RESUMO
Malnutrition is the primary cause of immunodeficiency worldwide and profoundly affects immune responses. Malnutrition diminishes immune function and therefore prevents the host from mounting an adequate protective response to infectious agents. In turn, infections alter nutrient status and can create a deficiency state. Thus, malnutrition and infection often act synergistically to increase morbidity and mortality. Almost all forms of immunity may be affected by PEM, but non-specific immune responses and cell-mediated immunity are more severely affected than humoral (antibody) responses. Altered immune functions due to the aging process mainly concern T-cell-mediated immune functions, such as diminished T-cell proliferation, antibody response after immunization with T-cell-dependent antigens, impaired delayed-type hypersensitivity response and IL-2 production, whereas anti-inflammatory cytokines are elevated. These findings indicate a yet unexplained shift from pro-inflammatory Th1 cell response to an anti-inflammatory Th2 response with aging. Aging and simultaneous nutritional deficiency exert a cumulative influence on the immune response. Maintaining optimal nutritional status is therefore crucial for aging in good health.