Helicobacter pylori-associated chronic idiopathic thrombocytopenic purpura and low molecular weight H. pylori proteins.

We examined the association between Helicobacter pylori infection and chronic idiopathic thrombocytopenic purpura (cITP) to clarify the development of H. pylori-associated cITP. cITP patients were classified into 3 different groups: Hp-negative (HP-N); Hp-positive, completely or partially responsive to treatment (CR); and Hp-positive and unresponsive to treatment (NR). Reactivity of antibodies to H. pylori before and after eradication was examined by immunoblotting. We used immunoblotting with immunoprecipitation to establish whether platelets form complexes with H. pylori proteins and if these complexes react with patients' sera. CR group showed large (>50 kDa) and low molecular weight protein bands, especially of 36, 27 and 17-kDa. These low molecular weight bands were detected significantly more in the CR group compared to other groups. When healthy human platelets were incubated with H. pylori lysate, they aggregated with the lysate, indicating that complexes were formed between the platelets and the lysate. The complexes immunoprecipitated with anti-human thrombocyte antibodies, and showed a 17 kDa band in the CR, but not in other groups. At least 3 low molecular weight proteins of H. pylori were involved in H. pylori-associated cITP. Immunocomplexes consisting of platelets, low molecular weight proteins of H. pylori and anti-H. pylori antibodies may represent an extra mechanism in development of H. pylori- associated cITP.