Interleukin‐7: An Interleukin for Rejuvenating the Immune System

A bstract : Infection of an individual (aged 20‐30 years) by a virus will cause a response from the T (thymus derived) lymphocytes of which there are approximately 3 × 10 11 . If the individual has not met the virus before, the response will come from the naive T cell subset (50 ± 10% of the total T cell pool at this age) containing recent thymic emigrants produced from the thymus at approximately 10 8 per day. Their antigen‐specific receptor has a defined specificity governed by the conformation of its two chains (α and β), and the repertoire of specificities is somewhere in the region of 2 × 10 7 to 10 8 . A successful response leads to clonal expansion and the generation of memory T cells to the infecting agent.