Guinea pigs were sensitized to either α, DNP-Lys7–10 or ε, DNP-Lys7–10 and boosted at 20 weeks with one or the other of these two compounds. This yielded four groups of boosted animals, two of which received homologous antigen and two the heterologous. The specificity of lymph-node lymphocytes and anti-DNP antibody produced was measured early (3 weeks) in the immune response and 2 weeks after booster injection. Antibody raised early in the immune response and after a homologous boost had greater affinity for the immunizing than for heterologous antigen. However, after heterologous boost, the antibody specificity changed so that it now had greater affinity for the boosting antigen than for the immunizing antigen. Although antibody specificity changed after heterologous boost, the specificity of the lymphnode lymphocytes from the same animals remained unchanged, i.e., responded maximally to the immunizing antigen. These results suggest that the antigen-sensitive thymidine-incorporating cell and the antigen-sensitive antibody-forming cell may have different triggering mechanisms.

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