Isolation, characterization, and antimicrobial properties of bovine oligosaccharide-binding protein. A microbicidal granule protein of eosinophils and neutrophils

Thymopentin plays a key role in restoring the function of macrophages to alleviate the sepsis process

Immune dysfunction is one of the leading causes of death of sepsis. How to regulate host immune functions to improve prognoses of septic patients has always been a clinical focus. Here we elaborate on the efficacy and potential mechanism of a classical drug, thymopentin (TP5). TP5 could decrease peritoneal bacterial load, and reduce inflammatory cytokine levels both in the peritoneal lavage fluid (PLF) and serum, alleviate pathological injuries in tissue and organ, coaxed by cecal ligation and perforation (CLP) in mice, ultimately improve the prognosis of septic mice. Regarding the mechanism, using RNA-seq and flow cytometry, we found that TP5 induced peptidoglycan recognition protein 1 (PGLYRP1) expression, increased phagocytosis and restored TNF-α expression of small peritoneal macrophage (SPM) in the septic mice. This may be increased SPM's ability to clear peritoneal bacteria, thereby attenuates the inflammatory response both in the peritoneal cavity and the serum. It was shown that TP5 plays a key role in restoring the function of peritoneal macrophages to alleviate the sepsis process. We reckon that this is closely relevant to SPM phagocytosis, which might involve increased PGLYRP1 expression and restored TNF-α secretion.

Immune Responses and Pathogenesis following Experimental SARS-CoV-2 Infection in Domestic Cats

Several reports demonstrated the susceptibility of domestic cats to SARS-CoV-2 infection. Here, we describe a thorough investigation of the immune responses in cats after experimental SARS-CoV-2 inoculation, along with the characterization of infection kinetics and pathological lesions. Specific pathogen-free domestic cats (n = 12) were intranasally inoculated with SARS-CoV-2 and subsequently sacrificed on DPI (days post-inoculation) 2, 4, 7 and 14. None of the infected cats developed clinical signs. Only mild histopathologic lung changes associated with virus antigen expression were observed mainly on DPI 4 and 7. Viral RNA was present until DPI 7, predominantly in nasal and throat swabs. The infectious virus could be isolated from the nose, trachea and lungs until DPI 7. In the swab samples, no biologically relevant SARS-CoV-2 mutations were observed over time. From DPI 7 onwards, all cats developed a humoral immune response. The cellular immune responses were limited to DPI 7. Cats showed an increase in CD8+ cells, and the subsequent RNA sequence analysis of CD4+ and CD8+ subsets revealed a prominent upregulation of antiviral and inflammatory genes on DPI 2. In conclusion, infected domestic cats developed a strong antiviral response and cleared the virus within the first week after infection without overt clinical signs and relevant virus mutations.

Common carp Peptidoglycan Recognition Protein 2 (CcPGRP2) plays a role in innate immunity for defense against bacterial infections

PGRP is a family of pattern recognition molecules of the innate immune system. PGRPs are conserved from insects to mammals and have diverse functions in antimicrobial defense. Here we cloned a common carp PGRP ortholog, CcPGRP2 containing a conserved C-terminal PGRP domain. We tested the expression levels of CcPGRP2 in the liver, spleen, kidney, foregut, midgut, and hindgut of the highest level in the liver. The expression of CcPGRP2 upregulated in common carp infected with Aeromonas hydrophila (A. hydrophila) or Staphylococcus aureus (S. aureus). Recombinant CcPGRP2 protein expressed in Escherichia coli (E. coli) system and the purified CcPGRP2 could maintain the integrity of intestinal mucosa of common carp infected with A. hydrophila. In addition, CcPGRP2 could agglutinate or bind both gram-positive and gram-negative bacteria in a Zn²⁺-dependent manner. CcPGRP2 has a stronger agglutination and bacterial binding ability in gram-positive bacteria than in gram-negative bacteria. It is perhaps because CcPGRP2 could bind peptidoglycan (PGN) with a higher degree to lipopolysaccharide (LPS). And CcPGRP2 shows antimicrobial activities in the presence of Zn²⁺. Our results of CcPGRP2 provided new insight into the function of PGRP in the innate immunity of the common carp.

CX3CR1-Expressing Myeloid Cells Regulate Host-Helminth Interaction and Lung Inflammation

Many helminth life cycles, including hookworm, involve a mandatory lung phase, where myeloid and granulocyte subsets interact with the helminth and respond to infection-induced lung injury. To evaluate these innate subsets in Nippostrongylus brasiliensis infection, reporter mice for myeloid cells (CX3CR1^GFP ) and granulocytes (PGRP^dsRED ) are employed. Nippostrongylus infection induces lung infiltration of reporter cells, including CX3CR1⁺ myeloid cells and PGRP⁺ eosinophils. Strikingly, CX3CR1^GFP/GFP mice, which are deficient in CX3CR1, are protected from Nippostrongylus infection with reduced weight loss, lung leukocyte infiltration, and worm burden compared to CX3CR1^+/+ mice. This protective effect is specific for CX3CR1 as CCR2-deficient mice do not exhibit reduced worm burdens. Nippostrongylus co-culture with lung Ly6C⁺ monocytes or CD11c⁺ cells demonstrates that CX3CR1^GFP/GFP monocytes secrete more pro-inflammatory cytokines and actively bind the parasites causing reduced motility. RNA sequencing of Ly6C⁺ or CD11c⁺ cells shows Nippostrongylus-induced gene expression changes, particularly in monocytes, associated with inflammation, chemotaxis, and extracellular matrix remodeling pathways. Analysis reveals cytotoxic and adhesion molecules as potential effectors against the parasite, such as Gzma and Gzmb, which are elevated in CX3CR1^GFP/GFP monocytes. These studies validate a dual innate cell reporter for lung helminth infection and demonstrate that CX3CR1 impairs monocyte-helminth interaction.

Relationship between polymorphism within Peptidoglycan Recognition Protein 1 gene (PGLYRP1) and somatic cell counts in milk of Holstein cows

Bovine peptidoglycan recognition protein 1 (PGLYRP1) is an important receptor that binds to murein peptidoglycans (PGN) of Gram-positive and Gram-negative bacteria and is, therefore, involved in innate immunity. The SNP T>C rs68268284 located in the 1st exon of the PGLYRP1 gene was identified by the PCR-RFLP method in a population of 319 Holstein cows. Somatic cell count (SCC) was measured 7–10 times in each of three completed lactations to investigate whether the PGLYRP1 polymorphism is associated with SCC. Using the GLM model, it was found that cows with the TT genotype showed significantly lower somatic cell counts than those with the CC genotype during the first lactation (P = 0.023). Moreover, during lactations 1–2 and 1–3, cows with the TT genotype reveal significantly lower SCC than CT heterozygotes, at P = 0.025 and P = 0.006, respectively. Computer-aided analysis showed that rs68268284 polymorphism could modify the PGLYRP1 functions because the mutated residue is located in a domain that is important for the binding of other molecules.

Structure-function analysis of PGRP-S1 from the oriental armyworm, Mythimna separata

Peptidoglycan recognition proteins (PGRPs) are well known for their abilities to recognize or hydrolyze peptidoglycan (PGN), one of the major bacterial cell wall components. However, much less is known about their antifungal activities. PGRP-S1 was previously identified from a crop pest, Mythimna separata (Walker) (Lepidoptera: Noctuidae). PGRP-S1 showed bacteriolytic activities against Gram-positive and Gram-negative bacteria. In this study, tissue expression analysis showed that PGRP-S1 was mainly expressed in the midgut of naïve larvae. The induction analysis showed that it was significantly induced in the larval midgut 12 h post the injection of Beauveria bassiana conidia. To identify the key residues that are related to its microbicidal activities, the structure of PGPR-S1 was predicted for structural comparison and molecular docking analysis. Six residues (H61, H62, Y97, H171, T175, and C179) were mutated to Ala individually by site-directed mutagenesis. The recombinant wild-type (WT) and mutant proteins were expressed and purified. The recombinant proteins bound to different polysaccharides, PGNs, and bacteria. H61A, Y97A, H171A, and C179A lost amidase activity. Accordingly, antibacterial assay and scanning electron microscopy confirmed that only H62A and T175A retained bacteriolytic activities. The germination of B. bassiana conidia was significantly inhibited by WT, H61A, Y97A, T175A, and C179A mutants. Electron microscopy showed that some conidia became ruptured after treatment. The growth of hyphae was inhibited by the WT, H61A, H62A, and T175A. In summary, our data showed that different residues of PGRP-S1 are involved in the antibacterial and antifungal activities.

Respiratory chain components are required for peptidoglycan recognition protein-induced thiol depletion and killing in Bacillus subtilis and Escherichia coli

Mammalian peptidoglycan recognition proteins (PGRPs or PGLYRPs) kill bacteria through induction of synergistic oxidative, thiol, and metal stress. Tn-seq screening of Bacillus subtilis transposon insertion library revealed that mutants in the shikimate pathway of chorismate synthesis had high survival following PGLYRP4 treatment. Deletion mutants for these genes had decreased amounts of menaquinone (MK), increased resistance to killing, and attenuated depletion of thiols following PGLYRP4 treatment. These effects were reversed by MK or reproduced by inhibiting MK synthesis. Deletion of cytochrome aa₃-600 or NADH dehydrogenase (NDH) genes also increased B. subtilis resistance to PGLYRP4-induced killing and attenuated thiol depletion. PGLYRP4 treatment also inhibited B. subtilis respiration. Similarly in Escherichia coli, deletion of ubiquinone (UQ) synthesis, formate dehydrogenases (FDH), NDH-1, or cytochrome bd-I genes attenuated PGLYRP4-induced thiol depletion. PGLYRP4-induced low level of cytoplasmic membrane depolarization in B. subtilis and E. coli was likely not responsible for thiol depletion. Thus, our results show that the respiratory electron transport chain components, cytochrome aa₃-600, MK, and NDH in B. subtilis, and cytochrome bd-I, UQ, FDH-O, and NDH-1 in E. coli, are required for both PGLYRP4-induced killing and thiol depletion and indicate conservation of the PGLYRP4-induced thiol depletion and killing mechanisms in Gram-positive and Gram-negative bacteria.

Mechanisms of Action of the PGLYRP1/Tag7 Protein in Innate and Acquired Immunity

One of the promising fields of modern molecular biology is the search for new proteins that regulate the various stages of the immune response and the investigation of the molecular mechanisms of action of these proteins. Such proteins include the multifunctional protein PGLYRP1/Tag7, belonging to the PGRP-S protein family, whose gene was discovered in mice at the Institute of Gene Biology, Russian Academy of Sciences, in 1996. PGLYRP1/Tag7 is classified as a protein of innate immunity; however, it can also participate in the regulation of acquired immunity mechanisms. In this paper, we consider the involvement of PGLYRP1/Tag7 in the triggering of antimicrobial defense mechanisms and formation of subsets of cytotoxic lymphocytes that kill tumor cells. The paper emphasizes that the multifaceted functional activity of Tag7 in the immune response has to do with its ability to interact with various proteins to form stable protein complexes. Hsp70-associated Tag7 can induce the death of tumor cells carrying the TNFR1 receptor. Tag7, associated with the Mts1 (S100A4) protein, can stimulate the migration of innate and adaptive immune cytotoxic lymphocytes to a lesion site. Involvement of Tag7 in the regulation of immunological processes suggests that it may be considered as a promising agent in cancer therapy. These properties of Tag7 were used to develop autologous vaccines that have passed the first and second phases of clinical trials in patients with end-stage melanoma and renal cancer. The C-terminal peptide of Tag7, isolated by limited proteolysis, was shown to protect the cartilage and bone tissue of the ankle joint in mice with induced autoimmune arthritis and may be a promising drug for suppressing the development of inflammatory processes.

A Fixed Cohort Field Study of Gene Expression in Circulating Leukocytes From Dairy Cows With and Without Mastitis

Specifically designed gene expression studies can be used to prioritize candidate genes and identify novel biomarkers affecting resilience against mastitis and other diseases in dairy cattle. The primary goal of this study was to assess whether specific peripheral leukocyte genes expressed differentially in a previous study of dairy cattle with postpartum disease, also would be expressed differentially in peripheral leukocytes from a diverse set of different dairy cattle with moderate to severe clinical mastitis. Four genes were selected for this study due to their differential expression in a previous transcriptomic analysis of circulating leukocytes from dairy cows with and without evidence of early postpartum disease. An additional 15 genes were included based on their cellular, immunologic, and inflammatory functions associated with resistance and tolerance to mastitis. This fixed cohort study was conducted on a conventional dairy in Washington state. Cows >50 days in milk (DIM) with mastitis (n = 12) were enrolled along with healthy cows (n = 8) selected to match the DIM and lactation numbers of mastitic cows. Blood was collected for a complete blood count (CBC), serum biochemistry, leukocyte isolation, and RNA extraction on the day of enrollment and twice more at 6 to 8-days intervals. Latent class analysis was performed to discriminate healthy vs. mastitic cows and to describe disease resolution. RNA samples were processed by the Primate Diagnostic Services Laboratory (University of Washington, Seattle, WA). Gene expression analysis was performed using the Nanostring System (Nanostring Technologies, Seattle, Washington, USA). Of the four genes (C5AR1, CATHL6, LCN2, and PGLYRP1) with evidence of upregulation in cows with mastitis, three of those genes (CATHL6, LCN2, and PGLYRP1) were investigated due to their previously identified association with postpartum disease. These genes are responsible for immunomodulatory molecules that selectively enhance or alter host innate immune defense mechanisms and modulate pathogen-induced inflammatory responses. Although further research is warranted to explain their functional mechanisms and bioactivity in cattle, our findings suggest that these conserved elements of innate immunity have the potential to bridge disease states and target tissues in diverse dairy populations.

Adaptive evolution of peptidoglycan recognition protein family regulates the innate signaling against microbial pathogens in vertebrates

The innate immune system is the first line of defense in vertebrates against microbial pathogens. This defense system depends on the peptidoglycan pathogen recognition of receptors (PGRPs) existing in both invertebrates and vertebrates. Although some studies revealed the structural and functional differences between them, however, the evolutionary history and the selection pressures on these genes during adaptive evolution are poorly understood. In this study, we examined four (PGLYRP1, PGLYRP2, PGLYRP3, and PGLYRP4) genes of 127 vertebrates' species, conserved across vertebrates to evaluate positive selection pressure drives by adaptive evolution. The codons under positive selection were recognized through likelihood tests by comparing different models based on ω ratios in these genes across the vertebrate species. The positive selection test used two sets of models M1a vs. M2a and M7 vs. M8. The results showed that the test of these genes in M1a vs. M2a was not significant with the likelihood value 2ΔlnL = 0, while the likelihood ratios (2ΔlnL) were 2ΔlnL = 12.386, 2ΔlnL = 4.9283, 2ΔlnL = 24.031, and 2ΔlnL = 103.39 for PGLYRP1, PGLYRP2, PGLYRP3, and PGLYRP4 in M7 vs. M8, respectively. Our study identified the evidence of robust positive selection for these four genes across the vertebrates. These protuberant changes in PGRPs evolution of vertebrates reveal their role in innate immunity. Our study provides an insight based on PGRP genes to understand the evolution of host and pathogens interaction that leads to the progress of the novel conducts for immune diseases that include proteins linked to the recognition of pathogens.

Formate dehydrogenase, ubiquinone, and cytochrome bd-I are required for peptidoglycan recognition protein-induced oxidative stress and killing in Escherichia coli

Mammalian Peptidoglycan Recognition Proteins (PGRPs) kill bacteria through induction of synergistic oxidative, thiol, and metal stress. PGRPs induce oxidative stress in bacteria through a block in the respiratory chain, which results in decreased respiration and incomplete reduction of oxygen (O₂) to hydrogen peroxide (H₂O₂). In this study we identify the site of PGRP-induced generation of H₂O₂ in Escherichia coli. Tn-seq screening of E. coli Tn10 insertion library revealed that mutants in formate dehydrogenase (FDH) genes had the highest survival following PGRP treatment. Mutants lacking functional FDH-O had abolished PGRP-induced H₂O₂ production and the highest resistance to PGRP-induced killing, and formate enhanced PGRP-induced killing and H₂O₂ production in an FDH-dependent manner. Mutants in ubiquinone synthesis (but not menaquinone and demethylmenaquinone) and cytochrome bd-I (but not cytochromes bo₃ and bd-II) also had completely abolished PGRP-induced H₂O₂ production and high resistance to PGRP-induced killing. Because electrons in the respiratory chain flow from dehydrogenases' substrates through quinones and then cytochromes to O₂, these results imply that the site of PGRP-induced incomplete reduction of O₂ to H₂O₂ is downstream from dehydrogenases and ubiquinone at the level of cytochrome bd-I, which results in oxidative stress. These results reveal several essential steps in PGRP-induced bacterial killing.

The Pglyrp1-Regulated Microbiome Enhances Experimental Allergic Asthma

Changes in intestinal or respiratory microbiomes in infants correlate with increased incidence of asthma, but the causative role of microbiome in the susceptibility to asthma and the host genes that regulate these changes in microbiome are mostly unknown. In this study, we show that decreased responsiveness to allergic asthma in Pglyrp1 ^-/- mice (lacking bactericidal peptidoglycan recognition protein 1) could be transferred to germ-free wild-type mice by colonization of mothers and newborns with microbiota from Pglyrp1 ^-/- mice. These colonized mice had decreased airway resistance and fewer inflammatory cells, less severe histopathology, and lower levels of IgE and proallergic cytokines and chemokines in the lungs. This microbiome-dependent decreased responsiveness to asthma was most pronounced in colonized germ-free BALB/c mice (genetically predisposed to asthma), only partially evident in outbred germ-free Swiss Webster mice, and marginal in conventional BALB/c mice following depletion of microbiome with antibiotics. Mice with a low asthmatic response colonized with microbiota from Pglyrp1 ^-/- mice had increased abundance of Bacteroidetes and decreased abundance of Firmicutes, Tenericutes, Deferribacteres, and Spirochaetes in the feces and increased abundance of Pasteurella in the oropharynx. These changes in bacterial abundance in the feces and oropharynx correlated with lower asthmatic responses in the lungs. Thus, our results show that Pglyrp1 enhances allergic asthmatic responses primarily through its effect on the host intestinal microbiome and identify several bacteria that may increase or decrease sensitivity to asthma. This effect of microbiome is strong in asthma-prone BALB/c mice and weak in asthma-resistant outbred mice and requires germ-free conditions before colonization with microbiota from Pglyrp1 ^-/- mice.

Paraimmunobiotic Bifidobacteria Modulate the Expression Patterns of Peptidoglycan Recognition Proteins in Porcine Intestinal Epitheliocytes and Antigen Presenting Cells

Peptidoglycan recognition proteins (PGLYRPs) are a family of pattern recognition receptors (PRRs) that are able to induce innate immune responses through their binding to peptidoglycan (PGN), lipopolysaccharide, or lipoteichoic acid, or by interacting with other PRR-ligands. Recently, progress has been made in understanding the immunobiology of PGLYRPs in human and mice, however, their functions in livestock animals have been less explored. In this study, we characterized the expression patterns of PGLYRPs in porcine intestinal epithelial (PIE) cells and antigen-presenting cells (APCs) and their modulation by the interactions of host cells with PRR-ligands and non-viable immunomodulatory probiotics referred to as paraimmunobiotics. We demonstrated that PGLYRP-1, -2, -3, and -4 are expressed in PIE cells and APCs from Peyer’s patches, being PGLYPR-3 and -4 levels higher than PGLYRP-1 and -2. We also showed that PGLYRPs expression in APCs and PIE cells can be modulated by different PRR agonists. By using knockdown PIE cells for TLR2, TLR4, NOD1, and NOD2, or the four PGLYRPs, we demonstrated that PGLYRPs expressions would be required for activation and functioning of TLR2, TLR4, NOD1, and NOD2 in porcine epitheliocytes, but PGLYRPs activation would be independent of those PRR expressions. Importantly, we reported for the first time that PGLYRPs expression can be differentially modulated by paraimmunobiotic bifidobacteria in a strain-dependent manner. These results provide evidence for the use of paraimmunobiotic bifidobacteria as an alternative for the improvement of resistance to intestinal infections or as therapeutic tools for the reduction of the severity of inflammatory damage in diseases in which a role of PGLYRPs-microbe interaction has been demonstrated.

A peptidoglycan recognition protein involved in immune recognition and immune defenses in Ruditapes philippinarum

Peptidoglycan recognition proteins (PGRPs) are important pattern recognition receptors in the innate immune system of invertebrates. In the study, a short PGRP (designed as RpPGRP) was identified and characterized from the manila clam Ruditapes philippinarum. The open reading frame of RpPGRP encoded a polypeptide of 249-amino acids with a calculated molecular mass of 27.2 kDa and an isoelectric point of 6.62. Multiple alignments and phylogenetic analysis strongly suggested that RpPGRP was a new member of the PGRP superfamily. In non-stimulated clams, RpPGRP exhibited different tissue expression pattern, and highly expressed in hepatopancreas and hemocytes. Expression of RpPGRP transcripts was significantly up-regulated in hemocytes of clams post Vibrio anguillarum or Micrococcus luteus challenge. The recombinant RpPGRP (rRpPGRP) exhibited high affinity to PGN, LPS and zymosan in a concentration-dependent manner. With a broad spectrum of bacterial binding activities, rRpPGRP exhibited strong agglutination activity to Escherichia coli, Vibrio splendidus, V. anguillarum and M. luteus. Furthermore, rRpPGRP exhibited Zn²⁺-dependent amidase activity and catalyzed the degradation of insoluble PGN. Especially, rRpPGRP exhibited significant antibacterial activity against E. coli and M. luteus. Moreover, the biofilm formation of E. coli could be inhibited after rRpPGRP incubation in the presence of Zn²⁺. This inhibitory effect of rRpPGRP might attribute to its amide bactericidal activity. Taken together, rRpPGRP played important roles in PGRP-mediated immune defense mechanisms, especially by recognizing antigens and eliminating bacteria.

Molecular characterization and expression analysis of two peptidoglycan recognition proteins (CcPGRP5, CcPGRP6) in larvae ontogeny of common carp Cyprinus carpio L. and upon immune stimulation by bacteria

Background

Although teleost fish developed acquired immunity firstly in evolution, innate immunity is still very important for them. Innate immunity depends on pattern recognition receptors (PRRs) to distinguish “self” and “non-self”, Peptidoglycan (PGN) recognition protein (PGRP) is one of the receptors and it can bind to multiple components of bacterial envelope.

Results

We report the cloning and expression analysis of two PGRPs (Ccpgrp5 and Ccpgrp6) from common carp (Cyprinus carpio L). The Ccpgrp5 gene encodes a protein of 199 amino acid (aa) with PGRP domain, Ami_2 domain and four Zn²⁺ binding sites required for amidase activity, but without signal peptide and transmembrane domain. The Ccpgrp6 gene encodes a protein of 446 aa with PGRP domain, Ami_2 domain, signal peptide, five Zn²⁺ binding sites required for amidase activity and two sites for N-glycosylation. The phylogenetic analysis revealed that the CcPGRP5 and CcPGRP6 are closely related to Ctenopharyngodon idella and Danio rerio. Ccpgrp5 and Ccpgrp6 were expressed in all tissues examined including liver, spleen, muscle, oral epithelium, head kidney, gill, skin, gonad, brain, foregut and hindgut and showed different distribution characteristics. During the embryonic and early larval developmental stages of common carp, Ccpgrp6 was detected to be highly expressed at 10 days post fertilization(dpf) and 36 dpf, while Ccpgrp5 were hardly detected using Real-time quantitative PCR. After being challenged with Aeromonas hydrophila, Ccpgrp5 in adult common carp was induced and up-regulated in all the tissues, especially in gill and spleen, but not in head kidney, while Ccpgrp6 was up-regulated in all the tissues, especially in liver, head kidney and gill. The varied expression profiling of Ccpgrp5 and Ccpgrp6 indicated they had different roles in the host immune response.

Conclusions

These results indicated the two PGRPs, especially Ccpgrp6, played an important role in the immune defense of common carp during larva development and against Aeromonas hydrophila, providing insight to further exploration of protecting fish against bacteria infectious disease.

Combining different proteomic approaches to resolve complexity of the milk protein fraction of dromedary, Bactrian camels and hybrids, from different regions of Kazakhstan

Nutritional suitability of milk is not only related to gross composition, but is also strongly affected by the microheterogeniety of the protein fraction. Hence, to go further into the evaluation of the potential suitability of non-bovine milks in human/infant nutrition it is necessary to have a detailed characterization of their protein components. Combining proven proteomic approaches (SDS-PAGE, LC-MS/MS and LC-ESI-MS) and cDNA sequencing, we provide here in depth characterization of the milk protein fraction of dromedary and Bactrian camels, and their hybrids, from different regions of Kazakhstan. A total 391 functional groups of proteins were identified from 8 camel milk samples. A detailed characterization of 50 protein molecules, relating to genetic variants and isoforms arising from post-translational modifications and alternative splicing events, belonging to nine protein families (κ-, α_s1-, α_s2-, β-; and γ-CN, WAP, α-LAC, PGRP, CSA/LPO) was achieved by LC-ESI-MS. The presence of two unknown proteins UP1 (22,939 Da) and UP2 (23,046 Da) was also reported as well as the existence of a β-CN short isoform (946 Da lighter than the full-length β-CN), arising very likely in both genetic variants (A and B) from proteolysis by plasmin. In addition, we report, for the first time to our knowledge, the occurrence of a α_s2-CN phosphorylation isoform with 12P groups within two recognition motifs, suggesting thereby the existence of two kinase systems involved in the phosphorylation of caseins in the mammary gland. Finally, we demonstrate that genetic variants, which hitherto seemed to be species- specific (e.g. β-CN A for Bactrian and β-CN B for dromedary), are in fact present both in Camel dromedarius and C. bactrianus.

Bovine neutrophils in health and disease

Bovine neutrophils have similarities to those of other species with respect to mechanisms of their activation and migration into tissue, modulation of immune responses and the balance between microbial killing and host tissue damage. However, bovine neutrophils have biochemical and functional differences from those of other species, which may yield insights about the comparative biology of neutrophils. Neutrophils play protective and harmful roles in the infectious diseases of cattle that occur at times of transition: respiratory disease in beef calves recently arrived to feedlots and mastitis and other diseases of postparturient dairy cows. An important research focus is the mechanisms by which risk factors for these diseases affect neutrophil function and thereby lead to disease and the prospect of genetic or pharmacologic improvement of disease resistance. Further, in keeping with the One Health paradigm, cattle can be considered a model for studying the role of neutrophils in naturally occurring diseases caused by host-adapted pathogens and are thus an intermediary between studies of mouse models and investigations of human disease. Finally, the study of bovine neutrophils is important for agriculture, to understand the pathogenesis of these production-limiting diseases and to develop novel methods of disease prevention that improve animal health and reduce the reliance on antimicrobial use.

Functional characterization of a short peptidoglycan recognition protein from Chinese giant salamander (Andrias davidianus)

Peptidoglycan (PGN) recognition proteins (PGRPs) are important pattern recognition receptors (PRRs) involved in immune defense against bacterial infections. In this study, a short PGRP (termed AdPGRP-S1) was cloned and functionally characterized from Chinese giant salamander (Andrias davidianus), the largest extant urodela amphibian species. AdPGRP-S1 was 184 aa in length and shared 38.7%-54.9% sequence identities with other vertebrates’ short PGRPs. It contained one typical PGRP domain at the C-terminal region and several conserved amino acid (aa) residues involved in amidase and PGN binding. AdPGRP-S1 was constitutively expressed in all tissues examined, with the highest expression level seen in spleen and intestine. It has been shown that AdPGRP-S1 could bind and degrade Lys-PGN and Dap-PGN. Further, AdPGRP-S1 had antibacterial activity against the Gram-negative bacteria, Edwardsiella tarda, and was able to trigger the activation of NF-κB signaling. These results demonstrated that AdPGRP-S1 possesses multiple functions in pathogen recognition, mediating ceullular signaling, and initiating antibacterial response. This is the first functional study of a salamander PGRP, providing insight to further understand the functional evolution of verterbates’ PGRPs.

How innate immunity proteins kill bacteria and why they are not prone to resistance

Recent advances on antibacterial activity of peptidoglycan recognition proteins (PGRPs) offer some insight into how innate immunity has retained its antimicrobial effectiveness for millions of years with no frequent emergence of resistant strains. First, PGRP can bind to multiple components of bacterial envelope (peptidoglycan, lipoteichoic acid, and lipopolysaccharide). Second, PGRP simultaneously induces oxidative, thiol, and metal stress responses in bacteria, which individually are bacteriostatic, but in combination are bactericidal. Third, PGRP induces oxidative, thiol, and metal stress responses in bacteria through three independent pathways. Fourth, antibacterial effects of PGRP are enhanced by other innate immune responses. Thus, emergence of PGRP resistance is prevented by bacteriostatic effect and independence of each PGRP-induced stress response, as PGRP resistance would require simultaneous acquisition of three separate mechanisms disabling the induction of all three stress responses. By contrast, each antibiotic has one primary target and one primary antibacterial mechanism, and for this reason resistance to antibiotics can be generated by inhibition of this primary mechanism. Manipulating bacterial metabolic responses can enhance bacterial killing by antibiotics and elimination of antibiotic-tolerant bacteria, but such manipulations do not overcome genetically encoded antibiotic resistance. Pathogens cause infections by evading, inhibiting, or subverting host immune responses.

Bactericidal peptidoglycan recognition protein induces oxidative stress in Escherichia coli through a block in respiratory chain and increase in central carbon catabolism

Mammalian Peptidoglycan Recognition Proteins (PGRPs) kill both Gram-positive and Gram-negative bacteria through simultaneous induction of oxidative, thiol and metal stress responses in bacteria. However, metabolic pathways through which PGRPs induce these bactericidal stress responses are unknown. We screened Keio collection of Escherichia coli deletion mutants and revealed that deleting genes for respiratory chain flavoproteins or for tricarboxylic acid (TCA) cycle resulted in increased resistance of E. coli to PGRP killing. PGRP-induced killing depended on the production of hydrogen peroxide, which required increased supply of NADH for respiratory chain oxidoreductases from central carbon catabolism (glycolysis and TCA cycle), and was controlled by cAMP-Crp. Bactericidal PGRP induced a rapid decrease in respiration, which suggested that the main source of increased production of hydrogen peroxide was a block in respiratory chain and diversion of electrons from NADH oxidoreductases to oxygen. CpxRA two-component system was a negative regulator of PGRP-induced oxidative stress. By contrast, PGRP-induced thiol stress (depletion of thiols) and metal stress (increase in intracellular free Zn²⁺ through influx of extracellular Zn²⁺ ) were mostly independent of oxidative stress. Thus, manipulating pathways that induce oxidative, thiol and metal stress in bacteria could be a useful strategy to design new approaches to antibacterial therapy.

Unveiling differentially expressed genes upon regulation of transcription factors in sepsis

In this study, we integrated the gene expression data of sepsis to reveal more precise genome-wide expression signature to shed light on the pathological mechanism of sepsis. Differentially expressed genes via integrating five microarray datasets from the Gene Expression Omnibus database were obtained. The gene function and involved pathways of differentially expressed genes (DEGs) were detected by GeneCodis3. Transcription factors (TFs) targeting top 20 dysregulated DEGs (including up- and downregulated genes) were found based on the TRANSFAC. A total of 1339 DEGs were detected including 788 upregulated and 551 downregulated genes. These genes were mostly involved in DNA-dependent transcription regulation, blood coagulation, and innate immune response, pathogenic escherichia coli infection, epithelial cell signaling in helicobacter pylori infection, and chemokine signaling pathway. TFs bioinformatic analysis of 20 DEGs generated 374 pairs of TF-target gene involving 47 TFs. At last, we found that five top ten upregulated DEGs (S100A8, S100A9, S100A12, PGLYRP1 and MMP9) and three downregulated DEGs (ZNF84, CYB561A3 and BST1) were under the regulation of three hub TFs of Pax-4, POU2F1, and Nkx2-5. The identified eight DEGs may be regarded as the diagnosis marker and drug target for sepsis.

Structural insights into ligand binding of PGRP1 splice variants in Chinese giant salamander (Andrias davidianus) from molecular dynamics and free energy calculations

Peptidoglycan (PGN) recognition proteins (PGRPs) are important pattern recognition receptors of the innate immune system. A number of PGRP splicing variants produced by alternative splicing of PGRP genes have been reported. However, several important aspects of interactions between PGRP splice variants and their ligands are still unclear. In the present study, three dimensional models of salamander PGRP1 (adPGRP1) and its splice variant (adPGRP1a) were constructed, and their key amino acids involved in interacting with PGNs were analyzed. The results revealed that adPGRP1a has a typical PGRPs structure containing five β-sheets and four α-helices, while adPGRP1 contained five β-sheets and only one α-helix due to the lack of 51 amino acids at its C-terminus. Molecular docking revealed that van der Waals and Coulombic interactions contributed to interactions in the protein-ligand complex. Further binding energy of adPGRP-PGNs computed by the MM-PBSA method revealed that adPGRP1a and adPGRP1 might selectively bind to different PGNs; the former might selectively bind Dap-type PGNs and the latter both types of PGNs. In addition, the binding energy of each residue of adPGRP1a and adPGRP1 was also calculated, revealing that residues involved in the interaction of protein-ligand complexes were different in adPGRP1a and adPGRP1. These results provided a first insight into the potential basis for interaction between PGRPs generated by alternative splicing and PGN derivatives.

Involvement of PGRP-SC2 from Artemia sinica in the innate immune response against bacteria and expression pattern at different developmental stages

Peptidoglycan-recognition protein-SC2 precursor-like protein (PGRP-SC2) is a vital protein in innate immunity with a vita role in response to bacteria challenge in invertebrates. Here, a 678-bp full-length cDNA of pgrp-sc2 from A. sinica was obtained containing a 558-bp open reading frame encoding 185 amino acids with a calculated molecular mass of 19.6 kDa. The predicted protein contains a PGRP and an Amidase2 domain, indicating that PGRP-SC2 is a PGRP family member and has N-acetylmuramoyl-l-alanine amidase activity. The expression and localization of pgrp-sc2/PGRP-SC2 in A.sinica during embryonic development and bacterial challenge were determined by qPCR, WB and ISH. During different A. sinica embryonic development stages, the expression level of pgrp-sc2/PGRP-SC2 was most highly expressed at 0 and 5 h and after challenge by Gram-positive bacteria, it increased with increasing bacterial concentrations, indicating that it plays a vital role in A. sinica early embryonic development and innate immunity.

A new role for PGRP-S (Tag7) in immune defense: lymphocyte migration is induced by a chemoattractant complex of Tag7 with Mts1

PGRP-S (Tag7) is an innate immunity protein involved in the antimicrobial defense systems, both in insects and in mammals. We have previously shown that Tag7 specifically interacts with several proteins, including Hsp70 and the calcium binding protein S100A4 (Mts1), providing a number of novel cellular functions. Here we show that Tag7-Mts1 complex causes chemotactic migration of lymphocytes, with NK cells being a preferred target. Cells of either innate immunity (neutrophils and monocytes) or acquired immunity (CD4(+) and CD8(+) lymphocytes) can produce this complex, which confirms the close connection between components of the 2 branches of immune response.

Peptidoglycan recognition in innate immunity

The innate immune system recognizes micro-organisms through a series of pattern recognition receptors that are highly conserved in evolution. Peptidoglycan (PGN) is a unique and essential component of the cell wall of virtually all bacteria, is not present in eukaryotes, and is an excellent target for the innate immune system. Indeed, higher eukaryotes, including mammals, have several PGN recognition molecules, including CD14, Toll-like receptor 2 (TLR2), nucleotide oligomerization domain (Nod)-containing proteins, a family of peptidoglycan recognition proteins (PGRPs), and PGN-lytic enzymes (lysozyme and amidase). These molecules induce host responses to micro-organisms, degrade PGN, or have direct antimicrobial effects.

Crystal structure of a peptidoglycan recognition protein (PGRP) in complex with a muramyl tripeptide from Gram-positive bacteria

Peptidoglycan recognition proteins (PGRPs) are pattern recognition receptors of the innate immune system that bind, and in some cases hydrolyse, bacterial peptidoglycans (PGNs). We determined the crystal structure of the C-terminal PGN-binding domain of human PGRP-Iα in complex with a muramyl tripeptide representing the conserved core of lysine-type PGNs. The peptide stem of the ligand is buried at the deep end of a long binding groove, with N-acetylmuramic acid situated in the middle of the groove, whose shallow end could accommodate N-acetylglucosamine. Both peptide and glycan moieties are essential for binding by PGRPs. Conservation of key PGN-contacting residues indicates that all PGRPs employ this basic PGN-binding mode. The structure identifies variable residues that likely mediate discrimination between lysine- and diaminopimelic acid-type PGNs. In addition, we propose a mechanism for PGN hydrolysis by Zn2+-containing catalytic PGRPs.

A short-type peptidoglycan recognition protein from tongue sole (Cynoglossus semilaevis) promotes phagocytosis and defense against bacterial infection

Peptidoglycan recognition proteins (PGRPs) are members of the innate immune system that interact with bacteria by binding to bacterial peptidoglycan. In this study, we examined the expression and function of a short type of PGRP, CsPGRP-SC2, from tongue sole (Cynoglossus semilaevis). CsPGRP-SC2 contains 164 amino acid residues and shares 54.5%-65.3% overall sequence identities with other teleost PGRPs. CsPGRP-SC2 possesses an amidase domain with a conserved zinc binding site. CsPGRP-SC2 expression occurred in multiple tissues and was upregulated by bacterial and viral infection. Purified recombinant CsPGRP-SC2 (rCsPGRP-SC2) was able to bind and agglutinate Gram-positive bacteria in a Zn(2+)-dependent manner. rCsPGRP-SC2 enhanced the uptake of the bound bacteria by host phagocytes and reduced bacterial dissemination and colonization in host tissues. These results indicate that CsPGRP-SC2 is an innate immune factor that participates in host defense against bacterial infection.

Peptidoglycan recognition proteins kill bacteria by inducing oxidative, thiol, and metal stress

Mammalian Peptidoglycan Recognition Proteins (PGRPs) are a family of evolutionary conserved bactericidal innate immunity proteins, but the mechanism through which they kill bacteria is unclear. We previously proposed that PGRPs are bactericidal due to induction of reactive oxygen species (ROS), a mechanism of killing that was also postulated, and later refuted, for several bactericidal antibiotics. Here, using whole genome expression arrays, qRT-PCR, and biochemical tests we show that in both Escherichia coli and Bacillus subtilis PGRPs induce a transcriptomic signature characteristic of oxidative stress, as well as correlated biochemical changes. However, induction of ROS was required, but not sufficient for PGRP killing. PGRPs also induced depletion of intracellular thiols and increased cytosolic concentrations of zinc and copper, as evidenced by transcriptome changes and supported by direct measurements. Depletion of thiols and elevated concentrations of metals were also required, but by themselves not sufficient, for bacterial killing. Chemical treatment studies demonstrated that efficient bacterial killing can be recapitulated only by the simultaneous addition of agents leading to production of ROS, depletion of thiols, and elevation of intracellular metal concentrations. These results identify a novel mechanism of bacterial killing by innate immunity proteins, which depends on synergistic effect of oxidative, thiol, and metal stress and differs from bacterial killing by antibiotics. These results offer potential targets for developing new antibacterial agents that would kill antibiotic-resistant bacteria.

Bacterial infections are still a major cause of morbidity and mortality because of increasing antibiotic resistance. New targets for developing new approaches to antibacterial therapy are needed, because discovering new or improving current antibiotics have become increasingly difficult. One such approach is developing new antibacterial agents based on the antibacterial mechanisms of bactericidal innate immunity proteins, such as human peptidoglycan recognition proteins (PGRPs). Thus, our aim was to determine how PGRPs kill bacteria. We previously proposed that PGRPs kill bacteria by inducing toxic oxygen by-products (“reactive oxygen species”, ROS) in bacteria. It was also previously proposed, but recently refuted, that bactericidal antibiotics kill bacteria by inducing ROS production in bacteria. These findings prompted us to evaluate in greater detail the mechanism of PGRP-induced bacterial killing, including the role of ROS in PGRP killing. We show here that PGRPs kill bacteria through synergistic induction of ROS, depletion of thiols, and increasing intracellular concentration of metals, which are all required, but individually not sufficient for bacterial killing. Our results reveal a novel bactericidal mechanism of innate immunity proteins, which differs from killing by antibiotics and offers alternative targets for developing new antibacterial therapies for antibiotic-resistant bacteria.

Exploration of the binding modes of buffalo PGRP1 receptor complexed with meso-diaminopimelic acid and lysine-type peptidoglycans by molecular dynamics simulation and free energy calculation

The peptidoglycan recognition proteins (PGRPs) are the key components of innate-immunity, and are highly specific for the recognition of bacterial peptidoglycans (PGN). Among different mammalian PGRPs, the PGRP1 binds to murein PGN of Gram-positive bacteria (lysine-type) and also have bactericidal activity towards Gram-negative bacteria (diaminopimelic acid or Dap-type). Buffaloes are the major sources of milk and meat in Asian sub-continents and are highly exposed to bacterial infections. The PGRP activates the innate-immune signaling, but their studies has been confined to limited species due to lack of structural and functional information. So, to understand the structural constituents, 3D model of buffalo PGRP1 (bfPGRP1) was constructed and conformational and dynamics properties of bfPGRP1 was studied. The bfPGRP1 model highly resembled human and camel PGRP structure, and shared a highly flexible N-terminus and centrally placed L-shaped cleft. Docking simulation of muramyl-tripeptide, tetrapeptide, pentapeptide-Dap-(MTP-Dap, MTrP-Dap and MPP-Dap) and lysine-type (MTP-Lys, MTrP-Lys and MPP-Lys) in AutoDock 4.2 and ArgusLab 4.0.1 anticipated β1, α2, α4, β4, and loops connecting β1-α2, α2-β2, β3-β4 and α4-α5 as the key interacting domains. The bfPGRP1-ligand complex molecular dynamics simulation followed by free binding energy (BE) computation conceded BE values of -18.30, -35.53, -41.80, -25.03, -24.62 and -22.30 kJ mol(-1) for MTP-Dap, MTrP-Dap, MPP-Dap, MTP-Lys, MTrP-Lys and MPP-Lys, respectively. The groove-surface and key binding residues involved in PGN-Dap and Lys-type interaction intended by the molecular docking, and were also accompanied by significant BE values directed their importance in pharmacogenomics, and warrants further in vivo studies for drug targeting and immune signaling pathways exploration.

Isolation and characterization of peptidoglycan recognition protein 1 from antler base of sika deer (Cervus nippon)

Peptidoglycan recognition proteins (PGRPs) are secreted innate immunity pattern recognition molecules. In this study, a new peptidoglycan recognition protein 1 named cnPGRP1 was isolated from an antler base of sika deer Cervus nippon. The antler base antimicrobial proteins (AAP) were subjected to consecutive chromatographic methods connected to Sephadex G-25 gel filtration column (CM) anion-exchange column, and RP-HPLC. The molecular weight of cnPGRP1 was 17.2 kDa under SDS-PAGE, and peptide mass fingerprint analysis by MALDI-TOF-MS as peptidoglycan recognition protein 1 matched to Dasypus novemcinctus. The matched amino acids sequences were RLYEIIQKWPHYRA. Both Gram-positive and Gram-negative bacteria can be killed by cnPGRP1 in the 50-250 μg/mL range through in vitro. Furthermore, cnPGRP1 has been found to bind Gram-positive bacteria, Gram-negative bacteria, and even fungus.

Stimulation of platelet apoptosis by peptidoglycan from Staphylococcus aureus 113

Peptidoglycan (PGN), a component of bacterial cell wall and belonging to "Microbe-Associated Molecular Patterns" (MAMP) triggers host reactions contributing to the pathophysiology of infectious disease. Host cell responses to PGN exposure include apoptosis. Bacterial infections may result in activation of blood platelets and thrombocytopenia. The present study explored, whether HPLC-purified fractions of PGNs from Staphylococcus aureus 113 triggers apoptosis of platelets. To this end platelets were exposed to PGN fractions and annexin-V binding determined to depict cell membrane scrambling, DiOC6 fluorescence to estimate depolarization of mitochondrial potential, Fluo-3AM staining for intracellular Ca(2+) activity ([Ca(2+)](i)) and immunofluorescence to quantify protein abundance of active caspase-3. As a result, a 30 min exposure to monomeric fraction (mPGN) (≥50 ng/ml) was followed by annexin-V binding, paralleled by increase of [Ca(2+)](i), mitochondrial depolarization, caspase-3 activation and integrin α(IIb)β(3) upregulation. The annexin-V binding was significantly blunted by anti-TLR-2 antibodies, in absence of extracellular Ca(2+), and by pancaspase inhibitor zVAD-FMK (1 μM). In conclusion, PGN triggers apoptosis of platelets in activation-dependent manner, characterized by mitochondrial depolarization, caspase-3 activation and cell membrane scrambling.

Identification of genes expressed by human airway eosinophils after an in vivo allergen challenge

Background

The mechanism for the contribution of eosinophils (EOS) to asthma pathophysiology is not fully understood. Genome-wide expression analysis of airway EOS by microarrays has been limited by the ability to generate high quality RNA from sufficient numbers of airway EOS.

Objective

To identify, by genome-wide expression analyses, a compendium of expressed genes characteristic of airway EOS following an in vivo allergen challenge.

Methods

Atopic, mild asthmatic subjects were recruited for these studies. Induced sputum was obtained before and 48h after a whole lung allergen challenge (WLAC). Individuals also received a segmental bronchoprovocation with allergen (SBP-Ag) 1 month before and after administering a single dose of mepolizumab (anti-IL-5 monoclonal antibody) to reduce airway EOS. Bronchoalveolar lavage (BAL) was performed before and 48 h after SBP-Ag. Gene expression of sputum and BAL cells was analyzed by microarrays. The results were validated by qPCR in BAL cells and purified BAL EOS.

Results

A total of 299 transcripts were up-regulated by more than 2-fold in total BAL cells following SBP-Ag. Mepolizumab treatment resulted in a reduction of airway EOS by 54.5% and decreased expression of 99 of the 299 transcripts. 3 of 6 post-WLAC sputum samples showed increased expression of EOS-specific genes, along with the expression of 361 other genes. Finally, the intersection of the 3 groups of transcripts (increased in BAL post SBP-Ag (299), decreased after mepolizumab (99), and increased in sputum after WLAC (365)) was composed of 57 genes characterizing airway EOS gene expression.

Conclusion

We identified 57 genes that were highly expressed by BAL EOS compared to unseparated BAL cells after in vivo allergen challenge. 41 of these genes had not been previously described in EOS and are thus potential new candidates to elucidate EOS contribution to airway biology.

Polymorphism in PGLYRP-1 gene by PCR-RFLP and its association with somatic cell score in Chinese Holstein

Bovine peptidoglycan recognition protein 1 (PGLYRP-1), an important pattern recognition molecule (PRM) of the innate immune system, is an effector molecule in killing different microorganisms directly. To investigate whether the PGLYRP-1 gene was associated with mastitis and milk production traits in dairy cattle, the polymorphism of this gene was analyzed by PCR-RFLP in a population of 524 Chinese Holstein. A total of ten single nucleotide polymorphism (SNP) loci were identified. The association analysis of single SNP locus showed that T-35A, T-12G and G+102C were significantly associated (P<0.05) with somatic cell score (SCS), while G+102C and G+649C were significantly associated (P<0.05) with 305-day milk yield. Association analysis between combined haplotypes and SCS, milk production traits indicated that H3H3 was associated with the lower SCS (P<0.01), and H2H2 was associated with the lower 305-day milk yield (P<0.01). These findings demonstrated that polymorphisms in PGLYRP-1 gene associated with mastitis resistance and 305-day milk yield, and the H3H3 would provide a useful genetic marker of combined haplotypes for mastitis resistance selection and breeding in Chinese Holstein.

Identification and characterization of two peptidoglycan recognition proteins with zinc-dependent antibacterial activity from the cotton bollworm, Helicoverpa armigera

Peptidoglycan recognition proteins (PGRPs) specifically bind to peptidoglycan and play an important role in the innate immune responses as pattern recognition receptors (PRRs). Here we identified and characterized two PGRPs (HaPGRP-B and HaPGRP-C) from the cotton bollworm, Helicoverpa armigera. The comparative analysis indicated that five amino acids which are required for T7 lysozyme Zn(2+) binding and amidase activity are conserved in HaPGRP-B and HaPGRP-C, suggesting that the two PGRPs are members of the amidase-type PGRPs. HaPGRP-B and HaPGRP-C mRNA increased in both the fat bodies and the hemocytes after an injection of Gram-negative Escherichia coli or Gram-positive Staphylococcus aureus. Recombinant HaPGRP-B and HaPGRP-C could agglutinate E. coli and S. aureus in a zinc-dependent manner. More importantly, both rHaPGRP-B and rHaPGRP strongly inhibited the growth of E. coli and S. aureus in the presence of Zn(2+). Moreover, the HaPGRP-B mRNA showed up-regulation post hormones (20E and methoprene) injection. Our results indicate that the two PGRPs of H. armigera may play an important role in defending against bacteria as amidase-type PGRPs and the hormones can function in regulating the expressions of PGRPs.

Assessment of microbiota and peptidoglycan in perianal fistulas

Transanal advancement flap repair has been advocated as the treatment of choice for high transsphincteric perianal fistulas, but fails in 1 of every 3 patients. Persistence of the fistula after flap repair might be the result of ongoing disease in the remaining fistula tract. In 10 specimens of the distal part of the fistula, microbiota was assessed by means of conventional microbiological culture and 16S rRNA gene sequencing. Proinflammatory bacterial peptidoglycan and recognition proteins were assessed by immunohistochemistry. Bacterial species were bowel derived, skin derived, or a combination of both. No mycobacterium species were identified. 16S rRNA gene sequencing failed to identify bacteria in all but 1 specimen, most likely as a result of low numbers of organisms. Peptidoglycan was detected in 90% of the patients, and a host response to peptidoglycan in 60%. Therefore, we suggest that peptidoglycan might play a role in the ongoing inflammation in perianal fistulas.

A novel short peptidoglycan recognition protein in amphioxus: identification, expression and bioactivity

Peptidoglycan recognition proteins (PGRPs) are widely distributed in invertebrates and vertebrates, and structure-activity relationship of insect and mammalian PGRPs has been well characterized, but functional and structural insights into PGRPs in other species are rather limited. Here we identified a novel short PGRP gene from the amphioxus Branchiostoma japonicum, named pgrp-s, which possesses a domain combination of ChtBD1 domain-PGRP domain, which is unique to all known PGRPs. Amphioxus pgrp-s was predominantly expressed in the hepatic caecum, hind-gut and muscle in a tissue-specific manner. Recombinant PGRP-S, rPGRP-S, and truncated protein with ChtBD1 domain deleted, rP86/250, both showed affinity to Dap-type PGN, Lys-type PGN and chitin. Consistently, they were also able to bind to Escherichia coli, Staphylococcus aureus and Pichia pastoris. Moreover, both rPGRP-S and rP86/250 had amidase enzymatic activity, capable of hydrolyzing Dap-type and Lys-type PGNs. Like vertebrate PGRPs, rPGRP-S was directly microbicidal, capable of killing E. coli, S. aureus and P. pastoris, whereas rP86/250 only inhibited the growth of E. coli and S. aureus, and its anti-P. pastoris activity was significantly reduced. It is clear that neither the binding of amphioxus PGRP-S nor its amidase enzymatic activity depend on the N-terminal ChtBD1 domain, but its antifungal activity does. Collectively, these data suggested that amphioxus PGRP-S may function as a multivalent pattern recognition receptor, capable of recognizing PGN and chitin, a microbicidal agent, capable of killing bacteria such as E. coli and S. aureus and fungus like P. pastoris, and probably a PGN scavenger, capable of hydrolyzing PGN.

Role of mouse peptidoglycan recognition protein PGLYRP2 in the innate immune response to Salmonella enterica serovar Typhimurium infection in vivo

Peptidoglycan recognition proteins (PGRPs) are a family of innate pattern recognition molecules that bind bacterial peptidoglycan. While the role of PGRPs in Drosophila innate immunity has been extensively studied, how the four mammalian PGRP proteins (PGLYRP1 to PGLYRP4) contribute to host defense against bacterial pathogens in vivo remains poorly understood. PGLYRP1, PGLYRP3, and PGLYRP4 are directly bactericidal in vitro, whereas PGLYRP2 is an N-acetylmuramyl-L-alanine amidase that cleaves peptidoglycan between the sugar backbone and the peptide stem. Because PGLYRP2 cleaves muramyl peptides detected by host peptidoglycan sensors Nod1 and Nod2, we speculated that PGLYRP2 may act as a modifier of Nod1/Nod2-dependent innate immune responses. We investigated the role of PGLYRP2 in Salmonella enterica serovar Typhimurium-induced colitis, which is regulated by Nod1/Nod2 through the induction of an early Th17 response. PGLYRP2 did not contribute to expression of Th17-associated cytokines, interleukin-22 (IL-22)-dependent antimicrobial proteins, or inflammatory cytokines. However, we found that Pglyrp2-deficient mice displayed significantly enhanced inflammation in the cecum at 72 h postinfection, reflected by increased polymorphonuclear leukocyte (PMN) infiltration and goblet cell depletion. Pglyrp2 expression was also induced in the cecum of Salmonella-infected mice, and expression of green fluorescent protein under control of the Pglyrp2 promoter was increased in discrete populations of intraepithelial lymphocytes. Lastly, Nod2(-/-) Pglyrp2(-/-) mice displayed increased susceptibility to infection at 24 h postinfection compared to Pglyrp2(-/-) mice, which correlated with increased PMN infiltration and submucosal edema. Thus, PGLYRP2 plays a protective role in vivo in the control of S. Typhimurium infection through a Nod1/Nod2-independent mechanism.

Host defenses against cryptococcosis

The interaction of pathogenic Cryptococcus species with their various hosts is somewhat unique compared to other fungal pathogens such as Aspergillus fumigatus and Candida albicans. Cryptococcus shares an intimate association with host immune cells, leading to enhanced intracellular growth. Furthermore, unlike most other fungal pathogens, the signs and symptoms of cryptococcal disease are typically self-inflicted by the host during the host's attempt to clear this invader from sensitive organ systems such as the central nervous system. In this review, we will summarize the story of host-Cryptococcus interactions to date and explore strategies to exploit the current knowledge for treatment of cryptococcal infections.

Molecular cloning and mRNA expression of two peptidoglycan recognition protein (PGRP) genes from mollusk Solen grandis

Peptidoglycan recognition proteins (PGRPs) play crucial role in innate immunity for both invertebrates and vertebrates, owing to their prominent ability in detecting and eliminating invading bacteria. In the present study, two short PGRPs from mollusk Solen grandis (designated as SgPGRP-S1 and SgPGRP-S2) were identified, and their expression patterns, both in tissues and toward three PAMPs stimulation, were then characterized. The full-length cDNA of SgPGRP-S1 and SgPGRP-S2 was 1672 and 1285 bp, containing an open reading frame (ORF) of 813 and 426 bp, respectively, and deduced amino acid sequences showed high similarity to other members of PGRP superfamily. Both SgPGRP-S1 and SgPGRP-S2 encoded a PGRP domain. The motif of Zn(2+) binding sites and amidase catalytic sites were well conserved in SgPGRP-S1, but partially conserved in SgPGRP-S2. The two PGRPs exhibited different tissue expression pattern. SgPGRP-S1 was highly expressed in muscle and hepatopancreas, while SgPGRP-S2 was highly in gill and mantle. The mRNA expression of SgPGRP-S1 could be induced acutely by stimulation of PGN, and also moderately by β-1,3-glucan, but not by LPS, while expression of SgPGRP-S2 was significantly up-regulated (P < 0.01) when S. grandis was stimulated by all the three PAMPs, though the expression levels were relatively lower than SgPGRP-S1. Our results suggested SgPGRP-S1 and SgPGRP-S2 could serve as pattern recognition receptors (PRRs) involved in the immune recognition of S. grandis, and they might perform different functions in the immune defense against invaders.

Convergent and divergent development among M cell lineages in mouse mucosal epithelium

M cells are specialized epithelial cells mediating immune surveillance of the mucosal lumen by transepithelial delivery of Ags to underlying dendritic cells (DC). At least three M cell phenotypes are known in the airways and intestine, but their developmental relationships are unclear. We used reporter transgenic mouse strains to follow the constitutive development of M cell subsets and their acute induction by cholera toxin (CT). M cells overlying intestinal Peyer's patches (PPs), isolated lymphoid follicles, and nasal-associated lymphoid tissue are induced by distinct settings, yet show convergent phenotypes, such as expression of a peptidoglycan recognition protein-S (PGRP-S) transgene reporter. By contrast, though PP, isolated lymphoid follicle, and villous M cells are all derived from intestinal crypt stem cells, their phenotypes were clearly distinct; for example, PP M cells frequently appeared to form M cell-DC functional units, whereas villous M cells did not consistently engage underlying DC. B lymphocytes are critical to M cell function by forming a basolateral pocket and possible signaling through CD137; however, initial commitment to all M cell lineages is B lymphocyte and CD137 independent. CT causes induction of new M cells in the airway and intestine without cell division, suggesting transdifferentiation from mature epithelial cells. In contrast with intestinal PP M cells, CT-induced nasal-associated lymphoid tissue M cells appear to be generated from ciliated Foxj1(+)PGRP-S(+) cells, indicative of a possible precommitted progenitor. In summary, constitutive and inducible differentiation of M cells is toward strictly defined context-dependent phenotypes, suggesting specialized roles in surveillance of mucosal Ags.

Peptidoglycan recognition proteins kill bacteria by activating protein-sensing two-component systems

Mammalian Peptidoglycan Recognition Proteins (PGRPs), similar to antimicrobial lectins, bind to bacterial cell wall and kill bacteria through an unknown mechanism. We show that PGRPs enter Gram-positive cell wall at the site of daughter cell separation during cell division. In Bacillus subtilis PGRPs activate the CssR-CssS two-component system that detects and disposes of misfolded proteins exported out of bacterial cells. This activation results in membrane depolarization, cessation of intracellular peptidoglycan, protein, RNA, and DNA synthesis, and production of hydroxyl radicals, which are responsible for bacterial death. PGRPs also bind to the outer membrane in Escherichia coli and activate functionally homologous CpxA-CpxR two-component system, which results in bacterial death. We excluded other potential bactericidal mechanisms (inhibition of extracellular peptidoglycan synthesis, hydrolysis of peptidoglycan, and membrane permeabilization). Thus we reveal a novel mechanism of bacterial killing by innate immunity proteins that bind to cell wall or outer membrane and exploit bacterial stress defense response to kill bacteria.

Bovine PGLYRP1 polymorphisms and their association with resistance to Mycobacterium avium ssp. paratuberculosis

Mycobacterium avium ssp. paratuberculosis (MAP) causes a chronic, granulomatous inflammatory condition of the intestines in ruminants and wild-type species. It causes significant economic losses to the dairy and beef industries owing to reduced productivity, premature culling and mortality. Bovine peptidoglycan recognition protein 1 is an important pattern recognition molecule that is capable of directly killing microorganisms. The goal of this study was to identify single nucleotide polymorphisms (SNPs) in the gene encoding bovine peptidoglycan recognition protein 1 and to assess their association with susceptibility to MAP infection in dairy cattle. Blood and milk samples were collected from Holsteins in Southwestern and Eastern Ontario and tested for MAP infection using blood and milk ELISAs. A resource population consisting of 197 infected (S/P > 0.25) and 242 healthy (S/P < 0.10) cattle was constructed. Sequencing of pooled DNA was used to identify three SNPs (c.102G>C, c.480G>A and c.625C>A) that were genotyped in the resource population. Statistical analysis was performed using a logistic regression model fitting the additive and dominance effects of each SNP in the model. SNP c.480G>A (P = 0.054) was found to be associated with susceptibility to MAP infection. Cows with a copy of the major allele 'G' at this locus had an odds ratio of 1.51 (95% CI: 0.99-2.31) for being infected with MAP.

Mouse peptidoglycan recognition protein PGLYRP-1 plays a role in the host innate immune response against Listeria monocytogenes infection

The role of mouse peptidoglycan recognition protein PGLYRP-1 in innate immunity against Listeria monocytogenes infection was studied. The recombinant mouse PGLYRP-1 and a polyclonal antibody specific to PGLYRP-1 were prepared. The mouse PGLYRP-1 showed antibacterial activities against L. monocytogenes and other Gram-positive bacteria. PGLYRP-1 mRNA expression was induced in the spleens and livers of mice infected with L. monocytogenes. The viable bacterial number increased, and the production of cytokines such as gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) was reduced in mice when mice had been injected with anti-PGLYRP-1 antibody before infection. The levels of IFN-γ and TNF-α titers in the organs were higher and the viable bacterial number was reduced in mice injected with recombinant mouse PGLYRP-1 (rmPGLYRP-1) before infection. PGLYRP-1 could directly induce these cytokines in spleen cell cultures. The elimination of intracellular bacteria was upregulated in NMuLi hepatocyte cells overexpressing PGLYRP-1. The enhancement of the elimination of L. monocytogenes from the organs was observed in IFN-γ(-/-) mice by rmPGLYRP-1 administration but not in TNF-α(-/-) mice. These results suggest that PGLYRP-1 plays a role in innate immunity against L. monocytogenes infection by inducing TNF-α.

Peptidoglycan recognition protein of Chlamys farreri (CfPGRP-S1) mediates immune defenses against bacterial infection

Peptidoglycan recognition protein (PGRP) is an essential molecule in innate immunity for both invertebrates and vertebrates, owing to its prominent ability in detecting and eliminating the invading bacteria. Several PGRPs have been identified from mollusk, but their functions and the underlined mechanism are still unclear. In the present study, the mRNA expression profiles, location, and possible functions of PGRP-S1 from Zhikong scallop Chlamys farreri (CfPGRP-S1) were analyzed. The CfPGRP-S1 protein located in the mantle, gill, kidney and gonad of the scallops. Its mRNA expression in hemocytes was up-regulated extremely after PGN stimulation (P<0.01), while moderately after the stimulations of LPS (P<0.01) and β-glucan (P<0.05). The recombinant protein of CfPGRP-S1 (designated as rCfPGRP-S1) exhibited high affinity to PGN and moderate affinity to LPS, but it did not bind β-glucan. Meanwhile, rCfPGRP-S1 also exhibited strong agglutination activity to Gram-positive bacteria Micrococcus luteus and Bacillus subtilis and weak activity to Gram-negative bacteria Escherichia coli. More importantly, rCfPGRP-S1 functioned as a bactericidal amidase to degrade PGN and strongly inhibit the growth of E. coli and Staphyloccocus aureus in the presence of Zn(2+). These results indicated that CfPGRP-S1 could not only serve as a pattern recognition receptor recognizing bacterial PGN and LPS, but also function as a scavenger involved in eliminating response against the invaders.

Review: Mammalian peptidoglycan recognition proteins (PGRPs) in innate immunity

Peptidoglycan recognition proteins (PGRPs or PGLYRPs) are innate immunity proteins that are conserved from insects to mammals, recognize bacterial peptidoglycan, and function in antibacterial immunity and inflammation. Mammals have four PGRPs - PGLYRP1, PGLYRP2, PGLYRP3, and PGLYRP4. They are secreted proteins expressed in polymorphonuclear leukocytes (PGLYRP1), liver (PGLYRP2), or on body surfaces, mucous membranes, and in secretions (saliva, sweat) (PGLYRP3 and PGLYRP4). All PGRPs recognize bacterial peptidoglycan. Three PGRPs, PGLYRP1, PGLYRP3, and PGLYRP4 are directly bactericidal for both Gram-positive and Gram-negative bacteria and have no enzymatic activity, whereas PGLYRP2 is an N-acetylmuramoyl-L-alanine amidase that hydrolyzes bacterial cell wall peptidoglycan. Peptidoglycan recognition proteins influence host- pathogen interactions not only through their antibacterial or peptidoglycan-hydrolytic properties, but also through their pro-inflammatory and anti-inflammatory properties that are independent of their hydrolytic and antibacterial activities. The PGRPs likely play a role both in antibacterial defenses and several inflammatory diseases. They modulate local inflammatory responses in tissues (such as arthritic joints) and there is evidence for association of PGRPs with inflammatory diseases, such as psoriasis.

Molecular cloning and characterization of peptidoglycan recognition proteins from the rockfish, Sebastes schlegeli

Peptidoglycan recognition proteins (PGRPs) are innate immune molecules that are structurally conserved through evolution in both invertebrate and vertebrate animals. Here we report the identification and characterization of two long forms of PGRP (SsPGRP-L1 and SsPGRP-L2) from the rockfish, Sebastes schlegeli. The deduced amino acid sequences of SsPGRP-L1 and SsPGRP-L2, 466 and 482 residues respectively, contain the conserved PGRP domain and the four Zn(2+)-binding amino acid residues required for amidase activity. In addition to peptidoglycan-lytic amidase activity, recombinant SsPGRPs have broad-spectrum antimicrobial activity like zebrafish PGRPs. RT-PCR analysis of total RNA shows that the expression patterns of SsPGRP-L1 and SsPGRP-L2 genes are different, though they are widely expressed in the tissues that come in contact with bacteria. Overall, these data suggest that rockfish PGRPs are involved in the innate host defense of S. schlegeli against bacterial infections.