Nutrition: a major factor influencing immunity in the elderly.

This paper reviews recent findings on immune ageing. Ageing per se affects mainly cell-mediated immunity: decreases in mature T-cells (CD3+) partly compensated with increases in less mature T-cells (CD2+CD3-) are observed. In addition antigen pressure throughout life induces increases in memory T-cells (CD45R0+) and borderline decreases in CD8+ subsets. Those changes lead to lower proliferative ability. In contrast B-cell subsets and innate immunity are less affected with ageing. These changes are mainly related to health status and are less important in very healthy elderly. Such changes are more important in undernourished elderly, and in elderly who exhibit decreases in micronutrient status. They are even stronger in elderly patients with protein energy malnutrition (PEM). In seniors with PEM, decreased immune functions, for all aspects of immunity, i.e. T-cell, B-cell subsets and functions and innate immunity, are strongly related to protein nutritional status. Refeeding can boost immune response but at a lower speed in patients exhibiting inflammatory process. The disequilibrium between normal macrophage functions and decreased T-cell functions is partly responsible for long-lasting inflammatory process in stressed patients. Therefore acute phase responses are more detrimental on nutritional status and nutrient reserves in aged patients than in adults. Such disequilibrium, stress after stress, pushes the elderly to frailty state.