Expression of AID mRNA, somatic hypermutation, and class switch recombination of the

IgH gene in germinal center non-Hodgkin lymphoma.cDNA pools were synthesized from total RNA of MCL (n = 3), FL (n = 3), DLBCL (n = 3), and B-CLL (n = 3). AID (nt 328-520) and β-actin cDNA (nt 391-660) were amplified by PCR and hybridized with radiolabeled internal oligonucleotides. Recombined V(D)J segments of the IgH transcripts were amplified using a set of degenerate primers and were subsequently sequenced. Point mutations of less than 3% in comparison with the published sequences were regarded as somatic hypermutation negative (−), point mutations of more than 3% but less than 6% were regarded as somatic hypermutation positive (+), and point mutations of more than 6% were regarded as strong positive for somatic hypermutation (++). Immunoglobulin heavy-chain expression was determined by standard immunohistochemistry, and the constant region of the IgH locus is indicated. n.d. denotes nondetectable IgH gene expression.