How infection site affects the immune system

A new study by scientists at the Gladstone Institutes shows that infection sites could affect the immune system's response to a virus and the way the virus spreads through the body. The researchers focused on common routes of sexual transmission of viruses, such as the lower female reproductive tract and the lower gastrointestinal tract that includes the large intestine and the anus.

These mucosal barriers-the body's openings lined with a membrane called mucosa are responsible for distinguishing between harmless bacteria that normally reside in human and potentially dangerous pathogens, as well as other substances, such as food or sperm. Human body is constantly trying to balance between tolerating harmless elements and defending against the threats.

Reseachers discovered that the body's reaction is different based on the infection site. They showed that the vaginal and rectal cavities activate a distinct immune response to the same pathogen. To conduct the study, research team created a new model of viral infection through the rectum that uses lymphocytic choriomeningitis virus (LCMV), a rodent virus often used in research to model other pathogens. They then compared their findings to their previous work on vaginal infection by LCMV.

In 2016, they showed that vaginal infection causes a delayed response by protective cells. As a result, the immune system takes longer to clear the virus from the female reproductive tract. They also noticed that the virus stayed in the vagina and didn't spread to other parts of the body. In contrast, the new study indicates that, after infection through the rectum, the virus rapidly spreads throughout the body. The scientists also found that the virus wasn't being carried through the blood. Instead, LCMV infects the body's own immune cells, which in turn spread the virus systemically. Interestingly, this is the same dissemination process used by the HIV virus.

The initial immune response elicited depends on the route of infection, and can actually dictate the dissemination of the virus. The researchers revealed that mucosal barriers have different tolerance mechanisms that affect the immune system's response to invading pathogens. Once a virus breaches one of the barriers, early events in the body's response to that virus can play a key role in determining the outcome of an infection.
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Potential Zika vaccine prevents pregnancy transmission and testicular damage

Zika infection typically results in mild or symptom-free infections in healthy individuals, infected pregnant women without symptoms may still give birth to a baby with birth defects like microcephaly.

Researchers has shown that a potential Zika vaccine can protect fetuses against infection and  protect males against testicular infection and injury. It also prevents a lowered sperm count after one vaccination.

Infected men without any signs of illness may still incur testicular injury and lowered sperm count. The Zika virus could infect the male reproductive system for several months, posing risk for sexual transmission.

Taking a single-dose vaccine could prevent Zika infection in non-human primates, prevent mother-to-fetus transmission, and stop male testis infection in mice. The vaccine provides a protective immune response, this vaccine exhibited an excellent safety profile in mouse and non-human primate models.
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Human semen keeps viruses

The current analysis revealed genetic evidence of many infectious viruses found in semen. Semen provides a hiding place and breeding ground for many dangerous viruses

Zika, Ebola, Marburg, Lassa fever, Chikungunya, Mumps, Epstein-Barr and Chhicken pox are present in human semen. Non-sexually transmitted viruses can persist in semen, and this increases the risk of sexual transmission.

 The presence of viruses in semen does not mean that every virus can be sexually transmitted, common viruses in semen are: hepatitis viruses, herpes viruses, and range of other viruses that can be pass from person-to-person via blood, saliva or other means.

It is easy for viruses to get in to the semen, but relatively hard for the immune system to kill the viruses, the immune system recognized sperm as foreign objects in the body and this subject sperm to attack from the immune system.

For sperm to survive, the testes are immunologic locations in the body, where the immune system does not have much access to, this immunological location can also protect dangerous viruses.

Zika is cleared from the bloodstream within one week of treatment, but can persist in semen for months, Ebola survivors can reigniting an outbreak because the virus remained latent and active in their testicles.
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