PCR analysis to detect IgH transcripts in L1236 cells as well as in H-RS cells of the patient’s affected bone marrow. Lane 1, L1236 cDNA; lane 2, L1309 cDNA; lane 3, section of the HD-affected bone marrow, cDNA; lane 4, no template; lane 5, 100-bp ladder. Using an oligonucleotide hybridizing to the CDRII of the V_H1 gene rearrangement in L1236 cells in combination with an oligonucleotide hybridizing to the second exon of all the 4 γ genes, a specific product was amplified from cDNA obtained from L1236 cells as well as from cDNA obtained from the patient’s bone marrow. No product was amplified from the cDNA obtained from L1309 cells, indicating the specificity of the product. Sequence analysis of the PCR product showed the sequence of the V_H1 gene rearrangement switched to Cγ4.