Lymphocyte responses to phytohaemagglutinin: age-related effects.

Cell-mediated immunity is depressed in elderly individuals compared to young individuals, and lymphocytes from elderly individuals have been reported to have impaired lymphocyte responsiveness to stimulation by PHA after 4 days of culture. We have confirmed this observation. However, after 8 days of culture, the lymphocyte responses were greater in elderly normal individuals than in young normal individuals. Responses of lymphocytes from young individuals decreased with time from 4 to 8 days in culture, while there were increased responses with time when lymphocytes from elderly individuals were studied. When adherent cells from lymphocytes of young individuals were removed by passage through protein-coated Degalan-bead columns, the lymphocyte responses to PHA were significantly increased at 8 days. Passage of lymphocytes from elderly individuals through coated Degalan bead columns did not alter the lymphocyte responses. Removal of macrophages from the mononuclear cells obtained from young individuals did not result in increased lymphocyte responses to PHA after 8 days in culture. Removal of adherent cells appeared to have the same effect regardless of the efficiency of removing B cells. The adherent cells removed by the protein coated columns, therefore, appear to be nonphagocytic mononuclear cells which are not B lymphocytes.