Influence of Foot-and-Mouth Disease Virus O/CHN/Mya98/33-P Strain Leader Protein on Viral Replication and Host Innate Immunity

Foot-and-mouth disease virus (FMDV) O/CHN/Mya98/33-P strain was isolated from the esophageal-pharyngeal fluid sample of cattle, and was shown to cause persistent infection. Its leader protein contains 200 amino acids with one amino acid deletion, which is upstream and next to the second initiation codon compared with the majority of FMDV Mya98 strains. The FMDV genome includes two initiation codons that can produce two different leader proteins, Lab (from the first AUG) and Lb (from the second AUG). For convenience, the inter-AUG region was named as La. Previously, it was found that a recombinant virus with Lab of FMDV O/CHN/Mya98/33-P strain had higher proliferation efficiency, and better ability to inhibit the host innate immune response. Three full-length infectious cDNA clones—rHN33-Lb, rHN33-La, and rHNGSLX-Lb—containing the FMDV O/CHN/Mya98/33-P strain leader proteins Lb, La, or the FMDV O/GSLX/2010 strain leader protein Lb, respectively, were constructed based on an established infectious clone r-HN rescued from FMDV O/HN/CHN/93 strain. After infecting pig kidney primary cells, rHN33-La showed higher replication efficiency than r-HN, and rHN33-Lb displayed better ability to resist host innate immunity than rHNGSLX-Lb. These results demonstrated that the inter-AUG region of FMDV strain O/CHN/Mya98/33-P leader protein must be involved in increasing viral replication efficiency. Additionally, the Lb of FMDV O/CHN/Mya98/33-P must be involve in increasing its ability to inhibit host innate immune response, and the distinctive amino acids G56 and/or R118 of FMDV leader protein may play essential roles in it.