Why is the immune system so fast to respond to allergens, but take days to fight off a legitimate infection?
In: 5304
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.
Latest Answers