Abstract: To research the mechanism of porcine reproductive and respiratory syndrome virus (PRRSV) infection mediated by immune complex, we investigated the effects of immune complex on the factors which affect the multiplication of PRRSV. In this study, 200 TCID₅₀ was inoculated in PAM cells, with an equal volume rabbit anti-pig IgG-IgG complex, which final concentration was 1.30 mg·mL^－1，and was added to the PAM cells before, after or with PRRSV infection. Cells and the supernatant were collected at 12, 24, 36 and 48 hours, respectively. While we also set the control group with PRRSV infection, immune complexes group and the healthy cells group, apart. The mRNA levels of IFN-α, IL-10 and TNF-α were detected by establishing relative quantitative PCR method. The PRRSV RNA copies of 48 hours were detected by establishing absolute quantitative PCR method. And the quantitative data was analysed. At the same time, the protein quantity of IFN-α was detected by the ELISA method. The immune complex could enhance the multiplication of PRRSV in PAM absolutely (P<0.05). At the same time, after the infection of 48 hours, the immune complex could raise the mRNA levels of IFN-α and TNF-α, but before the 36 hours, it had no evident regulation, while in all the times, the immune complex could decrease the mRNA level of IL-10. The protein level of INF-α is showed as a "down-up-down" tendency in healthy PAM cells during 12 to 48 hours. The result indicated that the expression and transcription of IFN-α was not happened at the same time. While PRRSV infected at the early stage, the immune complex could suppress the transcription levels of antiviral cytokines induced by PRRSV infection, and the virus' copy was promoted. But at the later, the enhancement of PRRSV was inhibited owing to the high concentration of antiviral cytokines. And the transcription of TNF-α induced by the immune complex had no obvious regulation. It might be reasoned for that the immune complex could combine with both activated and inhibitory FcγR to jointly regulate the cytokines transcription induced by PRRSV.