Phytohemagglutinin responsiveness of peripheral blood lymphocytes declines in aged humans. Older humans exhibit a rise in the incidence of autoantibodies. The incidence of autoantibodies becomes significantly greater among older subjects over 80 years of age and is most significant in humans with low lymphocyte phytohemagglutinin responses. Serum levels of IgG and IgA were increased in subjects surviving beyond the 7th decade. Correlations could not be detected between serum immunoglobulin levels, titers of individual autoantibodies and the lymphocyte response to phytohemagglutinin. These observations suggest that hyperglobulinemia, impaired lymphocyte phytohemagglutinin responsiveness, and increased frequency of autoantibodies are characteristic of surviving older humans and represent associated events in the natural history of human life.

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