Neutralization of Bovine Herpesvirus Type 4 by Pairs of Monoclonal Antibodies Raised against Two Glycoproteins and Identification of Antigenic Determinants Involved in Neutralization

In infected cattle, bovine herpesvirus type 4 (BHV-4) induces an immune response with low neutralizing antibody levels or in the absence of such antibodies. For the study of this phenomenon, monoclonal antibodies (MAbs) raised against two BHV-4 glycoproteins identified previously (150K/120K/51K and 120K/16.5K) were used in neutralization tests. None of the MAbs except for MAb 16 could neutralize alone; pairs of MAbs against the 150K/120K/51K and 120K/16.5K glycoproteins were able to neutralize BHV-4 infectivity. MAbs involved in neutralization were used in competitive binding assays to identify epitopes relevant for BHV-4 neutralization. These MAbs showed a low avidity and a weak neutralizing activity, and they partially decreased BHV-4 attachment to cells. These results suggest that the BHV-4 glycoprotein domains involved in viral infectivity are poorly exposed to the immune system.