Mechanisms Involved in Age‐dependent Decline of Immune Responsiveness and Apparent Resistance against Tolerance Induction in C57BL/6 Mice

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Abstract
The plaque‐forming antibody response of C57BL/6 mice to rabbit gamma globulin (RGG) decreases as a function of age. RGG in tolerogenic form induces tolerance of young mice but sensitizes older animals. If antigen is administered together with lipopolysaccharide, the age‐dependent decline in immune responsiveness is not observed, nor are older animals sensitized by tolerogen. The age‐dependent decline in immune responsiveness is due to a less of T helper capacity; sensitization by tolerogen is attributable to a subpopulation of B cells which becomes sensitized by the tolerogen. Older animals, treated with tolerogen, show a degree of central tolerance of T cells and a relatively slight, age‐dependent diminution in colchicine‐ or cyclophosphamide‐sensitive precursors of suppressor cells.