Reversal of age-associated thymic atrophy: treatments, delivery, and side effects.

Our ability to survive infectious agents depends on making adequate immune responses, but as we get older our thymus atrophies. Production and export of T cells bearing new antigen receptor specificities to the peripheral T cell pool declines and results in shrinkage of the repertoire. Other changes in the peripheral T cell pool include an increase in cells moving closer to their replicative limit. Age related immune dysfunction, evident through the increased susceptibility to infection, follows these changes. Improvement in immune function in the elderly may require us to rejuvenate the immune system starting first with reversing the atrophy seen in the thymus. This has been achieved experimentally with interleukin 7, growth hormone, growth hormone secretagogues, keratinocyte growth factor or through chemical or surgical castration. The widespread use of one or more of these treatments will depend upon their effectiveness, their ease of delivery and the extent of any side effects.