The effect of aging on cognate function and development of immune memory.

Immunological memory is one of the central features of the immune system and can be described as the ability of the immune system to respond more efficiently to a second encounter with the same pathogen. The immune system is dramatically affected by age-related changes and it is becoming apparent that immune memory exhibits significant defects as a result of aging. Although immune memory generated during youth functions well into old age, that generated later in life functions poorly. Importantly, age-related defects in the cognate helper function of CD4(+) T cells can potentially influence the development of both humoral and cell-mediated immune memory. These defects ultimately result in aged individuals who exhibit reduced responses to both infections and vaccinations.