Why is the immune system so fast to respond to allergens, but take days to fight off a legitimate infection?

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Why is the immune system so fast to respond to allergens, but take days to fight off a legitimate infection?

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Anonymous 0 Comments

Imagine you get punched in the face every day with a right hook from the same person. The force or angle may be slightly different, but in the grand scheme you’re taking the same punch that are annoying but not impactful. This is allergies.

All of a sudden, someone shows up and throws a left hook + upper-cut combo that knocks you unconscious and on your ass. This is the new illness

Anonymous 0 Comments

The immune system responds quickly because 1) it has memory to that antigen and 2) it has developed an IgE antibody response to the antigen. IgEs behave differently than IgG and IgM antibodies. These antibodies are very long lived and circulate in your system ready to bind their antigen. When they do they engage Fc epsilon receptors on mast cells and basophils, which leads to degranulation and release of histamine. Some times it is such a huge response that it requires an epipen to save a person’s life. BTW this is part of the innate immune response.

For a new infections your immune system creates an adaptive immune response. This takes ~7-10 days to amount a full immune response and create memory T and B cells. Once you have that memory it last a long time and sometimes for life. If you get reinfected by the same bug the memory cells usually mount an efficient response to clear it in such a way that you don’t notice and don’t have any symptoms.

Hope this helps.

Anonymous 0 Comments

Because an allergen causes a consistent system wide PH balance change due to intake towards a reaction based on contact then saturation vs reaction and an infection usually starts at a local source that changes the PH balance that then saturates from said source of infection.

Anonymous 0 Comments

You are allergic to things that your immune system is already primed to fight. In a sense you have been “vaccinated” to an allergen by prior exposure, and so you mount a fast and intense immune response.

When you get sick more slowly, your immune system has encountered something that it had not learned to fight, and the reactions take a few days to ramp up as it “learns” to first detect and then react to the unfamiliar infection.

Anonymous 0 Comments

The allergic response is like a mine going off while the response to infection is more like a tactical operation.

The first time you’re exposed to an allergen you won’t actually have a reaction. This is just sensitisation – so the mine is primed during this phase.

The next time you encounter the allergen your primed mine will recognise it and immediately go off.

What is the mine? Mostly mast cells which “degranulate” releasing histamine which is a molecule that produces all those allergic effects.

How is it primed? Well that involves a type of immune cell called a dendritic cell encountering the allergen during the sensitisation phase, eating it up and presenting it to other immune cells called T cells. These T cell will tell other immune cells called B cells to produce antibodies called IgE.

IgE is like a Y shape, with the “prongs” able to recognise the allergen. The “trunk” is able to be embedded into the surface of the mast cell, so just imagine a mast cell with loads of IgE sticking out of it. This is now primed, or sensitised.

When the allergen comes into the body next time, it will bind to the prongs of the IgE that are sticking out of the mast cells, and that will cause the degranulation and rapid allergic reaction, like a mine going off.

As for bacterial infection, the process is similar. The dendritic cell will eat the bacteria if it encounters it, and it will present bits of it to T cells. The difference is that the T cells will recognise that this is bacteria now, and not an allergen. So instead of getting B cells to produce IgE, they get them to produce antibodies that are more suited to fighting bacteria, like IgM and IgG. These are more like bullets that are shot at bacteria directly rather than priming an intermediate like mast cells.

Anonymous 0 Comments

The reason you react to allergens so acutely is because you have cells sat primed with antibodies ALREADY. Your body has seen the allergen (or something sufficiently structurally similar that it can’t tell the difference) before, and it is recognised by antibody that is already sat there waiting.

Whereas most infections that actually cause symptoms are ones your body has not met before. So it has to go through the entire process of mounting an acute response: releasing ‘attack cells’ that ‘eat’ the bacteria, ‘digest’ them and then ‘present’ identifiable bits of the digested bacteria to certain other specialised cells whose job it is to take those digested pieces, and start trying to create an antibody against the bug. It can take some time to find a decent antibody – and then after a good antibody has been identified, the body then has to mass produce it. Bacteria also have ‘cunning’ methods of circumventing this system, for instance by changing the identifiable elements of themselves, hiding them away, or actively neutralising the very cells that are involved in responding.

I think a reasonable analogy is to say it’s like trying to open a lock with a key when you already know which key you need, versus having no idea and having to try every single key on the keyring. And that some bacteria are then capable of switching/hiding the locks. Plus, some peoples bodies for whatever reason struggle to even make the keys in the first place!

Anonymous 0 Comments

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!

Anonymous 0 Comments

Familiarity and dosage of the irritant. That’s how immune systems work. With people with allergies, the immune system knows what that thing is, sees a quantity that makes it notice it, and thinks that it really doesn’t like it.

Plus I doubt things like pollen and such mutate their “appearance” (so to speak). If your body identifies a specific plant pollen as something it dislikes, it’ll remember and the pollen probably didn’t really change much since last time.

With infections, you probably are getting a smaller dose and it may have changed enough that your body doesn’t see it as “the flu we had a problem with last time we saw it.” Plus infectious things are fighting back, reproducing, and doing their own actual damage to the body.

Anonymous 0 Comments

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!

Anonymous 0 Comments

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.