Mainly unmutated V-H genes rearranged in B cells forming germinal centers in a cutaneous pleomorphic T-cell lymphoma

B cells in skin lesions of a pleomorphic cutaneous T-cell lymphoma with rea ctive germinal center hyperplasia were analyzed for their immunoglobulin V( H)DJ(H) gene rearrangements by micromanipulation and single cell polymerase chain reaction (PCR) analysis. In B lymphocytes located in germinal center -like structures, we found in 11/16 different V(H)DJ(H) rearrangements comp letely unmutated V-H genes, suggesting that those cells did not undergo ant igen-driven selection. Two V-H genes showed more than 98% germ-line identit y. In only three cells V-H segments were somatically mutated to a higher ex tent, but two of these rearrangements were non-productive. These results di ffer markedly from what we have previously detected in B cells present in m ycosis fungoides, another entity of cutaneous T-cell lymphomas where the Ig gene repertoire resembles the situation in peripheral blood with a signifi cantly higher proportion of mutated V-H genes. when investigating the large atypical B cells strongly expressing CD30 which were detected within the T -cell zone outside the germinal centers, we found again, in most cases, tha t the rearranged V-H genes were completely unmutated. The B cells were of p olyclonal origin. Due to this comparable Ig gene repertoire and mutational pattern, we suggest that these cells descend from the germinal center centr oblasts which migrated into the T-cell zone and obviously became stimulated to express the CD30 marker. The micromanipulation technique and molecular analysis on the single cell level may provide an important input into our u nderstanding of the mechanisms of immune regulation in cutaneous lymphomas.