Upregulation of innate and adaptive immune mechanisms facilitating prevention of gastric Helicobacter pylori infection in guinea pigs by per os administration of chitosan microparticles loaded with Mycobacterium bovis BCG.

BACKGROUND: Helicobacter pylori (H. pylori) rods frequently colonize and damage the gastric mucosa in humans, causing inflammation, gastric or duodenal ulcers and even gastric cancer. H. pylori negatively modulates the activity of immune cells, including macrophages and lymphocytes facilitating the persistence of infection. Increasing resistance of H. pylori isolates to commonly used antibiotics diminishes the success of therapy. These prompt searches for new therapeutic formulations to improve the effectiveness of immune mechanisms against H. pylori. Based on the previous in vitro studies indicating the immunomodulatory properties of Mycobacterium bovis-(Bacillus Calmette-Guérin) BCG vaccine bacilli, we developed chitosan microparticles-(CHI MPs) modified with N-acetylglucosamine-(G) or with Pluronic F-127-(P) to facilitate the delivery and persistence of live M. bovis BCG in the stomach and in the gut of Cavia porcellus susceptible to H. pylori infection.

METHODS: Animals (5/per group) were inoculated per os only with CHI MPs, G or P variant or both, or with such CHI MPs and then with the reference H. pylori CCUG17874 positive for cytotoxin-associated gene A-(cagA) (3 times in two-day intervals). Control animals received only H. pylori (positive control) or Brucella broth (negative control). Two assessment points have been selected: 7 and 28 days after the last H. pylori inoculation, mimicking early and chronic infection, respectively.

RESULTS: The gastric tissue of guinea pigs (4/5) receiving G/P CHI MPs loaded with M. bovis BCG before inoculation with H. pylori was not colonized with these bacteria after 28 days as shown by quantitative cagA polymerase chain reaction. Protection in this group was associated with an increased number of myeloid precursors in the bone marrow and enhanced macrophage infiltration in the gastric tissue. The bone marrow-derived macrophages from this group showed enhanced phagocytic activity, whereas in animals inoculated only with H. pylori, this activity was negatively modulated. The protective effect of the studied CHI MPs was also associated with increased gastric concentrations of secretory IgA and enhanced splenocyte proliferation.

CONCLUSIONS: The obtained results indicate the immunomodulatory potential of CHI MPs loaded with M. bovis BCG to improve innate and adaptive immune mechanisms, facilitating control of H. pylori infection in the guinea pig model.