The infection by Helicobacter pylori strains expressing CagA is highly prevalent in women with autoimmune thyroid disorders

H. pylori infection is putatively associated with extra-digestive disorders and may also play a role in the development of autoimmune thyroid diseases (ATD). It was recently found that monoclonal antibodies to an H. pylori st rain with cagA-positivity reacted with follicular cells of the thyroid glan d, and that an H. pylori organism possessing the cag pathogenicity island c arried a gene encoding for an endogenous peroxidase. The aims of this study was (1); To ascertain whether the infection by strains endowed with an inc reased inflammatory potential (those expressing CagA) could further enhance the risk of developing ATD (2); To verify the possible existence of an imm une cross-reactivity between autoantibodies to peroxidase and thyroglobulin and H. pylori antigens (3). To establish whether thyroid colloid antigens could cross-react with an anti-H. pylori serum. The study was partly design ed retrospectively. We examined 41 consecutive women with ATD, and, as a co ntrol, 33 consecutive age- and socio-economic class-matched women without a utoimmune thyroid disorders, living in the same area as patients, occurred at the same institution in the same period (six months). Both patients and controls were examined serologically for H. pylori infection and CagA statu s by Western blotting. Some serum samples were absorbed with H. pylori to d etermine whether the antibody levels decreased. Colloid proteins were resol ved electrophoretically and matched with a hyperimmune serum raised in rabb its against a CagA-positive H. pylori. Thirty-two patients (78.0%) tested s eropositive for H. pylori infection, vs. 16 controls (48.4%) (P = 0.008, OR = 3.78, RR = 1.61). The prevalence of anti-CagA antibodies was 71.8% in in fected patients, and 50% in infected controls (P = 0.161, n.s.). The overal l prevalence of infection by CagA-positive H. pylori was significantly high er in patients with ATD (23/41, or 56.0%) than that in controls (8/33, or 2 4.2%) (P = 0.006, OR = 3.99, RR = 2.31). The other tests gave negative or i nexplicable results. In conclusion: CagA-positive H. pylori infection incre ases the risk of ATD development.