Determination Of Cytokines Released By Porcine Alveolar Type Ⅱ Epithrelial Cells Invitro Infection With Highly Pathogenic Porcine Reproductive And Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome (PRRS), also called Blue ear disease, isrecognized by the whole world to be the most important infectious disease of pig. Thepathogen of PRRS was confirmed to be porcine reproductive and respiratory syndrome virus(PRRSV). Pregnant sows infected with PRRSV are often characterized by abortion, stillbirthand mummy fetus, and piglets infected often showed respiratory symptoms and interstitialpneumonia. PRRSV has a strict phagocytic cell tropism. It can replicate and proliferate in theAfrican green monkey kidney cell lines MA-104, CL-2621and Marc-145, also can infect3d4/21or3d4/31strain of swine mononuclear cell line derived from PAM. In vivo, PRRSVmainly infects PAM, causing severe lung injury. Alveolar typeⅡ epithelial cell(AECⅡ)plays a central role in repairing lung injury and maintaining normal lung function. AECⅡcan regulate the immune function by secreting and synthesizing alveolar surface activesubstances, which can maintain the alveolar surface tension, adjust the metabolism ofbioactive substances and ion transport, thus becoming an important target of many pathogens.In order to explore the relationship of porcine alveolar typeⅡ epithelial cell (PAECⅡ) withPRRSV infection and its role in lung injury caused by PRRSV infection, we adopted HuN4strain of HP-PRRSV to infect primitive cultivation of PAECⅡ. The qRT-PCR technique wasapplied to detect cytokines released by PAEC Ⅱa fter HP-PRRSV infection. The expressionchanges of IL-10, IFN-γ, TNF-α, NF-κB and IRF-1, IRF-3were detected to investigate therelationship between PRRSV and the target cell after PRRSV infection, so as to lay a goodfoundation for studying the pathogenic mechanism of HP-PRRSV. Our results are as follows:1. PRRSV can infect primitive separation of PAECⅡ.12hpi(hour post infection)，PAECⅡ gathered more apparently;24hpi, it showed more irregular form, and part of it died, withthe nucleus becoming more and more obvious;48hpi, most of it died, with the rest dispersingand disrupting. Replication of PRRSV in PAECⅡin vitro peaked at24hpi, and declined rapidly at48hpi. PAECⅡcan be used as another model for PRRSV infection of pig.2. The expression of cytokines from PAEC Ⅱ changed with the process of PRRSVinfection. For example, the expression of IRF-1and IRF-3were consistent with the viral loadin the cell. The expression increased at the early stage of infectionand decreased later (P <0.05). IRF-3regulates transcriptions of down stream genes, including the interferon, inhibiting virus replication. After PRRSV infection of PAECⅡ, the expression of IL-10, IFN-γ，NF-κBdeclined significantly, and with the increase of viral replication, the decline range becamegreater. The decreased expression of NF-κB directly reduces the transcription of IFN. Thedecreased expression of IFN-γ increased the degree of disease. However, the reduction ofIL-10weakened the immune suppression of the cell. The expression change of TNF-α showeda positive correlation with the amount of virus in the cell, indicating the important role ofTNF-α in the enhancement of the immune response.In conclusion, PAECⅡcan be used as another model of PRRSV research, and theinfection characteristics was different from that of PAM, thus can strengthen theunderstanding of pathogenic mechanism of PRRSV infection on the other hand.