system
Given the following post, respond as if you're commenting on Reddit:
human
If white blood cells are constantly dying and being replenished, how do new ones “know” what antibodies to produce?

How does that “memory” work?  

This comes from a friend asking whether the protection from a COVID-19 vaccine would be diluted somehow by a blood transfusion from an unvaccinated person.
gpt
When a T- or B-cell is activated by it's associated antigen, it proliferates, and those daughter cells differentiate into effector cells (helper, cytotoxic, regulatory for T's, plasma cells for B's) and memory cells. When the immune response is complete, the memory cells go dormant in your lymph nodes. If they are presented with a previous antigen and reactivated, they proliferate, and differentiate back into those same effector cells.