?d T Cells Provide Protective Function in Highly Pathogenic Avian H5N1 Influenza A Virus Infection

Dong, Peng; Ju, Xiangwu; Yan, Yiwu; Zhang, Siya; Cai, Menghua; Wang, Huaishan; Chen, Hui; Hu, Yu; Cui, Lianxian; Zhang, Jianmin; He, Wei

As the most abundant antigen on the surface of the influenza virus, HA is responsible for host receptor binding, internalization, and the subsequent membrane fusion events in the infected cell (23, 36) . In its mature form, natural HA is a homotrimer with multiple glycosylation sites. In our study, two forms of recombinant hemagglutinin, namely, HA trimers and HA monomers, were successfully expressed and purified. Consistent with previous reports, HAF proteins could form HA trimers like the natural form of HA proteins and had a fold on sequence at the C-terminus, and HA-his proteins existed mainly as HA monomers (23, 36) . Although a few oligomeric proteins were present in both groups, we believe that the oligomers in the HAF group were constructed with HA trimers, while those in the HA-his group were HA monomers. Both the HAF and HA-his proteins showed hemagglutination activity; however, a higher binding ability was observed for HAF than that of HA-his, which may be related to the protein conformation. Furthermore, Chih-Jen et al. found that the immunogenicity of HA trimers was stronger than that of HA monomers in mice immunized with these recombinant HA proteins (37) . In our previous study, we found that rHA proteins derived from HPAI H5N1 could activate γδ T cells in PBMCs (25) . Here, we further confirmed that HAF proteins could not only induce γδ T cell agglutination but could also directly activate γδ T cells via mechanisms such as CD69 upregulation, IFN-γ secretion and increased intracellular calcium mobilization.