Characterization of Toll-like receptor gene expression in goldfish (Carassius auratus) duringDactylogyrus intermediusinfection

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Toll-like receptors (TLRs), the first and best understood innate immune receptors, play a notable role in the innate immune system by sensing pathogenic agents and initiating appropriate immune responses. However, studies about the roles of fish TLRs in response to the infection of the ectoparasitic monogenean Dactylogyrus intermedius have been surprisingly vacant. In the present study, cDNA fragments of five members of TLRs family in goldfish (Carassius auratus) were cloned and the expression patterns of nine TLRs in five tissues at different time points during D. intermedius infection were subsequently investigated. We found that the expressions of TLR4, TLR5, TLR20 and TLR22 were significantly elevated after infection at some time points, of which the transcription of TLR5 was progressively increased nearly in all tissues, whereas the mRNA levels of other TLRs (TLR2, 3, 7, 9 and 21) were down-regulated or showed no significant change compared with the control at most time points. Additionally, this paper was also conducted to explore the expression of above TLRs after re-infected with D. intermedius. The results showed a significant upregulation of TLR4, TLR5 and TLR22 in all tested tissues at these two time points, especially the levels of TLR4 and TLR22 expression, were even higher comparing with the first infection. Besides, tissue-specific expression analysis revealed that spleen featured the highest expressions of almost all the TLR-encoding genes among detected tissues. The informations obtained here could be helpful towards understanding the functions of TLRs in response to parasitic infection in goldfish and provide new insights for the development of preventive and therapeutic approaches against D. intermedius infection.

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