eli5 does our immune cells try to attack the medication we take while we’re sick? Since medicine is a foreign object. Or does it think of it as a friend who’s there to help.
In: Biology
Most medications are pretty small molecules, so there’s not really a way for the immune system to “attack” them the same way it does with viruses, bacteria, or allergens. For perspective, a single red blood cell contains somewhere in the neighborhood of 200-300 MILLION molecules of hemoglobin, the compound they use to transport oxygen through the body. White blood cells are even larger than red blood cells, so the relatively simple molecular compounds found in most medications are just too small relatively to be noticed by something that’s evolved to identify and attack things like viruses and bacteria.
Some medications do contain allergens like egg proteins or other larger structures that can trigger an immune response in some people. These proteins or other complex molecules are large enough to attract attention, and an allergic reaction is just the immune system going haywire and attacking the substance. Still other medications, vaccines, are designed to elicit an immune response so they can prime the immune system to deal with threats in the future.
The immune system is primarily designed to attack biological threats (e.g. bacteria, viruses, amoeba), so it generally doesn’t attack medications
Most medications are small molecules, too small to fit the machinery different types of immune cells and non-cellular elements use to recognize and attack things. These mechanisms evolved to target things on the scales of proteins and (large) sugars.
Drugs that *are* on that scale, like monoclonal antibodies, can indeed be recognized and cleared, making the drug ineffective.
Our immune systems have very complex systems for recognizing self and no self.
Generally, the immune system does not act on molecules below a certain size and level of complexity. Many drugs are small molecules similar in size to a caffeine molecule single base of DNA, and molecules of this size generally are not acted on by the immune system.
Once molecules get bigger, the immune system can become more sensitive. For example, some people are allergic to antibiotics, which tend to have more complex molecules that are a few times the size of caffeine.
Once we get into larger molecules the size of antibodies, the risk of an immune reaction increases significantly. Makers of antibodies and larger classes of drugs have to take extreme care in the testing and development of drugs to make sure they are not recognized by the immune system.
In antibodies, there is a process of humanization that takes place to produce designs that look like human antibodies. If we tried to use mouse antibodies, for example, patients could get severe immune reactions.
Besides optimizing the design of drugs, we have to be careful with how they are used. For example, administering a drug directly by IV into the bloodstream can be very risky. There are immune reactions called infusion reactions that can occur. When doing IV of larger drug molecules, doctors have to carefully monitor the patient for signs of infusion reaction. Sometimes, doctors may choose to pretreat patients with steroids to avoid immune reactions to more risky drugs.
Humans can develop immunity to relatively common and benign molecules. There is a common additive in food, cosmetics and drugs called polyethylene glycol. It’s essentially a long chain sugar. Almost all of us have developed PEG antibodies. Most of the time we have no issues. However, when you are injected with a product containing PEG, there could be reactions.
PEG was used to stabilize the lipid droplets encapsulating the COVID 19 vaccines. One reason you were told to stay for 15 min at the clinic after innoculation was to monitor for signs of a severe allergic reaction.
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