Use of hydrophilic extra-viral domain of canine distemper virus H protein for enzyme-linked immunosorbent assay development

Expression and characterization of canine distemper virus hemagglutinin protein in suspension mammalian cells

Hundreds of millions of the domestic dogs worldwide are routinely inoculated with the modified live vaccines for canine distemper virus (CDV) every year. However, the corresponding serological diagnostic and detections are always lacking, thus, there is an urgent demand to establish its unique diagnostic technologies to produce high-quality antigenic biomolecules. In the present study, the ectodomain (et) of CDV hemagglutinin (H) protein was firstly expressed in a soluble and secreted forms by an Expi293F transient transfection system based on its antigenic secondary structure analysis. The yields of CDV H(et) protein was 2.6 g/L with purity over 95 % in supernatant of Expi293F cells. The CDV H(et) protein elicited comparative antibodies levels to the CDV virions in rabbit by ELISA and neutralization test. The purified polyclonal antibodies of immunized with CDV H(et) protein recognized both wild-type and vaccine CDV strains. More importantly, the purified polyclonal antibodies of CDV H(et) protein revealed significantly higher viral neutralizing activity than those from CDV-3 virions, which highlighted that the critical role of CDV H protein to elicit viral specific and protective neutralizing antibodies. Taken together, the CDV H(et) protein produced in mammalian expression systems was high-quality and good immunogenicity, and would be with great potential to serve as a serological diagnostic antigen or a novel CDV subunit vaccine in future.

Development of a monoclonal antibody recognizing novel linear neutralizing epitope on H protein of canine distemper virus vaccine strains (America-1 genotype)

Canine distemper virus (CDV) is an economically important virus responsible for canine distemper (CD), a highly contagious disease that afflicts various animal species worldwide. The hemagglutinin (H) protein is the major neutralizing target of virus. Therefore, it is often considered as immunogen to prepare neutralizing antibodies. The accurate identification of neutralizing epitope will provide important antigenic information and extend the knowledge of mechanisms of virus neutralization. In this study, we generated a neutralizing monoclonal antibody (mAb) 4C6 against CDV H protein, and defined the minimal linear epitope 238DIEREFDT245, which was highly conserved in America-1 genotype of CDV strains (vaccines). The mAb 4C6 could not react with a CDV strain that had two substitutions of D238Y and R241G in the epitope, which appeared in most CDV strains of the other genotypes. Besides, a few different amino acid mutations in the epitope were also included. Collectively, the epitope 238DIEREFDT245 was variable in the other genotypes of CDV strains. The epitope 238DIEREFDT245 was exposed to the surface of CDV H protein, showing good antigenicity. These data will provide insights into structure, function and antigenicity of H protein and lay the foundation for the development of diagnostic technologies and vaccine design for CDV.

Development of a double monoclonal antibody-based sandwich enzyme-linked immunosorbent assay for detecting canine distemper virus

Abstract

Canine distemper virus (CDV) infection causes mass mortality in diverse carnivore species. For effective virus surveillance, rapid and sensitive assays are needed to detect CDV in field samples. In this study, after BABL/c mice were immunized with recombinant CDV-fusion (F) protein, monoclonal antibodies (mAbs) against recombinant CDV-F protein (designated 1A5, 1A6, and 7D5) were produced using traditional hybridoma cell technology. Next, capture antibody (1A6, 800 ng/well) and horseradish peroxidase (HRP)–conjugated detection antibody (HRP-7D5, 1:100, 500 ng/well) were used in a double monoclonal antibody–based sandwich enzyme-linked immunosorbent assay (ELISA) for CDV detection after optimization of both mAb amounts per well using a checkerboard titration test. Based on sandwich ELISA test results for 120 known CDV-negative samples, the cutoff value for a positive result was set to an OD_450 nm value ≥ 0.196. As compared with test results obtained from commercial immune colloidal gold test strips, the low limits of detection for the two assays were revealed to be 100 TCID₅₀ per 100 μL. In addition, the sandwich ELISA agreed 100% and 96.4% with commercial immune colloidal gold test strips when testing serum and stool samples. The sandwich ELISA assay provided statistically similar CDV detection. Thus, the sandwich ELISA developed here to detect CDV in fecal and serum samples provided good sensitivity, high specificity, and good reproducibility and should serve as an ideal method for large-scale surveillance of CDV infections in carnivores.

Key points

• Three CDV mAbs that recognized different epitopes and bound to virion were generated.

• The sandwich ELISA based mAbs to detect CDV in fecal and serum samples was developed.

• The sandwich ELISA is an ideal method for detecting CDV infections in the field.

Identification of Linear B-Cell Epitopes on Hemagglutinin Protein of Canine Distemper Virus Using Two Monoclonal Antibodies

Canine distemper virus (CDV) belongs to the Morbillivirus genus of the Paramyxoviridae family, which causes a threat to the domestic dog and fur-animal industry. Hemagglutinin protein is a major membrane protein of the vital molecular factor in CDV tropism, also known to induce hosts to produce neutralizing antibodies. In the current study, we prepared two monoclonal antibodies, 1A5 and 2B8, against the H protein of the CDV-PS strain. A series of partially overlapping synthetic peptides covering the hemagglutinin protein (amino acids 50–204) were screened to define the linear epitope identified by 1A5 and 2B8 mAbs. ¹²⁰QKTNFFNPNREFDFR¹³⁴ (F8) and ¹⁷⁸ARGDIFPPY¹⁸⁶ (F14-1) are minimal linear epitopes recognized by 1A5 and 2B8 mAbs, respectively. Further investigations revealed that F8 is conserved in different CDV strains; however, F14-1 contains mutant residues 178, 179, and 180. The epitopes F8 and F14-1 localized at the surface of hemagglutinin protein in a three-dimensional (3D) structure. CDV-infected dog serum can also recognize the identified B-cell epitopes.