Naive vs. memory T cells

Your T cells come in two broad camps: naive and memory. Naive T cells have not met their target yet. They constantly circulate through your lymph organs, waiting for their specific antigen. They are made in the thymus and need low-level TCR and IL-7 signals to survive. When a naive T cell finally meets its antigen (plus a co-stimulus), it multiplies and turns into effector cells, and then long-lived memory T cells (central, effector, and tissue-resident kinds). Those memory cells make your next response faster and stronger. With age, the balance shifts. The naive pool shrinks (from the thymus shrinking and from cells converting type), while the memory pool expands. A big driver is persistent viruses like CMV, which inflate narrow (oligoclonal) CD8+ populations. The net effect: your T-cell receptor variety narrows, and you respond worse to new pathogens and vaccines.

Last reviewed: June 22, 2026

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