While it has been long proved that HIV-positive men can transmit HIV to sexual partners through their semen, a new study suggests that sperm cells may actually play a role in transmission, HealthDay News reports. The study is published in the October 26 online edition and the November 23 print edition of the Journal of Experimental Medicine.

According to researchers—led by Ana Ceballos of the University of Buenos Aires in Argentina—HIV attaches to the surface of sperm and can be transmitted to immune cells.

Researchers add that the virus is able to travel to these immune cells, called dendritic cells, by passing through tiny abrasions in the vagina or anus or through other methods. An acidic environment, such as that of the vagina following intercourse, increases the likelihood of dendritic cell infection.