Since African swine fever (ASF) was first reported in 1921, it has brought huge economic losses to the world pig industry. No vaccine or therapy is available. Rapid and effective diagnostics are key steps in managing ASF. We generated three monoclonal antibodies (mAbs) against the African swine fever virus (ASFV) phosphoprotein p30 and designated these as 7D2, 8C8 and 2F6. Epitope mapping revealed that mAb 7D2 recognized 26VFHAG SLYNW 35 of p30, and mAb 8C8 and 2F6 recognized 1MDFIL NISMK MEVIF KTDLR 20 of p30. Furthermore, epitope 1MDFIL NISMK MEVIF KTDLR 20 and 26VFHAG SLYNW 35 could be well recognized by ASFV-positive sera from natural infected pigs, suggesting that they were natural linear B-cell epitope. Conservation analysis indicated that epitope 1MDFIL NISMK MEVIF KTDLR 20 and 26VFHAG SLYNW 35 were highly conserved among the different strains of ASFV. This is the first research to characterize specific mAbs against p30 protein. These findings may facilitate further understanding the function of p30 protein and development of diagnostic tools.

Influenza A virus (IAV), a deadly zoonotic pathogen, occasionally cross-species transmission among humans, swine and avian. The ectodomain of matrix protein 2 (M2e) is highly conserved in IAV, and multi-copy M2e from different species are usually displayed on the surface of nanoparticles to improve immunogenicity and constitute universal IAV nanovaccines. In our previous study, three M2e were inserted into the C-terminal of Cap protein of porcine circovirus type 2 (PCV2) to form a universal nanovaccine that protects PCV2 and different subtypes of IAV. Howerer, M2e adopts at least two converted conformations, and the intermolecular linker of M2e enhances the conformational instability, which limits the recognition of B cell receptors and production of high-level antibodies. Here, we report that the permutation of the M2e affects immune effect of nanovaccines. Three M2e derived from humans, swine and avian IAV were inserted into the C-terminal of the Cap protein to form nanovaccines. Immunoprotective effects of different M2e arrangements were explored in mice. Results showed that the M2e closest to the surface of nanoparticle induced the most efficient protection against IAV derived from corresponding species. The results will help to develop more effective universal IAV and PCV2 bivalent nano-vaccines, as well as universal IAV vaccines for specific species.

Influenza A virus (IAV), a deadly zoonotic pathogen, occasionally cross-species transmission among humans, swine and avian. The ectodomain of matrix protein 2 (M2e) is highly conserved in IAV and has been widely concerned in the development of universal influenza vaccines. Due to low immunogenicity, multi-copy M2e are usually displayed on the surface of nanoparticles to constitute universal nanovaccines. Here, we report that the permutation of the M2e affects the immune effect of the nanovaccine. Three M2e derived from humans, swine and avian IAV were inserted into the C-terminal of the Cap protein of porcine circovirus type 2 (PCV2) to form self-assembled nanovaccine. Immunoprotective effects of different M2e arrangements were explored in mice. Results showed that the M2e closest to the surface of nanoparticle induced the most efficient protection against IAV derived from corresponding species. The results will help in the development of more effective universal influenza vaccines, especially for specific species.