Thymic involution

One of the major characteristics of vertebrate immunology is thymic involution, the shrinking of the thymus with age, resulting in changes in the architecture of the thymus and a decrease in tissue mass. This process is a conserved sequence or (orthologous sequences) in almost all vertebrates, from birds, teleosts, amphibians to reptiles, though the thymi of a few species of sharks are known not to involute. T-cells are named for the thymus where T-lymphocytes migrate from the bone marrow to mature. Its regression has been linked to the reduction in immunosurveillance in the elderly. Though thymic involution has been linked to senescence, it is not induced by senescence as the organ starts involuting from a young age – as early as the first year of life in humans.