The Magnificent IL-7; an interleukin for rejuvenating the immune system
Richard Aspinall, Sian Henson, Jeffrey Pido-Lopez and Pa Tamba Ngom
Department of Immunology, Faculty of Medicine, Imperial College, London.SW10 9NH, UK
Infection by a virus of an individual (aged 20-30) will cause a
response from the T (thymus derived) lymphocytes of which there are
approximately 3 x 1011. If the individual has not met the virus before,
the response will come from the naïve 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 2 chains (? and ?) and the repertoire of
specificities is somewhere in the region of 2 x 107 to 108. A
successful response leads to clonal expansion and the generation of
memory T cells to the infecting agent.
Ageing is accompanied by thymic atrophy, a reduction in thymic output
and a consequent reduction in the naive T cell pool. This is not
accompanied by a reduction in the absolute number of T cells because of
the expansion of the memory T cell subset. Successive rounds of
division within this subset may be responsible for the accrual of
defects and the accumulation of senescent cells. Within the thymus, age
related thymic atrophy is accompanied by a decline in the production of
Interleukin 7 (IL-7), a cytokine known to have an essential role in T
cell development. Therapeutic intervention with IL-7 in old mice
increases both the size of the thymus and its subsequent output
benefiting the functional performance of the T cells in the peripheral
T cell pool.
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