Semen Exposure Found to Enhance Resistance to HIV Infection
Although semen is a known vehicle for transmission of sexually transmitted infections (STIs), including the human immunodeficiency virus (HIV), a recent study looks to challenge that view to some degree.
Sex Work
The study, published in Nature Communications Journal and conducted by researchers at The Wistar Institute and the University of Puerto Rico found that women’s resistance to HIV may build up with repeated semen exposure.
Researchers found that recurrent and continuous exposure to semen may alter infection targets; i.e. circulating and vaginal tissue immune cells thus reducing the risk of infection.
“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,” said lead author Dr. Luis J. Montaner, D.V.M, D.Phil, the director of the HIV-1 Immunopathogenesis Laboratory at the Vaccine & Immunotherapy Center of The Wistar Institute.
This new research may explain why some female sex workers across the globe do not develop the infection. They seem not to become infected as much as expected despite their continual involvement in high-risk sexual activity.
Reduced Risk of Infection
In 2015, scientists reported that as a consequence of repeated exposure to semen, the cervicovaginal tissue of female sex workers underwent specific alterations. These alterations were considered to be associated with increased HIV resistance.
In the current study, the researchers continued further to find out how semen may contribute to infection resistance in hosts. For this project, they used non-human primates (NHP) domiciled at the Caribbean Primate Research Center. NHPs are commonly used in testing prophylactic treatments against HIV.
The team exposed animals to semen two times a week for about five months with or without inactivated simian immunodeficiency virus (SIV) particles. SIV may be described as the simian version of HIV. It progresses to a disorder similar to AIDS.
The animals were given low doses of intravaginal SIV after the conditioning period. Non-human primates that were frequently exposed to semen showed a 42 percent reduction in their risk of infection.
Exposure to semen seemed to result in the reduction of CCR5 receptor expression. The CCR5 receptor serves as a binding site that enables HIV to penetrate host cells.
Animals conditioned with semen had higher CCL5 cytokine levels. This is notable because the substance helps to naturally curb the virus in humans.
Increased Protection
These findings all seem to point to greater protection for women exposed to semen on a recurrent basis.
Furthermore, the researchers observed that repeated semen exposure produced higher levels of MX1 and other antiviral factors in the cervicovaginal tissue. Furthermore, there was a positive correlation with the production of a protein known as IFN-epsilon.
This protein offers protection against bacterial and viral pathogens and can be stimulated with semen. The scientists said it possesses direct anti-HIV properties. Tissue obtained from sex workers who have sex without condoms was found to have IFN-epsilon.
“Currently, condomless sex is assumed to only promote the likelihood of infection,” Montaner said. “Our observation, however, raises the hypothesis that frequent semen exposure may potentially reduce HIV transmission.”
However, findings from this study do not suggest that semen exposure can prevent HIV infection. The organic fluid may only add to resistance to the virus.
Animals that were initially resistant to infection due to semen exposure became infected at high virus doses.
References
Abdulhaqq, S.A., Martinez, M., Kang, G. et al. Repeated semen exposure decreases cervicovaginal SIVmac251 infection in rhesus macaques. Nat Commun 10, 3753 (2019). https://doi.org/10.1038/s41467-019-11814-5
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