Background: Direct transmission of avian influenza viruses with human receptor binding specificity to humans is a serious risk of newly emerging virus responsible for pandemy. The analysis of recent avian influenza hemagglutinin sequences and their glycans show their affinities to the human sialic acid receptors. The upregulation of proinflammatory cytokines and type I IFN genes, and host cell death responses contribute to the pathogenesis of influenza infection. Understanding the host cell-virus interactions and replication dynamic of the viruses in different cells is an essential step in surveillance and controlling programs against influenza.

Background: Influenza A viruses are globally important respiratory pathogens which cause a high degree of morbidity and mortality during annual epidemics. M2 protein which expressed on the viral surface facilitates virus entry to the host cells. The extracellular domain of M2 protein (M2e) consists of N-terminal 24 residue which shows remarkable conservation among all subtypes of influenza A viruses. In this study, we evaluated the immunogenicity of three tandem repeats of M2e along with different adjuvants in BALB/C mice model.

Materials and Methods: Recombinant protein (3M2e) was expressed in Escherichia coli and purified. Six weeks old BALB/c mice were immunized interdermally with three doses of 3M2e alone or supplemented with Alum/CpG motif as adjuvant. Control group was injected with PBS. Two weeks after the last immunization, specific anti-M2 was measured using ELISA method and finally mice were challenged with one lethal dose (LD90) of PR8 virus.

Results: The results showed that 3M2e can induce specific antibody alone. However, 3M2e protein supplemented with Alum-CpG induced higher level of specific antibodies, so that, there was a significant difference with 3M2e group (p<0.05). Anti-M2 antibodies mostly consisted of IgG2a subclass which considered as activity index of TH1 Cells. Moreover, this group showed enhanced protection against wild-type virus (survival rate=60%).

Conclusion: Applying Alum-CpG as a complex adjuvant may play a crucial role in integrating innate and acquisitive immunity. We increased density of M2e in combination with complex adjuvant and showed that this vaccine induced power immune responses and semi-protected mice against lethal challenge.