How does our immune system identify between medicine or bacteria/viruses/infection/etc that gets into our body and decides the former can go through while the latter can’t? Do they ever misidentify?
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A lot of medicines act by mimicking chemicals that our bodies naturally produce, so the immune system isn’t bothered by them.
But misidentification definitely can happen. That’s basically the definition of an “allergy”.
There are cells in your body that are part of your immune system, specially dedicated to fighting infection. They’re like your bloodstreams bouncers.
One of the types of cells ‘investigates’ “Helper T-cells” – like the bouncer checking your ID, and if they find a cell that it identifies as a threat, it’ll stick to it. Then the big boys, the “Cytotoxic T-cells” kill anything that’s been marked.
The whole identification process is extremely complicated, by TL;DR your body has a list, some of it is genetic and passed down from your parents, this is why hereditary immunity is a thing, and then it’s added to as your body encounters new things.
Yes, misidentification happens, in both directions.
When a harmless thing triggers your immune system, it usually just results in allergies.
But in some rare cases, your body can misidentify its own cells as foreign objects – this is what autoimmune disorders are.
And yes, sometimes some viruses/bacteria/whatever are so good at evading our immune system that they never trigger it at all. Ever hear about people who get Covid and spread it around but never have any symptoms or even know they had it? Their body didn’t identify infected cells as a threat, so no immune response, no fever, no runny nose, etc.
The immune system targets microbes and parasites. Medicines aren’t microbes, they’re chemicals.
There’s no real distinction between helpful drug or dangerous pathogen as far as immunity is concerned. Things are foreign or they aren’t. What makes the difference is that most drugs are such simple, small molecules that they can’t be sensed at all by most mechanisms of the immune system, because those are tuned to look for things on the scale of proteins.
However, when you use large, especially protein-based drugs like monoclonal antibodies, these absolutely provoke immune responses if other steps aren’t taken to counteract that (for instance, modern monoclonals are engineered to differ as little as possible from unmodified human sequences).
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