Bacterial infection has also been shown to induce TLR3 mRNA expression in zebra fish and channel catfish, as well as in channel blue back cross hybrids following infection with E. tarda and E. ictaluri. In our study, TLR3 expression was also upregulated 22. 5 fold postinfection, suggesting that this receptor might be involved in the immune response to bacterial blog of sinaling pathways infection in fish in addi tion to recognizing double stranded RNA as in mam mals. TLR22 is a fish specific member of this family that has also been found in the large yellow croa ker. Recently, TLR22 was found located on the puffer fish cell surface recognizing long dsRNA sequences, whereas mammalian nucleic acid sensing TLRs are loca lized in endosomes or the ER of myeloid cells, indicating that TLR22 may be a functional substitute for mamma lian TLR3 that monitors for infections by double stranded RNA viruses.

TLR22 was downregulated in the expression profile, implying that TLR22 was sup pressed in the early period of A. hydrophila infection. Taken together, these results indicate that TLRs are regulated by various components of Gram negative bac teria, suggesting that multiple TLR mediated signaling cascades may simultaneously be involved in immune response to bacterial infection. In our study, A. hydrophila infection led to a dramatic increase in the expression of proinflammatory cytokines such as IL 1b, IL 8, and TNF a. Studies have reported that these cytokines are induced within 24 h in human monocytes following Gram positive and Gram negative bacterial infection.

IL 1b is considered the prototypic multifunctional cytokine that affects nearly all cell types, either alone or in combination with other cytokines response to infection, injury, or immunologic challenge. IL 8 is a proinflammatory CXC chemo kine that has been shown to be regulated by a number of different stimuli including inflammatory signals, chemical and environmental stresses, and steroid hormones. GSK-3 Here, upregulation of these cyto kines was observed by real time PCR, which is consistent with the observed findings in DeepSAGE. Therefore, the upregulation of these proinflammatory cytokines strongly suggests that the proinflammatory response may represent an important antibacterial mechanism at the early phase of infection. The JAK STAT pathway is initiated in response to cytokines, such as interleukins and IFNs, and growth factors present in the surrounding microenvironment. Jak1 is a cytoplasmic tyrosine kinase that noncova lently associates with a variety of cytokine receptors and plays a nonredundant role in lymphoid cell precursor proliferation, survival, and differentiation.