Expression patterns of Toll-like receptors in natural triploid Carassius auratus after infection with Aeromonas hydrophila

Toll-like receptors (TLRs) play the important roles in the innate immune system. In the present study, we have cloned fragments of 13 members of TLR family in natural triploid Qihe crucian carp (C. auratus) and investigated the expression profiles of these TLRs in spleen and head kidney at different time points after A. hydrophila infection. The results showed that the expressions of certain TLRs including TLR4, TLR5, and TLR22 were significantly up-regulated after infection, and the expression levels of TLR5 and TLR22 were the highest in spleen with 52.56-fold and 28.14-fold increase, respectively, whereas the other TLRs were down-regulated or no significant changes were observed compared with the control at most time points. These findings suggested that three TLRs (TLR4, TLR5, and TLR22) may play important roles in the immune responses of C. auratus to A. hydrophila infection. Additionally, the expression of most TLRs was significantly up-regulated at 6 h post infection, which implied that the immune response of C. auratus reached the highest level at this time point. This work will facilitate our comprehensive understanding for the functions of TLRs in the process of bacterial infection in C. auratus and provide new insights for developing preventive and therapeutic measures against A. hydrophila infection.