Immunoprecipitation of viral polypeptides of equid herpesvirus 1 and 4 by serum from experimentally infected ponies

Development and validation of a monoclonal antibody blocking ELISA for the detection of antibodies against both equine herpesvirus type 1 (EHV1) and equine herpesvirus type 4 (EHV4)

A monoclonal antibody blocking ELISA was developed for the detection of antibodies directed against either EHV1 or EHV4. For this purpose, we selected a monoclonal antibody directed against a cross-reactive, conservative and immunodominant epitope of both EHV1 and EHV4. High antibody titres were found in rabbit antisera and SPF-foal antisera infected with either EHV1 or EHV4. After experimental challenge of conventional horses with EHV1 or EHV4 significant increases in CF and ELISA titres were found, whereas VN antibodies did not always increase significantly. In 344 paired serum samples submitted for diagnostic purposes a good agreement (kappa = 0.75, confidence limits = 0.63-0.88) was found between VN test and ELISA regarding a significant increase in titres. Also, a good correlation was found between VN and ELISA titres (r = 0.76, p<<0.0005). The relative sensitivity and specificity of the Mab blocking ELISA as compared with the VN test were 99.9 and 71%, respectively. The rather low relative specificity of the ELISA may be explained by a relatively low sensitivity of the VN test. The ELISA also detected increases in titre after vaccination with an EHV1 subunit vaccine, and after primary field infections in weaned foals. We concluded that the Mab blocking ELISA is more sensitive, easier to perform, more rapid and more reproducible than the VN test. We consider this test as a valuable tool for serological diagnosis of both EHV1 and EHV4 infections.

Primary and challenge infection of mice with equine herpesvirus 1, strain HSV25A

Clinical signs, haematology, lymphocyte subset analysis, viral clearance, lung histopathology and humoral and cell-mediated (CMI) immune responses were monitored throughout the acute and convalescent phases of infection in groups of BALB/c mice infected intranasally with equine herpesvirus 1 (EHV-1), strain HSV25A. Primary infection caused a leucocytosis due to a neutrophilia during days 1 and 2 post-infection (pi) and a B lymphocytosis at day 1 pi. Serum ELISA antibodies were detected by 7 days pi and neutralising antibodies by 2 weeks pi. Mice infected with EHV-1 were not protected against disease when challenged with EHV-1 12 weeks later. However, viral clearance from lungs was significantly faster and the antibody response was markedly enhanced within the first few days of challenge infection. A CMI response was detected by 5 days after primary infection, but the level of responsiveness was not increased by challenge infection, although the lungs of challenged mice had markedly increased numbers of mononuclear cells around blood vessels and bronchioles. Specific antibodies to glycoprotein (g) B were detected by 2 weeks pi, 4 weeks earlier than the detection of antibodies to gC and 10 weeks before those to gD. The primary response was relatively short-lived with neither ELISA antibody nor lymphocyte proliferation was evident by 6 months pi.

gp13 (EHV-gC): a complement receptor induced by equine herpesviruses

Equine herpesviruses type 1 (EHV-1) and type 4 (EHV-4) induce a complement receptor protein on the surface of infected cells capable of binding to the third component of complement (C3). The protein mediating the binding to the C3 component of complement was identified as glycoprotein 13 (gp13, EHV-gC), as expression of the cloned viral gene under the control of a CMV promoter induced C3 binding activity at the transfected cell surface. Comparable to glycoprotein C (gC) from herpes simplex virus type 1 (HSV-1-gC), glycoprotein III from pseudorabiesvirus (gIII, PRV-gC) and bovine herpesvirus-1 (gIII, BHV-1-gC), gp13 derived from EHV-infected cell lysates bound to C3 fixed to solid phase, showing preferential binding to the appropriate host complement component. Similar to wild-type isolates, a highly attenuated vaccine EHV-1 strain also displayed complement receptor activity despite apparent differences of the gp13 gene in restriction enzyme digest pattern and reactivity with monoclonal antibodies. In addition, other structural proteins were altered in the vaccine strain as compared to wild-type strains, which might contribute to its attenuated phenotype. In contrast to the situation observed with HSV-1-gC, the interaction of gp13 (EHV-gC) with horse complement was not inhibited by polyanionic substances like heparin or dextran sulfate. These results suggest structural differences in the particular binding mechanism of the respective viral envelope proteins.