Class switch recombination of the immunoglobulin heavy chain gene frequently occurs in B-cell lymphomas associated with rearrangement of the BCL2 gene.

B-cell lymphomas, mainly follicular lymphomas, carrying a t(14;18) chromosomal translocation associated with rearrangement of the BCL2 gene and the immunoglobulin heavy chain (IGH) gene, share many similarities with germinal center B cells in the secondary lymphoid follicle. In the germinal center, antigen-stimulated B cells proliferate and differentiate while undergoing isotype class switching of their immunoglobulin heavy chains. To examine whether BCL2-positive lymphoma cells show class switch recombination similar to that in the germinal center B cells, we studied the genomic configurations of the IGH gene loci in 38 patients with B-cell lymphomas. Sixteen (80%) out of 20 patients with BCL2-positive lymphomas showed class switch recombination on translocated and/or productive IGH gene loci. Lymphoma cells from 7 of the 16 patients expressed the gamma-heavy chain on their surfaces, indicating functional class switching to the gamma-constant gene on the productive allele. By contrast, 6 (33%) of the 18 patients lacking the BCL2 rearrangements exhibited class switch recombination. Statistical analysis revealed that the BCL2-positive lymphomas underwent switch recombination on either allele at a significantly higher frequency than the BCL2-negative lymphomas (P = 0.0099). This indicates that follicular lymphoma, not only morphologically but also functionally, recapitulates the germinal center. We propose that the up-regulated BCL2 expression itself is capable of playing an important role in immunoglobulin class switching.