Peroxiredoxin 1 of Procambarus clarkii govern immune responses during pathogen infection.

Members of the peroxiredoxin family are involved in a wide variety of physiological processes, including the ability to combat the effects of oxidative stress and immune responses, among others. Here, we cloned the cDNA of Procambarus clarkii Peroxiredoxin 1 (designated as PcPrx-1) and investigated its biological role in immune system functions in relation to microbial pathogens. The PcPrx-1 cDNA had 744 base pairs in an open reading frame that encoded 247 amino acid residues and contained a PRX_Typ2cys domain. The analysis of tissue specific expression patterns revealed that PcPrx-1 expression was ubiquitous in all tissues. In addition, the mRNA transcript of PcPrx-1 was found to be highest in the hepatopancreas. There was a significant upregulation of PcPrx-1 gene transcripts after exposure to LPS, PGN, and Poly I:C, but the transcription patterns were different after pathogen challenge. Double-stranded RNA was used to knockdown PcPrx-1, which resulted in a striking change in the expression of all the tested P. clarkii immune-associated genes, including lectin, Toll, cactus, chitinase, phospholipase, and sptzale. On the whole, these results suggest that PcPrx-1 is important to confer innate immunity against pathogens by governing the expression of critical transcripts that encode immune-associated genes.

A stimulator of interferon gene (CgSTING) involved in antimicrobial immune response of oyster Crassostrea gigas.

The stimulator of interferon gene (STING), an intracellular sensor of cyclic dinucleotides, is critical to the innate immune response, especially the induction of type I interferon (IFN) during pathogenic infection. A STING homologue (CgSTING) regulating the expression of IFN-like protein (CgIFNLP) was previously identified in the Pacific oyster Crassostrea gigas, and its involvement in antibacterial immunity was further investigated in the present study. The mRNA transcripts of CgSTING were ubiquitously detected in all the three subpopulations of haemocytes with the highest expression in semi-granulocytes. After the stimulation with Vibrio splendidus, the mRNA expression of CgSTING in haemocytes was significantly up-regulated and peaked at 72 h, which was 12.91-fold of that in control group (p < 0.01). The CgSTING protein was mainly located in the cytoplasm of haemocytes. After the expression of CgSTING was knocked down (0.12-fold of that in control group, p < 0.05) by RNAi, the mRNA expression levels of interleukin17-1 (CgIL17-1), interleukin17-3 (CgIL17-3), interleukin17-4 (CgIL17-4), defensins (Cgdefh1, Cgdefh2), big defensin (CgBigDef1), interferon-like protein (CgIFNLP), tumor necrosis factor (CgTNF) and nuclear factor-κB (CgRel) all decreased significantly at 12 h after V. splendidus stimulation, which was 0.12-fold-0.72-fold (p < 0.05) of that in control group, respectively. The positive signals of CgRel were observed in the haemocyte nucleus after V. splendidus stimulation. The nuclear translocation of CgRel was suppressed in CgSTING-RNAi oysters, and the green signals of CgRel were mainly observed in the haemocyte cytoplasm after V. splendidus stimulation. Furthermore, the number of V. splendidus in the haemolymph of CgSTING-RNAi oysters increased significantly, which was 26.78-fold (p < 0.01) of that in the control group at 12 h after V. splendidus stimulation. These results indicated that CgSTING played important role in the immune defense against bacterial infection by inducing the expressions of cytokines and defensins.

Genome-wide identification, evolutionary analysis, and antimicrobial activity prediction of CC chemokines in allotetraploid common carp, Cyprinus carpio.

Chemokines are a group of secreted small molecules which are essential for cell migration in physiological and pathological conditions by binding to specific chemokine receptors. They are structurally classified into five groups, namely CXC, CC, CX3C, XC and CX. CC chemokine group is the largest one among them. In this study, we identified and characterized 61 CC chemokines from allotetraploid common carp (Cyprinus carpio). The sequence analyses showed that the majority of CC chemokines had an N-terminal signal peptide, and an SCY domain, and all CC chemokines were located in the extracellular region. Phylogenetic, evolutionary and syntenic analyses confirmed that CC chemokines were annotated as 11 different types (CCL19, CCL20, CCL25, CCL27, CCL32, CCL33, CCL34, CCL35, CCL36, CCL39, and CCL44), which exhibited unique gene arrangement pattern and chromosomal location respectively. Furthermore, genome synteny analyses between common carp and four representative teleost species indicated expansion of common carp CC chemokines resulted from the whole genome duplication (WGD) event. Additionally, the continuous evolution of gene CCL25s in teleost afforded a novel viewpoint to explain the WGD event in teleost. Then, we predicted the three-dimensional structures and probable function regions of common carp CC chemokines. All the CC chemokines core structures were constituted of an N-loop, a three-stranded ß-sheet, and a C-terminal helix. Finally, 43 CC chemokines were predicted to have probable general antimicrobial activity. Their tertiary structures, cationic and amphiphilic physicochemical property supported the viewpoint. To verify the prediction, six recombinant CCL19s proteins were prepared and the antibacterial activity against Escherichia coli and Aeromonas hydrophila were verified. The results supported our prediction that rCCL19a.1s (rCCL19a.1_a, rCCL19a.1_b) and rCCL19bs (rCCL19b_a, rCCL19b_b), especially rCCL19bs, exhibited extremely significant inhibition to the growth of both E. coli and A. hydrophila. On the contrary, two rCCL19a.2s had no significant inhibitory effect. These studies suggested that CC chemokines were essential in immune system evolution and not monofunctional during pathogen infection.

CC chemokine 1 protein from Cromileptes altivelis (CaCC1) promotes antimicrobial immune defense.

Chemokines are a family of small signaling proteins that are secreted by various cells. In addition to their roles in immune surveillance, localization of antigen, and lymphocyte trafficking for the maintenance of homeostasis, chemokines also function in induce immune cell migration under pathological conditions. In the present study, a novel CC chemokine gene (CaCC1) from humpback grouper (Cromileptes altivelis) was cloned and characterized. CaCC1 comprised a 435 bp open reading frame encoding 144 amino acid residues. The putative molecular weight of CaCC1 protein was 15 kDa CaCC1 contains four characteristic cysteines that are conserved in other known CC chemokines. CaCC1 also shares 11.64%-90.28% identity with other teleost and mammal CC chemokines. Phylogenetic analysis revealed that CaCC1 is most closely related to Epinephelus coioides EcCC1, both of which are in a fish-specific CC chemokine clade. CaCC1 was constitutively expressed in all examined C. altivelis tissues, with high expression levels in skin, heart, liver, and intestine. Vibrio harveyi stimulation up-regulated CaCC1 expression levels in liver, spleen, and head-kidney. Functional analyses revealed that the recombinant protein (rCaCC1) could induce the migration of head-kidney lymphocytes from C. altivelis. Moreover, rCaCC1 significantly enhanced phagocytosis in head-kidney macrophages from C. altivelis. In addition, rCaCC1 exhibited antimicrobial activities against Staphylococcus aureus, Edwardsiella tarda, and V. harveyi. In vivo, CaCC1 overexpression improved bacterial clearance in V. harveyi infected fish. Conversely, CaCC1 knockdown resulted in a significant decrease of bacterial clearance. These results demonstrate the important roles that CaCC1 plays in homeostasis and in inflammatory response to bacterial infection.

Role of the gut microbiota in airway immunity and host defense against respiratory infections.

Colonization of the intestine with commensal bacteria is known to play a major role in the maintenance of human health. An altered gut microbiome is associated with various ensuing diseases including respiratory diseases. Here, we summarize current knowledge on the impact of the gut microbiota on airway immunity with a focus on consequences for the host defense against respiratory infections. Specific gut commensal microbiota compositions and functions are depicted that mediate protection against respiratory infections with bacterial and viral pathogens. Lastly, we highlight factors that have imprinting effects on the establishment of the gut microbiota early in life and are potentially relevant in the context of respiratory infections. Deepening our understanding of these relationships will allow to exploit the knowledge on how gut microbiome maturation needs to be modulated to ensure lifelong enhanced resistance towards respiratory infections.

Insulin-like growth factor binding protein 3 gene of golden pompano (TroIGFBP3) promotes antimicrobial immune defense.

Insulin-like growth factor binding protein 3 (IGFBP3), an important member of the IGFBP family, plays an important biological role in regulating cellular proliferation, differentiation, growth, apoptosis, and innate immunity. However, studies concerning IGFBP3 in teleosts are very limited and IGFBP3 function remains unclear. In this study, we conducted both in vivo and in vitro functional analyses of an IGFBP3 (TroIGFBP3) from the teleost fish golden pompano (Trachinotus ovatus). TroIGFBP3 is composed of 286 amino acid residues and shares a high amino acid sequence similarity (50.18%-93.71%) with other IGFBP3 sequences in humans and teleosts. TroIGFBP3 was widely distributed in various tissues, with the highest expression in the liver. TroIGFBP3 expression was significantly upregulated following Vibrio harveyi infection. The results of in vitro assays showed that TroIGFBP3 could stimulate macrophage activation and promote peripheral blood leukocytes (PBLs) proliferation. Meanwhile, TroIGFBP3 overexpression significantly inhibited bacterial infection in fish tissues, whereas TroIGFBP3 knockdown resulted in increased bacterial dissemination and colonization in golden pompano tissues in vivo. Furthermore, recombinant TroIGFBP3 could inhibit cellular proliferation and promote apoptosis of mouse tumor cells. Taken together, these results indicated that TroIGFBP3 plays a significant role in innate antibacterial immunity and provides a theoretical foundation for investigating the function of IGFBP3 in fish immune response.

Macrophage-Targeted Isoniazid-Selenium Nanoparticles Promote Antimicrobial Immunity and Synergize Bactericidal Destruction of Tuberculosis Bacilli.

Pathogenesis hallmarks for tuberculosis (TB) are the Mycobacterium tuberculosis (Mtb) escape from phagolysosomal destruction and limited drug delivery into infected cells. Several nanomaterials can be entrapped in lysosomes, but the development of functional nanomaterials to promote phagolysosomal Mtb clearance remains a big challenge. Here, we report on the bactericidal effects of selenium nanoparticles (Se NPs) against Mtb and further introduce a novel nanomaterial-assisted anti-TB strategy manipulating Ison@Man-Se NPs for synergistic drug-induced and phagolysosomal destruction of Mtb. Ison@Man-Se NPs preferentially entered macrophages and accumulated in lysosomes releasing Isoniazid. Surprisingly, Ison@Man-Se/Man-Se NPs further promoted the fusion of Mtb into lysosomes for synergistic lysosomal and Isoniazid destruction of Mtb. Concurrently, Ison@Man-Se/Man-Se NPs also induced autophagy sequestration of Mtb, evolving into lysosome-associated autophagosomal Mtb degradation linked to ROS-mitochondrial and PI3K/Akt/mTOR signaling pathways. This novel nanomaterial-assisted anti-TB strategy manipulating antimicrobial immunity and Mtb clearance may potentially serve in more effective therapeutics against TB and drug-resistant TB.

Rhinovirus-bacteria coexposure synergistically induces CCL20 production from human bronchial epithelial cells.

Exacerbations of chronic obstructive pulmonary disease are triggered by viral or bacterial pathogens, with human rhinovirus (HRV) and nontypeable Hemophilus influenzae (NTHI) among the most commonly detected pathogens. Patients who suffer from concomitant viral and bacterial infection have more severe exacerbations. The airway epithelial cell is the initial site of viral and bacterial interactions, and CCL20 is an epithelial chemokine that attracts immature dendritic cells to the airways and can act as an antimicrobial. As such, it contributes to innate and adaptive immune responses to infection. We used primary cultures of human bronchial epithelial cells and the BEAS-2B cell line to examine the effects of bacterial-viral coexposure, as well as each stimulus alone, on epithelial expression of CXCL8 and, in particular, CCL20. HRV-bacterial coexposure induced synergistic production of CXCL8 and CCL20 compared with the sum of each stimulus alone. Synergistic induction of CCL20 did not require viral replication and occurred with two different HRV serotypes that use different viral receptors. Synergy was also seen with either NTHI or Pseudomonas aeruginosa Synergistic induction of CCL20 was transcriptionally regulated. Although NF-κB was required for transcription, it did not regulate synergy, but NF-IL-6 did appear to contribute. Among MAPK inhibitors studied, neither SB203580 nor PD98059 had any effect on synergy, whereas U0126 prevented synergistic induction of CCL20 by HRV and bacteria, apparently via "off-target" effects. Thus bacterial-viral coexposure synergistically increases innate immune responses compared with individual infections. We speculate that this increased inflammatory response leads to worse clinical outcomes.

Clostridium difficile-mediated effects on human intestinal epithelia: Modelling host-pathogen interactions in a vertical diffusion chamber.

Clostridium difficile infection is one of the leading causes of healthcare associated diarrhoea in the developed world. Although the contribution of C. difficile toxins to disease pathogenesis is now well understood, many facets of host-pathogen interactions between the human intestinal epithelia and the C. difficile bacterium that may contribute to asymptomatic carriage and/or clinical disease remain less clear. Herein, we tested the hypothesis that C. difficile strains mediate intestinal epithelial cell (IEC) antimicrobial immunity via toxin dependent and independent means and that the 'anaerobic' environment has a significant impact on bacterial-IEC interactions. Crosstalk between three C. difficile PCR ribotypes (RT) [RT027 (strain R20291), RT012 (strain 630) and RT017 (strains M68 and CF5)] and IEC cell-lines were investigated. All RTs showed significant engagement with human Toll-like receptors (TLR)-5, TLR2-CD14 and TLR2/6 as measured by IL-8 release from TLR-transfected HEK cells. Co-culture studies indicated minimal impact of R20291 and 630 TcdA and TcdB on bacterial adherence to Caco-2 cells. An apical anaerobic environment had a major effect on C. difficile-T84 crosstalk as significantly greater cytokine immunity and trans-epithelial electrical resistance (TEER) dysfunction was recorded when co-cultures were performed in an Ussing chamber system compared to standard 5% CO2 conditions. Overall, this study suggests that anaerobic C. difficile engagement with human IECs is a complex interplay that involves bacterial and toxin-mediated cellular events.

Fish IL-26 collaborates with IL-10R2 and IL-20R1 to enhance gut mucosal barrier during the antibacterial innate immunity.

IL-26 is a cytokine that is crucial for the maintenance and function of the gut mucosal barrier. IL-26 signaling pathway relies on a heterodimeric receptor complex, which is composed of two distinct subunits, IL-10R2 and IL-20R1. However, there are no reports on the antibacterial immunity of IL-26 and its receptors in fish. For this purpose, in this study we identified IL-26 and its receptors IL-10R2 and IL-20R1 in Carassius cuvieri × Carassius auratus red var. (named WR-IL-26, WR-IL10R2 and WR-IL20R1, respectively). Phylogenetic analysis confirmed the conservation of these genes, with shared structural motifs similar to those found in higher vertebrates. Upon exposure to Aeromonas hydrophila, a common fish pathogen, there was a significant upregulation of WR-IL-26, WR-IL10R2 and WR-IL20R1 in the gut, indicating a potential role in the immune response to infection. A co-immunoprecipitation assay revealed that WR-IL-26 formed complexes with WR-IL10R2 and WR-IL20R1. In vivo experiments demonstrated that administration of WR-IL-26 activated the JAK1-STAT3 signaling pathway and protected the gut mucosa barrier from A. hydrophila infection. Conversely, silencing WR-IL10R2 and WR-IL20R1 via RNA interference significantly attenuated the activation of WR-IL-26-mediated JAK1-STAT3 pathway. These results provided new insights into the role of IL-26 and its receptors in the gut mucosa barrier and could offer novel therapeutic strategies for managing bacterial infections in aquaculture.

Anti-infective immune functions of type IV interferon in grass carp ( Ctenopharyngodon idella): A novel antibacterial and antiviral interferon in lower vertebrates.

Type IV interferon (IFN-υ) is a recently discovered cytokine crucial for host defense against viral infections. However, the role and mechanisms of IFN-υ in bacterial infections remain unexplored. This study investigated the antibacterial and antiviral functions and mechanisms of grass carp ( Ctenopharyngodon idella) IFN-υ (CiIFN-υ) both in vivo and in vitro. The CiIFN-υ gene was first identified and characterized in grass carp. Subsequently, the immune expression of CiIFN-υ significantly increased following bacterial challenge, indicating its response to bacterial infections. The eukaryotic recombinant expression plasmid of CiIFN-υ was then constructed and transfected into fathead minnow (FHM) cells. Supernatants were collected and incubated with four bacterial strains, followed by plate spreading and colony counting. Results indicated that CiIFN-υ exhibited more potent antibacterial activity against gram-negative bacteria compared to gram-positive bacteria and aggregated gram-negative bacteria but not gram-positive bacteria. In vivo experiments further confirmed the antibacterial function, showing high survival rates, low tissue edema and damage, reduced tissue bacterial load, and elevated proinflammatory response at the early stages of bacterial infection. In addition, the antiviral function of CiIFN-υ was confirmed through in vitro and in vivo experiments, including crystal violet staining, survival rates, tissue viral burden, and RT-qPCR. This study highlights the antibacterial function and preliminary mechanism of IFN-υ, demonstrating that IFN-υ possesses dual functions against bacterial and viral infections.

Exogenous alpha-linolenic acid and Vibrio parahaemolyticus induce EPA and DHA levels mediated by delta-6 desaturase to enhance shrimp immunity.

Globally, penaeid shrimp are the most farmed and traded aquatic organisms, although they are easily susceptible to microbial pathogens. Moreover, there is a desire to increase the nutritional value of shrimp, especially the levels of n-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which also possess immunomodulatory and anti-inflammatory properties. Some aquatic animals can synthesize EPA and DHA from dietary plant-sourced alpha-linolenic acid (ALA), but penaeid shrimps' ability to synthesize these n-3 PUFAs is unknown. Here, molecular biology techniques, including gas chromatography-mass spectrometry, qPCR, ELISA, etc., were used to demonstrate that exogenous ALA or Vibrio parahaemolyticus could modulate EPA and DHA levels and immune genes in Penaeus vannamei by inducing key enzymes involved in n-3 PUFAs biosynthesis, such as delta desaturases and elongation of very long-chain fatty acid (ELOVLs). Most importantly, knockdown or inhibition of ∆6 desaturase significantly decreased EPA and DHA levels and immune gene expression even with exogenous ALA treatment, consequently affecting shrimp antibacterial immunity and survival. This study provides new insight into the potential of P. vannamei to synthesize n-3 PUFAs from exogenous ALA or upon bacteria challenge, which could be leveraged to increase their nutritional content and antimicrobial immunity.

The amphibian immune system.

Amphibians are at the forefront of bridging the evolutionary gap between mammals and more ancient, jawed vertebrates. Currently, several diseases have targeted amphibians and understanding their immune system has importance beyond their use as a research model. The immune system of the African clawed frog, Xenopus laevis, and that of mammals is well conserved. We know that several features of the adaptive and innate immune system are very similar for both, including the existence of B cells, T cells and innate-like T cells. In particular, the study of the immune system at early stages of development is benefitted by studying X. laevis tadpoles. The tadpoles mainly rely on innate immune mechanisms including pre-set or innate-like T cells until after metamorphosis. In this review we lay out what is known about the innate and adaptive immune system of X. laevis including the lymphoid organs as well as how other amphibian immune systems are similar or different. Furthermore, we will describe how the amphibian immune system responds to some viral, bacterial and fungal insults. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'.

IFN regulatory factor 3 of golden pompano and its NLS domain are involved in antibacterial innate immunity and regulate the expression of type I interferon (IFNa3).

Introduction: The transcription factor interferon regulatory factor 3 (IRF3) plays an important role in host defence against viral infections. However, its role during bacterial infection in teleosts remains unclear. In the present study, we evaluated the antibacterial effects of Trachinotus ovatus IRF3 (TroIRF3) and how it regulates type I interferon (IFN). Methods: Subcellular localisation experiments, overexpression, and quantitative real-time PCR (qRT-PCR) were performed to examine the nuclear localisation signal (NLS) of TroIRF3 and its role in the antibacterial regulatory function of TroIRF3. We assessed the binding activity of TroIRF3 to the IFNa3 promoter by luciferase reporter assay. Results and Discussion: The results showed that TroIRF3 was constitutively expressed at high levels in the gill and liver. TroIRF3 was significantly upregulated and transferred from the cytoplasm to the nucleus after Vibrio harveyi infection. By overexpressing TroIRF3, the fish were able to inhibit the replication of V. harveyi, whereas knocking it down increased bacterial replication. Moreover, the overexpression of TroIRF3 increased type I interferon (IFNa3) production and the IFN signalling molecules. The NLS, which is from the 64-127 amino acids of TroIRF3, contains the basic amino acids KR74/75 and RK82/84. The results proved that NLS is required for the efficient nuclear import of TroIRF3 and that the NLS domain of TroIRF3 consists of the key amino acids KR74/75 and RK82/84. The findings also showed that NLS plays a key role in the antibacterial immunity and upregulation of TroIFNa3 induced by TroIRF3. Moreover, TroIRF3 induces TroIFNa3 promoter activity, whereas these effects are inhibited when the NLS domain is deficient. Overall, our results suggested that TroIRF3 is involved in the antibacterial immunity and regulation of type I IFN in T. ovatus and that the NLS of TroIRF3 is vital for IRF3-mediated antibacterial responses, which will aid in understanding the immune role of fish IRF3.

Tongue sole creatine kinases function as DAMP and activate antimicrobial immunity via TLR2.

Creatine kinase (CK) is an enzyme that regulates adenosine triphosphate (ATP) metabolism to maintain energy homeostasis. Although CK has been reported to be involved in pathogen infection, the immune function of CK remains elusive. In this study, we identified two muscle-type CK from the teleost tongue sole Cynoglossus semilaevis (designated CsCKM-1 and CsCKM-2). Bacterial infection modulated CsCKM-1/2 expression in tongue sole tissues and induced the release of CsCKM-1/2 into serum. Recombinant CsCKM-1/2 (rCsCKM-1/2) exhibited robust kinase activity and bound to bacterial pathogens and pathogen-associated molecular patterns. rCsCKM-1/2 also bound to tongue sole peripheral blood leukocytes (PBLs) and promoted PBLs to uptake bacterial pathogens, inhibit bacterial proliferation, and express proinflammatory cytokines. When co-expressed in HEK293T cells, CsCKM-1/2 were found to interact with the leucine rich domain of toll-like receptor 2 (TLR2). The presence of TLR2 antagonist significantly reduced CsCKM-1/2-induced immune response and antibacterial effect. Taken together, these results indicated that tongue sole creatine kinases function as damage-associated molecular pattern (DAMP) molecules and play an important role in antimicrobial immunity via TLR2.

Silent neonatal influenza A virus infection primes systemic antimicrobial immunity.

Infections with influenza A viruses (IAV) cause seasonal epidemics and global pandemics. The majority of these infections remain asymptomatic, especially among children below five years of age. Importantly, this is a time, when immunological imprinting takes place. Whether early-life infections with IAV affect the development of antimicrobial immunity is unknown. Using a preclinical mouse model, we demonstrate here that silent neonatal influenza infections have a remote beneficial impact on the later control of systemic juvenile-onset and adult-onset infections with an unrelated pathogen, Staphylococcus aureus, due to improved pathogen clearance and clinical resolution. Strategic vaccination with a live attenuated IAV vaccine elicited a similar protection phenotype. Mechanistically, the IAV priming effect primarily targets antimicrobial functions of the developing innate immune system including increased antimicrobial plasma activity and enhanced phagocyte functions and antigen-presenting properties at mucosal sites. Our results suggest a long-term benefit from an exposure to IAV during the neonatal phase, which might be exploited by strategic vaccination against influenza early in life to enforce the host's resistance to later bacterial infections.

Bacteria-based multiplex system eradicates recurrent infections with drug-resistant bacteria via photothermal killing and protective immunity elicitation.

BACKGROUND: The high mortality associated with drug-resistant bacterial infections is an intractable clinical problem resulting from the low susceptibility of these bacteria to antibiotics and the high incidence of recurrent infections. METHODS: Herein, a photosynthetic bacteria-based multiplex system (Rp@Al) composed of natural Rhodopseudomonas palustris (Rp) and Food and Drug Administration-approved aluminum (Al) adjuvant, was developed to combat drug-resistant bacterial infections and prevent their recurrence. We examined its photothermal performance and in vitro and in vivo antibacterial ability; revealed its protective immunomodulatory effect; verified its preventative effect on recurrent infections; and demonstrated the system's safety. RESULTS: Rp@Al exhibits excellent photothermal properties with an effective elimination of methicillin-resistant Staphylococcus aureus (MRSA). In addition, Rp@Al enhances dendritic cell activation and further triggers a T helper 1 (TH1)/TH2 immune response, resulting in pathogen-specific immunological memory against recurrent MRSA infection. Upon second infection, Rp@Al-treated mice show significantly lower bacterial burden, faster abscess recovery, and higher survival under near-lethal infection doses than control mice. CONCLUSIONS: This innovative multiplex system, with superior photothermal and immunomodulatory effects, presents great potential for the treatment and prevention of drug-resistant bacterial infections.

NOD1, NOD2, and NLRC5 Receptors in Antiviral and Antimycobacterial Immunity.

The innate immune system recognizes pathogen-associated molecular motifs through pattern recognition receptors (PRRs) that induce inflammasome assembly in macrophages and trigger signal transduction pathways, thereby leading to the transcription of inflammatory cytokine genes. Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) represent a family of cytosolic PRRs involved in the detection of intracellular pathogens such as mycobacteria or viruses. In this review, we discuss the role of NOD1, NOD2, and NLRC5 receptors in regulating antiviral and antimycobacterial immune responses by providing insight into molecular mechanisms as well as their potential health and disease implications.

Two NF-κB subunits are associated with antimicrobial immunity in Hyriopsis cumingii.

The NF-κB pathway activated by bacteria and viruses produces a series of antimicrobial peptides that participate in the innate immune response. In this study, two NF-κB subunits were cloned and identified from Hyriopsis cumingii (named Hcp65 and Hcp105) using RT-PCR and RACE. The predicted Hcp65 protein possessed a N-terminal Rel homology domain (RHD) and an Ig-like/plexins/transcription factors domain (IPT); the Hcp105 contained an RHD, an IPT domain, 6 ankyrin (ANK) domain and a death domain. Quantitative reverse transcription PCR (qRT-PCR) showed that Hcp65 and Hcp105 were constitutively expressed in the detected tissues, and were significantly up-regulated in hemocytes, hepatopancreas and gill of mussels challenged with lipopolysaccharide (LPS), peptidoglycan (PGN) and polyinosinic-polycytidylic acid (poly I: C). The dsRNA-mediated silencing of Hcp65 and Hcp105 caused significant reduction of immune genes such as lysozyme (HcLyso), theromacin (Hcther), whey acid protein (HcWAP), LPS-binding protein/bactericidal permeability protein (HcLBP/BPI) 1 and 2. In addition, subcellular localization experiments showed that Hcp65 and Hcp105 proteins were expressed in both the nucleus and cytoplasm of HEK-293T cells, and Hcp50 proteins (mature peptide of Hcp105) were mainly localized in the nucleus. The recombinant Hcp65 and Hcp50 protein could form homodimer and heterodimer and bind κB site in vitro. These results provide useful information for understanding the role of NF-κB in mollusks.

Japanese Flounder HMGB1: A DAMP Molecule That Promotes Antimicrobial Immunity by Interacting with Immune Cells and Bacterial Pathogen.

High mobility group box (HMGB) proteins are DNA-associated proteins that bind and modulate chromosome structures. In mammals, HMGB proteins can be released from the cell nucleus and serve as a damage-associated molecular pattern (DAMP) under stress conditions. In fish, the DAMP function of HMGB proteins in association with bacterial infection remains to be investigated. In this study, we examined the immunological functions of two HMGB members, HMGB1 and HMG20A, of Japanese flounder. HMGB1 and HMG20A were expressed in multiple tissues of the flounder. HMGB1 was released from peripheral blood leukocytes (PBLs) upon bacterial challenge in a temporal manner similar to that of lactate dehydrogenase release. Recombinant HMGB1 bound to PBLs and induced ROS production and the expression of inflammatory genes. HMGB1 as well as HMG20A also bound to various bacterial pathogens and caused bacterial agglutination. The bacteria-binding patterns of HMGB1 and HMG20A were similar, and the binding of HMGB1 competed with the binding of HMG20A but not vice versa. During bacterial infection, HMGB1 enhanced the immune response of PBLs and repressed bacterial invasion. Collectively, our results indicate that flounder HMGB1 plays an important role in antimicrobial immunity by acting both as a modulator of immune cells and as a pathogen-interacting DAMP.