Memory T cells is a small pool of cells able to be rapidly activated and expand, in order to protect against previously encountered pathogens. There is strong evidence for a model in which memory T cells descend from a population of cells that have previously expressed genes associated with effector-T-cell function, and have turned off effector-gene expression but retained a ‘memory’ of their developmental path.
This takes the form of DNA modifications that would enable them to rapidly become an effector cell upon pathogen reinfection. In essence, epigenetic modifications bookmark the chapter of infection in a memory T cell’s history, allowing the cell to rapidly ‘recall’ its effector capacity.
Reference: KD Omilusik https://www.nature.com/articles/d41586-017-08280-8
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