Survival and ultrastructural changes of Helicobacter pylori after phagocytosis by human polymorphonuclear leukocytes and monocytes

Abstract

Few studies have been carried out on the phagocytosis and killing of Helicobacter pylori by both polymorphonuclear leukocytes (PMNs) and monocytes. In this study, H. pylori was incubated for up to 60 min either alone or with phagocytes in the presence or absence of human serum. Both non-immune serum and immune serum were used. Reduction in the number of H. pylori, which corresponds to the killing of H. pylori, was analysed by a colony count and ultrastructural changes were studied by electron microscopy. No reduction in the number of H. pylori was found when the bacteria were incubated alone or with phagocytes in the absence of serum. It is remarkable that unopsonized H. pylori was phagocytosed. When immune serum was added to the suspensions of bacteria and phagocytes, the killing rate of H. pylori was found to depend on the ratio of H. pylori to phagocytes. Thus an excess of monocytes reduced the number of H. pylori, whereas an excess of PMNs resulted in complete killing of H. pylori. On incubation with PMNs and serum, ultrastructural changes were observed in the majority of the bacteria whether they were phagocytosed or not. Controls without serum did not show any changes in the morphology of H. pylori, indicating that components in the serum play an important role in the phagocytosis and killing of H. pylori. In contrast, several of the phagocytosed bacteria were found to be unaffected after incubation with monocytes and serum. Such preparations often contained large aggregates of platelets surrounding unaffected H. pylori. In the gastric mucosa, H. pylori is often found in excess as compared to the phagocytes. If these results can be compared to the situation in vivo, the phagocytes seem to be ineffective in the killing of H. pylori, and other immune mechanisms may therefore be of importance for the elimination of H. pylori from the gastric epithelium. The possible intracellular survival of H. pylori should be taken into account when treatment regimes for H. pylori infections are chosen.