Normal functions of the immune system include defense against infections and detection and destruction of malignant or autoreactive cells. As the immune system ages and these capabilities decline, there is increased susceptibility to infections and cancer and an increased incidence of autoimmune disorders. The study of age-related changes in immune function is a relatively new area of investigation, which is limited by incomplete understanding of the complexities of immune mechanisms in general . At present, most research is focused on defining normal changes in immune function at the basic science level, and much of the available data are from animal studies. In addition, there are no clinical interventions that have been definitively shown to counter immunologic aging.
This topic will review the changes observed in different components of the immune system with aging. The theoretical implications of these changes on health maintenance and vaccination of older adults are also discussed. Normal aging of other systems, nutrition in older adults, infections in older adults, and geriatric health maintenance (including current recommendations for vaccination) are reviewed elsewhere. (See "Normal aging" and "Geriatric nutrition: Nutritional issues in older adults" and "Evaluation of infection in the older adult" and "Geriatric health maintenance".)
Immunosenescence refers to the changes that occur in the immune system with increasing age. The clinical consequences of immunosenescence include an increased risk of infections, malignancy, and autoimmune disorders.
Infections — Pneumonia and influenza are among the top ten causes of death in individuals aged 65 and older . Nosocomial infections are also significantly increased in elderly individuals. This could be the result of decreased immunologic function, in addition to a decreased efficacy of vaccines in the elderly. However, there are several other factors that are likely to contribute to increased infections in elderly individuals: malnutrition, comorbid conditions (eg, diabetes, chronic obstructive pulmonary disease), diminished mucosal barriers, decreased cough reflex, and mechanical changes to the urinary tract system, among others .
The clinical presentation of infections in older patients may be different from that in younger patients. Older adults with severe infections tend to have fewer symptoms, and fever is absent or blunted in 20 to 30 percent. This suggests a decreased ability to mount inflammatory cytokine responses in the face of infection. Signs of infection in the elderly can be nonspecific and include falls, delirium, anorexia, or generalized weakness . (See "Evaluation of infection in the older adult".)