The factors that incite immune thrombocytopenic purpura (ITP) remain uncertain, though the association of ITP with hepatitis C, cytomegalovirus, and common childhood viruses suggests that infectious agents may contribute. In this issue of Blood, Michel and colleagues (page 890) report their experience investigating the association of Helicobacter pylori (H pylori) with ITP. Of 74 patients, 16 (21.6%) aged 10 years and older (mean age of 41 years) with chronic ITP and a platelet count less than 60 × 109/L were infected with H pylori, an incidence not significantly greater than expected for individuals of this age range in developed countries. Although H pylori was eradicated in 14 of 15 treated patients, transient improvement in the platelet count occurred in only 1.
These results contrast with other reports in which a higher incidence of H pylori infection was noted in patients with ITP (Table 5 of Michel et al). Gasbarrini et al documented H pylori infection in 11 of 18 patients; 8 of the 11 patients in whom H pylori was eradicated experienced significant platelet increments.1 Emilia et al observed H pylori in 13 of 30 patients with chronic ITP; increased platelet counts occurred in 6 of 12 patients following H pylori eradication.2 However, consistent with the findings of Michel et al, others have reported neither an increased incidence of H pylori in patients with ITP nor improvement in platelet counts after eradication. The reason for these inconsistent outcomes is uncertain but may reflect the results of studying diverse patient populations, failing to control for administration of concomitant therapies, or variable effects of genetically diverse H pylori strains in remote geographic regions.
How might H pylori infection contribute to the development of thrombocytopenia? H pylori expresses Lewis (Le) antigens in a strain-specific manner; Le antigens adsorb to platelets and might serve as targets for anti-Le antibodies in patients with an appropriate genetic background.3 In addition, both H pylori infection and ITP are associated with a T helper 1 (Th1)–type immune response characterized by increased levels of interferon γ and interleukin-2; hence, H pylori–induced alterations in cytokine profiles might promote development of immune thrombocytopenia. Some strains of H pylori bind von Willebrand factor (VWF) and induce glycoprotein Ib (GPIb)– and FcγRIIa-dependent platelet aggregation in the presence of H pylori antibodies.4 This interaction might contribute to the association of H pylori with cardiovascular disease and promote platelet consumption. Finally, direct antigen mimicry between H pylori and platelet glycoproteins must be considered.
Should patients with ITP be routinely screened for H pylori? At this point, probably not. However, since dramatic responses in patients with severe refractory ITP following H pylori eradication have been reported, screening of such individuals seems reasonable, as few nontoxic therapeutic approaches are available for these patients.
A multi-institutional study addressing the incidence of H pylori and the effect of its eradication on the course of chronic ITP is currently under development through the 17-center National Heart, Lung, and Blood Institute–funded Transfusion Medicine and Hemostasis (TMH) network (http://www.tmhnetwork.org). One hopes this prospective, randomized, double-blinded and placebo-controlled trial will provide a definitive answer concerning the role of Helicobacter pylori in ITP.