This reduced thymic output leads to the peripheral expansion of naïve and memory T cells to regenerate the T cell pool, which in turn leads to the accumulation of oligoclonally expanded, functionally impaired T cells (Akbar and Fletcher 2005 Messaoudi et al. This T cell immune decline is marked by a dramatic decline in the number of naïve T cells as a result of a thymic atrophy (Douek et al. This waning immunity in old age results from defects in numerous different leukocyte populations with the dysfunction being most pronounced in T cells. Indeed the mortality rate of older adults suffering urinary tract infections or tuberculosis is ten-fold higher than that of young adults (Yoshikawa 1997). ![]() 1984), sepsis (Chattopadhyay and Al-Zahawi 1983), urinary tract infections (Ackermann and Monroe 1996), infection with respiratory syncytial virus (Barker and Mullooly 1980) or influenza (Sprenger et al. The incidence and severity of infectious diseases, such as pneumonia (LaCroix et al. ![]() ![]() The immune system undergoes a dramatic restructuring with age, leading to a decline in immune responses and an increased vulnerability of old individuals.
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