Memory T cell

Memory T cells are a subset of infection- as well as potentially cancer-fighting T cells (also known as a T lymphocyte) that have previously encountered and responded to their cognate antigen; thus, the term antigen-experienced T cell is often applied. Such T cells can recognize foreign invaders, such as bacteria or viruses, as well as cancer cells. Memory T cells have become "experienced" by having encountered antigen during a prior infection, encounter with cancer, or previous vaccination. At a second encounter with the invader, memory T cells can reproduce to mount a faster and stronger immune response than the first time the immune system responded to the invader. This behaviour is utilized in T lymphocyte proliferation assays, which can reveal exposure to specific antigens.

Within the overall memory T cell population, at least three distinct subpopulations have been described and can be recognised by the differential expression of chemokine receptor CCR7 and L-selectin (CD62L).

More recently, other sub-populations have been explored using co-stimulatory molecules CD27 and CD28 expression in addition to CCR7 and CD62L. In addition, there have been reports that, in mouse, Sendai virus specific CD8+ T-cells low on CD43 expression mounted a higher memory recall response suggesting that memory CD8 T-cells can also be distinguished from activated effector CD8 T-cells using CD43 marker

Tissue resident memory T-cells (TRM) live in peripheral tissues and do not circulate as other T-cells do. Those peripheral tissues are the skin, gut and joints, and are thought to be a key source of the immune system's protective memory. Dysfunctional TRM cells are strongly implicated in autoimmune diseases, such as psoriasis, rheumatoid arthritis, inflammatory bowel disease. Specific to TRMs are genes involved in lipid metabolism, being highly active, roughly 20- to 30-fold more active than in other types of T-cells.

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