The Endoribonuclease Activity Essential for the Nonstructural Protein 11 of Porcine Reproductive and Respiratory Syndrome Virus to Inhibit NLRP3 Inflammasome-Mediated IL-1β Induction

NLRP3 inflammasome, which is multiprotein complex that induces the maturity and secretion of proinflammatory interleukin-1β (IL-1β), takes a bridge between the innate and adaptive immune responses to the invading pathogens. It has been shown that porcine reproductive and respiratory syndrome virus (PRRSV) could activate the NLRP3 inflammasome but induce the host's immunosuppression. This study aims to explore whether PRRSV could encode the component to antagonize the NLRP3 inflammasome. The obtained results showed that PRRSV could induce the expression and secretion of IL-1β in early infection through the pathway of NLRP3 inflammasome in porcine alveolar macrophages (PAMs), but the levels of pro-IL-1β mRNA and IL-1β protein decreased to a degree that was similar to the level of the mock-infected group in later infection. This work also found that PRRSV nonstructural protein (nsp) 11 could inhibit the expression of pro-IL-1β mRNA induced by lipopolysaccharide (LPS) and the secretion of IL-1β induced by LPS plus nigericin in PAMs. Furthermore, the mutation studies showed that the endoribonuclease activity was essential for nsp11 to inhibit the secretion of IL-1β. Therefore, it could be indicated that PRRSV could induce the activation of NLRP3 inflammasome, but the virus encoded nsp11 to inhibit this action.