Identification of immuno-reactive capsid proteins of malignant catarrhal fever viruses

•We analysed AlHV-1 virus proteins by proteomics and western blotting.•This identified eight virus proteins as candidate antigens.•Capsid and tegument candidates from OvHV-2 and AlHV-1 were expressed in bacteria.•Blotting showed that only ORF65 and ORF17.5 proteins were antigenic.•ORF65 was strongly detected by both vaccinated and infected cattle serum. Malignant catarrhal fever (MCF) is a fatal disease of cattle and other ungulates caused by certain gamma-herpesviruses including alcelaphine herpesvirus-1 (AlHV-1) and ovine herpesvirus-2 (OvHV-2). An attenuated virus vaccine based on AlHV-1 has been shown to induce virus-neutralising antibodies in plasma and nasal secretions of protected cattle but the targets of virus-specific antibodies are unknown. Proteomic analysis and western blotting of virus extracts allowed the identification of eight candidate AlHV-1 virion antigens. Recombinant expression of selected candidates and their OvHV-2 orthologues confirmed that two polypeptides, the products of the ORF17.5 and ORF65 genes, were antigens recognised by antibodies from natural MCF cases or from AlHV-1 vaccinated cattle. These proteins have potential as diagnostic and/or vaccine antigens.