Attenuated Porcine Reproductive and Respiratory Syndrome Virus Regains Its Fatal Virulence by Serial Passaging in Pigs or Porcine Alveolar Macrophages To Increase Its Adaptation to Target Cells

• DOI: 10.1128/spectrum.03084-22
• Publication Date: 2022-10-11T14:00:23Z
• Authors: Jingjing Wang; Mengsi Zhang; Xiaochun Cui; Xiang Gao; Weifeng Sun; Xinna Ge; Yongning Zhang; Xin Guo; Jun Han; Lei Zhou; Hanchun Yang
• Keywords: Alveolar macrophage; Serial passage

Porcine reproductive and respiratory syndrome (PRRS) is a globally important disease threatening the pork industry, modified live-virus (MLV) vaccines are widely used for its prevention. However, PRRS MLV shows high potential reversion to virulence, leading major concern about safety. Yet revertant mechanism still poorly understood. Here, attenuated virus JXwn06-P80, derived from highly pathogenic (PRRSV) strain JXwn06 by serial passaging in MARC-145 cells, was reversely passaged pigs through intranasal inoculation mimic natural infection 13 rounds, pathogenicity of viruses at 3rd, 5th, 9th, 10th, 11th passages evaluated pigs. From 9th passage, caused mortality, which related their increased adaptability replication efficiency (100 times higher than those JXwn06-P80) porcine alveolar macrophage (PAM) target cells. Similarly, JXwn06-P80 could also regain fatal virulence reverse passage PAMs 25 or more passages, indicating that directly contributes regained virulence. Next, full-genome sequences were analyzed explore genetic evolutionary processes during adaptation both vivo vitro. Finally, operation, four mutation sites, NSP12-W121R, ORF2b (open reading frame 2b)-H9D, ORF5-H15L, ORF5-V189L, finally identified partially contribute ability adapt PAMs, may be passage. These findings provided direct scientific evidence valuable clues exploring molecular mechanism. IMPORTANCE Reversion live vaccine public concern; however, limited, we present after cells found correlation between fitness primary PAMs. The process will provide offer implications understanding mechanisms other vaccines.