So how does the body "Remember" what diseases it can fight?

A common conspiracy theory is that the COVID vaccines (or vaccines in general) alter your DNA. The response of the entire scientific community is “no, really. They don’t.”

But… how DOES your body store that information, so it can produce more antibodies? Where is that little Wanted poster kept, if you will? Where is the information in my cells that tells it how to fight polio, measles, or chicken pox, but not smallpox (against which I was never vaccinated)? If it’s not in my DNA, how does my body retain that?

I think it keeps producing small amounts of antibodies, ready to ramp up production if need be.
But then, I an an engineer, not a physician.

and after the vaccine is injected and recognized by the immune system,

Both active disease and immunization in general are responsible for producing “memory” lymphocytes to rapidly and effectively fight further infections. Genetic alterations produce these specific memory cells.

Covid-19 vaccines do not alter the DNA of the host cells that take them up. Neither mRNA or adenovirus vector vaccines integrate into or change the cells’ DNA, and their constituents remain in the body only temporarily while stimulating the formation of protective antibodies (and memory cells) through the production of coronavirus spike proteins.

I asked this question myself, in the year 4 BC:

Here is a great site. It is complicated, but the topic is complicated.

https://primaryimmune.org/immune-system-and-primary-immunodeficiency

The tl;dr of the situation, though, is that the protein spike produced by the mRNA does induce the evolution of a line of immune cells modified to fight it (just like the normal, natural immune response to any foreign protein) but it doesn’t effect other cells.

Here’s an analogy: DNA is a printing press. mRNA is a page of written instructions printed from that press. The ribosome is the construction worker handed those instructions. The mRNA vaccine means that you take pages of instructions printed on someone else’s press and hand them to the construction worker, who then builds the spike protein. But the page of written instructions do not and can not land of top of the printing press and modify it any more than a real piece of paper laid on top of a real printing press can rebuild it. The only situation in which the prospect isn’t transparently idiotic on its face is for people with no understanding of genetics.

I’m starting to get it.

Basically, really simplifying, immature T-cells are created by stem cells in our marrow. The T-cells are then matured in the thymus - hence the name - and now can work to rid us of infection.

So to drill down a little bit more; how is the information necessary to attack a particular pathogen given to the T-cell? Why can my T-cells identify a cell infected with measles, but not one infected with smallpox? Or in other words, HOW is that particular information given to the T-cell?

The T-cells have sections of DNA for producing antibodies that have the ability to recombine/shuffle/mutate at a much higher rate than is normal for most DNA for most cells. Gazillions of t-cells evolve gazillions of different antibodies. Most of them are useless. Occasionally one of those randomly-generated antibodies is the right shape to latch onto an alien protein. The t-cell that happens to have evolved that gene begins reproducing like crazy so as to provide lots of copies of the antibody. The ones with useless antibody variations don’t. (They are incel cells?)

https://en.m.wikipedia.org/wiki/V(D)J_recombination

What an mRNA vaccine does is provide the instructions for building a protein that can allow for the selection of a t-cell to be stocked up on in case of a real infection.