山梨医科大学雑誌　第5巻1号　001-018(1990)

Effect of Aging on the Immune System

Yoshimura FUKAZAWA and Keiko KAGAYA

Abstract: Host defense mechanisms against microbial and viral infections as well as neoplastic cells constitute a close network, with phagocytes, natural killer (NK) cells, immunocytes including T and B cells, and cytokines released from and interacting with these cells.　 Although aging is accompanied by many changes in the immune system, it is unlikely that all immune cells and systems age at equal rates. Suffice to say, involution of the thymus plays one of major roles in immune senescence. Related to this event are the altered number and functions of T cell subpopulations involved in immunoregulation, a decrease in the immune response by both cell-mediated and humoral branches of the immune system, and an increase in autoimmune activity. The clinical implications of these changes are the elderly person's increased susceptibility to infections such as pneumococcal pneumonia, influenza and tuberculosis. Other changes include an increased susceptibility to heoplasms and perhaps acceleration of the aging process by increased autoimmune activity and immune complexes. The functions of macrophages, PMN, NK cells, and also the complement system are not seriously impaired with age. The evidence that lymphoid progenitors in bone marrow cells from young animals are able to differentiate into lymphoid cells in the aging anirnal, and that involution of thymus may be restored by manipulation of the endocrine system, suggest that there may be a potential for reconstitution of some immune defects in aged individuals by grafting or treatment with drugs to control various age-related diseases, including cancer.

Key words: Aging, B cells, T cells, Thymus




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