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 ti ssue (MALT) type, Strains expressing the CagA protein (CagA(+) strains ) have been strongly associated with severe gastritis, duodenal ulcera tion, and gastric adenocarcinoma. The aim of this study was to determi ne the presence of H. pylori as well as incidence of CagA(+) strains i n gastric MALT-type lymphoma. Methods: Sera of 68 patients with gastri c MALT-type lymphoma (22 with low grade, 36 with high grade, and 10 wi th secondary high grade) were obtained, and the serological response t o CagA was studied by immunoblotting using a purified recombinant CagA protein, a CagA(+) strain, and the corresponding isogenic CagA(-) mut ant, Results: Of the patients with MALT-type lymphoma, 98.5% (67 of 68 patients) were H. pylori seropositive. In the only seronegative patie nt, the bacterium was detected histologically by Warthin-Starry staini ng. Of the seropositive patients, 95.5% had serum immunoglobulin G ant ibodies to CagA compared with 67% of an H. pylori-positive control gro up (33 of 49 patients; P = 0.000037) with chronic active gastritis. Co nclusions: These results indicate infection of almost all patients wit h MALT-type lymphoma by CagA(+) H. pylori strains. Strains expressing the CagA protein seem to play a crucial role in the pathogenesis of ga stric MALT-type lymphoma.