Expression profile of Toll-like receptor mRNA in pigs co-infected with porcine reproductive and respiratory syndrome virus and porcine circovirus type 2

• We investigate the interaction effect of pigs co-infected with PRRSV and PCV2.
• There was an increased mRNA expression for TLRs2, 4 and 8 in co-infected pigs.
• There was a decreased mRNA expression for TLRs3, 7 and 9 in co-infected pigs.
• A positively synergistic interaction on the expression of TLRs4 and 8 was observed.
• There was negative synergistic interaction on the expression of TLRs3, 7 and 9.

Field and experimental studies have shown that co-infection of pigs with porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) increases the severity of the disease. The present study investigates the mRNA expression profile of Toll-like receptors (TLRs) in pigs co-infected with PRRSV and PCV2. SPF pigs were infected with PRRSV, PCV2 or in a combination of both. The mRNA expression levels of TLRs and related cytokines in peripheral blood mononuclear cells (PBMCs) of pigs were determined by quantitative real-time RT-PCR. The mRNA expression profiles of TLRs by PBMCs from pigs co-infected with PRRSV and PCV2 displayed two distinct patterns: an increased expression profile for TLRs2, 4 and 8, and a decreased expression profile for TLRs3, 7 and 9. An up-regulated expression of IL-1β and IL-10 mRNA and a down-regulated expression of INF-α and TNF-α mRNA in PBMCs of co-infected pigs were also observed.