1. ¹The Second Department of Internal Medicine, Shinshu University School of Medicine, Matsumoto, Japan
2. ²Department of Endoscopy, Shinshu University School of Medicine, Matsumoto, Japan
3. ³Department of Laboratory Medicine, Shinshu University School of Medicine, Matsumoto, Japan
4. ⁴Department of Internal Medicine, Maruko General Hospital, 335-5 Maruko-machi, Chisagata-gun, Nagano-ken 386-0493, Japan

Correspondence: Dr S Hosaka, E-mail: hosaka@ns.maruyamakai.or.jp

Revised 18 August 2004; Accepted 18 October 2004; Published online 11 January 2005.

Abstract

Gastric low-grade mucosa-associated lymphoid tissue (low-grade MALT) lymphomas has been associated with Helicobacter pylori (H. pylori) infection. Although infiltrating T cells with specificity for H. pylori are known to stimulate the development of MALT lymphomas, the effect of H. pylori eradication on rearranged immunoglobulin heavy chain (IgH) genes of low-grade gastric MALT lymphomas is unclear. Gastric biopsies from five cases were investigated by cloning and sequence analysis of rearranged IgH genes before and after the treatment for H. pylori. In all cases, IgH genes were mutated from their germline counterpart. The frequency of intraclonal sequence heterogeneity before the eradication of H. pylori varied from 0.25 to 0.49%. Clones obtained from the tumours before the eradication of H. pylori in cases 1 and 2 showed a tendency to display a mutation pattern by positive antigen selection and their monoclonarity disappeared after the eradication. The frequency of intraclonal sequence heterogeneity of the clones obtained from cases 3, 4 and 5 (0.12% in case 3, 0.10% in 4 and 0.18% in 5) after the eradication of H. pylori was lower than that in tumours before the eradication (0.30% in case 3, 0.49% in 4 and not determined in 5). These findings suggest that low-grade gastric MALT lymphomas expand due to the persistent presence of H. pylori in vivo. The characteristic feature of tumour clones obtained from the tumours after the eradication of H. pylori is a very low intraclonal heterogeneity, which may potentially be independent of H. pylori.