Clonal proliferation of B lymphocytes in the germinal centers of human reactive lymph nodes: possibility of overdiagnosis of B cell clonal proliferation.

Clonal expansion of the germinal center B cells of human reactive lymph nodes was analyzed. By micromanipulation, 28 germinal centers were microdissected from three nonneoplastic lymph nodes that had been fixed with formalin. Immunoglobulin heavy chain variable (V) region gene rearrangement was examined by seminested polymerase chain reaction (PCR) using two sets of primers (FR2-J and FR3A-J). An oligoclonal development (one to five clones) was found in each germinal center. Depending on the primer used, four or five (16%) of the germinal centers showed a single rearrangement band. The average number of B-cell clones in each germinal center was approximately 2.5. Next, the authors analyzed 50 endoscopic biopsy specimens from 6 patients with non-mucosa-associated lymphoid tissue (MALT) type gastric lymphoma, 25 patients with chronic gastritis, and 19 patients with nonspecific colitis. In addition to the samples from the 6 patients with malignant lymphoma, 8 of 44 biopsy samples (18.2%) from patients diagnosed as having chronic gastritis or nonspecific colitis showed one or two amplified bands. These results indicate that PCR analysis of immunoglobulin heavy chain V region gene rearrangement in small biopsy specimens could be misleading, causing overdiagnosis of reactive lymphoid tissue as B-cell clonal proliferation.