For eloquent nerds, please
November 19, 2018 4:39 PM   Subscribe

Mosquito A bites you and injects a nasty virus into your system. After the acute infectious period subsides, you are left with antigens which (hooray!) confer immunity upon you for that particular virus in the future. Is this the end of the matter?

Mosquito B now bites you, hops over to your sleeping partner, and gives them a healthy dose of your blood sample. Would your partner, having received a sample of your antigens, now be immune, completely or partially, to the original virus? I am totally ignorant when it comes to epidemiology, (if that is where I've ended up), so I may have totally misunderstood the lifestyle of antigens. Expeditions into Google only leave me with a headache from scientists incapable of writing an intelligible sentence. Is there a bug-oriented Richard Feynman out there who can make sense of this for me?
posted by alonsoquijano to Science & Nature (6 answers total) 2 users marked this as a favorite
You might be confusing antigens with antbodies. Antigens are the toxins to which your immune system creates antibodies. Immunity is conferred by the presence of antibodies in your blood, on the surface of certain types of white blood cells (this is an exceedingly basic description of a mind-blowingly complex system.)

In short, the answer is no - your partner would not get a sample of your antiBODIES such that they would be immune to the antigens also transferred to them by the mosquito. Antibodies confer immunity, and antibodies cannot be transferred in enough quantity (if at all) from the bite of a mosquito. The antigens (viruses) themselves that are transferred by the vector (the mosquito) will cause an immune reaction in your partner's body which will confer eventual immunity.

It's also worth it to note that mosquitoes do not transfer blood when they bite a human. They transfer their own saliva, and it is their saliva that contains the viruses they transmit. There are no human blood cells (or if there are, the quantity is microscopically minuscule) transmitted in a mosquito bite, and therefore no anitbodies (which are found on the surface of blood cells and confer immunity to the host they're in) in a mosquito bite.
posted by Everydayville at 4:51 PM on November 19, 2018 [8 favorites]

Right - in order to transfer immunity, the mosquito would need to transfer a population of memory B cells (which make the antibodies in response to future antigen exposure). These aren’t in general circulation to be transferred from one persons blood to another’s.
posted by Jorus at 4:54 PM on November 19, 2018 [2 favorites]

One more thing - if, indeed, blood cells were transmitted via mosquitoes from person to person, there'd likely be a massive, possibly fatal immune reaction to foreign blood cells (think similar to when a recipient rejects a donor organ) each time it happened. Evolution would not let this happen.
posted by Everydayville at 5:00 PM on November 19, 2018 [2 favorites]

The answers above are correct in practice, but you’re not conceptually wrong. “Passive Immunity” is conferred when large amounts of specific antibodies are transferred from one individual to another, giving the recipient enough antibodies in their blood (temporarily) to neutralize a pathogen. This is often a part of post-exposure rabies vaccination in humans. (Source: I am an immunologist.)
posted by juliapangolin at 6:32 PM on November 19, 2018 [4 favorites]

You're thinking of an effect a bit like from colostrum, in which a mother's first few milk feedings to a newborn carries a big dose of antibodies, giving the newborn some protection while its own adaptive immune system is sorting itself out. You need a pretty big dose to be useful though, vastly more than a mosquito's entire stomach can hold.

As others have said:
An antigen is something that gets into your body and provokes an immune response. For example, if you're infected by a virus several distinct parts of that virus might be detected by your immune system. Your immune system will then ramp up and start trying to destroy anything it recognises as containing those bits of virus. The parts of the virus that got the immune system's attention are called antigens.

An antibody is a fairly large protein molecule manufactured by your body. One end has one of a handful of standard adaptors that can interface with other parts of the immune system, and the other end is randomly generated in the hope that, one day, it'll turn out to be capable of binding to some infectious agent (bacteria, virus, etc) that the body has never encountered before. There are several different "classes" of antibodies with different roles in the immune system, but they all have a randomly-generated end that will hopefully turn out to match part of a pathogen someday. Antibodies binding to viruses can directly inactivate them by simply getting in the way of the structures the viruses need to attack cells. Antibodies binding to things like bacteria or fungi can also lead directly to their destruction by biochemical pathways, and/or by acting as "destroy me!" flags that patrolling immune cells are looking for. Crucially though, an antibody is just a big protein molecule that sticks to targets: it can't grow, replicate itself, etc.

Antibodies don't last forever in your blood, they degrade over a few days and get mopped up as part of the usual process of cleaning the blood. They need to be replaced by having a population of cells constantly churning them out. Your immune system has a memory effect, such that if a particular antibody turns out to be good at binding to a pathogen in an infection, more of it is made and the cells capable of making it are kept handy in case you get re-infected someday. In your scenario -- and in colostrum, and in the antibody therapy mentioned by juliapangolin -- a dose of antibodies can be given that might have a protective effect, but the cells capable of making those antibodies are not included (and would probably be destroyed by the recipient's immune system if they were, like any other unmatched transplant). So any protective effect will be short-lived, for as long as the antibodies last in the recipient's bloodstream before being degraded and removed.

1) you need to have quite a lot of a specific antibody in your blood to have a decent protective effect against the bateria/virus causing the infection
2) A mosquito's stomach is far, far too small to give you a big enough dose, even if it regurgigated its entire meal.*
3) Even with a large-enough dose of antibodies specific to the pathogen you're interested in, the protective effect can only last until those antibodies degrade in the recipient's blood, a matter of a few days.

There are some gene therapy research programmes going on to make e.g. patients' liver cells produce an antibody against a specific antigen on a pathogen, as an alternative form of vaccination. This is showing some promise, but during an infection the pathogens are always under evolutionary pressure to change their antigens enough that the immune system no longer recognises them, and the immune system is doing its best to keep up by churning out new variants of the antibodies that were working well up until this moment. Cells modified by gene therapy to produce antibody won't have the ability to change to keep up with the infection.

I've also read about some efforts to give doses of antibody with the hope that the donated antibody will help to attract the attention of the recipient's immune system, provoking a faster and stronger response to the disease than would otherwise have happened. What I read was quite speculative though, and I've no idea what became of that branch of research.

*Also, ew.
posted by metaBugs at 8:35 AM on November 20, 2018

My faith in the scientific community is restored, even if my plans to save the world from mosquito evil must be put in hold. What clear concise answers! Thank you all
posted by alonsoquijano at 4:29 PM on November 20, 2018

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