African Swine Fever immune evasion strategies

Lead Research Organisation: The Pirbright Institute
Department Name: UNLISTED

Abstract

African swine fever virus (ASFV) can result in very high mortality in domestic pigs, although persistent asymptomatic infections are observed in natural hosts including warthogs, bushpigs and soft ticks. Some less virulent isolates have been described, which either result in reduced mortality or cause few disease signs. The genome contains between 160 and 175 open reading frames, including many encoding proteins involved in evading host defence systems. The aims are to identify the molecular basis of virus pathogenesis and immune modulation. A practical outcome will be the development of effective vaccines. One approach involves studying the function of virus-encoded proteins involved in immune evasion, by identifying target proteins they interact with, their localisation within cells and host pathways they modulate. The methods used involve construction of ASFV gene deletion mutants and comparison of infections with wild type and mutant ASFV as well as studies using the expressed proteins. Virus proteins currently studied include a transmembrane protein, CD2v, which resembles the host CD2 protein in its extracellular domain. CD2v is known to be required for inhibition of lymphocyte proliferation and the mechanism by which it does this is under investigation as well as other functions of the protein. Studies of a virus inhibitor of toll-like receptor signalling have been initiated (in collaboration with Mike Parkhouse IGC, Oeiras) and studies on other novel immune evasion proteins will follow. A second approach involves comparison of complete genome sequences from high and low virulence isolates to identify genomic differences and comparing host responses following infections of macrophages, the main target cell for ASFV replication in vitro. Changes in host transcription that occur following infection with low and high virulence isolates have been characterised using microarrays and quantitative reverse transcriptase PCR.

Publications

10 25 50
 
Description The aim of the project was to identfy African swine fever virus proteins involved in evading host defence systems. This information is being applied to the development of rationally attenuated ASFV vaccines strains. One approach is to study the function of ASFV proteins predicted from sequence analysis to have a role in evading host defences. A second approach is to compare sequences of high and low virulence isolates to identify genome changes that may be assocaited with loss of virulence. The ASFV CD2v protein is a trans-membrane protein that is expressed on the surface of infected cells and on extracellular virus particles and mediates the binding of red blood cells to infected cells and extracellular virus particles. By using an engineered gene with diferent tags at each end we demonstarted that the CD2v protein is cleaved during virus infection into two fragments. The part of the protein containing the extracellular domain is more localised in the endoplasmic reticulum subcellular compartment and at the cell membrane. The part containing the cytoplasmic domain is more localised in membrane areas in the cytoplasm surrounding the virus factories. Processing of the protein occurs in virus-infected but not uninfected cells suggesting it is meadiated by a virus-induced protein. This work was published in Journal of Virology Goatley and Dixon 2011. Further work has suggested the celavage of the protein is within its transmembrane domain.

The complete genome sequence of the highly virulent Georgia 2007/1 ASFV isolate was determined. African swine fever is widespread in Africa but has occasionally been introduced into other continents. In June 2007, African swine fever was isolated in the Caucasus Region of the Republic of Georgia and subsequently in neighboring countries (Armenia, Azerbaijan, and the Russian Federation). We reported the complete genomic coding sequence of the Georgia 2007/1 isolate and comparison with other isolates. A genome sequence of 189,344 bp encoding 166 open reading frames (ORFs) was obtained. Phylogeny based on concatenated sequences of 125 conserved ORFs showed that this isolate clustered most closely with the Mkuzi 1979 isolate. Some ORFs clustered differently, suggesting that recombination may have occurred. Results provide a baseline for monitoring genomic changes in this virus. The genome complement was typical of other highly virulent isolates and did not contain the large deletions described in low virulence ASFV genomes.
Exploitation Route The information will help with design of rationally attenuated and subunit vacciones for ASFV. The data from sequencing of the Georgia 2007/1 isolate was also used in projects BB/H008969/8 and BB/G530468/1
Sectors Agriculture, Food and Drink

 
Description Findings have been used to gain further research funding which has lead to more publications.
First Year Of Impact 2009
Sector Agriculture, Food and Drink
 
Description OIE World Animal Health Organisation, Designated Disease Expert on African swine fever
Geographic Reach Multiple continents/international 
Policy Influence Type Implementation circular/rapid advice/letter to e.g. Ministry of Health
Impact Involved in giving advice to OIE and completion of chapters in OIE Guidelines for Diagnosis of African swine fever and Trade regulations.
URL http://www.oie.int/
 
Description Collaboration on ASFV transmission and epidemiology 
Organisation Royal Veterinary College (RVC)
Department Structure and Motion Laboratory
Country United Kingdom 
Sector Academic/University 
PI Contribution Animal experiments on the transmission mechanisms of ASFV
Collaborator Contribution Expertise in mathematical modelling and epidemiology
Impact Joint publications and Grant Applications
Start Year 2012
 
Description Collaboration with Arizona State University ASFV vaccine development 
Organisation Arizona State University
Country United States 
Sector Academic/University 
PI Contribution Immunisation and challenge of pigs with ASFV. Expertise on ASFV
Collaborator Contribution Reagents for immunisation of pigs. Expertise on viral vectored vaccines and DNA vaccines
Impact Patent Application and Publication in progress
Start Year 2010