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C Burkard, T Opriessnig, AJ Mileham, T Stadejek, T Ait-Ali, SG Lillico, CBA Whitelaw and AL Archibald
Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) has a narrow host cell tropism, limited to cells of the monocyte/macrophage lineage. CD163 protein is expressed at high levels on the surface of specific macrophage types and a soluble form is circulating in blood. CD163 has been described as a fusion receptor for PRRSV, with the scavenger receptor cysteine-rich domain 5 (SRCR5) region having been shown to be the interaction site for the virus.As reported earlier, we have generated pigs in which Exon 7 of the CD163 gene has been deleted using CRISPR/Cas9 editing in pig zygotes. These pigs express CD163 protein lacking SRCR5 (ΔSRCR5 CD163) and show no adverse effects when maintained under standard husbandry conditions. The ΔSRCR5 CD163 was not only detected on the surface of macrophage subsets, but the secreted, soluble protein can also detected in the serum of the edited pigs, as shown here by porcine soluble CD163-specific ELISA. Previous results showed that primary macrophage cells from ΔSRCR5 CD163 animals are resistant to PRRSV-1, subtypes 1, 2, and 3, as well as PRRSV-2 infection in vitro Here, ΔSRCR5 pigs were challenged with a highly virulent PRRSV-1, subtype 2 strain. In contrast to the wildtype control group, ΔSRCR5 pigs showed no signs of infection and no viremia or antibody response indicative of a productive infection. Histopathological analysis of lung and lymph node tissue showed no presence of virus replicating cells in either tissue. This shows that ΔSRCR5 pigs are fully resistant to infection by the virus.Importance Porcine Reproductive and Respiratory Syndrome virus (PRRSV) is the etiological agent of PRRS, causing late-term abortions, stillbirths, and respiratory disease in pigs, incurring major economic losses to the world-wide pig industry. The virus is highly mutagenic and can be divided into two species, PRRSV-1 and PRRSV-2, each containing several subtypes. Current control strategies mainly involve biosecurity measures, depopulation, and vaccination. Vaccines are at best only partially protective against infection with heterologous subtypes and sublineages and modified-live vaccines have frequently been reported to revert to virulence. Here we demonstrate that a genetic control approach results in complete resistance to PRRSV infection in vivo CD163 is edited such as to remove the viral interaction domain while maintaining protein expression and biological function, averting any potential adverse effect associated with protein knock-out. This research demonstrates a genetic control approach with potential benefits in animal welfare as well as to the pork industry.
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