Abstract
Canine distemper virus (CDV) can cause fatal infections in giant pandas. Vaccination is crucial to prevent CDV infection in giant pandas. In this study, two bacterium-like particle vaccines F(3)-GEM and H(4)-GEM displaying the trimeric F protein or tetrameric H protein of CDV were constructed based on the Gram-positive enhanced-matrix protein anchor (GEM-PA) surface display system. Electron microscopy and Western blot results revealed that the F or H protein was successfully anchored on the surface of GEM particles. Furthermore, one more bacterium-like particle vaccine F(3) and H(4)-GEM was also designed, a mixture consisting of F(3)-GEM and H(4)-GEM at a ratio of 1:1. To evaluate the effect of the three vaccines, mice were immunized with F(3)-GEM, H(4)-GEM or F(3) and H(4)-GEM. It was found that the level of IgG-specific antibodies and neutralizing antibodies in the F(3) and H(4)-GEM group was higher than the other two groups. Additionally, F(3) and H(4)-GEM also increased the secretion of Th1-related and Th2-related cytokines. Moreover, F(3) and H(4)-GEM induce IgG and neutralizing antibodies' response in dogs. Conclusions: In summary, F(3) and H(4)-GEM can provoke better immune responses to CDV in mice and dogs. The bacterium-like particle vaccine F(3) and H(4)-GEM might be a potential vaccine candidate for giant pandas against CDV infection.