Influence of the Viral Superoxide Dismutase (SOD) Homologue on Lumpy Skin Disease Virus (LSDV) Growth, Histopathology and Pathogenicity.

Nicola Douglass,Anna-Lise Williamson,Henry Munyanduki,Paidamwoyo Mutowembwa,Ruzaiq Omar,Livio Heath,Sophette Gers

doi:10.3390/vaccines8040664

Abstract

Lumpy skin disease is an important economic disease of cattle that is controlled by vaccination. This paper presents an investigation into the role of the lumpy skin disease virus (LSDV) superoxide dismutase (SOD) homologue on growth and histopathology of the virus both in vitro and in vivo. SOD homologue knock-out and knock-in recombinants (nLSDV∆SOD-UCT and nLSDVSODis-UCT, respectively) were constructed and compared to the Neethling vaccine (nLSDV) for growth in a permissive bovine cell line as well as on fertilized chick chorioallantoic membranes (CAMs). The infected CAMs were scored for histological changes. Deletion of the SOD homologue from LSDV reduced virus growth both in Madin-Darby bovine kidney (MDBK) cells as well as on CAMs. Furthermore, the knockout virus showed reduced inflammation in CAMs and more ballooning degeneration. A pilot experiment was performed in cattle to compare the lesions produced by the different LSDV constructs in the same animal. One animal developed a larger lesion to nLSDV∆SOD-UCT compared to both nLSDVSODis-UCT and nLSDV. Histological analysis of biopsies of these lesions shows less inflammation and necrosis associated with nLSDVSODis-UCT compared to nLSDV and nLSDV∆SOD-UCT. None of the vaccinated animals showed disseminated LSDV disease, indicating that the candidate vaccines are safe for further testing. Our results suggest that the SOD homologue may improve immunogenicity and reduce virulence.

Highlights

The interaction between poxviruses and their host cells is complex and involves multiple strategies of evasion both for the virus and host [1,2]
The putative amino acid sequences of the superoxide dismutase (SOD) homologues from the virulent lumpy skin disease virus (LSDV) 2490 strain, the Neethling strain of LSDV (nLSDV) vaccine strain and Herbivac were compared to those from selected poxviruses and the human and bovine SOD enzymes (Figure 1)
The LSDV SOD homologues show conservation of structural components (α helices and β-sheets) and the two LSDV viruses with full-length SOD homologues (LSDV 2490 and Herbivac) have retained all eight residues required for dimer formation [25,26,27]. nLSDV, due to its truncated SOD homologue, does not have the two residues at positions 112 and 113

Summary

Introduction

The interaction between poxviruses and their host cells is complex and involves multiple strategies of evasion both for the virus and host [1,2]. Host responses leading to cell death are associated with cell mediated immune clearance of virus-infected cells [1] and the targeting of the cellular superoxide dismutase. The Shope fibroma virus (SFV) SOD homologue has been shown to inhibit apoptosis by binding the copper chaperone for SOD (CCS) [5]. The inhibition of apoptosis is brought about by the upregulation of intracellular superoxide as a result of CCS being bound to the SFV SOD homologue and preventing the transfer of copper to the cellular SOD enzyme, a requirement for superoxide dismutase activity [6]. A SOD homologue knockout myxoma virus recombinant showed increased growth in rabbit kidney (RK13) and baby green monkey kidney (BGMK) cells [7]. The vaccinia virus SOD homologue had no effect on virus growth in cell culture, nor did it influence virulence in mice [8]

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