Molecular Mechanism of Aging
Immune System Compromise
Immune System is our defense system against infectious diseases. Not only does it protect us against viruses and bacteria, it also helps to identify and remove cancer cells and toxins. A multiplicity of cells, substances, and organs make up the immune system. The thymus, spleen, tonsils, bone marrow, and lymphatic system, for example, produce, store, and transport a host of cells and substances—B-lymphocytes and T-lymphocytes, antibodies, interleukins, and interferon, to name a few. Some cells form immune system have special interest to gerontologists. These include the class of white blood cells known as lymphocytes (B-cells and T-cells), which fight invading bacteria and other foreign cells. B-cells mature in the bone marrow, and one of their functions is to secrete antibodies in response to infectious agents or antigens. T-cells develop in the thymus, they are divided into cytotoxic T-cells and helper T-cells. Cytotoxic T-cells attack infected or damaged cells directly. Helper T-cells produce powerful chemicals, called lymphokines, that mobilize (called chemotaxis) other immune system substances and cells to the site of bacteria infection. They are an integral part of inflammatory reactions. One of the lymphokines called interleukins function as messengers to relay signals that regulate the immune responses. There are more than 20 interleukins identified so far. Interleukin-6 is speculated to interfere in some way with the immune response. Interleukin-2 stimulates T-cell proliferation.
Immune system compromise may result from a hereditary condition (such as inheriting genes for lupus or rheumatoid arthritis), from a disease process such as AIDS, or simply from normal aging. Scientists have long known that immune system’s defense efficiency decline with age. The thymus begins to shrink in adolescence. T-cells and to a lesser degree B-cells, both decline in number and function. The proportion of T-cells that proliferate and function declines as we age. In elderly adults lymphocytes mobilized in response to an infection are likely to be less responsive and less effective than those found in younger adults. In aged people compared to younger ones, fewer antibodies are produced, they are less vigorous and the duration of their response is shorter. So, the immune system of an older adults — including lymphocytes and other types of cells — typically reacts more slowly and weakly. Studies have also shown that in older people, T-cells destroyed by stresses such as irradiation or chemotherapy take longer to renew than they do in younger people. Different interleukins was found at different levels as people age. Interleukin-6 level rise with age while interleukin-2 tend to fall with age. Autoimmunization tend to increase when antibodies react against normal tissue cells from our own body by mistakenly identifying ones own tissues as foreign. Susceptibility to auto-immune diseases like fibromyalgia, lupus, scleroderma and arthritis increases with age. These autoantibodies contribute to causing atherosclerosis, rheumatoid arthritis and other pathological conditions. All these decline in immune system function result in increased susceptibility to disease & to abnormalities that result form autoimmune responses.
Some of the underlying mechanisms of immune system weakening may suggest this compromise is a programmed event. It was found that inducing the thymus to reconstitute itself can bring about improved immunity among the elderly. Changes in hormones and hormone-like substances may contribute to immune system weakening with age. The production of important hormones that impact on immune system functioning like melatonin, DHEA and HGH decreases with age. In older adults, important immune cells may be inhibited from doing their jobs by an increase in certain prostaglandins that tend to regulate important body processes such as body temperature and metabolism. Tissue glycation can contribute to immune system disfunction, (and tissue glycation is correlated with oxidative damage and inflammation).
Escaping from infectious disease is the most common reason of longevity. This requires a maintenance of immune system function when we age.
