Impact of age-related immune dysfunction on risk of infections.

The elderly have clearly been found to have both increased risk and severity of infections. Immunosenescence, the state of dysregulated immune function with aging, is felt to be a significant contributor to this increased risk. Extensive studies on inbred laboratory animals and in very healthy elderly humans have identified changes in immunity and have identified primarily phenotypic and functional changes in the T cell component of adaptive immunity. However, no compelling scientific evidence has shown that these changes have direct relevance to the common infections seen in the aged population. This perspective will attempt to shed light on this dilemma. First, it will review clinically relevant infections in the elderly, focusing on influenza and influenza vaccination and how chronic illness contributes to increased risk and severity of infection/failed vaccine response. Next, key changes in immunity will be reviewed, keeping perspective of the impact of confounding variables such as nutrition. If the goal is to prevent serious infections in the elderly, it appears that the field of geriatric immunology/infectious disease is faced with the tremendous challenge of studying a very diverse population of chronically ill individuals in addition to the study of the very healthy elderly. Grouping individuals by disease severity or by level of impairment of specific components of immunity may assist in advancing our ability to improve host defense in an at risk population.