, such as those who have had vasectomies, can transmit the virus.

In a new study, published in the Oct. 26 online edition and the Nov. 23 print issue of the Journal of Experimental Medicine, researchers found that the virus attaches to the surface of sperm and can be transmitted to immune cells.

Immune cells known as dendritic cells appear to be vulnerable, the study authors explained. The researchers, led by Ana Ceballos of the University of Buenos Aires in Argentina, think the virus gets to these cells by passing through tiny abrasions in the vagina or anus or perhaps through another method.

The researchers said that a slightly acid environment, which they likened to that in the vagina after sexual intercourse, boosts the likelihood of infection of these cells.

SOURCE: Journal of Experimental Medicine, news release, Oct. 26, 2009