Flounder (Paralichthys olivaceus) cDNA encoding a secreted immunoglobulin M heavy chain

Cloning and expressional analysis of secretory and membrane-bound IgM in rock bream (Oplegnathus fasciatus) under megalocytivirus infection and vaccination

In this study, for better understanding the humoral immunity of rock bream (Oplegnathus fasciatus), 2 transcripts of immunoglobulin M (IgM) heavy chain gene including membrane bound (m-IgM) and secretory (s-IgM) forms were sequenced and analyzed their tissue distribution and differential expression in rock bream under rock bream iridovirus (RBIV) infection and vaccination since RBIV has caused mass mortality in rock bream aquaculture in Korea. Consequently, s-IgM cDNA was 1902 bp in length encoding a leader region, a variable region, four constant regions (CH1, CH2, CH3, CH4) and a C-terminal region while m-IgM cDNA was 1689 bp in length encoding shorter three constant regions (CH1, CH2, CH3) and two transmembrane regions. The predicted s-IgM and m-IgM represent a high structural similarity to other species including human. In tissue distribution analysis in healthy fish, the highest expression of s-IgM was observed in head kidney followed by body kidney, spleen, and mid gut whereas m-IgM expression was the highest in blood followed by head kidney and spleen. In vitro, s-IgM expression was up-regulated by LPS in head kidney and spleen cells at 24 h with no change of m-IgM expression. In vivo upon vaccination, s-IgM expression was up-regulated in liver and blood but not in head kidney while m-IgM expression was only up-regulated in head kidney. After challenge with RBIV, s-IgM expression level was higher in vaccinated fish than in unvaccinated fish and m-IgM expression was up-regulated in head kidney of vaccinated group. In conclusion, differential expression of m-IgM and s-IgM may indicate their differential functions to produce the most effective IgM during adaptive immune response. Although it is not able to assess specific IgM at protein level due to a lack of antibody against rock bream IgM, the present study on s-IgM and m-IgM gene expressions upon infection and vaccination will be useful in developing efficient vaccines in the future.

Immunoglobulin Tau Heavy Chain (IgT) in Flounder, Paralichthys olivaceus: Molecular Cloning, Characterization, and Expression Analyses

Immunoglobulin tau (IgT) is a new teleost immunoglobulin isotype, and its potential function in adaptive immunity is not very clear. In the present study, the membrane-bound and secreted IgT (mIgT and sIgT) heavy chain genes were cloned for the first time and characterized in flounder (Paralichthys olivaceus), and found the nucleic acid sequence were exactly same in the Cτ1–Cτ4 constant domains of mIgT and sIgT, but different in variable regions and the C-terminus. The amino acid sequence of mIgT shared higher similarity with Bovichtus diacanthus (51.2%) and Dicentrarchus labrax (45.0%). Amino acid of flounder IgT, IgM, and IgD heavy chain was compared and the highest similarity was found between IgT Cτ1 and IgM Cμ1 (38%). In healthy flounder, the transcript levels of IgT mRNA were the highest in gill, spleen, and liver, and higher in peripheral blood leucocytes, skin, and hindgut. After infection and vaccination with Edwardsiella tarda via intraperitoneal injection and immersion, the qRT-PCR analysis demonstrated that the IgT mRNA level was significantly upregulated in all tested tissues, with similar dynamic tendency that increased firstly and then decreased, and higher in gill, skin, hindgut, liver, and stomach in immersion than in the injection group, but no significant difference existed in spleen and head kidney between immersion and injection groups. These results revealed that IgT responses could be simultaneously induced in both mucosal and systemic tissues after infection/vaccination via injection and immersion route, but IgT might play a more important role in mucosal immunity than in systemic immunity.

Molecular cloning and characterization of secretory and membrane-bound IgM of turbot

In recent years, increasing diseases especially bacterial diseases have brought a host of losses with the expansive cultivation of turbot (Scophthalmus maximus). In order to do more research about the immune system of turbot for better understanding the mechanism of resisting diseases, the immunoglobulin genes related to secretory and membrane-bound IgM (s-IgM and m-IgM) of turbot were cloned using homology sequences cloning and SMART RACE PCR method. The heavy chain of s-IgM cDNA is 1900 bp in length including a leader region, a variable region, four constant regions (CH1, CH2, CH3 and CH4) and a C-terminal while the cDNA of m-IgM is 1795 bp with the same leader region, variable region, three constant regions (CH1, CH2 and CH3) and two transmembrane regions (TM1 and TM2). The sequence of IgM gene was also obtained and the structure consisted of V-CH1-CH2-CH3-CH4-TM1-TM2 is similar to other fishes. The highest level of s-IgM expression was observed in spleen, followed by kidney, gills, eyes, skin of the healthy turbot whereas the same profile of m-IgM expression is found with low level. And s-IgM takes up dominant proportion of total IgM expression. Also the relative expressions of s-IgM and m-IgM were analyzed in turbot vaccinated with the live attenuated vaccine Vibrio anguillarum. Not only the transcriptions of both s-IgM and m-IgM in liver, spleen and kidney of turbot injected with V. anguillarum MVAV6203 were up-regulated but also the expressions of s-IgM and m-IgM in spleen, kidney, gut, skin and gills of bath-vaccinated turbot were increased. Comparing the ratio changes of relative expression of m-IgM and s-IgM in vaccinated turbot, we found that the proportion of m-IgM were increasing in both administration routes, which probably indicated that the increasing expression of m-IgM strengthen the phagocytic ability of B cells.

Immunoglobulin genes and their transcriptional control in teleosts

Immunoglobulin (Ig), which exists only in jawed vertebrates, is one of the most important molecules in adaptive immunity. In the last two decades, many teleost Ig genes have been identified by in silico data mining from the enormous gene and EST databases of many fish species. In this review, the organization of Ig gene segments, the expressed Ig isotypes and their transcriptional controls are discussed. The Ig heavy chain (IgH) locus in teleosts encodes the variable (V), the diversity (D), the joining (J) segments and three different isotypic constant (C) regions including Cμ, Cδ, and Cζ/τ genes, and is organized as a "translocon" type like the IgH loci of higher vertebrates. In contrast, the Ig light (L) chain locus is arranged in a "multicluster" or repeating set of VL, JL, and CL segments. The IgL chains have four isotypes; two κ L1/G and L3/F), σ (L2) and λ. The transcription of IgH genes in teleosts is regulated by a VH promoter and the Eμ3' enhancer, which both function in a B cell-specific manner. The location of the IgH locus, structure and transcriptional function of the Eμ3' enhancer are important to our understanding of the evolutional changes that have occurred in the IgH gene locus.

The up-regulation of large yellow croaker secretory IgM heavy chain at early phase of immune response

An immunoglobulin M (IgM) heavy-chain gene homologue was isolated from the spleen cDNA library of the large yellow croaker Pseudosciaena crocea (LycIgH). The complete cDNA of LycIgH is 1,987 nucleotides long, encoding a protein of 585 amino acids with a putative molecular weight of 64.5 kDa. The deduced LycIgH possesses a typical secretory IgM heavy chain organization with a variable region (V(H)) connected to four constant regions (C(H1-4)) by a diversity segment (D(H)) and a joining segment (J(H)). Tissue expression profile analysis showed that LycIgH was constitutively expressed in gills, intestine, liver, kidney, heart, spleen, muscle, and blood, while at a higher level in spleen, kidney and intestine. Upon stimulation with poly (I: C), the LycIgH transcripts were quickly increased in spleen and kidney at 12 h post induction (with 5.87- and 5.48-fold mRNA increases, respectively), followed by a recovery to normal level at 24 h. The LycIgH transcripts in spleen and kidney induced by inactivated bacterial vaccine reached their peak levels at 48 h (14.53-fold) and 12 h (3.70-fold), respectively. These results indicated the up-regulation of LycIgH expression in spleen and kidney by poly (I: C) or bacterial vaccine occurred at the early phase of induction and was differentially modulated in the two tissues by different stimulations.

What happens to the DNA vaccine in fish? A review of current knowledge

The primary function of DNA vaccines, a bacterial plasmid DNA containing a construct for a given protective antigen, is to establish specific and long-lasting protective immunity against diseases where conventional vaccines fail to induce protection. It is acknowledged that less effort has been made to study the fate, in terms of cellular uptake, persistence and degradation, of DNA vaccines after in vivo administration. However, during the last year some papers have given new insights into the fate of DNA vaccines in fish. By comparing the newly acquired information in fish with similar knowledge from studies in mammals, similarities with regard to transport, blood clearance, cellular uptake and degradation of DNA vaccines have been found. But the amount of DNA vaccine redistributed from the administration site after intramuscular administration seems to differ between fish and mammals. This review presents up-to-date and in-depth knowledge concerning the fate of DNA vaccines with emphasis on tissue distribution, cellular uptake and uptake mechanism(s) before finally describing the intracellular hurdles that DNA vaccines need to overcome in order to produce their gene product.

Possible evolutionary links between immunoglobulin light chains and other proteins involved in amyloidosis

With limited exceptions, proteins that account for the amyloidoses appear to be evolutionarily unrelated. Transthyretin is classified as having an "immunoglobulin-like" fold as found in light chain variable and constant domains. Thus, these amyloidogenic proteins have significant conformational similarity. In the absence of primary structure similarity sufficient to justify an inference of an evolutionary relationship, transthyretin is considered an analog of immunoglobulin domains having accrued the immunoglobulin-like fold by some form of convergent evolution of structure. Improvements in sequence comparison tools and strategies, coupled with recent logarithmic increases in the availability of primary structure data, now make it possible to suggest that transthyretin and immunoglobulins may have a common evolutionary origin. In addition, lactadherin, the medin fragment of which accounts for the most common form of human amyloid, also appears to be evolutionarily linked to transthyretin and immunoglobulins.

Cloning and Expression of Partial Japanese Flounder (Paralichthys olivaceus) IgD

The cDNA sequence of the Japanese flounder (Paralychthys olivaceus) IgD has been previously reported (GenBank accession no. AB052658) and this was followed by the detection of IgD mRNA expression in some flounder organ tissues. However, it has not been determined whether the flounder IgD gene is virtually expressed into IgD protein. To characterize the flounder immunoglobulins utilized in elucidating the mechanism, evolution and diversity of the flounder immune system, antibodies specific to IgD and IgM were necessary. In the present study, partial flounder recombinant IgD (rIgD), IgM (rIgM) and the conserved regions of IgD and IgM (rCIg) were produced by cloning the cDNA sequence using isotype specific primers which were designed to produce unique fragments of IgD and IgM specific amino acid sequences. The production of recombinant Igs was ascertained by SDS-gel electrophoresis and immunoblot analysis using anti-T7 d Taq antibody. The produced recombinant Igs were purified using affinity columns, and used as immunogens. Antibodies specific to the isotype of flounder Igs were generated by immunizing rabbits with rfIgs and the antibodies produced were identified by enzyme-linked immunosorbent assay (ELISA) and immunoblotting. Specificities of the generated antibodies were evaluated by testing cross-reactivity between recombinant IgM and IgD. By ELISA, rabbit antibodies against the rfIgD fragment (anti-rfIgD) failed to recognize any kind of flounder serum Igs, whereas respective antibodies against rfCIg (anti-rfCIg) and rfIgM fragments (anti-rfIgM) reacted with serum Igs. Likewise, in immunoblot assays, though anti-rfIgD did not, both anti-rfCIg and anti-rfIgM bound with the ~85 kd flounder IgM heavy chain. By flow cytometry analysis, anti-rfCIg, anti-rfIgD and anti-rfIgM reacted with 6%, 3% and 6.5% of cells, respectively, suggesting that flounder IgD is not secreted in serum but expressed on flounder B-like cell surfaces as in mammals. Antibodies produced against recombinant flounder Igs could be used to develop sandwich assay systems for detecting flounder Igs and for further investigating the flounder immune system.

Characterization of serum immunoglobulin M of grouper and cDNA cloning of its heavy chain

Immunoglobulin M (IgM) from the whole serum of grouper fish, Epinephelus coioides was purified by affinity chromatography using protein A-Sepharose column. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions revealed that the relative molecular masses (Mr) of the equimolar heavy and light chains of IgM were 78,000 and 27,000, respectively. The cDNAs encoding IgM heavy chain comprising its variable (VH) and constant (CH) regions have been cloned and sequenced from a grouper kidney cDNA library by antibody screening method. Five VH (130-142 amino acids) and four CH (450-454 amino acids) families were identified. The variable and constant regions were conserved with their putative domains. All the four constant region domains (CH1-CH2-CH3-CH4) contained each three conserved cysteine residues, which are considered to form the inter- and intra-chain disulfide bridges. There were three carbohydrate acceptor sites in the constant region. In general, the pattern of IgM gene organization seems to resemble that of other teleosts. Moreover, the CH genes in grouper IgM occur as multifamily as reported in Atlantic salmon and common carp.

Immunoglobulin V(H)families and light chain isotypes in the spotted wolffish (Anarhichas minor Olafsen)

The spotted wolffish (Anarhichas minor Olafsen) is a species of the Perciformes, the most diverse and numerous order of all fish. A cDNA library from head kidney tissue was screened for immunoglobulin (Ig) heavy and light chain transcripts, and showed highest identity to Ig sequences from other perciform species. So far only one Ig class is described in spotted wolffish, but three V(H)families were identified among the heavy chain transcripts. Highest diversity was located at the CDR3 region and demonstrates the importance of this gene element to the antibody repertoire. Two V(L)families were identified among the light chain clones and three distinct isotypes were present. Use of polymerase chain reaction and in situ hybridisation techniques revealed individual variations in the relative expression of the three isotypes of light chains.