Natural mannose-binding lectin (MBL) down-regulates phagocytosis of Helicobacter pylori

Considering the role of lectin-carbohydrate interactions between Helicobacter pylori bacteria and the host cells we addressed the question on how mannose binding lectin - MBL, present in human plasma, may influence the phagocytosis of H. pylori by peripheral blood granulocytes. For phagocytosis assay the granulocytes separated from peripheral blood of healthy H. pylori-seronegative donors were used. Phagocytosis was estimated by fluorescence assay using FITC-labelled H. pylori cells. The MBL level in the serum samples as well as MBL-binding to H. pylori bacteria were estimated by ELISA. In this study all H. pylori isolates bound recombinant mannose binding lectin-MBL as shown by ELISA. The ingestion of H. pylori bacteria in the medium with human serum depleted in natural MBL (nMBL) was more intensive than in the medium with complete serum containing nMBL. Moreover, the ingestion of H. pylori bacteria in the medium with complete serum was increased by an addition of anti-rMBL IgG. The results indicate that interaction of bacterial and host lectins may regulate the phagocytosis of H. pylori bacteria and in this way influence an outcome of the infection caused by these microbes.