Two populations of memory T cells

Our 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 found 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...