BALB/c mice recognize B:9-23 peptide and develop an IgG1 anti-peptide response that is dose-dependent. Solid lines represent anti–B:9-23 antibodies in mice receiving repeated injections of B:9-23 at 100 μg/dose, whereas dashed lines represent mice receiving B:9-23 at 10 μg/dose. Serum was diluted at 1:500 for assay.