Immune response to CagA protein is associated with improved platelet count after Helicobacter pylori eradication in patients with idiopathic thrombocytopenic purpura

BACKGROUND: Improvement in platelet counts has been reported after eradication of Helicobacter pylori in patients with idiopathic thrombocytopenic purpura (ITP). We examined the levels of serum markers of gastritis and anti-CagA (cytotoxin-associated gene A) IgG antibody in patients with ITP to investigate whether these factors are associated with the platelet response after H. pylori eradication therapy. MATERIALS AND METHODS: One hundred and sixteen consecutive patients with ITP were assessed for H. pylori infection by (13)C-urea breath test and serum H. pylori antibody test. Patients with H. pylori infection received eradication therapy. Before and after eradication therapy, we evaluated serum levels of gastrin, pepsinogen (PG)-I, and PG-II and the anti-CagA IgG antibody titer. RESULTS: H. pylori infection was found in 67 (58%) of the 116 patients with ITP. Fifty-two infected patients received eradication therapy, which was successful in 44 patients (85%). Twenty-seven patients (62%) showed an increased platelet count and were identified as responders. The duration of ITP was shorter in responders than in nonresponders (p = .017). There was no difference of the levels of gastrin and PGs between responders and nonresponders. Before eradication therapy, the serum anti-CagA antibody titer did not differ significantly between responders and nonresponders. However, reduction in the anti-CagA antibody titer after eradication therapy was significantly greater in responders than in nonresponders (p = .013). CONCLUSIONS: H. pylori eradication therapy improves the platelet count in H. pylori-positive patients with ITP of short duration. Immune response of hosts to CagA protein of H. pylori may play a role in the pathogenesis of ITP.