The immune system
The onset of aging of the immune system refers to the time of puberty, when atrophic processes occur in the thymus gland( thymus).It is with the thymus and thymus-dependent complex of the immune system that the weakening of immune functions during aging is primarily associated. The mass of the thymus is maximal in 5-15 years, by 20-30 years its decrease occurs, which is especially expressed in 50-90 years.
Thymus involution is accompanied by a decrease in the concentration of its hormones in the blood. The concentration of thymopoietin begins to decline at 30 years, after 60 years it is practically absent.
Aging of the immune system can be more accurately described as changes in the number, distribution and activity in populations of lymphocytes, in the specificity of AT and in cytokines. In this regard, age-related changes in the immune system - a process leading to the state of immune dysregulation. In addition to the age-related decline in the diversity of the T-lymphocyte spectrum, there is a change in the balance in the subsets of T cells, which reflects a decrease in the formation of T-lymphocytes in the thymus with age. For the elderly, a decrease in the function of T-lymphocytes is characteristic. The ratio of CD4 / CD8 T-lymphocytes increases with age.
Aging has a significant effect on the development of B-lymphocytes. Pre-B lymphocytes are the most numerous cell line in the red bone marrow, their number decreases with age by 60-90%.The defect underlying the decrease in the number of pre-B lymphocytes is due to a violation of the conversion of pro-B- to pre-B lymphocytes. Despite the reduction in the formation of B-lymphocytes in the bone marrow, the number of B-lymphocytes in the peripheral blood does not change with age, which is due to the lengthening of the life of B lymphocytes and their ability to self-renew.
Most foreign Ag stimulates CD5-B lymphocytes, which in response to stimulation synthesize AT.With aging, there is a decrease in the response of CD5-, but not CD5 + B-lymphocytes, to foreign Ag. The trace of these age processes is a series of regular changes. Concentrations of circulating natural AT, for example AT to blood groups of blood, begin to decline at an early age, and by the age of 80, their level is 50% or lower from that of young people( the main reason for the difficulty in determining blood types in the elderly).
The formation of AT in elderly people in virtually all vaccines( including against hepatitis, influenza and tetanus) is reduced compared to young people [Schwab R. et al., 1989].At the same time, the intensity of the immune response in the form of formation of AT to the majority of T-independent Ag( for example, pneumococcal polysaccharide) is maintained at the same level throughout life. Nevertheless, the duration of protective immunity after the introduction of pneumococcal vaccine in the elderly is less than in young people( Shapiro E.D. et al., 1991).For this reason, elderly people over 65 years of age should be revaccinated with pneumococcal vaccine every 5-8 years.
Although the immune response in the form of AT to all foreign Ag is decreased with age, Ig production and lymphocyte count does not change. Moreover, the concentration of IgG and IgA in the serum increases with age( IgM and IgD - decrease).The decrease in IgM content corresponds to a decrease in AT-to-Ar blood group and a relative deficiency in the response to mitogens from the T-lymphocyte side,
Age, years
Fig. Age-related cross-over in the function of the immune system
Age, years
Fig. Age-related cross-over in the function of the immune system
and an increase in IgG reflects the ability of the immune system to maintain the reactivity to Ar, which the body has encountered before.
In contrast to the decrease in production of the majority of ATs to foreign Ar, the level of AT synthesized by CD5 + B-lymphocytes increases with aging. These age-dependent changes in the Ig specificity, that is, the transition from the synthesis of AT to foreign arteries to the production of AT to autologous Ar, are shown in Fig. When comparing the AT content to salmonella and antinuclear antibodies at different periods of human life, it has been found that the AT titer to foreign Ag( salmonella) decreases with age, while the number of individuals with antinuclear AT increases with age( Rowley MJ et al., 1968).
Despite the increase in the formation of autoantibodies during aging, the incidence of autoimmune diseases does not increase with age. Autoimmune diseases often develop in the middle third of human life. The exception is pernicious anemia and autoimmune thyroiditis, which occur in the late period of life.
Due to involutional processes in the immune system, the risk of developing infectious, autoimmune and malignant diseases is increased in old age.