Virus and host genes involved in re-programming of macrophage transcription in response to high and low virulence African swine fever virus isolates

Lead Research Organisation: The Pirbright Institute
Department Name: UNLISTED

Abstract

We will study African swine fever virus (ASFV), which causes major losses to farmers in Africa and is a threat to pig farming worldwide. The virus codes for proteins, called evasion proteins, which help it to evade the host's defence systems and avoid being eliminated from the host. In our previous work we showed that ASFV evasion proteins prevent the host from switching on its defence genes. We compared two virus strains, one (high virulence) which kills 100 per cent of infected pigs and one (low virulence) which does not kill pigs but can infect pigs for long periods without causing disease. The high virulence isolate was more effective at switching-off host defence genes than the low virulence isolate as we predicted. In this project we will identify which of the proteins from the high virulence isolate switch-off host defence genes. We will also study other host proteins that are switched-on following virus infection to understand their role in pathogenesis and evasion.

Technical Summary

We showed previously that transcription of macrophage immunomodulatory genes initially increases following infection with a high virulence African swine fever virus (ASFV)isolate, but returns to equivalent levels as in uninfected cells at later times during infection. In contrast transcription levels of some host defence genes remains elevated at late times following infection with a low virulence isolate. We will investigate if virus genes that are known not to be expressed by the low virulence isolate but are expressed by the high virulence isolate, are involved in suppressing host immunomodulatory gene transcription. To do this we will use virus deletion mutants and express these virus genes individually in macrophages infected with a low virulence isolate. We will study expression of cell surface and secreted proteins encoded by genes that are differentially expressed in ASFV infected macrophages to gain an understanding of their potential role in pathogenesis and activation of host responses.

Publications

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Costard S (2009) African swine fever: how can global spread be prevented? in Philosophical transactions of the Royal Society of London. Series B, Biological sciences

 
Description Sequencing of the genomes of low and high virulence African swine fever virus isolates showed that the low virulence isolates (OURT88/3 and BA71V) had a large deletion near the left end of the genome that encodes 5 or 6 copies of a related gene family called multigene family 360 (MGF360) and 1 or 2 copies of the multigene family 505/530 (MGF505) genes. These genes were present in the genomes of all virulent ASFV isolates analysed. The expression and localisation of these genes and an additionla 2 copies of MGF360 were studied in infected and uninfected cells to gain an idea of their function. The results showed different localisations for some of these individual genes suggesting they may have different functions. \these localisations varied from within the cell nucleus in the nucleolus, cytoplasmic or assocaited with the plasma membrane.

The low virulence isolate, (OURT88/3) lacking the 5 MGF 360 and 2 MGF 505 genes induced much higher levels of interferon beta gene transcription in infected porcien macrophages compared to virulent isolates which have those genes intact. This was also observed following infection of macrophages with an ASFV virus from which these genes had been deleted in comparison to the parental virus. However none of these ASFV genes inhibited expression of an interferon beta dependent reporter gene in response to stimuli including double-stranded RNA . Possibly the genes act through blocking a different inducer of interferon or they may require another virus factor or MGF family member for function.

Secretion of the host protein galectin-3 was observed following infection of macrophages with high and low virulence ASFV isolates. Galectin-3 is known to be involved in inducing apoptosis in lymphocytes, a key feature of ASFV pathogenesis, galectin-3 may possibly be involved in this process.
Exploitation Route Further research
Sectors Agriculture, Food and Drink