Why is the immune system so fast to respond to allergens, but take days to fight off a legitimate infection?
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“Fight” is the key word here.
Allergens trigger the immune system to respond, but they’re not actually harmful. Your cell cops swarm the area and then stand around doing nothing useful because there’s no real threat.
An actual infection is different. The cell cops show up and find an army of hostile foreign pathogens that must be hunted down and destroyed. These pathogens have devised a vast number of devious tricks to evade or defeat your immune system, and so it’s an actual fight that only ends when either you or the invaders are dead.
Allergens are proteins that your body is able to quickly recognize and react to. Sometimes our body assumes that they are more dangerous than they really are and they over react. Think of that as mixing up bee venom with scorpion venom. Sometimes the meat suit gets its priorities confused when it comes to similar proteins. When that happens your immune system causes a lot of collateral damage trying to neutralize the “deadly” proteins.
Bacteria on the other hand are living creatures that want to survive and reproduce. They can react to their environment and sometimes can change their metabolism rate depending on if they want to be efficient and release less waste products, or if they want to multiple quickly and make the environment less hospitable to other life forms.
And viruses are organic machines designed to do one function, and they do that one function well.
Both of these cell types produce byproducts, but with all of the other similar byproducts produced by our own bodies, and the tons of other living creatures inside of you, it’s pretty difficult to pick them out right away when a infection is struggling to take root. And even then your body has a different immune response depending on how many foreign “threatening” proteins are inside of your body.
If you have a similar cold virus that your catching for the second time, your body can quickly pick up on it and send out a appropriate response. If you don’t understand the proteins you might send out “scout” cells that try to figure out how to neutralize the foreign cells, and then they go back and signal your body on how to precede. If you are going to die soon if nothing is done, your body pulls out every single thing that it has. It thrown caution and efficiency to the wind and chucks every thing that might work. At that point either you stop the infection or you die.
But if your body immediately jumped into the most extreme response to any foreign matter then it would quickly exhaust itself and something as simple as a flu season or a splinter could become fatal. But if your body is unable to respond and escalate quickly enough than a virus could become unstoppable before you put the proper reaction in place. It’s a tough balance when it comes to fighting living creatures in your body.
In addition to what others said, our body IS fast to respond to infections. You just don’t notice the symptoms for 2-3 days because the infection is being held back. As the pathogen grows and spreads, a larger and larger immune response is generated which gives you the fever, body aches, fatigue, etc. Certain organisms have traits that allow them to beat your immune system long enough to grow while others are destroyed immediately because your immune cells are constantly surveying for infections.
Your immune system fights off most germs as quickly as it responds to allergens.
Our bodies are invaded by germs constantly. Every breath you take. Every bite of food. Every cut in your skin brings germs into your body. Nearly all of these germs are killed within minutes or hours by immune cells that respond instantly.
It appears to us that infections take days to fight off because we only notice the ones that get out of control, but the overwhelming majority are so quick and painless we never even know the germs were there.
An allergen is a simple particle. It will sit there and be easily attacked until neutralized. If your immune system never responded you’d be fine.
An infection is living bacteria or virus. It will reproduce as long and attack body functions as long as it can. If your immune system never responded you’d die quickly.
In reality most of the things you notice as a “cold” or upper respiratory infection are a result of the body fighting the legitimate infection. Your body responding to an allergen is a different set of cells as well. The immune response to an infection involves specialized cells ( B and T cells, amongst others) which have to activate, develop, and replicate to get ready. Where as allergens trigger a cell that is already just sitting around (mast cells) waiting for something to do. The mast cells sense their allergen and dump histamine and other stuff. Depending on the strength of the response, and where the allergen is, affects the response from itching to full on throat closure and blood pressure decline.
I think you are exposed to millions of pollen or dust particles all at once, so the immune reaction is immediately strong. But with diseases, you are only exposed to a handful of microorganisms, so the immune response is minor until the number of microorganisms becomes large.
The immune system is really a few different systems – the biggest distinction between an allergic response and an infectious response has to do with differences between a few of these.
One branch of your immune system works by acting very quickly against a broad set of particles it has learned to associate with infection. Its job is to try and stop an infection before it happens, or quickly stop one that has developed from getting worse by prepping the injured area for a more sustained and effective response. The signals this branch of the immune system uses do things like widen blood vessels and allow them to leak – this allows more oxygen, heat and later-responding cells to get to where the problem is faster and get out of the blood into the tissue causing trouble. It also causes redness, warmth, itching and swelling. When you have a severe allergy, it means your body has basically learned to over-use this rapid response pathway against something that isn’t actually a threat; instead of that response happening just where the problem is (such as your skin getting red and warm when you have cellulitis, or your nose being stuffy when you have a cold), it triggers the rapid response everywhere in your body, all at once – your mouth and throat swell, all your blood vessels try to dilate at once and your blood pressure tanks, and your lungs become constricted. Anaphylactic shock, in other words.
Meanwhile, there are slower systems that are used to go after threats more specifically – these are involved in allergies as well, because you need to first “learn” the antigen to make the antibodies to it, but they really shine when fighting off infection. All over your body, 24/7, there are protein machines and specialized cells that are constantly breaking down proteins they find, collecting snippets of them, and presenting them to the immune system to scan for problems. The immune system has specialized cells that scan these protein snippets (i.e. antigens) and compare them against a kind of database of every protein in the body. If they find something that’s not in the database, and there are other factors that indicate something going wrong (markers for cell damage or local inflammation, for instance), then they start building antibodies against that thing. This process takes a few days, though it’s much shorter when you have already been exposed – if that’s the case, the immune system can both discern the problem faster and has a library of cells that are already good at making antibodies against it.
Kurzgesagt is an unbelievably cool YouTube channel that has a couple short, beautifully animated videos on the immune system. Watched them recently and they really helped me grasp the scale of what happens during a full-on immune response. Can’t recommend the videos, or channel, highly enough!
I think it is interesting that experts even always explain pathogens and our bodies response to them as if they are acting consciously. It’s almost hard to explain without these metaphors. There is absolutely no intention to these things right? But it really seems like there is!
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