CLL mAb with stereotypic IGHV1-69, IGHD3-16, and IGHJ3 rearrangements immunoprecipitate observable proteins. A total of 6% SDS-PAGE of immunoprecipitate from HEp-2 cell extracts treated with mAb having stereotypic IGHV1-69, IGHD3-16, and IGHJ3 rearrangements (CLL068, 2 different recombinant mAb preparations) or not (CLL412, 2 different recombinant mAb preparations, or IgG) is shown with protein size (kilodalton) markers. Another mAb having stereotypic IGHV1-69, IGHD3-16, and IGHJ3 rearrangements (CLL258) showed similar results (Figure S1). mAb heavy chain (IgH) and light chain (IgL) as well as 225- and 45-kDa protein bands are indicated.