Mosquito Bites Leave A Lasting Impression On Our Immune System

By Roni Dengler | May 17, 2018 1:06 pm
(Credit: Kokhanchikov/Shutterstock)

(Credit: Kokhanchikov/Shutterstock)

Mosquito bites are like a gross form of French kissing — the insects swap your blood with their saliva, and leave a trail of salivary secretions behind like mosquito cooties. Some of those compounds prevent clotting as the insects slurp up your blood. Now researchers find mosquito spit aggravates your immune system for days afterward. The findings could help scientists develop vaccines for mosquito-born diseases like Zika.

Rebecca Rico-Hesse, a virologist at Baylor College of Medicine in Houston, Texas, wanted to know how mosquitoes exploit our immune systems with their drool. So, she and her team exposed mice with human-like immune systems to live mosquitoes. Then, they sized up the mice’s immune response as it reacted to the mosquito spittle.

The bug’s saliva toyed with their immune systems in both bone marrow and skin cells with effects that lasted up to seven days after biting, the team reports today in PLoS: Neglected Tropical Diseases. The researchers say their discovery could explain how these tissues might act as virus incubators and help spread disease.

Master Manipulators

In 2012, Rico-Hesse was looking to untangle how Dengue virus causes Dengue hemorrhagic fever — an illness that affects 400 million people each year and can lead to death — when she came across a strange occurrence. Mice infected with the virus from mosquito bites fared far worse than mice that had received an injection of the virus but hadn’t been served as a mosquito meal. The result made Rico-Hesse take a step back.

It seems that mosquito bites caused the immune system to behave differently, and in ways that could potentially give infectious diseases a leg up.

To find out, Rico-Hesse and her team set starving Aedes aegypti mosquitoes on mice that had received a dose of human stem cells to make their immune systems look more like a human’s. Each mouse endured eight mosquito bites total. Then the team checked out different parts of the immune system — blood, bone marrow, spleen, and skin cells — six and 24 hours after biting, as well as seven days later. By then, the immune system should have returned to normal.

Sneaky Viruses

Instead, the team discovered immune cells that had disappeared from the skin at least six hours post-bite came back seven days later after maturing in bone marrow, something that shouldn’t have happened. If those cells harbored a virus, they could then pass it on to new mosquitoes, who could infect others.

The research is pointing out new ways in which mosquito bites affect our immune systems, and it goes beyond simple itching and scratching.

“Mosquito saliva has evolved to modify our immune system,” Rico-Hesse said. And as their new research shows, viruses and parasites could be hijacking that activity to get to the cells they reproduce in, like bone marrow cells, faster, according to her.

Essentially, viruses might be taking advantage of the immune system’s response to travel from their point of entry — the skin — to a place they can multiply in that’s away from attacks by the immune system.

“It’s mind-blowing,” Rico-Hesse said. “No one has ever seen this before.”

Ultimately, the work could lead to infection-blocking vaccines, said Duane Gubler, an international health expert who was not involved in the research.

That’s what Rico-Hesse hopes, too. “If we can make a vaccine that would protect us against the effects of the [mosquito] saliva, or blocking our immune reaction … then we could stop global vector-born diseases,” she said.

CATEGORIZED UNDER: Health & Medicine, Living World
  • OWilson

    A healthy human immune system response to invasive toxoids is the very basis of immunology.

  • nik

    Sounds like a ”wolf in sheep’s clothing’ syndrome.
    After being bitten by a ‘sheep,’ the the ‘wolf’ of the parasitic infection can sneak in with the sheep thereafter.
    Something I noticed while in the tropics was that, after about three months, I developed an immunity to the local breed of mosquito. They would land, take a sniff, and take off, without biting. Or, if they bit, (infrequently) I got no swelling, and itchy spot, just a tiny pin-head sized blister, that I assumed was the anticoagulant being ejected.
    The ‘tiger’ mozzies were a different matter. They were very infrequent, thank goodness, so presumably not enough contact for my body to react in the same way. Also If I went a few miles away, then I got bitten again, so it was a very localised effect.
    Some people responded in the same way as I, while others were constantly covered in bites, even when they used a mosquito net, which I didnt.

    • OWilson

      I too, seemed to have picked up an immunity to mosquito bites in Canada, and in the Caribbean where I reside now!

      People around me get bit, swell up and feel real pain, but they don’t seem to bite me, at least I have no reaction.

      I still can’t lie in bed and hear that buzzing though. That’s what really drives me crazy!

      • nik

        I read an article a year or two back, and if I remember correctly, the effect was confined to Europeans for some reason that they had not discovered.
        Obviously something in the history of Europeans had aroused that response in their DNA,/immune system.
        Most probably living near swamps, and being eaten alive, I would guess
        Anyway, I thank my DNA for it. My son, however, doesn’t seem to have inherited it, poor chap!


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