The immune system changes dramatically with age. There is a decline in the production of naive lymphocytes by the central lymphoid organs, the thymus and bone marrow. This leads to a reduced diversity and altered repertoire of antigen specificities recognized by the immune system. Thus, with age there is a progressive decline in the capacity of the immune system to react with foreign antigens associated with an increased reactivity with autoantigens. As T cells specific for certain microbial antigens decline with age, their capacity to prevent reactivation of certain chronic infections such as herpes zoster diminishes. This results in the increased reactivation of herpes zoster in persons over 45 years old.
