Age-associated changes within CD4+ T cells.

As individuals age their ability to respond and clear pathogens declines, leading to a greater incidence and severity of infectious diseases. Additionally, the efficacy of vaccines is frequently decreased in elderly persons. Increased susceptibility to infections and reduced protection after vaccination reflect the impact of age-related changes on the immune system. The immune system undergoes a wide range of changes with increasing age. The aim of this review is to summarize cellular and molecular aspects of aging CD4(+) T cells. CD4(+) T cells play an essential role in mediating both humoral and cellular immune responses. Therefore, age-associated dysfunctions within CD4(+) T cells have a strong clinical impact. Improving our understanding of the aged CD4(+) T cells, in particular but also of the aged immune system in general, is crucial for developing effective prevention and treatment programs which will facilitate healthy aging and improve the quality of life of the elderly population.