T lymphocytes (T cells) are important players in cell-mediated immunity. They recognize epitopes from processed antigens. These are peptides on cell surfaces presented by major histocompatibility molecules. T cell responses are designed to recognize intracellular invaders and eliminate infected cells. They also “help” in other immune responses by secreting cytokines. T cell memory involves three distinct types of memory cells: central memory, tissue resident, and effector memory cells. These components of the immune system are a major part of the adaptive immune response.