Anti-Id titers in vaccinated and control mice measured by ELISA. Sera were diluted 1:20 in BSA 2% in PBS, preabsorbed on polyclonal human Ig, and then serially diluted on plates with 1 of 4 Id proteins (7D11-idiotope–positive: 2A12, 1H1, and 2C12; 7D11-idiotope–negative: 1B11) or with 1 of 3 class-matched irrelevant human Igs (same V_H family as the Id). The irrelevant Igs were tested separately but are shown as a single bar since they were all equally negative. Reactivity of the target proteins with treatment MoAb 7D11 is shown.