Age-related effects on the number of human lymphocytes in culture initially responding to an antigenic stimulus.

Lymphocyte transformation responses to the antigen streptokinase-streptodornase were evaluated in a group of 14 healthy elderly subjects by enumeration of antigen-responsive cells, first-generation responding lymphocytes and progeny generated per responding cell. Peak lymphocyte transformation responses to the antigen were diminished in the elderly subjects when compared to a group of young adult subjects. Antigen-responsive cells were found by limiting-dilution analysis to be significantly decreased in the elderly subjects (geometric means of antigen-responsive cells per 10(5) mononuclear cells = 4.35 in the elderly versus 14.79 in the younger group, P less than 0.001). The number of cells recruited into the first-generation lymphocyte response per antigen-responsive cell were equivalent in the two groups. Also, the proliferation into progeny of each first-generation lymphocyte was of the same magnitude for the elderly and young subjects within the six to eight cell divisions required for this response. Therefore, in this system the diminished total lymphocyte transformation responses to the antigen streptokinase-streptodornase of cells from elderly humans can be accounted for by a reduction in the number of lymphocytes initially responsive to the antigen.