Ig gene fingerprinting analysis of IgM-expressing B cells from 13 patients with HCV-associated immunocytoma. The μV_H region transcripts were PCR amplified using a degenerate FW1 primer and a primer from the C_H1 exon of the Cμ gene (scheme). To obtain better size fractionation and easier visualization of these fragments, radioactively labeled complementary copies of the CDR3/FW4 regions were synthesized by primer extension of a consensus ³²P-labeled FW3 oligonucleotide. Autoradiograms obtained after the size separation of these fragments on sequencing polyacrylamide gel electrophoresis gels are shown in the lower part of the figure. Monoclonal B-cell populations contain a single band in the fingerprint (samples LC3-PB, SS-PB, HAZ-PB, MS-PB1, and SEG-PB1), representing the unique CDR3 length of their V_HDJ_H rearrangement. Polyclonal B-cell populations show a ladder of bands, consistent with the different CDR3 lengths of their V_HDJ_H rearrangements. Entirely polyclonal B-cell populations show a Gaussian distribution of the bands in the fingerprint (samples LC8-PB, LC9-PB). A band of stronger intensity, as seen in cases LC2-PB, LC6-PB, LC7-PB, MS-BM2, SEG-BM2, LC4-BM2, and LC4-PB2, indicates a monoclonal B-cell expansion within a polyclonal B-cell population. The source of the analyzed sample is indicated after each case. Samples in cases MS, SEG, and LC4 were collected at two different time points separated by more than one year (indicated as 1 and 2).