memory cell

noun Immunology.

1. any small, long-lived lymphocyte that has previously encountered a given antigen and that on reexposure to the same antigen rapidly initiates the immune response (memory T cell) or proliferates and produces large amounts of specific antibody (memory B cell): the agent of lasting immunity.

A cell in the immune system that, when exposed to an invading pathogen, replicates itself and remains in the lymph nodes searching for the same antigen, resulting in a more efficient and rapid response to any subsequent attack.