Identification of a rabbit Ig light chain recombinant protein bound to serum immunoglobulins from different marine fish species.

The structures of fish serum immunoglobulin differ among different fish species. In this study, we accidently isolated a rabbit immunoglobulin (Ig) light chain bound to serum immunoglobulin from different marine fish species using phage display. Fish Ig was separated using a protein A column. The phage library was generated from variable regions of rabbit spleen B cells immunized with bluefin tuna Thunnus orientalis Ig. Fish Ig-specific phages were enriched using two rounds of bio-panning with yellowtail Seriola quinqueradiata serum Ig, followed by two rounds of bio-panning with red seabream Pagrus major serum Ig. The enriched phages demonstrated an increase in binding specificity to the tuna, yellowtail, and red seabream Igs compared to the phages listed in the unpanned library. A recombinant protein of a single clonal phage, which encodes the rabbit Ig light chain, was produced, and the binding specificities to fish Igs were analyzed using enzyme-linked immunosorbent assay (ELISA) and western blotting. The recombinant protein exhibited binding properties to fish Igs in the ELISA. However, the recombinant protein that bound to serum protein(s), but not IgM, was detected via western blotting. The recombinant protein may provide a novel information on the common structural feature in the fish immunoglobulins.

Identification and expression analysis of Fc receptor-like proteins in Japanese flounder (Paralichthys olivaceus).

Fc receptors (FcRs) are specific to the Fc portion of immunoglobulin (Ig) molecules. Here, four Fc receptor-like proteins, JF-FcR-like protein 1-4, were identified in Japanese flounder. Their open reading frames encoded 358, 255, 519 and 441 amino acid residues, respectively. JF-FcR-like protein mRNAs were mainly detected in kidney and spleen of healthy fish. Injection of formalin-killed cells (FKCs) of Edwardsiella tarda significantly increased the spleen mRNA levels of JF-FcR-like protein 1 but not the other JF-FcR-like proteins. Injection of FKC of Streptococcus iniae did not significantly affect any of the JF-FcR-like protein mRNAs. These findings suggest that the FcR-like proteins have different involvements in pathogen responses.

Class B CpG-ODN2006 is highly associated with IgM and antimicrobial peptide gene expression through TLR9 pathway in yellowtail Seriola lalandi.

The purpose of this study was to characterize the TLR9 gene from yellowtail (Seriola lalandi) and evaluate its functional activity using the class B Cytosine-phosphate-guanine-oligodeoxynucleotide2006 (CpG-ODN2006) in an in vivo experiment after one-week immunostimulation. The gene expressions of TLR9, Immunoglobulin M (IgM), antimicrobial peptides and cytokines were evaluated by real time PCR, and humoral immune parameters were analyzed in serum. The TLR9 nucleotide sequence from yellowtail was obtained using the whole-genome shotgun sequencing method and bioinformatics tools. The yellowtail full-length cDNA sequence of SlTLR9 was 3789 bp in length, including a 66-bp 5'-untranslated region (UTR), a 3'-UTR of 528 bp, and an open reading frame (ORF) of 3192 bp translatable to 1064 amino acid showing a high degree of similarity with the counterparts of other fish species and sharing common structural architecture of the TLR family, including LRR domains, one C-terminal LRR region, and a TIR domain. Gene expression studies revealed the constitutive expression of TLR9 mRNA in all analyzed tissues; the highest levels were observed in intestine, liver and spleen where they play an important role in the fish immune system. The expression levels of TLR9 after B class CpG-ODN2006 (the main TLR9-agonist) was significantly up-regulated in all analyzed tissues, with the high expression observed in spleen followed by intestine and skin. The CpG-B has been shown as a potent B cell mitogen, and interestingly, IgM mRNA transcript was up-regulated in spleen and intestine, which was highly correlated with TLR9 after CpG-ODN2006 stimulation. The antimicrobial peptides, piscidin and NK-lysine, were up-regulated in spleen and gill after CpG-ODN2006 injection with a high correlation (r ≥ 0.82) with TLR9 gene expression. Cytokine genes were up-regulated in spleen, intestine and skin after CpG-ODN was compared with the control group. No significant correlation was observed between TLR9 and IL-1ß, TNF-α and Mx gene expressions. The results showed that CpG-ODN2006 intraperitoneal injection enhanced lysozyme, peroxidase and superoxide dismutase activities in serum and demonstrated that CpG-ODN2006 can induce a specific immune response via TLR9 in which IgM and antimicrobial peptides must have an important role in the defense mechanisms against infections in yellowtail.

Temperature-dependent regulation of gene expression in Japanese flounder Paralichthys olivaceus kidney after Edwardsiella tarda formalin-killed cells.

Temperature affects the activities of the immune system and the susceptibility of fish to pathogens. To investigate the modulation of temperature on immune related gene expression in formalin-killed cells (FKC) of Edwardsiella tarda-injected Japanese flounder Paralichthys olivaceus, fish reared at 15 or 22 °C were injected with FKC of E. tarda. The up-regulation of immune related genes was detected in FKC-injected fish at both temperatures by qPCR. The mRNA expression of IFNγ was highly up-regulated at 6 h post injection (hpi) in FKC-injected fish at 15 °C, whereas at 22 °C, strong up-regulation of the gene was detected at 3 hpi The mRNA expression level of IRF1 was detected from 3 hpi to day 14 post injection in fish reared at 15 °C, but the gene was up-regulated from 3 to 6 hpi in fish reared at 22 °C. Comprehensive gene expression profiling showed that immune related genes are differentially expressed between 15 and 22 °C. Genes involved in the IFNγ signaling pathway were up-regulated at 22 °C but not at 15 °C. These results demonstrate that gene(s) involved in IFNγ signaling pathway in Japanese flounder stimulated with FKC of E. tarda are regulated by temperature.

Molecular cloning and comparative responses of Toll-like receptor 22 following ligands stimulation and parasitic infection in yellowtail (Seriola lalandi).

TLR22 is exclusively present in teleosts and amphibians and is expected to play the distinctive role in innate immunity. In this study, we cloned the full-length cDNA sequence of yellowtail (Seriola lalandi) TLR22 (SlTLR22). The complete cDNA sequence of SlTLR22 was 4208 bp and encodes a polypeptide of 961 amino acids. Analysis of the deduced amino acid sequence indicated that SlTLR22 has typical structural features of proteins belonging to the TLR family. These included 17 LRR domains (residues 91-633) and one C-terminal LRR domain (LRR-CT, residues 693-744) in the extracellular region, and a TIR domain (residues 800-943) in the cytoplasmic region. Comparison with homologous proteins showed that the deduced SlTLR22 has the highest sequence identity to turbot TLR22 (76%). Quantitative real-time PCR (qPCR) analysis demonstrated the constitutive expression of SlTLR22 mRNA in all examined tissues with higher levels in the head kidney, intestine, skin and spleen. Further, SlTLR22 expression was significantly up-regulated following TLR ligands injection with lipopolysaccharide (LPS), CpG ODN2006 and polyinosinic: polycytidylic acid (poly I:C) in spleen and liver. Amyloodinium ocellatum infection also induced a high expression of SlTLR22 in spleen, intestine, muscle, skin and gill, with maximum increases ranging from 1000 to 100 fold upon different ligands and organs. Finally, histological examination in gill tissue confirmed infection by the parasite and histopathological lesion was observed also in spleen and skin. These findings suggest a possible role of SlTLR22 in the immune responses to the infections of a broad range of pathogens that include DNA and RNA viruses and parasites.

Development and evaluation of polyclonal antisera for detection of the IgM heavy chain of multiple fish species.

Antibodies are widely considered to be essential tools for detection of immune responses in various fish species. Here we produced the peptide polyclonal antisera (anti-fish IgH-1 and anti-fish IgH-2) to detect IgM of various fish species. The peptides were designed based on the conserved sequence of the fish immunoglobulin heavy chains of seven fish species (Japanese flounder, seabream, yellowtail, carp, rainbow trout, hybrid sturgeon and banded houndshark). By Western blotting, anti-fish IgH-1 antiserum detected the IgMs of all fish species except banded houndshark. Anti-fish IgH-2 antiserum clearly reacted with the IgMs of only three of the fish species (seabream, yellowtail and rainbow trout). Attempts to use the antisera to measure fish antibody titer by ELISA were unsuccessful. These results demonstrate that anti-fish IgH-1 peptide polyclonal antiserum is a potentially applicable tool for detecting immunoglobulins in various fish species by Western blotting.

TLR21's agonists in combination with Aeromonas antigens synergistically up-regulate functional TLR21 and cytokine gene expression in yellowtail leucocytes.

The purpose of this study was to characterize the TLR21 gene from yellowtail (Seriola lalandi) and its functional activity using TLR agonist stimulation and Aeromonas antigens. The TLR21 nucleotide sequence from yellowtail was obtained using the whole-genome shotgun sequencing method and bioinformatics tools. Basal TLR21 gene expression was analyzed in several tissues. Subsequently, the gene expression of TLR21 and cytokines IL-1ß and TNF-α was evaluated in TLR agonist (CpG-ODN2006, LPS, and Poly I:C) exposing head kidney leucocytes, which were then subjected to Aeromonas antigen stimulation. The yellowtail full-length cDNA sequence of SlTLR21 was 3615 bp (980 aa) showing a high degree of similarity with the counterparts of other fish species and sharing the common structural architecture of the TLR family, including LRR domains, one C-terminal LRR region, and a TIR domain. Gene expression studies revealed the constitutive expression of TLR21 mRNA in all the analyzed tissues; the highest levels were observed in spleen and head kidney where they play an important role in the fish immune system. Transcripts of TLR21 and the downstream IL-1ß and TNF-α cytokine genes were most strongly up-regulated after exposure to the TLR agonists following Aeromonas antigen stimulation, suggesting they are involved in immune response. The results indicated that TLR agonists, in combination with Aeromonas antigens in head kidney leucocytes, synergistically enhance TLR21 and cytokines in yellowtail.