Nasal Administration of M2e/CpG-ODN Encapsulated in N-Trimethyl Chitosan (TMC) Significantly Increases Specific Immune Responses in a Mouse Model

The nasal passage is the primary entry point for many infectious agents. Therefore, nasal vaccines that can overcome the limitations associated with antigen uptake are likely to play an important role in protecting these infectious agents. Thus, adjuvants and antigen-carrying systems that can induce a suitable mucosal and systemic immune response against their accompanying antigens are highly important. In this study, synthetic oligodeoxynucleotides containing CpG motifs (CpG-ODN) accompanied by the recombinant ectodomain of influenza M2 protein were encapsulated in N-trimethyl chitosan (TMC) nanoparticles. After the preparation of TMC nanoparticles, the morphological characteristics and loading efficiency and in vitro antigen release, as well as their ability to induce efficient immune responses against M2e in intranasal inoculation in the mouse model, were studied. Based on the size and zeta potential of the nanoparticles prepared in this study, it was determined that they were all nanosized, and their positive zeta potential ranged from 25 to 28 mV, while their polydispersity index was between 0.1 to 0.2, indicating a narrow range of particle sizes. A significant increase in serum levels of the total M2e-specific IgG antibody and BALF anti-M2e IgA was observed in mice intranasally immunized with M2e/CpG-ODN/TMC as opposed to those that were intranasally immunized with M2e/TMC, M2e/CpG-ODN, free M2e, and CpG-ODN/TMC. There was also a significant change in the IgG2a/IgG1 ratio in favour of IgG2a seems that CpG-ODN is responsible for directing the immune system towards Th1. Our findings show that CpG-ODN can significantly enhance the mucosal and systemic humoral immune response against M2e when encapsulated in a suitable carrier such as TMC for intranasal administration. In conclusion, when combined with a suitable carrier, CpG-ODN can be considered an effective adjuvant for mucosal administration.