T cell senescence

The aging of the immune system, referred to as immunosenescence, is associa ted with a dramatic reduction in responsiveness as well as functional dysre gulation. This deterioration of immune function with advancing age contribu tes to the increased incidence among the elderly of morbidity and mortality from infectious disease, and possibly autoimmunity and cancer. In mammals, the defense for fighting infectious agents is composed of the innate and a daptive immune systems. Macrophages, granulocytes, and natural killer cells are the major components of the innate system whereas T and B lymphocytes comprise the adaptive system. Although both compartments are affected, adap tive immunity is most susceptible to the deleterious effects of aging. Inna te immunity functions immediately after birth and manifests little change t hroughout life. In contrast, adaptive immunity is immature at birth, peaks at puberty and progressively declines thereafter. Though marginal alteratio ns in B lymphocytes are apparent, the dramatic decline in humoral and cell- mediated responses is predominantly the consequence of senescent T cells. T he following review focuses on the aging effect on T cells as reflected in altered function, subset representation, development, lifespan and activati on. Age-associated alterations in antigen presenting cells are also discuss ed since these cells are required for T cell activation and may impact T ce ll function.