Mannose Receptor Mediates the Activation of Chitooligosaccharides on Blunt Snout Bream (Megalobrama amblycephala) Macrophages

Effects of phoxim on antibacterial infection of silver carp

The efficacy of phoxim in treating bacterial sepsis in silver carp is significant, yet its underlying mechanism remains elusive. This study aimed to establish a model of Aeromonas veronii infection in silver carp and subsequently treat the infected fish with 10 μg/L phoxim. Kidney and intestine samples from silver carp were collected for transcriptome analysis and assessment of intestinal microbial composition, with the aim of elucidating the mechanism underlying the efficacy of phoxim in treating bacterial sepsis in silver carp. The results of transcriptome and intestinal microbial composition analysis of silver carp kidney indicated that A. veronii infection could up-regulate the expression of il1β, il6, nos2, ctsl, casp3 et al., which means, signifying that the kidney of silver carp would undergo inflammation, induce apoptosis, and alter the composition of intestinal microorganisms. Phoxim immersion might enhance the energy metabolism of silver carp and change its intestinal microbial composition, potentially elevating the antibacterial infection resistance of silver carp. These findings may contribute to an understanding of how phoxim can effectively treat bacterial sepsis in silver carp.

GCRV-II invades monocytes/macrophages and induces macrophage polarization and apoptosis in tissues to facilitate viral replication and dissemination

Grass carp reovirus (GCRV), particularly the highly prevalent type II GCRV (GCRV-II), causes huge losses in the aquaculture industry. However, little is known about the mechanisms by which GCRV-II invades grass carp and further disseminates among tissues. In the present study, monocytes/macrophages (Mo/Mφs) were isolated from the peripheral blood of grass carp and infected with GCRV-II. The results of indirect immunofluorescent microscopy, transmission electron microscopy, real-time quantitative RT-PCR (qRT-PCR), western blot (WB), and flow cytometry analysis collectively demonstrated that GCRV-II invaded Mo/Mφs and replicated in them. Additionally, we observed that GCRV-II induced different types (M1 and M2) of polarization of Mo/Mφs in multiple tissues, especially in the brain, head kidney, and intestine. To assess the impact of different types of polarization on GCRV-II replication, we recombinantly expressed and purified the intact cytokines CiIFN-γ2, CiIL-4/13A, and CiIL-4/13B and successfully induced M1 and M2 type polarization of macrophages using these cytokines through in vitro experiments. qRT-PCR, WB, and flow cytometry analyses showed that M2 macrophages had higher susceptibility to GCRV-II infection than other types of Mo/Mφs. In addition, we found GCRV-II induced apoptosis of Mo/Mφs to facilitate virus replication and dissemination and also detected the presence of GCRV-II virus in plasma. Collectively, our findings indicated that GCRV-II could invade immune cells Mo/Mφs and induce apoptosis and polarization of Mo/Mφs for efficient infection and dissemination, emphasizing the crucial role of Mo/Mφs as a vector for GCRV-II infection.IMPORTANCEType II grass carp reovirus (GCRV) is a prevalent viral strain and causes huge losses in aquaculture. However, the related dissemination pathway and mechanism remain largely unclear. Here, our study focused on phagocytic immune cells, monocytes/macrophages (Mo/Mφs) in blood and tissues, and explored whether GCRV-II can invade Mo/Mφs and replicate and disseminate via Mo/Mφs with their differentiated type M1 and M2 macrophages. Our findings demonstrated that GCRV-II infected Mo/Mφs and replicated in them. Furthermore, GCRV-II infection induces an increased number of M1 and M2 macrophages in grass carp tissues and a higher viral load in M2 macrophages. Furthermore, GCRV-II induced Mo/Mφs apoptosis to release viruses, eventually infecting more cells. Our study identified Mo/Mφs as crucial components in the pathway of GCRV-II dissemination and provides a solid foundation for the development of treatment strategies for GCRV-II infection.

CD206 modulates the role of M2 macrophages in the origin of metastatic tumors

Tumor metastasis is a key factor affecting the life of patients with malignant tumors. For the past hundred years, scientists have focused on how to kill cancer cells and inhibit their metastasis in vivo, but few breakthroughs have been made. Here we hypothesized a novel mode for cancer metastasis. We show that the phagocytosis of apoptotic tumor cells by macrophages leads to their polarization into the M2 phenotype, and that the expression of stem cell related as well as drug resistance related genes was induced. Therefore, it appears that M2 macrophages have "defected" and have been transformed into the initial "metastatic cancer cells", and thus are the source, at least in part, of the distal tissue tumor metastasis. This assumption is supported by the presence of fused cells with characteristics of both macrophage and tumor cell observed in the peripheral blood and ascites of patients with ovarian cancer. By eliminating the expression of CD206 in M2 macrophages using siRNA, we show that the growth and metastasis of tumors was suppressed using both in vitro cell line and with experimental in vivo mouse models. In summary, we show that M2 macrophages in the blood circulation underwent a "change of loyalty" to become "cancer cells" that transformed into distal tissue metastasis, which could be suppressed by the knockdown of CD206 expression.

Transcriptome analysis of the hepatopancreas from the Litopenaeus vannamei infected with different flagellum types of Vibrio alginolyticus strains

Vibrio alginolyticus, one of the prevalently harmful Vibrio species found in the ocean, causes significant economic damage in the shrimp farming industry. Its flagellum serves as a crucial virulence factor in the invasion of host organisms. However, the processes of bacteria flagella recognition and activation of the downstream immune system in shrimp remain unclear. To enhance comprehension of this, a ΔflhG strain was created by in-frame deletion of the flhG gene in V. alginolyticus strain HN08155. Then we utilized the transcriptome analysis to examine the different immune responses in Litopenaeus vannamei hepatopancreas after being infected with the wild type and the mutant strains. The results showed that the ΔflhG strain, unlike the wild type, lost its ability to regulate flagella numbers negatively and displayed multiple flagella. When infected with the hyperflagella-type strain, the RNA-seq revealed the upregulation of several immune-related genes in the shrimp hepatopancreas. Notably, two C-type lectins (CTLs), namely galactose-specific lectin nattectin and macrophage mannose receptor 1, and the TNF receptor-associated factor (TRAF) 6 gene were upregulated significantly. These findings suggested that C-type lectins were potentially involved in flagella recognition in shrimp and the immune system was activated through the TRAF6 pathway after flagella detection by CTLs.

Characterization and functional analysis of a novel C-type lectin in blunt snout bream (Megalobrama amblycephala)

C-type lectins, one of the pattern recognition receptors (PRRs), play significant roles in innate immune responses through binding to the pathogen-associated molecular patterns (PAMPs) presented on surfaces of microorganisms. Here, a novel C-type lectin (named as MaCTL) from blunt snout bream (Megalobrama amblycephala) was cloned and characterized. The open reading frame (ORF) of MaCTL is 573 bp long encoding a putative protein of 190 amino acids (aa), which contains a typical feature of signal peptide at 1-23 aa, a characteristic CRD domain at 45-178 aa and a WND/EPN motif that is required for carbohydrates-binding specificity. Phylogenetic analysis indicated that MaCTL is a novel member of CTL family and possessed the highest similarity to that of grass carp (92.11%). The qRT-PCR analysis revealed that MaCTL expressed widely in all examined normal tissues, including heart, liver, spleen, kidney, head-kidney, gill, intestine and muscle, with the higher expression in the spleen, liver and muscle. The expression of MaCTL in spleen was significantly elevated, peaking at 9 h and 6 h after LPS stimulation and Aeromonas hydrophila challenge, respectively, suggesting its association with involvement in innate immune response. The recombinant MaCTL protein (rMaCTL) agglutinated markedly both Gram-positive (Staphylococcus aureus) and Gram-negative bacteria, including Escherichia coli, Vibrio anguillarum, Vibrio vulnificus and Aeromonas hydrophila, in a Ca2+-dependent manner. Meanwhile, rMaCTL showed the binding effects on the five bacteria and four carbohydrates, such as glucose, surose, LPS and PGN. Moreover, rMaCTL could remarkably inhibit the growth of three types of bacteria in vitro. Overall, the results obtained above demonstrated firmly that MaCTL binds to carbohydrates on the surface of diverse pathogens as a PRR and elicits antimicrobial responses, which shed new light on a better understanding of antibacterial functions of CTLs in teleost fish.

Chitooligosaccharide boosts the immunity of immunosuppressed blunt snout bream against bacterial infections

The immunosuppression hazard of fish brought by intensive aquaculture needs to be addressed urgently, while chitooligosaccharide (COS) shows the potential application in the prevention the immunosuppression of fish due to its superior biological properties. In this study, COS reversed the cortisol-induced immunosuppression of macrophages and improved the immune activity of macrophages in vitro, promoting the expression of inflammatory genes (TNF-α, IL-1β, iNOS) and NO production, and increasing the phagocytic activity of macrophages. In vivo, the oral COS was absorbed directly through the intestine, significantly ameliorating the innate immunity of cortisol-induced immunosuppression of blunt snout bream (Megalobrama amblycephala). Such as facilitated the gene expression of inflammatory cytokines (TNF-α, IL-1β, IL-6) and pattern recognition receptors (TLR4, MR) and potentiated bacterial clearance, resulting in an effective improvement in survival and tissue damage. Altogether, this study demonstrates that COS offers potential strategies in the application of immunosuppression prevention and control in fish.

Pleiotropic Modulation of Chitooligosaccharides on Inflammatory Signaling in LPS-Induced Macrophages

Chitooligosaccharide (COS) is a green and non-toxic cationic carbohydrate that has attracted wide attention in recent years due to its anti-inflammatory activity. However, the anti-inflammatory mechanism of COS remains unclear. In this study, RNA-seq was used to investigate the integrated response of COS to LPS-induced damage in macrophages. The results showed that the experimental group with COS had 2570 genes with significant differences compared to the model group, and that these genes were more enriched in inflammatory and immune pathways. The KEGG results showed that COS induces the pleiotropic modulation of classical inflammatory pathways, such as the Toll-like receptor signaling pathway, NF-κB, MAPK, etc. Based on the RNA-seq data and the RT-qPCR, as well as the WB validation, COS can significantly upregulate the expression of membrane receptors, such as Tlr4, Tlr5, and MR, and significantly inhibits the phosphorylation of several important proteins, such as IκB and JNK. Overall, this study offers deep insights into the anti-inflammatory mechanism and lays the foundation for the early application of COS as an anti-inflammatory drug.

Chitosan oligosaccharide alleviates and removes the toxicological effects of organophosphorus pesticide chlorpyrifos residues

The abuse of chlorpyrifos (CHP), a commonly used organophosphorus pesticide, has caused many environmental pollution problems, especially its toxicological effects on non-target organisms. First, CHP enriched on the surface of plants enters ecosystem circulation along the food chain. Second, direct inflow of CHP into the water environment under the action of rainwater runoff inevitably causes toxicity to non-target organisms. Therefore, we used rats as a model to establish a CHP exposure toxicity model and studied the effects of CHP in rats. In addition, to alleviate and remove the injuries caused by residual chlorpyrifos in vivo, we explored the alleviation effect of chitosan oligosaccharide (COS) on CHP toxicity in rats by exploiting its high water solubility and natural biological activity. The results showed that CHP can induce the toxicological effects of intestinal antioxidant changes, inflammation, apoptosis, intestinal barrier damage, and metabolic dysfunction in rats, and COS has excellent removal and mitigation effects on the toxic damage caused by residual CHP in the environment. In summary, COS showed significant biological effects in removing and mitigating blood biochemistry, antioxidants, inflammation, apoptosis, gut barrier structure, and metabolic function changes induced by residual CHP in the environment.

Dual-Targeting Polymer Nanoparticles Efficiently Deliver DNA Vaccine and Induce Robust Prophylactic Immunity against Spring Viremia of Carp Virus Infection

Spring viremia of carp virus (SVCV) is highly contagious and lethal to most cyprinid fish, causing serious economic losses to the carp aquaculture industry. Although DNA vaccines can generate long-term humoral and cellular immune responses, which provide protective immunity against SVCV, the major drawback of DNA vaccines is their low immunogenicity in clinical tests. Here, we construct a dual-targeted polymer DNA vaccine delivery platform (MCS-PCHG) by using mannosylated chitosan to encapsulate the poly(d,l-lactide-co-glycolide)-loaded DNA vaccine containing the heavy-chain C_H3 region (CH3) of common carp IgM and the antigenic domain (G131c). The developed nanovaccine delivery platform showed good biocompatibility in vivo and in vitro. With the modification of the mannose moiety and the modification of CH3, the constructed MCS-PCHG could efficiently activate the maturation of antigen-presenting cells. Moreover, we observe significantly high level of immune-related genes expression, serum antigen-specific IgM, SVCV-neutralizing antibody titers in fish vaccinated with MCS-PCHG. Next, the protective efficacy of MCS-PCHG was further evaluated by challenge test. The highest survival rate (ca. 84%) was observed in fish vaccinated with MCS-PCHG after challenging with SVCV. This study presents a novel design for smart, dual-targeted polymer nanoparticles, which are inherently biocompatible, promising for targeted vaccine delivery. IMPORTANCE Spring viremia of carp virus (SVCV) affects global cyprinid fish farming industry, with no available commercial vaccine. Herein, we developed a dual-targeting polymer nanovaccine (MCS-PCHG) by using mannose and common carp IgM heavy chain C_H3 region (CH3) as antigen presenting cell (APCs) recognition moiety, attaining the effective delivery of antigen. This dual-targeting polymer vaccine can efficiently activate the APCs, and further induce robust and durable adaptive immune response with good protection against SVCV infection. Our study provides valuable theoretical basis for developing efficient vaccine against infectious diseases in aquaculture.

Identification and functional analysis of Mannose receptor in Asian swamp eel (Monopterus albus) in response to bacterial infection

Mannose receptor (MR), as a member of the C-type lectin (CLEC) family, plays an important role in the internalize pathogen-associated ligands and activate immune response. In the present study, MR was identified and characterized from Asian swamp eel (Monopterus albus) (namely MaMR). The open reading frame of MaMR was 4311 bp in length encoding 1437 amino acids of a ∼162.308 kDa protein, including a cysteine-rich (CR) domain, a fibronectin type II (FNII) domain, eight C-type lectin-like domains (CTLDs), a transmembrane domain and a short cytoplasmic domain. Phylogenetic analysis indicated that MaMR shared the highest similarity with that of Paralichthys olivaceus. The expression of MaMR was found in all the examined tissues, with the highest expression in the spleen and kidney. After injection with Edwardsiella tarda, the transcript level of MaMR was initially reduced and then significantly elevated in the liver, spleen, foregut and hindgut. In the isolated peripheral blood leukocytes, the expression of MaMR was significantly induced post stimulated with LPS and LTA. Then the MaMR-CTLD4-8 recombinant protein was purified. Bacterial agglutination and binding assay showed that rMaMR-CTLD4-8 could bind with both Gram-positive and Gram-negative bacteria and agglutinate bacteria in the presence of calcium in vitro. Further analysis revealed that MaMR and TLR2 coordinately induced the expression of TRAF6 and promoted the phosphorylation level of p65, leading to the expression of proinflammatory cytokines il-1β and tnf-α in EPC cells. Taken together, these results reveal that MaMR plays an important role in the immune response of fish to pathogen infections.

The Effect of N-Acetylation on the Anti-Inflammatory Activity of Chitooligosaccharides and Its Potential for Relieving Endotoxemia

Endotoxemia is mainly caused by a massive burst of inflammatory cytokines as a result of lipopolysaccharide (LPS) invasion. Chitooligosaccharides (COS) is expected to be a potential drug for relieving endotoxemia due to its anti-inflammatory properties. However, the structural parameters of COS are often ambiguous, and the effect of degree of acetylation (DA) of COS on its anti-inflammatory remains unknown. In this study, four COSs with different DAs (0%, 12%, 50% and 85%) and the same oligomers distribution were successfully obtained. Their structures were confirmed by ¹H NMR and MS analysis. Then, the effect of DA on the anti-inflammatory activity and relieving endotoxemia potential of COS was researched. The results revealed that COS with a DA of 12% had better anti-inflammatory activity than COSs with other DAs, mainly in inhibiting LPS-induced inflammatory cytokines burst, down-regulating its mRNA expression and reducing phosphorylation of IκBα. Furthermore, this COS showed an obviously protective effect on endotoxemia mice, such as inhibiting the increase in inflammatory cytokines and transaminases, alleviating the injury of liver and intestinal tissue. This study explored the effect of DA on the anti-inflammatory activity of COS for the first time and lays the foundation for the development of COS as an anti-inflammatory drug against endotoxemia.

The mannose receptor ligands and the macrophage glycome

A unique glycan-binding protein expressed in macrophages and some types of other immune cells is the mannose receptor (MR, CD206). It is an endocytic, transmembrane protein with multiple glycan-binding domains and different specificities in binding glycans. The mannose receptor is important as it has major roles in diverse biological processes, including regulation of circulating levels of reproductive hormones, homeostasis, innate immunity, and infections. These different functions involve the recognition of a wide range of glycans, and their nature is currently under intense study. But the mannose receptor is just one of many glycan-binding proteins expressed in macrophages, leading to an interest in the potential relationship between the macrophage glycome and how it may regulate cognate glycan-binding protein activities. This review focuses primarily on the mannose receptor and its carbohydrate ligands, as well as macrophages and their glycomes.

Oral Administration of Nanopeptide CMCS-20H Conspicuously Boosts Immunity and Precautionary Effect Against Bacterial Infection in Fish

Massive mortalities caused by bacterial infections in intensive aquaculture result in serious economic losses. In this study, a novel antimicrobial peptide gcIFN-20H was efficiently expressed in Pichia pastoris (GS115) and loaded on carboxylmethyl chitosan (CMCS) to prepare CMCS-20H nanoparticles. Through physical characterization assays (TEM, DLS, BCA, and Raman) and biological activity tests (antimicrobial activity and cytotoxicity), CMCS-20H nanopeptide was verified to be spherical nanoparticles with sustained release, antimicrobial activity, and negligible toxicity. CMCS-20H nanoparticles are more resistant to intestinal degradation than unloaded gcIFN-20H by indirect immunofluorescence assay. Oral administration was then carried out for 42 days. Complement C3 content, lysozyme, and total superoxide dismutase activities are highest in CMCS-20H group by serum biochemistry index assays. After challenge with Aeromonas hydrophila, the survival rate in CMCS-20H group is highest (46%), which is 64% higher than the control group (28%). Meanwhile, the tissue bacterial loads (intestine, spleen, head kidney, trunk kidney, hepatopancreas, muscle, and blood) in the CMCS-20H group are significantly lower than other groups. By PAS staining analysis, the number of intestinal villi goblet cells and the thickness of mucin in the CMCS-20H group obviously increased. CMCS-20H effectively enhances mRNA expressions of some important immune genes (IL-1β, IL-6, TNF-α, IL-2, IFN-γ2, and IgM). The minimal tissue lesions (Intestine, spleen, and trunk kidney) were seen in the CMCS-20H group by histopathological examination. 16S rRNA sequencing showed that oral CMCS-20H maintains the intestinal microbiome homeostasis in bacterial infection. The results indicate that the novel nanopeptide CMCS-20H as the immunopotentiator can remarkably boost fish immunity and precautionary effect by oral administration and address the theoretical mechanisms and insights into the promising application prospect in aquaculture.