CDR3 Sequences of MALT Lymphoma Show Homology with Those of Autoreactive B‐Cell Lines

We have examined the CDR3 sequence and adjacent regions of immunoglobulin genes from B‐cell lymphoma of mucosa‐associated lymphoid tissue (MALT). Twenty‐nine sequences (15 sequences from 13 low‐grade MALT lymphomas, marginal zone B‐cell lymphomas; 7 sequences from 6 highgrade MALT lymphomas; 7 sequences from 7 diffuse large cell lymphomas) were obtained after cloning of the polymerase chain reaction‐amplified segments. In the low‐grade MALT, high‐grade MALT and diffuse large cell lymphomas, the mean length of the CDR3 region was 47.6 ± 10.31 (range 21 to 60), 38.71 ± 10.37 (range 27 to 57) and 40.86 ± 3.34 (range 39 to 48) nucleotides, respectively. The length of the CDR3 region was significantly greater in the low‐grade MALT lymphoma group than in the other two groups. CDR3 sequences in lymphoma cell clones of 14 cases showed 60 to 81% homology with autoantibody‐associated lymphocyte clones including rheumatoid factor. The incidences of these autoantibody‐associated lymphocyte clones were higher in the high‐grade MALT (4/6) and diffuse large lymphomas (5/7) than in the low‐grade MALT lymphoma (5/13). Cases with more than 70% homology at the nucleotide level were found to have 71 to 82% homology with autoantibodies at the protein level in the low‐grade MALT lymphomas (2/13), and 67% homology in the high‐grade MALT lymphomas (2/7). These results indicate that MALT lymphomas may be derived from the malignant transformation of autoreactive B‐cells.