What does the memory lymphocytes do?

Ready 2 fight again: You are born with a huge number of lymphocytes, each intended to fight a different antigen that may or may not even exist in nature. If you meet an infectious agent with such an antigen, the lymphocytes that fight it will proliferate to do so better, then settle down and become inactive. Meet it again, there is a huge fighting force, the basis for acquired immunity.

Recall antigens: They are there to boost your immune response to chemical structures that are foreign to your body and have been encountered previously and your lymphocytes have manufactured antibodies to. They remember those and can respond quickly.