Human immune response towards recombinant Helicobacter pylori urease and cellular fractions

Abstract

Vaccination against Helicobacter pylori is of particular clinical interest. Recombinant urease, the major protein in H. pylori, has been used for mucosal vaccination trials in different animal models, but was found to be ineffective in humans. The current study therefore investigated the human immune response towards recombinant H. pylori urease A and B (rUreA/B) expressed in E. coli compared to different cellular fractions of H. pylori (cytosol, total, inner and outer membrane). Monocyte-derived dendritic cells (Mo-DC) were generated from monocytes isolated by magnetic antigen cell separation (MACS) from healthy volunteers and cultured in the presence of hrIL-4 and hrGM-CSF. Mo-DC were stimulated for 48 h with the recombinant proteins (1 μg/ml) or cellular fractions (1–10 μg/ml) and cytokine release was determined in the culture supernatant by ELISA. rUreA and rUreB were effective in inducing IL-12 secretion (6–10 fold) and, to a much lesser extent (2 fold), IL-10 secretion from Mo-DC. Total and outer membrane preparations from H. pylori stimulated IL-12 secretion significantly, and were even more potent than intact bacteria. Mo-DCs pulsed with rUreA activated allogenic CD56 + NK-cells, as determined by TNF-α and IFN-γ secretion, but not allogenic CD4 +/CD45RA + naïve T-cells. In contrast, Mo-DCs pulsed with H. pylori total membrane or outer membrane preparations activated allogenic naive T-cells in co-culture systems, as determined by increased TNF-α secretion. It appears that outer membrane preparations of H. pylori, but not recombinant urease are more effective in inducing a Th1 polarized response in humans in vitro.