How is it possible to not have an allergic reaction when first exposed to an allergen and to then have an allergic reaction a week or two after the exposure?

Question

I know that allergic reactions like this are possible because I’ve had one. I took a medication and was fine for the first five days. Then, on day six, I started breaking out in hives.

How does this happen? I have a hard time understanding how the body can have an allergic reaction at a point when the allergen probably isn’t even in the body anymore.

In: Biology

Answer 1

The body has two subsections to the immune system

The innate immune system, is all the stuff that floats around in the body looking for anything foreign, when it finds it, it attacks it indiscriminately. It essentially looks for markers on your cells, and attacks anything that isn’t carrying those markers, or releases chemicals that damage everything near a target.

The adaptive immune system, isn’t concerned with immediately destroying threats, it gathers components of anything the innate immune system destroys, with the end goal of generating antibodies to that specific threat.

The innate immune system is useful because it’ll destroy anything, but it’s slow. Meanwhile the adaptive immune system’s antibodies are numerous, fast and amplify the innate immune system, but they’re targeted to a specific theat.

What this means is the first time you take that drug, your body’s innate immune system attacks it, the response is slow. That attack provides your adaptive immune system the components it needs to generate antibodies to parts of that drug, which amp up the innate system’s immune response the next time your body sees it.

A delayed reaction is a bit more complex, in that they are not antibody mediated, the cells that find foreign components and present them to the antibody making cells, produce chemicals called cytokines, these cytokines essentially tell the rest of the immune system “follow me, make more immune cells and start fighting”, the problem is some of these immune cells actually damage your own cells when they’re activated, so these cytokines start a kind of cascade that takes a while to ramp up, but ends up attracting too many of these self damaging cells, which is where your delayed reaction comes from.