A. pleuropneumoniae LPS-induced proinflammatory cytokine expression is time and dose dependent. PAMs were treated with 100 ng/ml A. pleuropneumoniae LPS for 0, 1.5, 3, 6, and 12 h. (A and B) qRT-PCR was performed to analyze the expression of IL-1β, IL-6, TNF-α, and resistin mRNA (A), and ELISA was used to detect the levels of cytokines in the supernatants (B). PAMs were exposed to 0, 10, 100, or 1,000 ng/ml A. pleuropneumoniae LPS for 6 h. (C and D) qRT-PCR was performed to analyze the expression of IL-1β, IL-6, TNF-α, and resistin mRNA (C), and ELISA was used to detect the levels of cytokines in the supernatants (D). *, P < 0.05 compared with the control group.