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Two populations of memory T cells
Genome Biology volume 2, Article number: spotlight-20010306-01 (2001)
Understanding of protective immunity comes mainly from studies of lymphocytes in the blood and lymphoid tissues, such as the spleen and lymph nodes. It is generally thought that naive CD4+T cells proliferate following an encounter with microbial antigen, then differentiate into memory cells that produce anti-microbial lymphokines. Following the encounter, the memory T cells retreat into lymphoid tissues where they remain ready to mount a response should the same antigen recur.
Marc Jenkins and colleagues of the University of Minnesota Medical School, Minneapolis, injected normal mice with several million naive CD4+T cells. They then tracked the injected cells by immunohistological analysis of thin sections through the whole bodies of recipient mice.
In 1 March Nature, Jenkins et al report finding that in mice exposed to antigen, the T cells proliferated, migrated to non-lymphoid tissues, such as the lungs, liver, gut and salivary glands, and then disappeared from these organs. When antigen was injected together with lipopolysaccharide, a microbial product, T-cell proliferation and migration were enhanced. Two discrete populations of memory cell survived for months. One, which resided in lymph nodes, secreted interleukin-2; the second, larger, population was found in non-lymphoid tissues and secreted the anti-microbial lymphokine interferon-? (Nature 2001, 410:101-105).
This suggests that protective immunity generates memory cells that are specialized to proliferate in the secondary lymphoid tissues or to fight infection at the site of microbial entry.