MUTATIONS IN A TOLL-LIKE RECEPTOR MOTIF IN THE NS4B OF CLASSICAL SWINE FEVER VIRUS SKIN BRESCIA INFLUENCES VIRULENCE IN SWINE

摘要

NS4B is one of the non-structural proteins of classical swine fever virus. By using functional genetics, we have discovered, in the predicted amino acid sequence of NS4B of CSFV strain Brescia, a motif that resembles those found in the toll-like receptor (TLR) proteins, a group of host cell proteins involved in the development of anti-viral mechanisms. We have located the TLR motif in two groups of amino acid triplets at amino acid positions 2531 -3 (residues IYK) and 2566-8 (residues VGI) of the CSFV NS4B glycoprotein. We have constructed a recombinant CSFV (derived from an infectious clone containing the genetic information of the highly virulent strain Brescia) containing amino acid substitutions in the three amino acid residues at positions 2566, 2567 and 2568, where the VGI triplet has been replaced by an AAA triplet inside the NS4B glycoprotein. The obtained virus, named NS4B-VGIv, was completely attenuated in swine, showing a limited ability in spreading during the infection in vivo. Although attenuated, NS4B-VGIv efficiently protected swine from challenge with virulent BICv at 3 and 28 days post-infection.