Intranasal co-administration of recombinant active fragment of Zonula occludens toxin and truncated recombinant EspB triggers potent systemic, mucosal immune responses and reduces span of E. coli O157:H7 fecal shedding in BALB/c mice.

Abstract

Escherichia coli O157:H7 with its traits such as intestinal colonization and fecal-oral route of transmission demands mucosal vaccine development. E. coli secreted protein B (EspB) is one of the key type III secretory system (TTSS) targets for mucosal candidate vaccine due to its indispensable role in the pathogenesis of E. coli O157:H7. However, mucosally administered recombinant proteins have low immunogenicity which could be overcome by the use of mucosal adjuvants. The quest for safe, potent mucosal adjuvant has recognized ΔG fragment of Zonula occludens toxin of Vibrio cholerae with such properties. ΔG enhances mucosal permeability via the paracellular route by altering epithelial tight junction structure in a reversible, ephemeral and non-toxic manner. Therefore, we tested whether recombinant ΔG intranasally co-administered with truncated EspB (EspB + ΔG) could serve as an effective mucosal adjuvant. Results showed that EspB + ΔG group induced higher systemic IgG and mucosal IgA than EspB alone. Moreover, EspB alone developed Th2 type response with IgG1/IgG2a ratio (1.64) and IL-4, IL-10 cytokines whereas that of EspB + ΔG group generated mixed Th1/Th2 type immune response evident from IgG1/IgG2a ratio (1.17) as well as IL-4, IL-10 and IFN-γ cytokine levels compared to control. Sera of EspB + ΔG group inhibited TTSS mediated haemolysis of murine RBCs more effectively compared to EspB, control group and sera of both EspB + ΔG, EspB group resulted in similar levels of efficacious reduction in E. coli O157:H7 adherence to Caco-2 cells compared to control. Moreover, vaccination with EspB + ΔG resulted in significant reduction in E. coli O157:H7 fecal shedding compared to EspB and control group in experimentally challenged streptomycin-treated mice. These results demonstrate mucosal adjuvanticity of ΔG co-administered with EspB in enhancing overall immunogenicity to reduce E. coli O157:H7 shedding.