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Interleukin (IL)-22 is an IL-10 family cytokine secreted by CD4+ T cells and plays an important role in regulating inflammation and infection elimination. IL-22 homologues have been reported in the teleost, but the functions of IL-22 are still unclear. In this study, we identified two duplicated IL-22 genes in common carp (Cyprinus carpio L.), termed Cc _IL-22A and Cc _IL-22B. Sequence analysis showed that Cc _IL-22A and Cc _IL-22B had four conserved cysteine residues, which could form two intra-chain disulfide bridges. The Cc _ IL-22A and Cc _ IL-22B were constitutively expressed in various tissues, with the highest expression in the gill. The mRNA expression levels of Cc _ IL-22A and Cc _ IL-22B were significantly up-regulated in the gill, intestine, head kidney, and spleen of common carp challenged with Aeromonas. hydrophila. In vivo study showed that the expression levels of pro-inflammatory cytokines were significantly up-regulated in the head kidney and spleen when Cc _IL-22A or Cc _IL-22B were over-expressed. Furthermore, the over-expression of Cc _IL-22A and Cc _IL-22B indicated a protective effect on tissues, with only lymphocytic infiltration observed in comparison to the control and pcN3 groups, without obvious change in tissue morphology. Similar stimulatory effects of rIL-22A and rIL-22B were observed in vitro. When HKLs were stimulated with rIL-22A or rIL-22B, the expression levels of critical signaling molecules in the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) pathway were significantly induced, including JAK1 , JAK3 , STAT1 , and STAT3 , as well as pro-inflammatory cytokines (IL-1β and TNF-α). Together, these results suggest that Cc _IL-22A and Cc _IL-22B may regulate inflammatory responses through the JAK-STAT signaling pathway and have a significant impact on the immune defense of common carp against bacterial infection. Therefore, our study provides a new perspective on the functions of Cc _IL-22A and Cc _IL-22B in the immune defense mechanism of fish. • Common carp IL-22A and IL-22B (Cc _IL-22A and Cc _IL-22B) were identified and characterized. • Cc_IL-22s widely expressed in all tested tissues and responded to bacterial infection. • In vivo , Cc _IL-22s over-expression affected the expression of inflammatory cytokines. • Recombinant Cc _IL-22s induced the expression of genes in JAK–STAT pathway. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are non-coding RNA molecules that regulate gene expression in fish, but its regulatory mechanism of the skin mucosal immune response remains poorly understood. In order to investigate the immunological role of miRNAs, three sRNA libraries (mSC, mST1, mST2) from skin samples of crucian carp (Carassius auratus) infected with Aeromonas hydrophila at three time points (0, 6 and 12 hpi) were constructed and examined using Illumina Hiseq 2000 platform. All of the identified miRNA, rRNA and tRNA were 69444 (13.39%), 29550 (5.70%) and 10704 (2.06%) in skin, respectively. At 6 and 12 hpi, 829 and 856 miRNAs were differentially expressed, respectively. Among these DEMs, 53 known and 10 novel miRNAs were all significantly differentially expressed during early infection (p < 0.01). GO and KEGG enrichment analyses revealed that 118111 target-genes were primarily involved in cellular process, metabolic process, biological regulation and stress response, such as antigen processing and presentation, complement and coagulation cascades, phagosome, MAPK, TLR, NF-κB and JAK-STAT signaling pathways. These results will help to elucidate the mechanism of miRNAs involved in the skin mucosal immune response of crucian carp against Aeromonas hydrophila infection. • This was first report on skin miRNAs profiles of C. auratus upon A. hydrophila infection. • 829 and 856 DEMs in skin were identified at 6 and 12 hpi, respectively. • 10 novel miRNAs were significantly differentially expressed during early infection. • Antigen presentation, complement, MAPK, TLR and NF-κB pathways were significantly involved in skin mucosal immunity. [ABSTRACT FROM AUTHOR]

Lipopolysaccharide (LPS) is a classical pathogen-associated molecular pattern that can trigger strong inflammatory response mainly by TLR4-mediated signaling pathway in mammals, but the molecular mechanism of anti-LPS immunity is unclear in teleost fishes. In this study, we analyzed the gene expression features based on transcriptome analysis in Schizothorax prenanti (S. prenanti), after stimulation with two sources of LPS from Aeromonas hydrophila and Escherichia coli (Ah. LPS and Ecoli. LPS). 921 different expression genes (DEGs) after Ah. LPS stimulation and 975 DEGs after Ecoli. LPS stimulation were acquired, but only 706 and 750 DEGs were successfully annotated into the databases, respectively. Both of two groups of DGEs were significantly enriched into immune-related pathways by KEGG enrichment analysis, such as "Toll-like receptor signaling pathway", "Cytokine-cytokine receptor interaction" and "JAK-STAT signaling pathway". The annotated DEGs from Ah. LPS and Ecoli. LPS stimulation shared 470 DEGs, including 88 immune-related DEGs (IRGs) identified mainly by KEGG enrichment to immune-related signaling pathways. Among the shared IRGs, four pattern-recognition genes (TLR5 , TLR25 , PTX3 and C1q) were induced with high expression foldchange, and IFN-γ and relative genes also showed higher expression levels than control. Meanwhile, inflammatory signals were highlighted by upregulating the expression of inflammatory cytokines (IL-1β , IL-10 and IL-8). Moreover, some non-shared IRGs (including TLR2 and TLR4) were identified, suggesting that different sources of LPS own different potentials for the induction of immune gene expression. In conclusion, TLR5, TLR25, PTX3 and C1q may function as the sensing molecules to catch the invasion signal of LPS. The anti-LPS immune response may be involved into TLR25/TLR5-mediated inflammatory signals that regulate subsequently the activation of PTX3/C1q-modulated complement pathway upon the induction of PTX3 expression, and the crosstalk between IFN-γ and TLR signaling pathways in teleost fishes. This study will contribute to further explore the molecular mechanism of LPS-induced immunity in teleost fishes. • 921 different expression genes (DEGs) after Ah. LPS stimulation and 975 DEGs after Ecoli. LPS stimulation were acquired. • The stimulation with Ah. LPS and Ecoli. LPS shared 470 DEGs including 88 immune-related DEGs (IRGs). • TLR5, TLR25, PTX3 and C1q were predicted as the potential pattern-recognition molecules in LPS sensing. • IFN-γ-mediated signaling pathway may play an important role in protecting teleost fishes against LPS. [ABSTRACT FROM AUTHOR]