Scientists have found that the vaginal immune response is suppressed when infected with RNA viruses. The Zika virus is an RNA virus. So what does this mean for women exposed to the Zika virus?
From the Gladstone Institutes, researchers compared mice infected with Zika virus two different ways: systemically like when an individual is bitten with a mosquito, and via the vagina like when an individual has sex with someone infected with the virus. The immune system reaction is vastly different in each scenario, raising concerning for the health of women, especially pregnant women, exposed to Zika via sexual transmission.
"The dampened vaginal immune response is especially concerning, because it gives the virus more time to spread to the fetus if a woman is pregnant or becomes pregnant during the course of infection,” explained senior author of the recent study, Shomyseh Sanjabi, PhD.
During the study, the mice that were infected with Zika through the vagina were still infected after three days, when the mice infected with Zika systemically had already recovered from the infection. The scientists found that for the mice infected through the vagina, something was not happening that should have been to mount a healthy immune response. Infected cells normally release interferon first thing after being infected with the virus, fighting the infection but also warning adjacent cells of the virus’s presence, launching a full-on immune attack. Even after three days of infection, vagina-infected mice seemed to have produced zero interferon.
"Interferon is elicited as the first step in an immune response, and the fact that we barely detected it in the vagina was very alarming,” said first author Shahzada Khan, PhD. “Without interferon, the rest of the immune system cannot be triggered efficiently, making it extremely difficult for the body to fight viral infections."
However, once the infection reached the lymphoid tissue - about one week after the initial vaginal infection - the immune system kicked in high gear and began fighting the infection. Even after this step occurred, though, Zika virus never fully disappeared from the vagina.
The researchers also tried “priming” the vagina with an inflammatory drug, essentially giving the cells a quick start to trigger an immune response by releasing interferons. Following a Zika infection, the mice were protected, ridding themselves of the virus after two days.
"There is something unique going on in the female reproductive tract that makes women particularly vulnerable to RNA viruses," said Sanjabi. "Our next goal is to figure out why this is the case - whether it's a defense mechanism elicited by the pathogens themselves or an immunological loophole in the vaginal tissue."
Sanjabi’s study was recently published in the Journal of Experimental Medicine
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Source: Gladstone Institutes