Transcription profiling analysis of the mechanisms of vaccine‐induced protection against H. pylori

Abstract

Development of a vaccine against H. pylori is regarded as desirable alternative to the current antibiotic therapy regimens. Mice immunized with an attenuated recombinant Salmonella typhimurium expressing H. pylori urease subunits A&B have dramatically reduced bacterial loads after a single dose. The mechanism(s) of protection against this largely extra-cellular pathogen are not fully understood. The aim of this study was to identify genes that were regulated specifically in response to immunization, in order to gain a broader picture of the immune response in the immunized gastric epithelium. Gene expression in RNA isolated from the gastric mucosa of immunized and infected Balb/c mice was compared with that in infected only mice at 1, 3, and 14 days after challenge with a mouse-adapted strain of H. pylori. We show that infection with H. pylori causes an immediate reaction in vivo, which was clearly divided into acute and chronic phases, and further that the transcriptional response in the H. pylori infected and immunized gastric mucosa is unique. Analysis of gene expression patterns at day 14 post-infection suggested not only the beginning of a lymphocytic infiltrate, but of an integrated epithelial response characterized by increased expression of genes controlling cell cycle and turnover. This observation was confirmed in independent experiments. The global approach has brought new insights to the effect of immunization on the gastric epithelium and has led us to propose a new multi-factorial model for the mechanisms underlying vaccine-induced protection.

Local recall responses in the stomach involving reduced regulation and expanded help mediate vaccine‐induced protection against Helicobacter pylori in mice

“…2B); a similar trend was observed in the antrum region although this did not reach statistical significance. Carriervaccinated mice had similar gastritis scores to that of vaccinated mice, in keeping with our previous observations [25].The increased gastritis in vaccinated mice is known to result at least in part from influx of CD4 1 cells. We therefore determined the total numbers of CD4 1 cells (isolated from the stomachs of five mice at each time point) infiltrating the mucosa over time.…”

“…This reduction was modest (1.8-fold) on day 3, although statistically significant (po0.04), and became substantial by days 7 and 21 (ten-fold, po0.004 and 100-fold, po0.0001, respectively). Analysis at later time points (day 35 and day 70, 1 year) revealed that the degree of protection did not further increase after day 21 (data not shown) [24,25]. It is noteworthy that carrier-vaccinated C57BL/6 mice also exhibited reductions in H. pylori colonisation compared with the control non-vaccinated mice ('carrier effect'), and this reduction was statistically significant at both 7 and 21 days post challenge (po0.003).…”

“…In this study, healthy (H. pylori negative) adult volunteers were vaccinated orally with recombinant S. Typhi expressing H. pylori antigen, and later challenged with a well-characterised H. pylori strain [16]. Vaccine-specific CD4 1 T-cell responses were detected and found to correlate with reductions in colonisation in some vaccinated volunteers.Clearly, CD4 1 T cells alone are not capable of killing bacteria directly, and a multi-factorial model has been proposed where the 'protective' population of CD4 1 T cells produce signals, soluble or otherwise, that stimulate epithelial or other cells to produce anti-bacterial factors [17].Studies in both experimentally infected mice and naturally infected humans have shown that Treg cells (defined in these studies as CD4 1 CD25 1 Foxp3 1 cells) are important for modulating the inflammatory response against H. pylori, and indeed are thought to contribute to the persistence of the pathogen [18][19][20].Given the predicted role for CD4 1 T cells in protection, and the implied importance of Treg in bacterial persistence, this study focussed on characterising the CD4 1 T helper and Treg response after vaccination at the systemic and local gastric level to gain a better understanding of the mechanism underlying the protective response against H. pylori. …”

“…Other workers conclude that a strong gastritis is important for bacterial clearance, as SCID mice, which are deficient in T cells, have a higher bacterial colonisation levels than wild-type and the colonisation in wild-type mice decreases as gastritis worsens [41]. It should be noted however that this is probably an over-simplification of the model because mouse strains such as BALB/c and also gerbils that develop little or no post-immunisation gastritis are also well protected by vaccination [17,42].This study is the first detailed investigation into the effect of prophylactic vaccination against H. pylori on the local immune response in the gastric mucosa. The effect of vaccination was characterised as increased infiltration, proliferation and Th1 cytokine production by CD4 1 T cells isolated from the stomach as well as increased infiltration of neutrophils.…”

“…Clearly, CD4 1 T cells alone are not capable of killing bacteria directly, and a multi-factorial model has been proposed where the 'protective' population of CD4 1 T cells produce signals, soluble or otherwise, that stimulate epithelial or other cells to produce anti-bacterial factors [17].…”