A person who contracts chicken pox as an adult lacks which of the following?

Explanation

Memory cells are a kind of T cell that is created when an antigen such as the chicken pox virus appears. Unlike plasma cells, which fight an antigen for about two weeks, memory cells remain in a person’s system for a very long time, ready to reactivate immediately should the same antigen reappear. Memory cells are always specific to a pathogen, so that an adult person who has never had a certain virus will not have memory cells in his or her system to attack that antigen. That person may, however, have memory cells keyed to another antigen.