Immunity, stem cells, and aging

Aging is the age-dependent biochemical change in tissues and the deterioration in the performance of various biological functions, including a significant decline in immune function, that leads to an increased susceptibility to diseases and mortality. A decreased number of stem cells and a reduction in their regenerative capability are linked with the process of aging. The age-associated accumulation of cell-intrinsic factors such as DNA damage response, enhanced reactive oxygen species production, epigenetic changes, telomere attrition, and polarity changes induces stem cell aging; these processes indirectly diminish the immune cell function. Unsurprisingly, the B and T cell progenitor population significantly declines with age in lymphoid organs such as bone marrow and thymus. This may be directly related to the reduced stem cell function with aging. Various signaling pathways are reported to regulate the aging process associated with stem cells and dysregulated Arf/p53 activity, which influences the lifespan and causes significant decreases in stem cell function and regenerative capacity. Similarly, over the aging process, stem cells are also affected by several intrinsic changes and are responsive to extrinsic pathways such as transforming growth factor-β, WNT, and Notch, which decreases their differentiation, self-renewal, and homing and plasticity potentials. Therefore, immune boosters, the prevention of stem cell aging, and the modulation of stem cell aging-associated signaling pathways might be useful in preventing the aging process.