Altered enzyme function and premature sequestration of erythrocytes in aged individuals

Experimentation performed to determine the parameters of the life-span of the erythrocyte in hosts of various ages have determined that, in aged individuals, the rate of turnover of cells is considerably increased over that observed in young individuals. These observations are based on studies in humans, rats, mice, and rabbits in which either in situ 59Fe labelling or age-density gradient separation were used. The mechanisms for the recognition of the effete red cell in the aged host and the nature of the membrane alterations that bring about the premature sequestration are not fully understood. However, it has been consistently observed that the red cells of aged individuals have higher levels of IgG bound to their membranes than do young cells, with the most dense cells having the highest levels of immunoglobulin. Studies of most enzymes, particularly those involved in protection against oxidative damage have shown reduced activity as a function of both cell and donor age. Evidence of enzyme damage has been observed even in the youngest circulating red blood cells of old individuals. This fact leads us to hypothesize that the erythrocyte of the aged individual as it differentiates and is released from the bone marrow is less functional and partially damaged. The erythrocytes of both old and young individuals age in the circulation, accumulating subtle alterations that are recognized by the immune and/or reticuloendothelial systems and lead to sequestration. The cells of the elderly individual accumulate a greater degree of damage due to their initially reduced capacity to protect themselves from environmental stress. These alterations eventually bring them to their early sequestration.