Head Kidney-Derived Macrophages of Common Carp (Cyprinus carpio L.) Show Plasticity and Functional Polarization upon Differential Stimulation

Mutations in the Aeromonas salmonicida subsp. salmonicida type III secretion system affect Atlantic salmon leucocyte activation and downstream immune responses

Deletion mutants of Aeromonas salmonicida subsp. salmonicida were used to determine the effect of the type three secretion system (TTSS) on Atlantic salmon anterior head kidney leucocytes (AHKL). One strain had a deletion in the outer membrane pore gene, ascC; and the other in three effector genes: aopO, aopH and aexT (we call this strain Deltaaop3). Host cell invasion success and 24h survival were depressed in DeltaascC, as was 24h survival of Deltaaop3, when compared to the wild type strain. Challenge of AHKLs with A449 or TTSS mutants stimulated expression of the inflammatory mediators IL-8, IL-1 and TNFalpha at two bacterial concentrations (A(600) 0.1, 0.01). Expression of IL-12 was not stimulated in DeltaascC challenged cells, whereas A449 and Deltaaop3 challenge resulted in an up-regulation of IL-12 in AHKLs, 2- and 4-fold higher than PBS, respectively. Only the wild type strain elicited a significant increase in IL-10 expression (5.5x at A(600) 0.1). Inducible nitric oxide synthetase (iNOS) and arginase (I+II) genes were also significantly up-regulated upon exposure to all strains. However, iNOS:arginase ratio was elevated in the effector mutant challenge. These results suggest that A. salmonicida subsp. salmonicida may enhance survival within the host cell through polarization of macrophages/leucocytes to an alternative, rather than classical, activation state. Furthermore, the short-term survival and lack of T-cell signalling cytokine stimulation in DeltaascC, may help explain its inefficiency at providing protection to subsequent wild type challenge.

Teleost B7 expressed on monocytes regulates T cell responses

In mammals, professional APCs induce adaptive immunity via the activation of T cells. During this process, B7 family molecules present upon APCs are known to play crucial roles in optimal T cell stimulation. In contrast, the confirmation of APCs in a nonmammalian vertebrate has yet to be achieved. To obtain further insights into the evolutionary origin of APCs, we have identified three members of the B7 family in the teleost Takifugu rubripes (fugu): B7-H1/DC, B7-H3, and B7-H4. The three fugu B7s were expressed on the surface of blood monocytes. The B7(+) monocytes, which are composed of at least two distinct populations, expressed the MHC class II component gene. The fugu B7 molecules bound to activated T cells, indicating that putative B7 receptors were expressed upon T cells. Fugu B7-H1/DC inhibited T cell proliferation concomitant with increasing levels of both IL-10 and IFN-gamma expression, whereas both B7-H3 and B7-H4 promoted T cell growth following IL-2 induction and the suppression of IL-10. These observations indicate that fugu B7s regulate T cell responses via receptors upon T cells. We suggest that fish B7(+) monocytes are APCs and that a costimulatory system has already developed in fish via the evolutionary process.

Allelic discrimination, three-dimensional analysis and gene expression of multiple transferrin alleles of common carp (Cyprinus carpio L.)

We cloned and sequenced four different transferrin (Tf) alleles (C, D, F and G) of European common carp (Cyprinus carpio carpio L.) and studied allelic diversity with respect to differences in sequence, constitutive transcription and three-dimensional structure. Most of the disulfide bonds were conserved between human and carp Tf, and modeling confirmed the overall conservation of the three-dimensional structure of carp Tf. While the iron-binding sites in the C-lobe of carp Tf were completely conserved, in the N-lobe the majority of iron-coordinating residues were not conserved. This may have a serious impact on the ability of carp Tf to bind iron with both the C- and N-lobe. In contrast to human Tf, we could not detect potential N-glycosylation sites in carp Tf, which does not seem to be a glycoprotein. Comparison of the cDNA of the four Tf alleles of carp indicated 21 polymorphic sites of which 13 resulted in non-synonymous changes. Allelic diversity did not seem to influence the overall conservation of carp Tf. Neither the iron binding sites nor the receptor binding of carp Tf seemed influenced by allelic diversity. Possibly, interaction with pathogen-associated receptors for Tf could be influenced by allelic diversity. Basal gene expression of Tf alleles D and G was especially high in carp liver. Although we could detect a higher transcription level of allele D than of Tf allele G in head kidney, thymus and spleen, the differences seem minor with respect to the very high transcription level in liver. Preliminary results with Tf-typed serum suggest a difference in the ability of Tf alleles D and G to modulate LPS-induced NO production in carp macrophages.

Rainbow trout (Oncorhynchus mykiss) possess multiple novel immunoglobulin-like transcripts containing either an ITAM or ITIMs

The recognition of pathogens by the innate immune system relies on a wide range of inhibitory and activating receptors. Some of these non-rearranging receptors belong to the immunoglobulin superfamily (IgSF) and in teleost fish the novel immune-type receptor (NITR) and the novel immunoglobulin-like transcript (NILT) have been reported. Here we describe the identification and characterisation of three new NILTs from rainbow trout (Oncorhynchus mykiss), with one NILT alternatively spliced into a long isoform containing two Ig domains and a short isoform containing one Ig domain. The cytoplasmic regions contain either immunoreceptor tyrosine-based inhibitory motifs (ITIMs) or an immunoreceptor tyrosine-based activating motif (ITAM) for downstream signalling. Alignment of the various NILT Ig domains revealed a high similarity, especially between Ig domains from NILTs found in this study. Furthermore, a phylogenetic tree showed that NILTs are more closely related to the triggering receptor expressed on myeloid (TREM) cells and NKp44 than to NITRs. The expression of NILTs was studied in six different tissues and two different cell lines, with expression apparent in immunologically important tissues. Expression of NILTs was also shown to be an early event in development, with both eyed eggs and embryos expressing all four genes. The results obtained in this study and future experiments will contribute to our knowledge of the immune system in fish and provide useful information for the control of inflammatory processes in rainbow trout.

The induction of nitric oxide response of carp macrophages by transferrin is influenced by the allelic diversity of the molecule

The central role of transferrin (Tf) as an iron transporting protein has been extended by observations that modified versions of Tf also participate in the regulation of innate immunity. We report on the isolation of two carp Tf proteins (alleles D and G) to purity using rivanol precipitation and ion-exchange chromatography, and describe the activation of head kidney-derived carp macrophages by cleaved Tf. We demonstrate the superiority of the D-type over the G-type Tf in inducing nitric oxide (NO) and confirm previous observations that full-length Tf cannot induce NO in fish macrophages. We believe that cleaved Tf fragments should be considered to be "alarmins". We discuss the possibility that parasites such as Trypanoplasma borreli cleave Tf and use Tf fragments to their advantage by modulating the NO induction in carp macrophages.

Morphine affects the inflammatory response in carp by impairment of leukocyte migration

Opioid peptides are evolutionary conserved and in teleost fish their specific receptor types have been identified not only on neuroendocrine cells but also on immunocytes. In the present work we have studied the effects of morphine, ligand for the mu3 opioid receptor, on innate immune responses of common carp. Both in vitro and in vivo, during zymosan-induced peritonitis, morphine reduced gene expression of pro-inflammatory cytokines/chemokines and chemokine receptors. Furthermore, in vitro morphine administration also affects nitric oxide production, chemotaxis and apoptosis of head kidney leukocytes. These results provide evidence for an anti-inflammatory function of morphine and suggest an evolutionary conserved cross-talk between chemokines and opioids.

Long-term culture of a cell population from Siberian sturgeon (Acipenser baerii) head kidney

In vitro cultures of native fish cell lines are of great importance, both for basic research and applied science. In particular, there is strong demand for long-term growable cell lines from breeding fish, like sturgeon. Here, we describe the culture of cells from Siberian sturgeon (Acipenser baerii) head kidney. The cells have so far been cultured over a period of 12 months (24 passages). Cytochemical and immunocytochemical examination suggests that, in vitro, the cells exhibit markers that are indicative for different cell types. In particular, fat storing cells (adipocytes) were observed, and the expression of cytokeratins and glial fibrilar acidic protein (GFAP) can be concluded on the basis of immuncytochemical analysis. The observation of different morphologies additionally underlines the heterogeneity of the cell population and matches the typical behaviour of in vitro cultures of stem/progenitor cells. Different applications can be imagined.

Expression profiles of matrix metalloproteinase 9 in teleost fish provide evidence for its active role in initiation and resolution of inflammation

Matrix metalloproteinase 9 (MMP-9) belongs to a family of zinc-dependent endopeptidases. As a consequence of its ability to cleave structural extracellular matrix molecules, mammalian MMP-9 is associated with vital inflammatory processes such as leucocyte migration and tissue remodelling and regeneration. Interestingly, MMP-9 genes have been identified in fish, but functional data are still limited and focus on the involvement of MMP-9 in embryonic development, reproduction and post-mortem tenderization. Here, we describe the involvement of MMP-9 in the innate immunity of carp. In carp, MMP-9 was most notably expressed in classical fish immune organs and in peritoneal and peripheral blood leucocytes, indicating a role of MMP-9 in immune responses. In our well-characterized zymosan-induced peritonitis model for carp, we analysed expression of the MMP-9 gene and the gelatinolytic levels of both pro- and activated forms of MMP-9. The biphasic profile of MMP-9 mRNA expression indicated involvement during the initial phase of inflammation and during the later phase of tissue remodelling. Also, in vitro stimulation of carp phagocytes with lipopolysaccharide or concanavalin A increased MMP-9 gene expression, with a peak at 24 hr. The increase of MMP-9 mRNA correlated with the peak of MMP-9 gelatinolytic level in culture supernatants. These results provide evidence for an evolutionarily conserved and relevant role of MMP-9 in the innate immune response.

Trypanoplasma borreli cysteine proteinase activities support a conservation of function with respect to digestion of host proteins in common carp

Trypanoplasma borreli is an extracellular parasite that is transmitted by a leech vector and is naturally found in the blood of cyprinid fish. High parasitemia and associated severe anemia together with splenomegaly are typical of infection of common carp, Cyprinus carpio L. Papain-like cysteine proteinases expressed by trypanosome parasites contribute to the pathogenicity of trypanosomes, and are considered an important target for the development of new trypanocidal drugs. T. borreli is a member of the Parabodonida, sharing a common ancestor with the other Kinetoplastida. We demonstrate the presence of a cysteine proteinase expressed by T. borreli. Alignment of the sequence with other kinetoplastid cysteine proteinase sequences supports the phylogenetic hypotheses based on analyses of ribosomal RNA genes. We expressed the T. borreli cysteine proteinase in Escherichia coli, refolded the purified protein into a biologically active proteinase and showed it has cathepsin L-like activity. Addition of the (non)active proteinase to in vitro-derived carp head kidney-derived macrophages did not significantly modulate macrophage activity. Immunization of carp with the recombinant proteinase did induce a very high increase in proteinase-specific antibodies but only slightly lowered parasitemia. Digestion of host hemoglobin and immunoglobulin by the cysteine proteinase likely contribute to the pathogenicity of T. borreli. The possibility that digestion by the cysteine proteinase of host transferrin could contribute to an innate activation profile of macrophages in vivo is discussed. Our findings suggest a conservation of function with respect to cysteine proteinase activity in the Parabodonida in support of the hypotheses on the phylogeny of the Kinetoplastida.

Differential contribution of neutrophilic granulocytes and macrophages to nitrosative stress in a host-parasite animal model

Tyrosine nitration is a hallmark for nitrosative stress caused by the release of reactive oxygen and nitrogen species by activated macrophages and neutrophilic granulocytes at sites of inflammation and infection. In the first part of the study, we used an informative host-parasite animal model to describe the differential contribution of macrophages and neutrophilic granulocytes to in vivo tissue nitration. To this purpose common carp (Cyprinus carpio) were infected with the extracellular blood parasite Trypanoplasma borreli (Kinetoplastida). After infection, serum nitrite levels significantly increased concurrently to the upregulation of inducible nitric oxide synthase (iNOS) gene expression. Tyrosine nitration, as measured by immunohistochemistry using an anti-nitrotyrosine antibody, dramatically increased in tissues from parasite-infected fish, demonstrating that elevated NO production during T. borreli infection coincides with nitrosative stress in immunologically active tissues. The combined use of an anti-nitrotyrosine antibody with a panel of monoclonal antibodies specific for several carp leukocytes, revealed that fish neutrophilic granulocytes strongly contribute to in vivo tissue nitration most likely through both, a peroxynitrite- and an MPO-mediated mechanism. Conversely, fish macrophages, by restricting the presence of radicals and enzymes to their intraphagosomal compartment, contribute to a much lesser extent to in vivo tissue nitration. In the second part of the study, we examined the effects of nitrosative stress on the parasite itself. Peroxynitrite, but not NO donor substances, exerted strong cytotoxicity on the parasite in vitro. In vivo, however, nitration of T. borreli was limited if not absent despite the presence of parasites in highly nitrated tissue areas. Further, we investigated parasite susceptibility to the human anti-trypanosome drug Melarsoprol (Arsobal), which directly interferes with the parasite-specific trypanothione anti-oxidant system. Arsobal treatment strongly decreased T. borreli viability both, in vitro and in vivo. All together, our data suggest an evolutionary conservation in modern bony fish of the function of neutrophilic granulocytes and macrophages in the nitration process and support the common carp as a suitable animal model for investigations on nitrosative stress in host-parasite interactions. The potential of T. borreli to serve as an alternative tool for pharmacological studies on human anti-trypanosome drugs is discussed.

Comparative analysis of the acute response of the trout, O. mykiss, head kidney to in vivo challenge with virulent and attenuated infectious hematopoietic necrosis virus and LPS-induced inflammation

BACKGROUND

The response of the trout, O. mykiss, head kidney to bacterial lipopolysaccharide (LPS) or active and attenuated infectious hematopoietic necrosis virus (IHNV and attINHV respectively) intraperitoneal challenge, 24 and 72 hours post-injection, was investigated using a salmonid-specific cDNA microarray.

RESULTS

The head kidney response to i.p. LPS-induced inflammation in the first instance displays an initial stress reaction involving suppression of major cellular processes, including immune function, followed by a proliferative hematopoietic-type/biogenesis response 3 days after administration. The viral response at the early stage of infection highlights a suppression of hematopoietic and protein biosynthetic function and a stimulation of immune response. In fish infected with IHNV a loss of cellular function including signal transduction, cell cycle and transcriptional activity 72 hours after infection reflects the tissue-specific pathology of IHNV infection. attIHNV treatment on the other hand shows a similar pattern to native IHNV infection at 24 hours however at 72 hours a divergence from the viral response is seen and replace with a recovery response more similar to that observed for LPS is observed.

CONCLUSION

In conclusion we have been able to identify and characterise by transcriptomic analysis two different types of responses to two distinct immune agents, a virus, IHNV and a bacterial cell wall component, LPS and a 'mixed' response to an attenuated IHNV. This type of analysis will lead to a greater understanding of the physiological response and the development of effective immune responses in salmonid fish to different pathogenic and pro-inflammatory agents.

In vivo kinetics of cytokine expression during peritonitis in carp: evidence for innate and alternative macrophage polarization

Despite the discovery of many cytokine genes in fish, knowledge on their functional homology is limited. To enlighten the biological function of inflammation-related mediators, we studied their kinetics of gene expression during peritonitis in carp. Zymosan-induced intraperitoneal influx of phagocytes reached a maximum at 24h. In peritoneal leukocytes (PTL) up-regulation of IL-1beta, TNF-alpha, CXCa, and chemokine receptor CXCR1 preceded this peak. Delayed up-regulation of these genes in the head kidney (HK) indicates emigration of antigen-presenting cells from peritoneum into HK and/or systemic spreading of inflammation. In turn, early increase in expression of anti-inflammatory genes in HK (6h) precede their up-regulation in the focus of inflammation. In PTL peaks of IL-10 and arginase 2 expression were recorded at 96 and 168h, respectively. These results give evidence that carp macrophages in vivo differentiate into a continuum of different activation states with innate and alternative activation representing the extremes.