Given a scientific passage and an answer, generate a question for the given answer.

Passage: Most plasma cells live for just a few days, but some of them live much longer. They may even survive for the lifetime of the individual. Long-living plasma cells are called memory cells. They retain a "memory" of a specific pathogen long after an infection is over. They help launch a rapid response against the pathogen if it invades the body again in the future. Answer: memory cells
What are long living plasma cells called?