MALT-type lymphoma of the stomach is associated with Helicobacter pylori strains expressing the CagA protein

Background & Aims: Helicobacter pylori is considered to be involved in the pathogenesis of gastric lymphoma of mucosa-associated lymphoid tissue (MALT) type, Strains expressing the CagA protein (CagA(+) strains) have been strongly associated with severe gastritis, duodenal ulceration, and gastric adenocarcinoma. The aim of this study was to determine the presence of H. pylori as well as incidence of CagA(+) strains in gastric MALT-type lymphoma. Methods: Sera of 68 patients with gastric MALT-type lymphoma (22 with low grade, 36 with high grade, and 10 with secondary high grade) were obtained, and the serological response to CagA was studied by immunoblotting using a purified recombinant CagA protein, a CagA(+) strain, and the corresponding isogenic CagA(-) mutant, Results: Of the patients with MALT-type lymphoma, 98.5% (67 of 68 patients) were H. pylori seropositive. In the only seronegative patient, the bacterium was detected histologically by Warthin-Starry staining. Of the seropositive patients, 95.5% had serum immunoglobulin G antibodies to CagA compared with 67% of an H. pylori-positive control group (33 of 49 patients; P = 0.000037) with chronic active gastritis. Conclusions: These results indicate infection of almost all patients with MALT-type lymphoma by CagA(+) H. pylori strains. Strains expressing the CagA protein seem to play a crucial role in the pathogenesis of gastric MALT-type lymphoma.