Immunological memory cells.

This article reviews immunological memory cells, currently represented by T and B lymphocytes and natural killer (NK) cells, which determine a rapid and effective response against a second encounter with the same antigen. Among T lymphocytes, functions of memory cells are provided by their subsets: central memory, effector memory, tissue-resident memory, regulatory memory and stem memory T cells. Memory T and B lymphocytes have an essential role in the immunity against microbial pathogens but are also involved in autoimmunity and maternal-fetal tolerance. Furthermore, the evidence of immunological memory has been established for NK cells. NK cells can respond to haptens or viruses, which results in generation of antigen-specific memory cells. T, B and NK cells, which have a role in immunological memory, have been characterized phenotypically and functionally. During the secondary immune response, these cells are involved in the reaction against foreign antigens, including pathogens, and take part in autoimmune diseases, but also are crucial to immunological tolerance and vaccine therapy.