Decreased Helicobacter pylori-specific gastric secretory IgA antibodies in infected patients.

Despite an increase in local Helicobacter pylori-specific IgA production in H. pylori infection, the bacterium is able to persist over decades. We focused on IgA and secretory IgA (sIgA) in gastric juice because sIgA is more relevant in local protection and more resistant to degradation than nonsecretory IgA. H. pylori-specific IgA and sIgA in gastric juice, saliva, and serum of H. pylori-infected patients were compared. Samples from 28 H. pylori-positive and 16 negative patients were tested by means of immunoblotting for the presence of H. pylori-specific IgA and sIgA. In gastric juice the majority of H. pylori-specific IgA was not of the secretory type, whereas total IgA was bound mainly to the secretory component as shown by immunoblot and slot blot. In contrast H. pylori-specific IgA antibodies in saliva of infected patients were of the secretory type as shown by immunoblot. The presence of specific, nonsecretory IgA may be a consequence of the damaged mucosal epithelium at the site of H. pylori infection allowing IgA to bypass the secretory transport system. Considering the resistance of secretory IgA against hydrolysis and proteolysis, these data suggest that the predominantly nonsecretory IgA specific for H. pylori may lead to a decreased protection against H. pylori.