Effects of Aging on the Lymphatic System and Immunity

Effects of Aging on the Lymphatic System and Immunity

Stem cells used in immunity originate in the liver and spleen during the first nine weeks of embryonic development. Later, the bone marrow becomes the main source of stem cells, which it continues to supply into adulthood. Lymphocyte precursors become immuno-competent in the thymus and bone marrow, later pop-ulating other lymphoid tissues. A newborn’s immune system relies mostly on antibodies and helper T lym-phocytes. As the body encounters harmful and harm-less microbes, the helper T cells “learn” and become stronger. When these encounters do not occur, the immune system is more likely to develop allergies. Normal immune development can be interfered with by overuse of antibiotics, which can kill of harmful as well as harmless bacteria.

Over time, the immune system can be impaired by the nervous system. Factors such as depression, emotional stress, and grief can all be harmful to its function. Diet even plays a part. For example, vitamin D is needed for CD8 cells to activate and become cytotoxic T cells. Deficiency of vitamin D is linked to multiple sclerosis and other autoimmune diseases.

The lymphatic system becomes less effective at fighting disease as we age, resulting in lowered immu-nity. T cells weaken, and fewer of them can respond to infections. As the thymus shrinks with age, there are lower circulating levels of thymic hormones. The number of helper T cells is reduced, B cells are less responsive, and antibody levels do not rise after expo-sure to antigens with the same speed they used to. Viral and bacterial infections are able to proliferate more. This is why vaccinations for diseases such as influenza and pneumococcal pneumonia are recommended for elderly patients. With decreased immunity, tumor cells are not eliminated as effectively, and cancer rates increase with age. In many older people, the immune system develops chronic low-grade inflammation because of increased production of inflammatory agents. Chronic inflammation may cause or promote many age-related diseases, including Alzheimer’s dis-ease and atherosclerosis.