Interleukin-7: An interleukin for rejuvenating the immune system

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 × 10¹¹. 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 10⁸ 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 × 10⁷ to 10⁸. A successful response leads to clonal expansion and the generation of memory T cells to the infecting agent.