Targeting peptide-enhanced antibody and CD11c+ dendritic cells to inclusion bodies expressing protective antigen against ETEC in mice

Abstract

Enterotoxigenic Escherichia coli (ETEC) remains a massive burden in developing countries with increasing morbidity andmortality rates; it is also animportantpathogen inthe farming industry andis a leading cause of bacterial diarrhea. Our previous study showed that nanometer-sized inclusion bodies (IBs) of the fimbrial adhesin subunit protein (FaeG), mutation heat-stable enterotoxin a (mSTa), heat-labile enterotoxin b (LTb), and STb (nontargeting) fusion protein as an oral vaccine induced both systemic andmucosal immune responses. In this study, to enhance the protective efficacy to ETEC, we used Yersinia enterocolitica adhesive and M-cell-targeting peptides to analyze highefficiency antigen-specific immune presentation in the gut. Here, we showed that immunization with the IBs of ETEC-FaeG-mSTa-LTb-STb-induced a specific systemic and mucosal immune response in the gut, whereas the combination of both targeting peptides resulted in the highest titer, protective immune response against ETEC. A lymphocyte proliferation assay has shown that the IBs induced immunologicmemory. The specific antibody of the targeting groups could effectively neutralize toxins, thereby protecting the cells of the small intestine and reducing the levelof cAMPandcGMP,andthegroupswith double targeting showedthe best effect.Themostimportant findingwas that the targeting peptides stimulate the T helper (Th) cells through Th17 and Th1 and that Th1 cells dominated the cellular immune response.We found that the targeting peptide could also activateCD11c+ on lymphoid dendritic cells, which processed and presented antigens to T cells through Th1-mediated IFN-g and IL-12, thereby enhancing the antibody titers. The double-targeting peptide had a better effect on stimulating the immune cells to enhance the antibodytiters.