t of telomerase, DNA may replicate many more times and in turn, we may be able to live longer. Yet instead of slowing or stopping the process of aging, this possibility may only prolong it, since it has already been accepted that damaged, not a shortage of, DNA plays a large role in aging. The Bodys Weakened Immune System During aging, the efficiency of the immune system declines. Normally, novel antigens, foreign molecules found on the surface of viruses and bacteria, activate the production of antibodies secreted by white blood cells, or lymphocytes, called B-cells. The antigens act to neutralize the virus or bacteria, rendering it harmless. If the novel antigens are missed by the antibodies, a Aback-up@ process comes into play. Macrophage cells safeguard the body and envelope foreign antigens that they later expose to T-cells for destruction. The pieces of virus that the macrophages pick up trigger the appropriate T-cell, which in turn replicates, producing more copies of itself. These T-cells, called memory T-cells, can recognize and destroy cells infected with the virus (Ricklefs and Finch, 1995, 35). These two methods of protecting the body from invasion make up the primary immune response, and this is the component of the immune system that decreases in efficiency as we age. The secondary response is the body=s resistance against pathogens it has already met. The reason for the decline in the immune system=s efficiency is that over time, we come in contact with more viral and bacterial infections so that more of our T-cells have been stimulated, converted to memory T-cells, and therefore, used. That is, they cannot be used to fight off any new viruses or bacteria that invade the body. It is possible that the total number of T-cells is set early in life. If this is so, then as we grow older, having already fought off a number of infections, we have a smaller amount of Aunemployed@ T-cells available to fight of infections that come...
