Neuroendocrine-immune interactions: a theoretical approach to aging

Among the systemic theories of aging, both a 'nervous-neuroendocrine' and an 'immune' hypothesis have been proposed. The discovery of the complex interactions working among the neuroendocrine and the immune systems suggests the revision of the systemic theories of aging, particularly in the light of the recent evidence that some age-associated alterations in the neuroendocrine and in the immune systems are mutually interdependent even at very old age, as revealed by the fact that experimental manipulation of one of the two systems modifies and sometimes restores the function of the other one. These findings clearly demonstrate that at least some of the age-related alterations of the nervous, neuroendocrine and immune networks are not per se intrinsic and irreversible and that the definition of the temporal priority in the age-related deterioration is rather is rather difficult to be assigned to one or other homeostatic apparatuses. As an alternative to pure, either 'neuroendocrine' or 'immune', theories of aging, it has been hypothesized that, due to the strict interactions existing among the nervous, neuroendocrine and immune systems during the whole life of the organism, it is the disruption of such interactions in old age which is responsible for most of the age-associated dysfunctions (Fabris, 1986). This theoretical approach is discussed in the light of a stochastic or single-cause oriented hypothesis of aging.