ABSTRACT
Various immunological functions and responses are affected by the aging process. In humans, responsiveness to thymus-dependent antigens originally contacted in early life decreases with advancing age (1,2). T-cell functions, such as primary delayed skin reaction in response to antigens to which individuals have not been sensitized previously (e.g., dinitrochlorobenzene) and the proliferative capacity of T cells in response to phytohemagglutinin (PHA), also decline with age (3-8). The data of Girad et al. (9) regarding cell-mediated immunity in 880 hospitalized patients indicated a decrease in the absolute number of circulating T lymphocytes and also functional impairment of T cells.
