GP13 (EHV-GC) - A COMPLEMENT RECEPTOR-INDUCED BY EQUINE HERPESVIRUSES

Equine herpesviruses type 1 (EHV-1) and type 4 (EHV-4) induce a comple ment receptor protein on the surface of infected cells capable of bind ing to the third component of complement (C3). The protein mediating t he binding to the C3 component of complement was identified as glycopr otein 13 (gp13, EHV-gC), as expression of the cloned viral gene under the control of a CMV promoter induced C3 binding activity at the trans fected cell surface. Comparable to glycoprotein C (gC) from herpes sim plex virus type 1 (HSV-1-gC), glycoprotein III from pseudorabiesvirus (gIII, PRV-gC) and bovine herpesvirus-l (gIII, BHV-1-gC), gp13 derived from EHV-infected cell lysates bound to C3 fixed to solid phase, show ing preferential binding to the appropriate host complement component. Similar to wild-type isolates, a highly attenuated vaccine EHV-1 stra in also displayed complement receptor activity despite apparent differ ences of the gp13 gene in restriction enzyme digest pattern and reacti vity with monoclonal antibodies. In addition, other structural protein s were altered in the vaccine strain as compared to wild-type strains, which might contribute to its attenuated phenotype. In contrast to th e situation observed with HSV-1-gC, the interaction of gp13 (EHV-gC) w ith horse complement was not inhibited by polyanionic substances like heparin or dextran sulfate. These results suggest structural differenc es in the particular binding mechanism of the respective viral envelop e proteins.