Isolation and characterization of monocyte/macrophage from peripheral blood of half smooth tongue sole (Cynoglossus semilaevis)

LECT2 mediates antibacterial immune response induced by Nocardia seriolae infection in the northern snakehead

Leukocyte-derived chemotaxin-2 (LECT2) is a multifunctional immunoregulator that plays several pivotal roles in the host's defense against pathogens. This study aimed to elucidate the specific functions and mechanisms of LECT2 (CaLECT2) in the northern snakehead (Channa argus) during infections with pathogens such as Nocardia seriolae (N. seriolae). We identified CaLECT2 in the northern snakehead, demonstrating its participation in the immune response to N. seriolae infection. CaLECT2 contains an open reading frame (ORF) of 459 bp, encoding a peptide of 152 amino acids featuring a conserved peptidase M23 domain. The CaLECT2 protein shares 62%-84 % identities with proteins from various other fish species. Transcriptional expression analysis revealed that CaLECT2 was constitutively expressed in all examined tissues, with the highest expression observed in the liver. Following intraperitoneal infection with N. seriolae, CaLECT2 transcription increased in the spleen, trunk kidney, and liver. In vivo challenge experiments showed that injecting recombinant CaLECT2 (rCaLECT2) could protect the snakehead against N. seriolae infection by reducing bacterial load, enhancing serum antibacterial activity and antioxidant capacity, and minimizing tissue damage. Moreover, in vitro analysis indicated that rCaLECT2 significantly enhanced the migration, respiratory burst, and microbicidal activity of the head kidney-derived phagocytes. These findings provide new insights into the role of LECT2 in the antibacterial immunity of fish.

Mechanism of Chinese sturgeon IFN-γ inhibition on Mycobacterium marinum (Acipenser sinensis)

IFN-γ plays a crucial role in both innate and adaptive immune responses and is a typical Th1 cytokine that promotes Th1 response and activates macrophages. When macrophages were incubated with IFN-γ, their phagocytosis ratio against Mycobacterium marinum increased significantly, as observed under fluorescence microscopy. The macrophages engulfed a large number of M. marinum. The proliferative ability of macrophages treated with IFN-γ was significantly weaker on the 4th and 7th day after phagocytosis and subsequent re-infection with marine chlamydia (P < 0.001). This suggests that IFN-γ enhances the phagocytosis and killing ability of macrophages against M. marinum. IFN-γ protein also significantly increased the production of reactive oxygen species (H2O2) and nitric oxide (NO) by macrophages. Additionally, the expression levels of toll-like receptor 2 (tlr2) and caspase 8 (casp8) were significantly higher in macrophages after IFN-γ incubation compared to direct infection after 12 h of M. marinum stimulation. Apoptosis was also observed to a higher degree in IFN-γ incubated macrophage. Moreover, mRNA expression of major histocompatibility complex (MHC) molecules produced by macrophages after IFN-γ incubation was significantly higher than direct infection. This indicates that IFN-γ enhances antigen presentation by upregulating MHC expression. It also upregulates tlr2 and casp8 expression through the TLR2 signaling pathway to induce apoptosis in macrophages. The pro-inflammatory cytokine showed an initial increase followed by a decline, suggesting that IFN-γ enhances the immune response of macrophages against M. marinum infection. On the other hand, the anti-inflammatory cytokine showed a delayed increase, significantly reducing the expression of pro-inflammatory cytokines. The expression of both cytokines balanced each other and together regulated the inflammatory reaction against M. marinum infection.

ceRNA crosstalk mediated by ncRNAs is a novel regulatory mechanism in fish sex determination and differentiation

Competing endogenous RNAs (ceRNAs) are vital regulators of gene networks in mammals. The involvement of noncoding RNAs (ncRNAs) as ceRNA in genotypic sex determination (GSD) and environmental sex determination (ESD) in fish is unknown. The Chinese tongue sole, which has both GSD and ESD mechanisms, was used to map the dynamic expression pattern of ncRNAs and mRNA in gonads during sex determination and differentiation. Transcript expression patterns shift during the sex differentiation phase, and ceRNA modulation occurs through crosstalk of differentially expressed long ncRNAs (lncRNAs), circular RNAs (circRNAs), microRNAs (miRNAs), and sex-related genes in fish. Of note was the significant up-regulation of a circRNA from the sex-determining gene dmrt1 (circular RNA dmrt1) and a lncRNA, called AMSDT (which stands for associated with male sex differentiation of tongue sole) in Chinese tongue sole testis. These two ncRNAs both share the same miRNA response elements with gsdf, which has an up-regulated expression when they bind to miRNA cse-miR-196 and concurrent down-regulated female sex-related genes to facilitate testis differentiation. This is the first demonstration in fish that ceRNA crosstalk mediated by ncRNAs modulates sexual development and unveils a novel regulatory mechanism for sex determination and differentiation.

Dietary supplementation of Bacillus velezensis improves Vibrio anguillarum clearance in European sea bass by activating essential innate immune mechanisms

Bacillus spp. supplementation as probiotics in cultured fish diets has a long history of safe and effective use. Specifically, B. velezensis show great promise in fine-tuning the European sea bass disease resistance against the pathogenicity caused by several members of the Vibrio family. However, the immunomodulatory mechanisms behind this response remain poorly understood. Here, to examine the inherent immune variations in sea bass, two equal groups were fed for 30 days with a steady diet, with one treatment supplemented with B. velezensis. The serum bactericidal capacity against live cells of Vibrio anguillarum strain 507 and the nitric oxide and lysozyme lytic activities were assayed. At the cellular level, the phagocytic response of peripheral blood leukocytes against inactivated Candida albicans was determined. Moreover, head-kidney (HK) total leukocytes were isolated from previously in vivo treated fish with LPS of V. anguillarum strain 507. Mechanistically, the expression of some essential proinflammatory genes (interleukin-1 (il1b), tumor necrosis factor-alpha (tnfa), and cyclooxygenase 2 (cox2) and the sea bass specific antimicrobial peptide (AMP) dicentracin (dic) expressions were assessed. Surprisingly, the probiotic supplementation significantly increased all humoral lytic and cellular activities assayed in the treated sea bass. In addition, time-dependent differences were observed between the control and probiotic treated groups for all the HK genes markers subjected to the sublethal LPS dose. Although the il1b was the fastest responding gene to a significant level at 48 h post-injection (hpi), all the other genes followed 72 h in the probiotic supplemented group. Finally, an in vivo bacteria challenge against live V. anguillarum was conducted. The probiotic fed fish observed a significantly higher survival. Overall, our results provide clear vertical evidence on the beneficial immune effects of B. velezensis and unveil some fundamental immune mechanisms behind its application as a probiotic agent in intensively cultured European sea bass.

PU.1 Regulates Cathepsin S Expression in Large Yellow Croaker (Larimichthys crocea) Macrophages

Different morphologies have been detected in teleost macrophages. In this study, two macrophage cell lines were sub-cloned from a large yellow croaker head kidney cell line, LYCK. One type of sub-cloned cells was fusiform but the other was round, named LYC-FM and LYC-RM cells respectively, based on their morphologies. Both types showed the characteristics of macrophages, including expression of macrophage-specific marker genes, possession of phagocytic and bactericidal activities, and production of reactive oxygen species (ROS) and nitric oxide (NO). The transcription factor PU.1, crucial for the development of macrophages in mammals, was found to exist in two transcripts, PU.1a and PU.1b, in large yellow croaker, and constitutively expressed in LYC-FM and LYC-RM cells. The expression levels of PU.1a and PU.1b could be upregulated by recombinant large yellow croaker IFN-γ protein (rLcIFN-γ). Further studies showed that both PU.1a and PU.1b increased the expression of cathepsin S (CTSS) by binding to different E26−transformation−specific (Ets) motifs of the CTSS promoter. Additionally, we demonstrated that all three domains of PU.1a and PU.1b were essential for initiating CTSS expression by truncated mutation experiments. Our results therefore provide the first evidence that teleost PU.1 has a role in regulating the expression of CTSS.

An l-rhamnose-binding lectin from Nile tilapia (Oreochromis niloticus) possesses agglutination activity and regulates inflammation, phagocytosis and respiratory burst of monocytes/macrophages

Rhamnose-binding lectins (RBLs), a Ca²⁺-independent lectin family, are widely present in vertebrates and invertebrates, which involve in the innate immune response. However, the functional characterization and related regulation mechanisms of RBLs remain unclear in teleost fish. In this study, an l-rhamnose-binding lectin-like (OnRBL-L) was identified and functionally characterized from Nile tilapia (Oreochromis niloticus). The open reading frame of OnRBL-L is 678 bp encoding 225 aa. The sequence of OnRBL-L has relatively conservative characteristic peptide motifs, including YGR, DPC, and KYL-motif. Expression analysis showed that OnRBL-L was abundantly distributed in intestine tissue, and widely existed in all detected tissues. Meanwhile, the expression of OnRBL-L increased significantly in vivo (liver, spleen, head kidney, intestine, gills and peripheral blood) and in vitro (monocytes/macrophages) following challenges with two important tilapia pathogenic bacteria Streptococcus agalactiae and Aeromonas hydrophila. In addition, the recombinant OnRBL-L was found to bind and agglutinate S. agalactiae and A. hydrophila. Furthermore, OnRBL-L could participate in non-specific cellular immune defense, including reducing the expression of pro-inflammatory factors (IL-6、IL-8 and TNF-α), and enhancement of the phagocytosis and respiratory burst of MO/MФ. Overall, our results provide new insights into the understanding of RBL as an important pattern recognition molecule and regulator in non-specific cell immunity in an early vertebrate.

Analysis of lncRNA and mRNA expression profiles in peripheral blood leukocytes of the half-smooth tongue sole (Cynoglossus semilaevis) treated with chitosan oligosaccharide

Long noncoding RNAs (lncRNAs) play a multifaceted role in transcriptional regulation and are important regulators of immune function. Scarce information is available regarding lncRNAs in fish. Peripheral blood mononuclear cells participate in the immune response of fish and aid resistance to infection with pathogenic microorganisms. Chitosan oligosaccharide can improve cellular and humoral immunity to enhance disease resistance in fish. In this study, we obtained peripheral blood leukocytes from half-smooth tongue sole and studied the effect of chitosan oligosaccharide on the lncRNA-mRNA expression profile of these cells using high-throughput sequencing and bioinformatics techniques. A total of 609 differentially expressed mRNAs and 50 differentially expressed lncRNAs were identified. The GO term enrichment analysis of the differentially expressed genes was annotated by 220 GO terms, 137 biological processes, 18 cellular components, and 65 molecular functions. Sixteen KEGG pathways, including immune signaling pathways, metabolism, and genetic information processing, were significantly enriched in differentially expressed genes. Thirty-six differentially expressed lncRNAs and 32 differentially expressed mRNAs produced a coexpression network containing 90 relationship pairs. The prediction of lncRNA target genes revealed 244 lncRNAs that potentially cis-regulated 294 differentially expressed mRNAs. qPCR verified that the expression levels of 17 differentially expressed lncRNAs and 15 differentially expressed mRNAs were consistent with the RNA-Seq results. Among them, 6 lncRNAs and 7 mRNAs were differentially expressed genes obtained from the prediction and analysis of lncRNA target genes, and 8 lncRNAs and 4 mRNAs were differentially expressed genes that participated in the construction of the coexpression network. In peripheral blood leukocytes after chitosan oligosaccharide treatment, as well as in peripheral blood and spleen after Vibrio anguillarum stimulation, lncRNAs and mRNAs showed significant differential expression. The results indicated that they may be related to the immune response, providing novel reference information for further research on the role of lncRNAs in immune regulation in half-smooth tongue sole.

Cloning, expression profile of the complement component C9 gene and influence of the recombinant C9 protein on peripheral mononuclear leukocytes transcriptome in half-smooth tongue sole (Cynoglossus semilaevis)

The ninth complement component (C9) is a terminal complement component (TCC) that is involved in creating the membrane attack complex (MAC) on the target cell surface. In this study, the CsC9 (C9 of Cynoglossus semilaevis) cDNA sequence was cloned and characterized. The full-length CsC9 cDNA measured 2,150 bp, containing an open reading frame (ORF) of 1,803 bp, a 5'-untranslated region (UTR) of 24 bp and a 3'-UTR of 323 bp. A domain search revealed that the CsC9 protein contains five domains, including two TSP1s, an LDLRA, an EGF, and a MACPF. Quantitative real-time PCR analysis showed that CsC9 at the mRNA level was expressed in all the tested tissues, with the highest expression being observed in the liver. CsC9 expression is significantly upregulated in the tested tissues after challenge with Vibrio anguillarum. To further characterize the role of CsC9, peripheral blood mononuclear cells of C. semilaevis were used for transcriptome analysis after incubation with recombinant CsC9 (rCsC9) protein. A total of 3,775 significant differentially expressed genes (DEGs) were identified between the control and the rCsC9-treated group, including 2,063 upregulated genes and 1,712 downregulated genes. KEGG analyses revealed that the DEGs were enriched in cell adhesion molecules, cytokine-cytokine receptor interactions, T cell receptor signaling pathways, B cell receptor signaling pathways and Toll-like receptor signaling pathways. The results of this study indicate that in addition to participating in MAC formation, CsC9 might play multiple roles in the innate and adaptive immunity of C. semilaevis.

Fish Galectin8-Like Exerts Positive Regulation on Immune Response Against Bacterial Infection

Galectin-8 is a member of the galectin family that is involved in immune response against pathogens. However, the roles of fish galectin-8 during pathogen infection require comprehensive studies. In this study, a galectin-8 homolog (OnGal8-like, OnGal8-L) was characterized from Nile tilapia (Oreochromis niloticus), and its roles in response to bacterial infection were analyzed. The OnGal8-L contains an open reading frame of 891 bp, encoding a peptide of 296 amino acids with two CRD regions of tandem-repeat galectin and two carbohydrate recognition sites. The OnGal8-L protein shares 46.42% identities with reported Oreochromis niloticus galectin-8 protein. Transcriptional expression analysis revealed that OnGal8-L was constitutively expressed in all examined tissues and was highly expressed in spleen. The transcript levels of OnGal8-L were up-regulated in the spleen, head kidney, and brain, following Streptococcus agalactiae (S. agalactiae) challenge. Further in vitro analysis indicated that the recombinant protein of OnGal8-L (rOnGal8L) could agglutinate erythrocyte, S. agalactiae, and A. hydrophila and bind S. agalactiae, A. hydrophila, and various PAMPs (lipopolysaccharides, lipoteichoic acid, poly I:C, peptidoglycan, galactose, mannose, and maltose). Also, rOnGal8L could regulate inflammatory-related gene expression, phagocytosis, and a respiratory burst of monocytes/macrophages. Moreover, in vivo analysis showed that OnGal8-L overexpression could protect O. niloticus from S. agalactiae infection through modulating serum antibacterial activity (AKP, ACP, and LZM), antioxidant capacity (CAT, POD, and SOD), and monocyte/macrophage proliferation and cytokine expression, as well as reducing bacterial burden and decreasing tissue damage. Our results collectively indicate that OnGal8-L plays important regulatory roles in immune response against bacterial infection.

Establishment and characterization of two head kidney macrophage cell lines from large yellow croaker (Larimichthys crocea)

Two continuous macrophage cell lines (LCM07 and LCM10) were established for the first time from the head kidney of the marine fish large yellow croaker (Larimichthys crocea). To date, both cell lines have been subcultured for more than 100 passages in 12 months. Notably, the LCM07 and LCM10 cells have distinct morphology and immune function. LCM07 cells showed strong contact inhibition in crowded conditions, while this was not observed in the LCM10 cells because they could grow in an overlapping manner. Correspondingly, LCM10 cells were slenderer than LCM07 cells. LCM07 cells had stronger phagocytic ability than LCM10 cells, while LCM10 cells had stronger respiratory burst activity after incubation with lipopolysaccharide (LPS) and phorbol ester (PMA). LCM07 cells had stronger Escherichia coli killing ability than LCM10 cells. The mRNA of macrophage markers, namely that of CD11b, CD114, CD68, CD86, CD209, and CD163, were all expressed in primary macrophages as well as the two cell lines. The mRNA expression levels of selected inflammatory cytokines, namely interleukin (IL)-1β, IL-8, and tumor necrosis factor (TNF)α, were all upregulated after incubation with LPS. LPS also regulated key components of the mitogen-activated protein kinase (MAPK) signaling pathway, i.e., p38, ERK (extracellular signal-regulated kinase), and JNK (Jun N-terminal kinase) and their phosphorylated forms. Arachidonic acid (ARA) downregulated the LPS-induced upregulation of IL-1β, IL-8, and TNFα, revealing that LCM07 and LCM10 cells are useful for studying nutritional immunity. In conclusion, two distinct macrophage cell lines have been established for the first time from the head kidney of marine fish, which could be useful for studying immunity and nutritional immunity.

Functional characterization of galectin-3 from Nile tilapia (Oreochromis niloticus) and its regulatory role on monocytes/macrophages

Galectin-3 is a kind of β-galactoside-binding lectin involved in host defense against pathogen infection. However, the immune functions of fish galectin-3 remain poorly understood. In this study, the roles of a fish galectin-3 (OnGal-3) from Nile tilapia (Oreochromis niloticus) on the binding activity on bacterial pathogens or PAMPs, the agglutinating activity on bacterial pathogens and the regulatory effects on monocytes/macrophages activity were investigated. After in vitro challenge of Streptococcus agalactiae and Aeromonas hydrophila, OnGal-3 expressions were significantly up-regulated in monocytes/macrophages. In addition, recombinant OnGal-3(rOnGal-3) protein showed strong binding activity on bacterial pathogens or PAMPs. Also, rOnGal-3 agglutinated Gram-positive and Gram-negative bacteria. Moreover, rOnGal-3 could induce the inflammatory factors expressions in monocytes/macrophages and enhance phagocytosis and respiratory burst activity of monocytes/macrophages. These results suggest that fish galectin-3 participates in anti-bacterial immune response through recognizing pathogens and modulating monocytes/macrophages activity.

Advances in salmonid fish immunology: A review of methods and techniques for lymphoid tissue and peripheral blood leucocyte isolation and application

Evaluating studies over the past almost 40 years, this review outlines the current knowledge and research gaps in the use of isolated leucocytes in salmonid immunology understanding. This contribution focuses on the techniques used to isolate salmonid immune cells and popular immunological assays. The paper also analyses the use of leucocytes to demonstrate immunomodulation following dietary manipulation, exposure to physical and chemical stressors, effects of pathogens and parasites, vaccine design and application strategies assessment. We also present findings on development of fish immune cell lines and their potential uses in aquaculture immunology. The review recovered 114 studies, where discontinuous density gradient centrifugation (DDGC) with Percoll density gradient was the most popular leucocyte isolation method. Fish head kidney (HK) and peripheral blood (PB) were the main sources of leucocytes, from rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Phagocytosis and respiratory burst were the most popular immunological assays. Studies used isolated leucocytes to demonstrate that dietary manipulations enhance fish immunity, while chemical and physical stressors suppress immunity. In addition, parasites, and microbial pathogens depress fish innate immunity and induce pro-inflammatory cytokine gene transcripts production, while vaccines enhance immunity. This review found 10 developed salmonid cell lines, mainly from S. salar and O. mykiss HK tissue, which require fish euthanisation to isolate. In the face of high costs involved with density gradient reagents, the application of hypotonic lysis in conjunction with mico-volume blood methods can potentially reduce research costs, time, and using nonlethal and ethically flexible approaches. Since the targeted literature review for this study retrieved no metabolomics study of leucocytes, indicates that this approach, together with traditional technics and novel flow cytometry could help open new opportunities for in vitro studies in aquaculture immunology and vaccinology.

In vitro immune response of chinook salmon (Oncorhynchus tshawytscha) peripheral blood mononuclear cells stimulated by bacterial lipopolysaccharide

We investigated cellular functional and targeted immune cytokine responses of farmed Chinook salmon (Oncorhynchus tshawytscha) peripheral blood mononuclear cells (PBMCs) in vitro to LPS from Escherichia coli (E. coli) serotypes O111: B4 and O55: B5, and a phorbol ester phorbol 12-myristate 13-acetate (PMA). Bacterial LPS and PMA significantly (p < 0.05) induced reactive oxygen species (ROS) production in O. tshawytscha PBMCs, and enhanced by interferon (IFN)-inducible cytokine production. Cellular phagocytosis was significantly enhanced with PMA and E. coli serotype O111: B4 LPS after 1 and 2 h respectively. At the molecular level, LPS and PMA significantly (p < 0.05) upregulated pro-inflammatory cytokine gene transcripts for IFNγ, TNF-α, and anti-inflammatory IL-10, 24 h post-stimulation. This response is postulated to be mediated via the MyD88 and TRIF pathways in TLR4, or synergistic TLR1 and TLR2 receptors. This is the first report of LPS induced immune related in vitro responses in farmed O. tshawytscha PBMCs.

Screening of immuno-modulatory potential of different herbal plant extracts using striped catfish (Pangasianodon hypophthalmus) leukocyte-based in vitro tests

Many medicinal plants have been shown to possess biological effects, including immuno-modulatory activities on human and other mammals. However, studies about the potential mechanisms of plant extracts on the humoral and tissular immunities in fish have received less attention. This study aimed to screen the immunestimulating properties of 20 ethanol plant extracts on striped catfish Pangasianodon hypophthalmus leukocytes. The peripheral blood mononuclear cells (PBMCs) and head kidney leukocytes (HKLs) of striped catfish (50 ± 5 g per fish) were stimulated at 10 and 100 μg of each plant extract per mL of cell culture medium. Several humoral immune parameters (lysozyme, complement and total immunoglobulin) were examined at 24-h post stimulation (hps). Furthermore, the responses of four cytokine genes, namely il1β, ifrγ 2a and b, and mhc class II were assessed by quantitative real-time PCR at 6, 12, 24, and 48 hps. The results showed that lysozyme, complement as well as total immunoglobulin levels in both PBMCs and HKLs were regulated by some of the plant extracts tested in a concentration-dependent manner; some plant extracts induced the highest immune responses at the low dose (10 μg mL^-1) while others were more efficient at high dose (100 μg mL^-1). Among the extracts, five extracts including garlic Allium sativum L. (As), neem Azadirachta indica A. Juss (Ai), asthma-plant Euphorbia hirta L. (Eh), bhumi amla Phyllanthus amarus Schum. et Thonn (Pa), and ginger Zingiber officinale Rosc (Zo) induced significant changes in the expression of pro-inflammatory cytokine (il1β), antiviral cytokines (ifrγ 2a and b) and adaptive immune cytokine (mhc class II) in striped catfish cells. Pa always modulated the strongest expression of the four cytokines in PBMCs and HKLs over the whole experimental period (p < 0.05), whereas Zo did not stimulate the mhc class II expression in striped catfish leukocytes throughout experimental periods. These in vitro results demonstrated that some plant extracts could differently modulate great potential immune response in fish, supporting their applications in further in vivo experiments.

Characterisation of Chinook salmon (Oncorhynchus tshawytscha) blood and validation of flow cytometry cell count and viability assay kit

New Zealand Chinook salmon (Oncorhynchus tshawytscha) industry has great potential for growth and expansion. While production is relatively free of health problems, there is limited literature on haematology, and immunological tools to safeguard against possible future health threats. The current study aim was to characterise New Zealand farmed O. tshawytscha peripheral blood cellular composition, develop a micro-volume method to isolate peripheral blood mononuclear cells (PBMCs) and validate a microcapillary flow cytometry assay kit for PBMC cell count and viability assessment. We used light microscopy to characterise peripheral blood and PBMC cellular composition in combination with a flow cytometer Sysmex XT 2000i Haematology Analyser. ImageJ version 1.52 was used for cell size characterisation of freshly stained blood. The stability of PBMCs stained with the Muse^® Cell Count and Viability Assay Kit and the Trypan blue assay stains were studied at 4 °C and 21 °C for 60 min; while the Muse^® Cell Count and Viability Assay Kit was validated against the Trypan blue assay haemocytometer chamber to assess PBMC count and viability. Findings showed that O. tshawytscha smolt yearlings had total blood cell counts in the range of 1.9-2.7 × 10⁶ μL^-1. Differential cell counts revealed five cell types, comprising 97.18% erythrocytes, 2.03% lymphocytes, 0.67% thrombocytes, 0.09% monocytes, and unquantifiable neutrophils. Using micro-volumes of blood and Lymphoprep™, we successfully isolated fish PBMCs. Significantly, stained PBMCs remained stable for up to 45 min at 4 °C and 21 °C; while validation of the Muse^® protocol showed that this microfluidic instrument delivered more accurate and precise viability results than the haemocytometer. The Muse^® protocol is rapid, easy to use, has quick calibration steps, and is suitable for field use to facilitate onsite sample processing. These findings pave the way for future assessments of fish health and in vitro immunological studies in O. tshawytscha.

Purification and functional characterization of serum transferrin from Nile tilapia (Oreochromis niloticus)

Transferrin (TF), an iron-binding multifunctional protein, could participate in the iron-withholding strategy, an effective antimicrobial defense mechanism in innate immunity, and is involved in host defense against pathogenic infection. In this study, a TF homologue (OnTF) was purified from serum of Nile tilapia (Oreochromis niloticus) through a two-step affinity chromatography, and characterized its antibacterial function and the role in inflammatory response. The identification by mass spectrometry showed that peptide sequence of the purified OnTF was highly consistent with its amino acids sequence, containing two conserved iron binding lobes: N-lobe and C-lobe. The native OnTF was able to bond iron ions, and possessed capability to inhibit the growth of both bacterial pathogens (Streptococcus agalactiae and Aeromonas hydrophila) in vitro. Upon infections of S. agalactiae and A. hydrophila, the expression of OnTF protein was significantly up-regulated in vivo and in vitro. In addition, the OnTF participated in the regulation of inflammation, migration, and enhancement of phagocytosis and respiratory burst activity in head kidney macrophages/monocytes. Taken together, the results of this study indicated that OnTF is likely to involve in innate immunity to play a role in host defense against bacterial infection in Nile tilapia.

Functional characterization of a mannose-binding lectin (MBL) from Nile tilapia (Oreochromis niloticus) in non-specific cell immunity and apoptosis in monocytes/macrophages

Mannose-binding lectin (MBL), a soluble pattern recognition receptor, is able to recognize antigen and participate in non-specific cell immunity, such as regulation of inflammation, migration, opsonization, phagocytosis and killing, which plays an important role in innate immunity. In this study, we have investigated the contributing mechanisms and effects of MBL on the cell immunity of Nile tilapia (Oreochromis niloticus) monocytes/macrophages. The mRNA expression level of OnMBL was significantly up-regulated in monocytes/macrophages after in vitro bacterial infection (Streptococcus agalactiae and Aeromonas hydrophila). Recombinant OnMBL ((r)OnMBL) protein could participate in the regulation of inflammation, migration, and enhancement of phagocytosis and respiratory burst activity in monocytes/macrophages. Moreover, the (r)OnMBL could induce the apoptosis of monocytes/macrophages. Taken together, the results of this study indicated that OnMBL is likely to involve in immune regulation, which may play an important role in host defense of innate immunity in Nile tilapia.

Phagolysosomal activity of macrophages in Nile tilapia (Oreochromis niloticus) infected in vitro by Aeromonas hydrophila: Infection and immunotherapy

The biochemical mechanisms involved in phagocytosis and the intracellular survival of Aeromonas hydrophila (Ah) in host macrophages (MΦs) are complex processes that affect infection success or failure. Thus, in the present study, we described the in vitro infection of Nile tilapia MΦs by a homologous bacterium and tested the effects of anti-A. hydrophila immunoglobulin Y (IgY) on the phagolysosomal activity and intracellular survival of the pathogen. The anti-Ah IgY modulated lysosomal acid phosphatase (LAP) activity as well as the production of reactive oxygen intermediates (ROIs) and nitric oxide (NO), thereby potentiating phagocytosis and the elimination of Ah. Thus, we assume that the specific IgY had a beneficial effect on infection control and postulated the use of the Nile tilapia MΦs as an important in vitro experimental model for the functional and therapeutic study of Ah infection.

Inhibition of miR-155 attenuates abdominal aortic aneurysm in mice by regulating macrophage-mediated inflammation

The aim of the present study was to identify abdominal aortic aneurysms (AAA)-associated miR-155 contributing to AAA pathology by regulating macrophage-mediated inflammation. Angiotensin II (AngII)-infused apolipoprotein E-deficient (ApoE-/-) mice and THP-1 cells model of miR-155 overexpression and deficiency were used in the experiments. The expression of miR-155 was detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Cytokines were evaluated using enzyme-linked immunoabsorbent assay (ELISA). Western blotting was used to measure the levels of MMP-2, MMP-9, iNOS, and monocyte chemoattractant protein (MCP)-1 proteins. Immunostaining and transwell were used to determine CD68, elastic collagen, proliferation, and migration of vascular smooth muscle cells (VSMCs). The results showed that miR-155 and cytokines were up-regulated in AAA patients or ApoE-/- mice. Overexpression of miR-155 enhanced MMP-2, MMP-9, iNOS, and MCP-1 levels, and stimulated the proliferation and migration of VSMCs. Meanwhile, inhibition of miR-155 had the opposite effect. In addition, histology demonstrated accumulation of CD68 and elastic collagen-positive areas significantly decreased in miR-155 antagomir injection group. In conclusion, the results of the present study suggest that inhibiting miR-155 is crucial to prevent the development of AAA by regulating macrophage inflammation.