The many roles of apoptosis in immunity as modified by aging and nutritional status.

Apoptosis plays a vital role in the elimination of anti-self clones, down regulation of immune responses and the killing of virally infected and malignant cells. There is ample evidence that as we age the immune system not only becomes less potent, but dysregulated which includes apoptotic dependent functions. Reductions in the production of naive T and B-cells, reduced cytolytic killing capacity, accumulation of larger numbers of malignant cells, enhanced inflammatory responses, etc., in the aged suggest that apoptosis is dysregulated. Changes in nutritional status can also alter apoptosis. A short period of zinc deficiency (ZD) in young adult mice greatly accelerated apoptosis among pre-B and pre-T cells by 50% to 300% providing a mechanistic explanation for the lymphopenia and thymic atrophy long associated with this and other nutritional deficiencies. Since apoptosis has been shown to be altered by aging and nutritional status, it seemed important to determine how ZD affected these processes in the aged mouse. It was quickly discovered that the pre-B cells were reduced by 80% in the 28 month aged mouse making further studies problematic. In marked contrast to suboptimal zinc, caloric restriction (CR) which when initiated in younger mice delayed the onset of autoimmunity and immunosenescence. CR appeared to also slow the aging of mitochondria and, thereby, reduced the release of reactive oxygen species that damage cells. Thus, it is probable that CR also helped maintain the integrity of mitochondria and apoptotic processes as mice aged. Though CR is not a very practical nutritional model for humans, the outcome of these studies reinforce the potential value of anti-oxidants in our diets. In contrast to their normal nutritional role some nutrients especially small amounts of free metals can induce apoptosis. There is considerable zinc in neurons. As will be discussed, a number of investigators think that this zinc is released during Alzheimer's, Parkinsons's, or brain injury and accelerates apoptosis in surrounding tissues causing greater damage. Data are discussed that indicate nanomoles of free zinc is, indeed, a potent inducer of apoptosis in a variety of tissues. In sum, there is no doubt that nutritional status as well as individual nutrients can modulate apoptosis and that their impact on cell death may become greater in the aged.