Immunosenescence is the gradual deterioration in immune system function associated with
ageing. This decline is partly due to involution of the thymus, which leads to a reduction in
the output of naive T cells into the circulating lymphocyte pool. Expansion of existing naive
and memory T cell populations, to compensate for the reduction in thymic output, can lead to
reduced diversity in the T cell repertoire with increasing age, resulting in impairment of
immune responses to novel antigenic challenges, such as during infection and vaccination …