Modulation of the gastrointestinal immune environment by chitosan microparticles loaded with Mycobacterium bovis BCG in a Cavia porcellus model in vivo, leading to reduced experimental H. pylori gastric colonization

The increasing antibiotic resistance of the gastric pathogen Helicobacter pylori (Hp), which can escape the host immune mechanisms, underscores the need for new therapeutics that will allow them to bypass these obstacles. This study aimed to design chitosan (CHI) microparticles (MPs) loaded with Mycobacterium bovis ( M. bovis ) Bacillus Calmette-Guérin (BCG) with immunomodulating properties and assess their efficacy against Hp infection in Cavia porcellus . Chitosan has been selected due to its mucoadhesive and antibacterial properties. MPs have been modified with N-Acetyl- D -Glucosamine (Glc-NAc) (G MPs) or with Pluronic F127 (P MPs) to deliver mycobacteria to the stomach or the gut, being a center of mucosal immune system. Animals were inoculated orally only with G MPs or P MPs loaded with M. bovis BCG, with both types of MPs, with Hp alone or first with tested MPs and then with Hp. Oral inoculation of animals with MPs resulted in release of mycobacteria in the stomach or the gut, which was followed by the reduction of Hp colonization as shown by quantitative polymerase chain reaction (qPCR) in conjunction with diminishing the amount of mucin involved in Hp attachment as shown by immunofluorescence. Infiltration of gastric mucosa of animals pre-exposed to MPs and then inoculated with Hp with different T lymphocyte subpopulations CD4 + , CD8 + , Foxp3 + (regulatory cells), naïve or memory lymphocytes and eosinophils indicates that all these cells and cytokine profiles may develop environment reflecting immune tolerance or immune regulation rather than protection. The anti-Hp effect of the MPs studied may partly result from chitosan's mucoadhesive, antibacterial and immunomodulatory properties. In conclusion, chitosan MPs (G and P variants) loaded with M. bovis BCG are candidates for further study on a new anti-Hp formula, based on the immunomodulatory and antibacterial properties of mycobacteria and chitosan. • Chitosan microparticles (MPs) deliver M. bovis BCG to the stomach and the gut. • Viable M. bovis BCG act there locally and immunologically. • MPs formulation diminishes H. pylori colonization as shown by qPCR. • MPs promote the environment reflecting immune tolerance or regulation. • Hypothetically MPs induce immune training, mucin modulation, and T-cell response.