Basically, memory B-cells remember the code for anti-bodies and they are produced "on demand". Please see the graph in the figure below. https://askabiologist.

Basically, memory B-cells remember the code for anti-bodies and they are produced "on demand". Please see the graph in the figure below. https://askabiologist.asu.edu/memory-b-cell https://askabiologist.asu.edu/memory-b-cell