A 29K envelope glycoprotein of equine arteritis virus expresses neutralization determinants recognized by murine monoclonal antibodies.

A panel of six neutralizing murine monoclonal antibodies (MAbs) to equine arteritis virus (EAV) was produced. The MAbs were characterized by Western immunoblotting assay and competitive ELISA. The six MAbs identify a single neutralization site on a 29K envelope glycoprotein. Deglycosylation of viral proteins prior to immunoblotting showed that the 29K protein is the glycosylated form of a 20K protein. Equine anti-EAV serum also strongly bound the 29K glycoprotein, as well as an unglycosylated protein of 17K. The equine antisera to EAV blocked the binding of a selected MAb to EAV, whereas normal equine serum did not. Two neutralization-resistant escape mutant (EM) variants of the EAV prototype were produced using MAb 6D10. The phenotypic properties of the EM viruses were characterized by neutralization and immunoblotting assays with two MAbs (6D10 and 5G11). The two MAbs failed to neutralize either EM virus, and they did not react in an immunoblot assay with any proteins of the EM viruses. In contrast, binding of the equine antiserum to viral proteins was equivalent with prototype and EM virus strains. These data clearly indicate that a 29K envelope glycoprotein expresses at least one neutralization determinant of EAV.