Mammalian Cell-Line-Expressed CD2v Protein of African Swine Fever Virus Provides Partial Protection against the HLJ/18 Strain in the Early Infection Stage.

A cell line expressing the CD2v protein of ASFV was generated. The efficient expression of CD2v protein was determined by immunofluorescence and Western blotting. The CD2v protein was Ni-affinity purified from the supernatant of cell cultures. The CD2v-expressing cells showed properties of hemadsorption, and the secreted CD2v protein exhibited hemagglutinating activity. The antigenicity and immunoprotection ability of CD2v were evaluated by immunizing pigs alone, combined with a cell-line-expressed p30 protein or triple combined with p30 and K205R protein. Immunized pigs were challenged with the highly virulent ASFV strain HLJ/18. Virus challenge results showed that CD2v immunization alone could provide partial protection at the early infection stage. Protein p30 did not show synergistic protection effects in immunization combined with CD2v. Interestingly, immunization with the triple combination of CD2V, p30 and K205R reversed the protection effect. The viremia onset time was delayed, and one pig out of three recovered after the challenge. The pig recovered from ASFV clinical symptoms, the rectal temperature returned to normal levels and the viremia was cleared. The mechanism of this protection effect warrants further investigation.

Comprehensive mapping of antigenic linear B-cell epitopes on K205R protein of African swine fever virus with monoclonal antibodies.

African swine fever virus causes an acute, highly contagious swine disease with high mortality, leading to enormous losses in the pig industry. The K205R, a nonstructural protein of African swine fever virus, is abundantly expressed in the cytoplasm of infected cells at the early stage of infection and induces a strong immune response. However, to date, the antigenic epitopes of this immunodeterminant have not been characterized. In the present study, the K205R protein was expressed in a mammalian cell line and purified using Ni-affinity chromatography. Furthermore, three monoclonal antibodies (mAbs; 5D6, 7A8, and 7H10) against K205R were generated. Indirect immunofluorescence assay and western blot results showed that all three mAbs recognized native and denatured K205R in African swine fever virus (ASFV)-infected cells. To identify the epitopes of the mAbs, a series of overlapping short peptides were designed and expressed as fusion proteins with maltose-binding protein. Subsequently, the peptide fusion proteins were probed with monoclonal antibodies using western blot and enzyme-linked immunosorbent assay. The three target epitopes were fine-mapped; the core sequences of recognized by the mAbs 5D6, 7A8, and 7H10 were identified as 157FLTPEIQAILDE168, 154REKFLTP160, and 136PTNAMFFTRSEWA148, respectively. Probing with sera from ASFV-infected pigs in a dot blot assay demonstrated that epitope 7H10 was the immunodominant epitope of K205R. Sequence alignment showed that all epitopes were conserved across ASFV strains and genotypes. To our knowledge, this is the first study to characterize the epitopes of the antigenic K205R protein of ASFV. These findings may serve as a basis for the development of serological diagnostic methods and subunit vaccines.

Newcastle disease virus-based MERS-CoV candidate vaccine elicits high-level and lasting neutralizing antibodies in Bactrian camels.

Middle East respiratory syndrome coronavirus (MERS-CoV), a member of the Coronaviridae family, is the causative pathogen for MERS that is characterized by high fever, pneumonia, acute respiratory distress syndrome (ARDS), as well as extrapulmonary manifestations. Currently, there are no approved treatment regimens or vaccines for MERS. Here, we generated recombinant nonvirulent Newcastle disease virus (NDV) LaSota strain expressing MERS-CoV S protein (designated as rLa-MERS-S), and evaluated its immunogenicity in mice and Bactrian camels. The results revealed that rLa-MERS-S showed similar growth properties to those of LaSota in embryonated chicken eggs, while animal immunization studies showed that rLa-MERS-S induced MERS-CoV neutralizing antibodies in mice and camels. Our findings suggest that recombinant rLa-MERS-S may be a potential MERS-CoV veterinary vaccine candidate for camels and other animals affected by MERS.