Study On The Mechanism Of Interleukin-12 (IL-12) Production Induced By Porcine Reproductive And Respiratory Syndrome Virus(PRRSV)

Porcine reproductive and respiratory syndrome (PRRS), caused by Porcine reproductive and respiratory syndrome virus (PRRSV), is one of the most economically important infectious disease in global swine industry. Clinical signs of PRRS include the reproductive failure in sows and serious respiratory disorder of piglets. Other features such as fever, anorexia, malaise, cough and dyspnea were also observed. Since it was first reported in North America in 1987, PRRS has been spread worldwide. In 2006, an atypical PRRS featured with high fever, high morbidity, and high mortality broke out in China and a highly pathogenic PRRSV (HP-PRRSV) was isolated. PRRSV is able to induce abnormal cytokines expression from infected pigs, resulting in the suppression of host immune responses.IL-12, also known as natural killer cell stimulatory factor (NKSF) or cytotoxic lymphocyte maturation factor (CLMF), is a heterodimeric cytokine composed of IL-12p40 and IL-12p35. The most important role of IL-12 is to facilitate the differentiation of Thl cells from naive T cells and promote cell mediated immune response required for effective elimination of virus and other intracellular pathogens. It has been proved that IL-12 is important for the control of PRRSV infection. In this paper, to further understand the pathogenesis of PRRSV, we investigated the mechanism of PRRSV regulated IL-12 expression.Here, we revealed that both highly pathogenic PRRSV (HP-PRRSV) and classical PRRSV isolate (CH-1a) are able to induce the production of IL-12p40 and IL-12p35 in PAM cells in vitro. When pigs were infected with HP-PRRSV, the expression levels of IL-12p40 and IL-12p35 in lungs rather than other organs were significantly elevated. In consistent, HP-PRRSV infection also induced the expression of IFN-γ in lungs. To better study the mechanism of PRRSV induced IL-12p40 production, we determined the unknown 5’terminal region of porcine IL-12p40, based on which, the promoter of porcine IL-12p40 were subsequently obtained using genome walking technology. Sequencing analysis indicated that porcine IL-12p40 promoter is highly conserved with mouse and human IL-12p40 promoters which contain control elements such as ISRE, NF-κB, C/EBP β, AP-1 and TATA box. Using inhibitors of different signaling pathways, we found that the production of IL-12p40 during PRRSV infection depends on the activation of p38 MAPK, JNK and NF-κB signaling pathways while the production of IL-12p35 depends on p38 MAPK and PKC routes. AP-1 is a classical transcriptional factor involved in JNK signaling pathway. We observed that AP-1 inhibitor could also remarkably reduce the induction of IL-12p40 by HP-PRRSV. Both JNK-AP-1 and NF-κB signaling pathways were activated during HP-PRRSV infection. Taken together, these results indicated that HP-PRRSV could induce IL-12p40 expression through the activation of JNK-AP-1 and NF-κB signaling pathways. In addition, we compared the expression levels of IL-12 in PAMs after PRRSV, PRV and SeV infection, finding the inducing capacity of PRRSV in IL-12 production to be significant weaker than other viruses.In summary, we demonstrated that PRRSV infection is able to induce the production of IL-12p40 and IL-12p35. IL-12p40 induction by PRRSV depends on the activation of JNK-AP-1 and NF-κB signaling pathways while the expression of IL-12p35 depends on p38 MAPK and PKC routes. Our findings may help us better understand the underlying mechanism of IL-12 production in PRRSV infection.