IgG1 antibodies to B:9-23 are detectable within 3 weeks of weekly B:9-23 immunization (100 μg/dose) and peak 2–3 weeks prior to anaphylaxis, in NOD mice. Anaphylaxis occurred at 12 weeks of age in this experiment. Serum obtained from mice is diluted 1:30,000 prior to measurement (lower limit of detection is 1:106 dilution). Various symbols represent the anti–B:9-23 antibody level in individual mice followed over multiple injections. Arrows represent a subcutaneous injection of B:9-23 peptide.