Recent research at The Wistar Institute and the University of Puerto Rico(UPR) declared the conventional belief about semen wrong. Previously, it was believed that semen can only act as the causative agent for the transmission of HIV-1 between opposite genders. The researchers discovered recurrent and sustained exposure of semen may decrease the chance of infections due to the changings that occur in the characteristics of the circulating and vaginal tissue immune cells. The study got published in the journal Nature Communications.
The findings helped understand why a number of female sex workers test negative for infection, even with their high-risk sexual activity.
A previous study on the topic was published in a 2015 paper. It was conducted by the researchers at the University of Puerto Rico in collaboration with the laboratory of Luis J. Montaner and. Herbert Kean, M.D. Family Professor and director of the HIV-1 Immunopathogenesis Laboratory at Wistar’s Vaccine & Immunotherapy Center. It explained how sex working women with recurrent semen exposure ultimately develop changes in their cervicovaginal tissue that anticipated greater resistance to HIV infection.
The current study directly aimed to understand if semen could be a leading cause of this resistance.
A lead author of the study, Montaner said: “While HIV infection has been with us for more than 30 years, this is the first study that describes how semen exposure over time could result in local tissue changes that limit HIV infection in humans.”
He explained; “Apart from defining a new factor that may regulate HIV transmission, this unexpected finding could directly impact the design of future HIV vaccine studies that commonly recruit female sex workers. Currently, condom-less sex is assumed to only promote the likelihood of infection. Our observation, however, raises the hypothesis that frequent semen exposure may potentially reduce HIV transmission.”
A co-director of the study, Edmundo N. Kraiselburd, Ph.D., professor at the University of Puerto Rico. In the Caribbean Primate Research Center, he superintended the utilization of pre-clinical research model the non-human primates (NHP) for testing prophylactic anti-HIV involvements.
Kraiselburd said; “This research clearly shows the valuable information the macaque model can provide when used to study what may determine HIV infections in humans.”
During the course of the study, the non-human primates were allowed to undergo semen exposure with or without inactivated particles of the simian immunodeficiency virus (SIV). SIV is an HIV-like virus that infects primates and causes a disease similar to AIDS. It was conducted twice a week for over 5 months. After the initial semen exposure, they sustained low-dose intravaginal SIV challenges.
The researchers concluded the risk of developing infection decreases by 42% in these animals exposed to semen. Scientists reported activation of the bodily immune response in the cervicovaginal microenvironment and in the bloodstream.
As an immune response CD4+ cells circulation is observed, and lower activity of the CCR5 receptors with the influence of semen. CCR5 receptors provide a binding site for HIV thus allowing them to enter the host cells. Moreover, semen-exposed animals had elevated CCL5 cytokine. In the cervicovaginal environment CCL5 naturally suppresses HIV in response to the SIV challenge.
The study affirmed the belief that with frequent exposure of semen cervicovaginal tissue levels of antiviral factors such as MX1 significantly increases. This has a positive impact on the levels of IFN-epsilon. IFN-epsilon originates by the semen, aids protection against the bacterial and viral pathogens in human cells.
IFN-epsilon is reported to have anti-HIV characteristics thus it may be induced in tissues from a sex worker who intercourse without using any preventive measures such as condoms.
Conclusively, semen-exposed NHPs that were not infected after exposure to low viral amount get infected when high doses of virus were subsequently administered, which confirms that frequent and repeated semen treatment induces only partial protection and not total blockage of HIV infection.
“Importantly, we show that semen exposure can promote host resistance but does not protect against infection,” said Montaner. “Therefore, our data do not change the fact that prevention methods, such as condom use and PrEP (pre-exposure prophylaxis) remain our best strategies to prevent infection.”