LOW-GRADE PULMONARY MUCOSA-ASSOCIATED LYMPHOID-TISSUE LYMPHOMA WITH OR WITHOUT INTRACLONAL VARIATION

We examined the immunoglobulin heavy chain variable (Ig V-H) region ge nes of 11 low-grade pulmonary mucosa-associated lymphoid tissue (MALT) lymphomas by a two-step polymerase chain reaction (PCR) and sequencin g analysis. We observed frequent somatic mutations with the positive s elective pressure of the rearranged Ig VH genes in all cases, indicati ve of postgerminal center cell origin. Eight cases demonstrated intrac lonal variations (hypermutation with intraclonal variation type), but the other cases showed only one major clone without intraclonal hetero geneity (hypermutation without intraclonal variation type). The former might reflect the reentry of marginal zone B cells into a germinal ce nter environment leading to further mutations. The latter might be no longer susceptible to hypermutation mechanisms and seemed to be stable . Four cases used Ig V-H genes (hv3019b9, VH26, and VH4.21), which are frequently found in a variety of autoantibodies, such as cold aggluti nins, rheumatoid factors, and anti-DNA antibodies.