Analysis of sterile germ line switch transcripts in HCL expressing multiple sIg isotypes. Germline transcripts are transcribed from I exon promoters during initiation of isotype-switching events, and splicing generates Iα-Cα and Iγ-Cγ transcripts. Germline transcripts were sought in our HCL cases by using RT-PCR employing primers and assay conditions as reported.17 Both Iα-Cα and Iγ-Cγ transcripts of predicted size, as indicated, were identified and paralleled sIg expression in each case. Each RT-PCR product was excised and sequenced to verify the identity of transcripts. Minor bands in a few cases were shown by sequence analysis to be unrelated nonspecific amplification products. To exclude contamination from normal circulating lymphocytes, germ line transcripts were also assayed in cDNA generated from 3 healthy peripheral lymphocyte control preparations (labeled A, B, or C), and these were found to be negative even when 40 PCR cycles were used. Template cDNA levels were compared by reference VH (V) or β-actin (β) genes as shown.
