The A2 gene of alcelaphine herpesvirus-1 is a transcriptional regulator affecting cytotoxicity in virus-infected T cells but is not required for malignant catarrhal fever induction in rabbits

Alcelaphine herpesvirus-1 (AlHV-1) causes Malignant Catarrhal Fever (MCF). The A2 gene of AlHV-1 is a member of the bZIP transcription factor family. An A2 gene knockout (A2?AlHV1) virus, revertant (A2revAlHV-1) virus, and wild-type virus (wtAlHV-1) were used to infect three groups of rabbits. A2?AlHV1-infected rabbits succumbed to MCF, albeit with a delayed onset compared to the control groups, so A2 is not a critical virulence factor. We also performed differential gene transcription analysis by RNAseq and qRT-PCR validation of selected gene transcripts in infected large granular lymphocyte (LGL) T cells obtained in culture from the MCF-affected animals in each of the groups. This revealed that A2 was apparently involved in the transcriptional regulation of immunological, cell cycle and apoptosis pathways. In particular, there was a bias towards ?d T cell receptor (TCR) expression and downregulation of aß TCR. TCR signalling, apoptosis, cell cycle, IFN-?, NF?B and NFAT pathways were affected. Of particular interest was partial inhibition of the cytotoxicity-associated pathways involving perforin and the granzymes A and B in the A2?AlHV1-infected LGLs compared to controls. In functional assays, A2?AlHV1-infected LGLs were significantly less cytotoxic than wtAlHV-1- and A2revAlHV-1-infected LGLs using rabbit corneal epithelial cells (SIRC) as targets. This implies that A2 is involved in a pathway enhancing the expression of LGL cytotoxicity. This is important as virus-infected T cell cytotoxicity in vivo has been suggested as a potential mechanism of disease induction in MCF.