It is a matter definitively acquired that the immune response (the most efficient defense mechanism of our body) undergoes a gradual reduction with age. The thymus is present at birth, both in humans and in animals: it’s located in the chest behind the breastbone. This organ, after puberty, shows a rapid involution and in adult subject is reduced to a small mass of tissue atrophic. Atrophy of the thymus results in a progressive loss of the efficiency of cell-mediated immunity.
The thymus produces T-lymphocytes (T = thymus) and, by stimulating factors (the thymopoietin and lymphokines), their differentiation into active cells, which neutralize foreign substances (the so-called antigens). In addition to the thymus have a regressive processes also other organs forming part of the immune system, such as bone marrow (which reduces the number of cells, replaced by adipose tissue), spleen and lymphonodes (in which the number and cellularity germinal centres is reduces).
The increased susceptibility of the elderly to infectious processes and their complications is attributed to the reduced efficiency of the cell-mediated immunity, at least in part.
Other aspects indicative of a reduced efficiency of the immune system are changes in blood concentrations of immunoglobulins (proteins that neutralize no-self components to the body). Characteristic, in fact, is the increase of self-nature immunoglobulin antibody ( directed towards the body’s own components), both organ-specific (anti-endothelium, anti-gastric cells, anti-smooth muscle, anti-neuronal cells , etc..) both not organ-specific (anti-DNA, anti-mitochondria, etc..).
In other words, the body is no longer able to recognize as some of his own constituents, or because the latter undergo changes or because the recognition mechanisms are altered. As a result we have an increase in the so-called auto-immune diseases (such as pernicious anemia, rheumatoid arthritis, etc..) or aggravation of other diseases common in old age, dependent on other primary cause (such as stroke, ischemic heart disease, vascular dementia, etc..).
With age the activity of other cells involved in immune mechanisms decreases, such as macrophages and neutrophils, and especially cytotoxic cells K (Killer) and NK (Natural Killer). The increased incidence of certain cancers in the elderly is linked with the loss of efficiency of these systems.
Recent research indicates that in healthy elderly deficiency of the immune system is relatively less pronounced, suggesting that the observed alterations may be the result of concomitant diseases, rather than the cause,
Other research on centenarians show that defense systems, in these individuals of exceptional biological resistance, maintain a high degree of efficiency, so it can be considered a genetic marker of longevity. The immunocompetent cells, in fact, retain adequate replicative capacity and response to antigenic stimulus.
Starting from the immunological aging hypothesis, an Italian reseacher, C. Franceschi, suggests that the potential of our immune system, genetically determined, are progressively depleted throughout life in relation to antigenic aggression, resulting from repeated contact with foreign substances that invade the body, particularly viruses and bacteria.
The improvement of hygienic conditions, which occurred in civilized countries, may have reduced significantly the antigenic aggression, preserving as long as the immune system and preventing a rapid depletion. This factor could justify, together with others, the significant increase in life expectancy.