Early Thymus Involution--Manifestation of an Aging Program or a Program of Development?

Abstract

"I see no physical reason why it should not have been possible for life to construct ageless individuals", said Carl von Weizsacker in 1979 at the Conference on DNA. An obvious biological reason for senescence may be the action of a built-in aging program. Many gerontologists believe that early thymic involution is an argument in favor of the existence of such a program. On the other hand, this involution may be a result of the program of development rather than aging. According to the concepts of noninfectious immunology, the immune system of vertebrates is also designed for immune surveillance over initial tumor development and for tissue-specific regulation of cell proliferation both in ontogenesis and during physiological and reparative regeneration of organs and tissues. Natural anti-tissue autoantibodies are the main effectors of such regulation. Therefore, the number of inherited genes of the variable part of immunoglobulin (V-genes) is not less than the number of all proliferative-competent cell types (~100). For the same reason, the maximal rate of growth, which is usually observed in the prepubertal period, coincides with the maximal thymus index and the maximal number of immunoglobulin-secreting cells as well as the minimal force of mortality during ontogeny. Thus, the circa-pubertal beginning of thymic involution is probably caused by the programmed deceleration of the growth rate in ontogeny, and not by the early manifestation of an aging program. This approach allows us to understand the mechanism of the well-known antitumor effect of the regeneration process of the organ homologous to the tumor, and hence we can try to use it in practical oncology.