Follow up: Does that information deteriorate or do these cells ‘forget’?
Edit: If you’re able to answer the question, but can’t ELI5, then maybe explain in a way that a lay-person would understand i.e. not jargon-heavy.
In: Biology
Not an ELI5 but if you want some more detailed explanation of specific mechanisms check these out.
https://en.m.wikipedia.org/wiki/Somatic_hypermutation
https://en.m.wikipedia.org/wiki/Affinity_maturation#:~:text=In%20immunology%2C%20affinity%20maturation%20is,antibodies%20of%20successively%20greater%20affinities.
T cells exposed to pathogens express proteins on their surface. Conversely ones that have not been exposed do not. The former are considered effector memory t cells and the others naive. If you are looking for more information do some research on t cells that express cd28 or cd95.
The entire process is quite complex and does not fit in the format of this subreddit. But a very simplified answer is that the body produces a type of cells called B-cells. Each of them have an antigen associated with it with a random marker. However if the marker triggers on the stem cell that created the B-cell it is deleted so that only B-cells that react to proteins that your body can not make is every being made. This does mean that technically you have some antibodies against every possible virus and bacteria ever. But these are in too small numbers to do anything. But when a B-cell gets a match it will alert the rest of the immune system such as the T-cells to the intruder, start making more copies of the antibody and multiply itself so it can go hunt for more intruders. These B-cells will linger around in your blood stream for long after the infection is over. However as with any cells they do have a limited lifespan and will die. And if there have not been any other infections of the same type they will not have made more of the same cells.
In terms of “previous pathogens,” the memory of these pathogens are stored in B cells, specifically the “plasma” type of B cells. Plasma B cells were once regular B cells that were secreting antibodies specific to an antigen from an infection, vaccine etc, and once the infection subsides, the B cells matures into a plasma B cell. Plasma B cells are the quiescent forms of the B cell that are dormant in different tissues such as lymph nodes, spleen. Assuming that you had a sufficient immunologic response to that antigen (infection/vaccine), you would have many of these B cells (not exactly sure of the number but I guess in the hundred thousands?) and once the infection subsides, they lie dormant until it’s activated by a T cell that looks for that same antigen. This is why some vaccines require multiple doses to ensure that the body builds a sufficient immune response to create enough plasma B cells that will fight the future infection!
I am assuming that the definitions of antigen and antibody is known but if you don’t it’s fine! Antigen is any molecular compound that the body identifies it to be foreign. Antibodies are specific molecules that binds to specific antigens that “mark” it for destruction.
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