Microbicidal/cytotoxic proteins of neutrophils are deficient in two disorders: Chediak-Higashi syndrome and "specific" granule deficiency

The lysosomal trafficking regulator "LYST": an 80-year traffic jam

Lysosomes and lysosome related organelles (LROs) are dynamic organelles at the intersection of various pathways involved in maintaining cellular hemostasis and regulating cellular functions. Vesicle trafficking of lysosomes and LROs are critical to maintain their functions. The lysosomal trafficking regulator (LYST) is an elusive protein important for the regulation of membrane dynamics and intracellular trafficking of lysosomes and LROs. Mutations to the LYST gene result in Chédiak-Higashi syndrome, an autosomal recessive immunodeficiency characterized by defective granule exocytosis, cytotoxicity, etc. Despite eight decades passing since its initial discovery, a comprehensive understanding of LYST's function in cellular biology remains unresolved. Accumulating evidence suggests that dysregulation of LYST function also manifests in other disease states. Here, we review the available literature to consolidate available scientific endeavors in relation to LYST and discuss its relevance for immunomodulatory therapies, regenerative medicine and cancer applications.

A Novel CEBPE Variant Causes Severe Infections and Profound Neutropenia

PURPOSE

Specific granule deficiency (SGD) is a rare inborn error of immunity resulting from loss-of-function variants in CEBPE gene (encoding for transcription factor C/EBPε). Although this genetic etiology has been known for over two decades, only a few patients with CEBPE variant-proven SGD (type I) have been reported. Herein, we describe two siblings with a novel homozygous CEBPE deletion who were noted to have profound neutropenia on initial evaluation. We aimed to evaluate the immunohematological consequences of this novel variant, including profound neutropenia.

METHODS

Light scatter characteristics of granulocytes were examined on various automated hematology analyzers. Phagocyte immunophenotype, reactive oxygen species generation, and Toll-like receptor (TLR) signaling were assessed using flow cytometry. Relative expression of genes encoding various granule proteins was studied using RT-PCR. Western blot analysis and luciferase reporter assay were performed to explore variant C/EBPε expression and function.

RESULTS

Severe infections occurred in both siblings. Analysis of granulocyte light scatter plots revealed automated hematology analyzers can provide anomalously low neutrophil counts due to abnormal neutrophil morphology. Neutrophils displayed absence/marked reduction of CD15/CD16 expression and overexpression (in a subset) of CD14/CD64. Three distinct populations of phagocytes with different oxidase activities were observed. Impaired shedding of CD62-ligand was noted on stimulation with TLR-4, TLR-2/6, and TLR-7/8 agonists. We demonstrated the variant C/EBPε to be functionally deficient.

CONCLUSION

Homozygous c.655_665del variant in CEBPE causes SGD. Anomalous automated neutrophil counts may be reported in patients with SGD type I. Aberrant TLR signaling might be an additional pathogenetic mechanism underlying immunodeficiency in SGD type I.

Neutrophil Recruitment in Pneumococcal Pneumonia

Streptococcus pneumoniae (Spn) is the primary agent of community-acquired pneumonia. Neutrophils are innate immune cells that are essential for bacterial clearance during pneumococcal pneumonia but can also do harm to host tissue. Neutrophil migration in pneumococcal pneumonia is therefore a major determinant of host disease outcomes. During Spn infection, detection of the bacterium leads to an increase in proinflammatory signals and subsequent expression of integrins and ligands on both the neutrophil as well as endothelial and epithelial cells. These integrins and ligands mediate the tethering and migration of the neutrophil from the bloodstream to the site of infection. A gradient of host-derived and bacterial-derived chemoattractants contribute to targeted movement of neutrophils. During pneumococcal pneumonia, neutrophils are rapidly recruited to the pulmonary space, but studies show that some of the canonical neutrophil migratory machinery is dispensable. Investigation of neutrophil migration is necessary for us to understand the dynamics of pneumococcal infection. Here, we summarize what is known about the pathways that lead to migration of the neutrophil from the capillaries to the lung during pneumococcal infection.

Constitutive immune mechanisms: mediators of host defence and immune regulation

The immune system enables organisms to combat infections and to eliminate endogenous challenges. Immune responses can be evoked through diverse inducible pathways. However, various constitutive mechanisms are also required for immunocompetence. The inducible responses of pattern recognition receptors of the innate immune system and antigen-specific receptors of the adaptive immune system are highly effective, but they also have the potential to cause extensive immunopathology and tissue damage, as seen in many infectious and autoinflammatory diseases. By contrast, constitutive innate immune mechanisms, including restriction factors, basal autophagy and proteasomal degradation, tend to limit immune responses, with loss-of-function mutations in these pathways leading to inflammation. Although they function through a broad and heterogeneous set of mechanisms, the constitutive immune responses all function as early barriers to infection and aim to minimize any disruption of homeostasis. Supported by recent human and mouse data, in this Review we compare and contrast the inducible and constitutive mechanisms of immunosurveillance.

PepN is a non-essential, cell wall-localized protein that contributes to neutrophil elastase-mediated killing of Streptococcus pneumoniae

Streptococcus pneumoniae (Spn) is an asymptomatic colonizer of the human nasopharynx but can also cause disease in the inner ear, meninges, lung and blood. Although various mechanisms contribute to the effective clearance of Spn, opsonophagocytosis by neutrophils is perhaps most critical. Upon phagocytosis, Spn is exposed to various degradative molecules, including a family of neutrophil serine proteases (NSPs) that are stored within intracellular granules. Despite the critical importance of NSPs in killing Spn, the bacterial proteins that are degraded by NSPs leading to Spn death are still unknown. In this report, we identify a 90kDa protein in a purified cell wall (CW) preparation, aminopeptidase N (PepN) that is degraded by the NSP neutrophil elastase (NE). Since PepN lacked a canonical signal sequence or LPxTG motif, we created a mutant expressing a FLAG tagged version of the protein and confirmed its localization to the CW compartment. We determined that not only is PepN a CW-localized protein, but also is a substrate of NE in the context of intact Spn cells. Furthermore, in comparison to wild-type TIGR4 Spn, a mutant strain lacking PepN demonstrated a significant hyper-resistance phenotype in vitro in the presence of purified NE as well as in opsonophagocytic assays with purified human neutrophils ex vivo. Taken together, this is the first study to demonstrate that PepN is a CW-localized protein and a substrate of NE that contributes to the effective killing of Spn by NSPs and human neutrophils.

Neutrophil evasion strategies by Streptococcus pneumoniae and Staphylococcus aureus

Humans are well equipped to defend themselves against bacteria. The innate immune system employs diverse mechanisms to recognize, control and initiate a response that can destroy millions of different microbes. Microbes that evade the sophisticated innate immune system are able to escape detection and could become pathogens. The pathogens Streptococcus pneumoniae and Staphylococcus aureus are particularly successful due to the development of a wide variety of virulence strategies for bacterial pathogenesis and they invest significant efforts towards mechanisms that allow for neutrophil evasion. Neutrophils are a primary cellular defense and can rapidly kill invading microbes, which is an indispensable function for maintaining host health. This review compares the key features of Streptococcus pneumoniae and Staphylococcus aureus in epidemiology, with a specific focus on virulence mechanisms utilized to evade neutrophils in bacterial pathogenesis. It is important to understand the complex interactions between pathogenic bacteria and neutrophils so that we can disrupt the ability of pathogens to cause disease.

SMARCD2 subunit of SWI/SNF chromatin-remodeling complexes mediates granulopoiesis through a CEBPɛ dependent mechanism

Recent studies suggest that individual subunits of chromatin-remodeling complexes produce biologically specific meaning in different cell types through combinatorial assembly. Here we show that granulocyte development requires SMARCD2, a subunit of ATP-dependent SWI/SNF (BAF) chromatin-remodeling complexes. Smarcd2-deficient mice fail to generate functionally mature neutrophils and eosinophils, a phenotype reminiscent of neutrophil-specific granule deficiency (SGD) in humans, for which loss-of-function mutations in CEBPE (encoding CEBPɛ) have been reported. SMARCD2-containing SWI/SNF complexes are necessary for CEBPɛ transcription factor recruitment to the promoter of neutrophilic secondary granule genes and for granulocyte differentiation. The homologous SMARCD1 protein (63% identical at the amino acid level) cannot replace the role of SMARCD2 in granulocyte development. We find that SMARCD2 functional specificity is conferred by its divergent coiled-coil 1 and SWIB domains. Strikingly, both CEBPE and SMARCD2 loss-of-function mutations identified in patients with SGD abolish the interaction with SWI/SNF and thereby secondary granule gene expression, thus providing a molecular basis for this disease.

Killing of staphylococci by θ-defensins involves membrane impairment and activation of autolytic enzymes

θ-Defensins are cyclic antimicrobial peptides expressed in leukocytes of Old world monkeys. To get insight into their antibacterial mode of action, we studied the activity of RTDs (rhesus macaque θ-defensins) against staphylococci. We found that in contrast to other defensins, RTDs do not interfere with peptidoglycan biosynthesis, but rather induce bacterial lysis in staphylococci by interaction with the bacterial membrane and/or release of cell wall lytic enzymes. Potassium efflux experiments and membrane potential measurements revealed that the membrane impairment by RTDs strongly depends on the energization of the membrane. In addition, RTD treatment caused the release of Atl-derived cell wall lytic enzymes probably by interaction with membrane-bound lipoteichoic acid. Thus, the premature and uncontrolled activity of these enzymes contributes strongly to the overall killing by θ-defensins. Interestingly, a similar mode of action has been described for Pep5, an antimicrobial peptide of bacterial origin.

The antimicrobial propeptide hCAP-18 plasma levels in neutropenia of various aetiologies: a prospective study

The underlying cause of neutropenia may be difficult to determine due to similar clinical presentation in many neutropenic conditions. The neutrophil protein hCAP-18 (pro-LL-37) is a major component of neutrophil secondary granules and in this prospective study we assessed the use of hCAP-18 levels in blood plasma for differential diagnosis of neutropenic patients (n = 133) of various aetiologies. Plasma levels of hCAP-18 were determined using immunoblot and ELISA. Patients with severe congenital neutropenia (n = 23) presented with the lowest levels of plasma hCAP-18 and differential diagnostic accuracy revealed high sensitivity (100%) and specificity (98.8%) for hCAP-18 ELISA. The correlation coefficient of the hCAP-18 ELISA versus immunoblotting was (R = 0.831) and that of the peptide LL-37 ELISA versus immunoblotting was (R = 0.405) (P < 0.001). Plasma hCAP-18 levels thus displayed high diagnostic value in differential diagnosis of chronic neutropenia. Neutropenic patients with Shwachman-Diamond syndrome, Barth syndrome, Cohen syndrome, acute myeloid leukaemia and specific granule deficiency presented with reduced plasma hCAP-18 levels as well. The blood plasma level of hCAP-18 was thus low in conditions in which the neutrophil antibacterial propeptide hCAP-18 is deficient, i.e. severe congenital neutropenia and neutrophil-specific granule deficiency, and in conditions in which bone marrow myelopoiesis is negatively affected.

Soluble elastin peptides in cardiovascular homeostasis: Foe or ally

Elastin peptides, also known as elastin-derived peptides or elastokines, are soluble polypeptides in blood and tissue. The blood levels of elastin peptides are usually low but can increase during cardiovascular diseases, such as atherosclerosis, aortic aneurysm and diabetes with vascular complications. Generally, elastin peptides are derived from the degradation of insoluble elastic polymers. The biological activities of elastin peptides are bidirectional, e.g., a pro-inflammatory effect on monocyte migration induction vs. a protective effect on vasodilation promotion. However, recent in vivo studies have demonstrated that elastin peptides promote the formation of atherosclerotic plaques in hypercholesterolemic mice and induce hyperglycemia and elevations in plasma lipid levels in fasted mice. More important, the detrimental effects induced by elastin peptides can be largely inhibited by genetic or pharmacological blockade of the elastin receptor complex or by neutralization of an antibody against elastin peptides. These studies indicate new therapeutic strategies for the treatment of cardiovascular diseases by targeting elastin peptide metabolism. Therefore, the goal of this review is to summarize current knowledge about elastin peptides relevant to cardiovascular pathologies to further delineate their potential application in cardiovascular disease.

Skin fibroblasts from individuals with Chediak-Higashi Syndrome (CHS) exhibit hyposensitive immunogenic response

Background

Chediak-Higashi Syndrome (CHS) is a rare autosomal recessive disease characterized by immunodeficiency, oculocutaneous albinism, neurological dysfunction, and early death. Individuals with CHS present with increased susceptibility to infections of the skin, upper-respiratory tract, gastrointestinal tract, and oral tissues. Classical CHS is caused by mutations in the gene encoding lysosomal trafficking regulator (LYST). Although defects in cytotoxic T cell lytic secretory granule secretion and neutrophil phagocytosis are suggested to contribute to the immunodeficiency in CHS, the underlying molecular mechanisms are unknown. We hypothesized that skin fibroblasts from CHS subjects exhibit impaired immune response due to defective trafficking of inflammatory factors.

Methods and results

Primary skin fibroblasts from CHS subjects or healthy controls were assessed for genes encoding inflammatory response factors using PCR array. At baseline, we found CD14, IL1R1 and TLR-1 were down-regulated significantly (≥2 fold change) and the genes encoding TLR-3, IL-1β and IL-6 were up-regulated in CHS cells compared to control cells. When challenged with E. coli lipopolysaccharide (LPS), CHS cells were less responsive than control cells, with only 8 genes significantly up-regulated (3–68 fold change) compared to baseline values, whereas 28 genes in control cells were significantly up-regulated at a much higher magnitude (3–4,629 fold change). In addition, 50% of the genes significantly up-regulated in LPS-treated control cells were significantly lower in LPS-treated CHS cells. IL-6, a fibroblast-derived proinflammatory cytokine essential for fighting infections was significantly lower in culture media of CHS cells with or without LPS. Furthermore, Western blot and immunofluorescent staining revealed that TLR-2 and TLR-4 were diminished on cell membranes of CHS cells and dissociated from Rab11a.

Conclusions

For the first time, results from our study indicate defective trafficking of TLR-2 and TLR-4 contributes to the hyposensitive response of CHS skin fibroblasts to immunogenic challenge, providing a potential therapeutic target for clinical intervention in CHS.

Congenital defects in neutrophil dynamics

Neutrophil granulocytes are key effector cells of the vertebrate immune system. They represent 50-70% of the leukocytes in the human blood and their loss by disease or drug side effect causes devastating bacterial infections. Their high turnover rate, their fine-tuned killing machinery, and their arsenal of toxic vesicles leave them particularly vulnerable to various genetic deficiencies. The aim of this review is to highlight those congenital immunodeficiencies which impede the dynamics of neutrophils, such as migration, cytoskeletal rearrangements, vesicular trafficking, and secretion.

In vitro studies on the antimicrobial peptide human beta-defensin 9 (HBD9): signalling pathways and pathogen-related response (an American Ophthalmological Society thesis)

PURPOSE

Human β-defensins (HBDs) are an important part of the innate immune host defense at the ocular surface. Unlike other defensins, expression of HBD9 at the ocular surface is reduced during microbial infection, but activation of toll-like receptor 2 (TLR2) in corneal epithelial cells has been shown to up-regulate HBD9. Our purpose was to test the hypothesis that TLR2 has a key role in the signalling pathway(s) involved in the overexpression or underexpression of HBD9, and accordingly, different pathogens would induce a different expression pattern of HBD9.

METHODS

The in vitro RNAi silencing method and response to dexamethasone were used to determine key molecules involved in signalling pathways of HBD9 in immortalized human corneal epithelial cells. The techniques included cell culture with exposure to specific transcription factor inhibitors and bacteria, RNA extraction and cDNA synthesis, quantitative real-time polymerase chain reaction, and immunohistology.

RESULTS

This study demonstrates that TLR2 induces HBD9 mRNA and protein expression in a time- and dose-dependent manner. Transforming growth factor-β-activated kinase 1 (TAK1) plays a central role in HBD9 induction by TLR2, and transcription factors c-JUN and activating transcription factor 2 are also involved. Dexamethasone reduces TLR2-mediated up-regulation of HBD9 mRNA and protein levels in mitogen-activated protein kinase phosphatase 1 (MKP1)-dependent and c-JUN-independent manner. HBD9 expression differs with gram-negative and gram-positive bacteria.

CONCLUSIONS

TLR2-mediated MKPs and nuclear factor-κB signalling pathways are involved in HBD9 expression. TAK-1 is a key molecule. These molecules can be potentially targeted to modulate HBD9 expression. Differential expression of HBD9 with different bacteria could be related to differences in pathogen-associated molecular patterns of these organisms.

Human α-defensin expression is not dependent on CCAAT/enhancer binding protein-ε in a murine model

Specific granule deficiency (SGD) is a rare congenital disorder characterized by recurrent infections. The disease is caused by inactivating mutations of the CCAAT/enhancer binding protein-ε (C/EBP-ε) gene. As a consequence, specific and gelatinase granules lack most matrix proteins. Furthermore, azurophil granules contain diminished amounts of their most abundant proteins, α-defensins, also known as human neutrophil peptides (HNPs). In accordance with this, in vitro models have demonstrated induction of HNPs by C/EBP-ε. Since mice do not express myeloid defensins, they cannot per se be used to characterize the role of C/EBP-ε in controlling HNP expression in vivo. We therefore crossed a transgenic HNP-1-expressing mouse with the Cebpe^-/- mouse to study the in vivo significance of C/EBP-ε for HNP-1 transcription and expression. Surprisingly, neither expression nor processing of HNP-1 was affected by lack of C/EBP-ε in these mice. Transduction of C/EBP-ε into primary bone marrow cells from HNP-1 mice induced some HNP-1 expression, but not to levels comparable to expression human cells. Taken together, our data infer that the HNP-1 of the transgenic mouse does not show an expression pattern equivalent to endogenous secondary granule proteins. This limits the use of these transgenic mice as a model for human conditions.

Defensin-based anti-infective strategies

Cationic and amphiphilic peptides are widely distributed in eukaryotic organisms and constitute a first line of host defense against invading pathogens. Some of these host defense peptides (HDPs) combine specific antibiotic activities with modulation of immune responses. Moreover, they are active against bacteria resistant to conventional antibiotics and show only modest resistance development under in vitro selection pressure. Based on these features, HDPs and particularly defensins are considered a promising source of novel anti-infective agents. This review summarizes the current knowledge about defensins from different kingdoms and discusses their potential for therapeutic application.

Resistance to antimicrobial peptides in Gram-negative bacteria

Antimicrobial peptides (AMPs) are present in virtually all organisms and are an ancient and critical component of innate immunity. In mammals, AMPs are present in phagocytic cells, on body surfaces such as skin and mucosa, and in secretions and body fluids such as sweat, saliva, urine, and breast milk, consistent with their role as part of the first line of defense against a wide range of pathogenic microorganisms including bacteria, viruses, and fungi. AMPs are microbicidal and have also been shown to act as immunomodulators with chemoattractant and signaling activities. During the co-evolution of hosts and bacterial pathogens, bacteria have developed the ability to sense and initiate an adaptive response to AMPs to resist their bactericidal activity. Here, we review the various mechanisms used by Gram-negative bacteria to sense and resist AMP-mediated killing. These mechanisms play an important role in bacterial resistance to host-derived AMPs that are encountered during the course of infection. Bacterial resistance to AMPs should also be taken into consideration in the development and use of AMPs as anti-infective agents, for which there is currently a great deal of academic and commercial interest.

Compositional modification of nascent in vitro dental plaques by human host-defence peptides

Salivary host-defence peptides include defensins, histatins and cathelicidin. We have investigated the effects of these peptides on the microbial composition of dental plaques. Salivary consortia, established within hydroxyapatite disc models, were exposed during development to physiological levels of human neutrophil proteins (HNP) 1 and 2; human β defensins (hβD) 1, 2 and 3; histatins (His) 5 and 8; and cathelicidin (LL37). Effects on aggregation and microbial composition were determined using fluorescence microscopy; and differential culture with PCR-DGGE, respectively. LIVE/DEAD microscopic analysis indicated that HDPs decreased total bacterial viability, whilst β defensins, paired HNPs, His 5, His 8 and the HDPs combined inhibited bacterial aggregation. According to differential culture, all test HDPs (except His 5) significantly decreased the abundance of Gram-negative anaerobes and lactobacilli (except HNP 2, hβD 1, paired HNPs and His 5). Combined HNPs and paired hβD 1 and 3 inhibited streptococci, whereas HNP 1, hβD 1, hβD 3, His 5 and LL37 increased streptococcal numbers. According to cluster analyses of DGGE profiles, HDP-exposed plaques were compositionally distinct from undosed controls. Thus, whilst HDPs reportedly exhibit variable potency against oral bacteria in endpoint susceptibly tests, exposure of nascent plaques can markedly influence bacterial viability, composition and microbial aggregation.

Multifunctional cationic host defence peptides and their clinical applications

With the rapid rise in the emergence of bacterial strains resistant to multiple classes of antimicrobial agents, there is an urgent need to develop novel antimicrobial therapies to combat these pathogens. Cationic host defence peptides (HDPs) and synthetic derivatives termed innate defence regulators (IDRs) represent a promising alternative approach in the treatment of microbial-related diseases. Cationic HDPs (also termed antimicrobial peptides) have emerged from their origins as nature's antibiotics and are widely distributed in organisms from insects to plants to mammals and non-mammalian vertebrates. Although their original and primary function was proposed to be direct antimicrobial activity against bacteria, fungi, parasites and/or viruses, cationic HDPs are becoming increasingly recognized as multifunctional mediators, with both antimicrobial activity and diverse immunomodulatory properties. Here we provide an overview of the antimicrobial and immunomodulatory activities of cationic HDPs, and discuss their potential application as beneficial therapeutics in overcoming infectious diseases.

Neutrophil elastase, proteinase 3, and cathepsin G as therapeutic targets in human diseases

Polymorphonuclear neutrophils are the first cells recruited to inflammatory sites and form the earliest line of defense against invading microorganisms. Neutrophil elastase, proteinase 3, and cathepsin G are three hematopoietic serine proteases stored in large quantities in neutrophil cytoplasmic azurophilic granules. They act in combination with reactive oxygen species to help degrade engulfed microorganisms inside phagolysosomes. These proteases are also externalized in an active form during neutrophil activation at inflammatory sites, thus contributing to the regulation of inflammatory and immune responses. As multifunctional proteases, they also play a regulatory role in noninfectious inflammatory diseases. Mutations in the ELA2/ELANE gene, encoding neutrophil elastase, are the cause of human congenital neutropenia. Neutrophil membrane-bound proteinase 3 serves as an autoantigen in Wegener granulomatosis, a systemic autoimmune vasculitis. All three proteases are affected by mutations of the gene (CTSC) encoding dipeptidyl peptidase I, a protease required for activation of their proform before storage in cytoplasmic granules. Mutations of CTSC cause Papillon-Lefèvre syndrome. Because of their roles in host defense and disease, elastase, proteinase 3, and cathepsin G are of interest as potential therapeutic targets. In this review, we describe the physicochemical functions of these proteases, toward a goal of better delineating their role in human diseases and identifying new therapeutic strategies based on the modulation of their bioavailability and activity. We also describe how nonhuman primate experimental models could assist with testing the efficacy of proposed therapeutic strategies.

Biological roles of host defense peptides: lessons from transgenic animals and bioengineered tissues

Host defense peptides (HDPs) have long been recognized as microbicidal agents, but their roles as modulators of innate and adaptive immunity have only more recently been appreciated. The study of transgenic animal and tissue models has provided platforms to improve our understanding of the immune modulatory functions of HDPs. Here, the characterization of transgenic animals or tissue models that over-express and/or are deficient for specific HDPs is reviewed. We also attempt to reconcile this data with evidence from human studies monitoring HDP expression at constitutive levels and/or in conjunction with inflammation, infection models, or disease states. We have excluded activities ascribed to HDPs derived exclusively from in vitro experiments. An appreciation of the way that HDPs promote innate immunity or influence the adaptive immune response is necessary in order to exploit their therapeutic or adjuvant potential and to open new perspectives in understanding the basis of immunity. The potential applications for HDPs are discussed.

Neutrophil granules in health and disease

Neutrophil granules store proteins that are critically important for the neutrophil to move from the vascular bed to tissues and to kill microorganisms. This is illustrated in nature when individual proteins are deleted due to inherited mutations of their cognate genes, and such deficiencies result in the conditions leucocyte adhesion deficiency and chronic granulomatous disease. The granules of the neutrophil have traditionally been divided into two or three major types but are instead a continuum where several subtypes can be identified with differences in protein content and propensity for mobilization. This is explained by the 'targeting by timing hypothesis' which states that granules are filled with granule proteins that are synthesized at the time the granule is formed. The heterogeneity of granules arises because the synthesis of granule proteins is individually controlled and major differences exist in the timings of biosynthesis during granulocytopoiesis. This is largely controlled by gene transcription.

Purification of antimicrobial peptides from human skin

Human skin is a rich source of human antimicrobial peptides. Its cellular source is the keratinocyte, which terminally differentiates in the uppermost parts of the skin, eventually forming the stratum corneum, the horny layer. The easy availability of human stratum corneum makes it possible to identify and characterize human antimicrobial peptides with a biochemical approach. Moreover, the availability of lesional scales of patients with psoriasis, an inflammatory skin disease, allows the identification of human-inducible peptide antibiotics, which are absent in healthy skin. With this strategy, the beta-defensins hBD-2 and hBD-3, RNase-7 as well as psoriasin/S100A7 have been discovered as human antimicrobial peptides and proteins. A detailed description of the strategies and methods is presented, which allowed a successful identification and characterization of human antimicrobial peptides. We used various HPLC techniques, combined with antimicrobial testing as read-out system. In parallel, SDS-PAGE analyses as well as electrospray ionization mass spectrometry were used for further biochemical characterization as well as purity assessment.

Manual annotation and analysis of the defensin gene cluster in the C57BL/6J mouse reference genome

Background

Host defense peptides are a critical component of the innate immune system. Human alpha- and beta-defensin genes are subject to copy number variation (CNV) and historically the organization of mouse alpha-defensin genes has been poorly defined. Here we present the first full manual genomic annotation of the mouse defensin region on Chromosome 8 of the reference strain C57BL/6J, and the analysis of the orthologous regions of the human and rat genomes. Problems were identified with the reference assemblies of all three genomes. Defensins have been studied for over two decades and their naming has become a critical issue due to incorrect identification of defensin genes derived from different mouse strains and the duplicated nature of this region.

Results

The defensin gene cluster region on mouse Chromosome 8 A2 contains 98 gene loci: 53 are likely active defensin genes and 22 defensin pseudogenes. Several TATA box motifs were found for human and mouse defensin genes that likely impact gene expression. Three novel defensin genes belonging to the Cryptdin Related Sequences (CRS) family were identified. All additional mouse defensin loci on Chromosomes 1, 2 and 14 were annotated and unusual splice variants identified. Comparison of the mouse alpha-defensins in the three main mouse reference gene sets Ensembl, Mouse Genome Informatics (MGI), and NCBI RefSeq reveals significant inconsistencies in annotation and nomenclature. We are collaborating with the Mouse Genome Nomenclature Committee (MGNC) to establish a standardized naming scheme for alpha-defensins.

Conclusions

Prior to this analysis, there was no reliable reference gene set available for the mouse strain C57BL/6J defensin genes, demonstrating that manual intervention is still critical for the annotation of complex gene families and heavily duplicated regions. Accurate gene annotation is facilitated by the annotation of pseudogenes and regulatory elements. Manually curated gene models will be incorporated into the Ensembl and Consensus Coding Sequence (CCDS) reference sets. Elucidation of the genomic structure of this complex gene cluster on the mouse reference sequence, and adoption of a clear and unambiguous naming scheme, will provide a valuable tool to support studies on the evolution, regulatory mechanisms and biological functions of defensins in vivo.

Susceptibility to infectious diseases based on antimicrobial peptide production

In the last few years, the great impact of antimicrobial peptides on infectious disease susceptibility and natural resistance has been reported. In some cases, susceptibility to diseases is related to antimicrobial peptide polymorphisms and gene copy numbers, but for the vast majority of infectious diseases, these phenomena need to be elucidated. This review is focused on the current knowledge about susceptibility and resistance conferred by genetic variations in antimicrobial peptide expression in infectious diseases.

Human neutrophils kill Streptococcus pneumoniae via serine proteases

Neutrophils, or polymorphonuclear leukocytes, comprise a crucial component of innate immunity, controlling bacterial and fungal infection through a combination of both oxidative and nonoxidative mechanisms. Indeed, neutrophils are believed to play an important role in controlling infection caused by the major human pathogen Streptococcus pneumoniae. However, the method by which neutrophils kill the pneumococcus as well as other Gram-positive bacteria, is not fully understood. We investigated human neutrophil killing of the pneumococcus in a complement-dependent opsonophagocytic assay. In contrast to other Gram-positive organisms, inhibition of the NADPH oxidase did not affect killing of S. pneumoniae. Supernatant from degranulated neutrophils killed the pneumococcus, suggesting a role for granular products. When neutrophil granule proteases were inhibited with either a protease mixture, or specific serine protease inhibitors 4-(2-Aminoethyl)benzenesulfonylfluoride and diisopropylfluorophosphate, killing by neutrophils was inhibited in a manner that correlated with increased intracellular survival. All three compounds inhibited intracellular activity of the three major neutrophil serine proteases: elastase, cathepsin G, and proteinase 3. Additionally, purified elastase and cathepsin G were sufficient to kill S. pneumoniae in a serine protease dependent-manner in in vitro assays. Inhibition studies using specific inhibitors of these serine proteases suggested that while each serine protease is sufficient to kill the pneumococcus, none is essential. Our findings show that Gram-positive pathogens are killed by human neutrophils via different mechanisms involving serine proteases.

Host defence peptides: antimicrobial and immunomodulatory activity and potential applications for tackling antibiotic-resistant infections

The rapidly increasing incidence of multidrug-resistant infections and the alarmingly low rate of discovery of conventional antibiotics create an urgent need for alternative strategies to treat bacterial infections. Host defence peptides are short cationic molecules produced by the immune systems of most multicellular organisms; they are a class of compounds being actively researched. In this review, we provide an overview of the antimicrobial and immunomodulatory activities of natural host defence peptides, and discuss strategies for creating artificial derivatives with improved biological and pharmacological properties, issues of microbial resistance, and challenges associated with their adaptation for clinical use.

Approach to the child with recurrent infections

Children with a history of recurrent, severe, or unusual infections present a diagnostic challenge. It is important to maintain a high index of suspicion for the diagnosis of immunodeficiency, for early diagnosis and treatment can improve outcome. Differentiation between infections caused by common risk factors, or immune dysfunction should be based on a detailed history and physical examination and, if indicated, followed by appropriate laboratory studies. This paper aims at providing guidelines for the evaluation of children with recurrent infections. It provides an overview of the diagnostic approach including important details required from the history, physical examination, and an appropriate choice of screening test to be ordered.

Human antimicrobial proteins effectors of innate immunity

We live in a world populated by an enormous number of micro-organisms. This necessitates the existence of highly effective mechanisms to control microbial growth. Through many research efforts, a chemical defense system based on the production of antimicrobial proteins (AMPs) has been identified. AMPs are endogenous, small proteins exhibiting antimicrobial activity against a wide variety of micro-organisms. The wide distribution of these molecules in the plant and animal kingdom reflects their biological significance. Various human AMPs show a potent effect on pathogenic micro-organisms including antibiotic-resistant bacteria. Thus, there is great interest in understanding the role of AMPs within innate immunity and evaluating their use and/or specific induction to fend off infections. In this review, we provide an overview of the characteristics of human AMPs and discuss examples where AMPs may be involved in the pathogenesis of infectious and inflammatory diseases.

Vitamin D3 induces pro-LL-37 expression in myeloid precursors from patients with severe congenital neutropenia

The innate immune system produces a number of effector molecules that are important for protection against bacterial infections. Neutrophils and antimicrobial peptides are major components of innate defense with the capacity of rapid bacterial killing. Patients with severe congenital neutropenia (SCN) experience recurrent and chronic infections despite recombinant G-CSF-mobilized neutrophils. We have shown previously that these neutrophils are deficient in that they lack the antimicrobial peptide LL-37. Here, we show that pro-LL-37 mRNA is not expressed in neutrophil precursors from patients with SCN, although the gene and promoter region for pro-LL-37, CAMP, does not display any mutations. The hormonal form of vitamin D3 [1,25(OH)2D3] induced the expression of pro-LL-37 in isolated neutrophil progenitors and in EBV-transformed B cells from patients with SCN, whereas all-trans retinoic acid only induced expression in transformed B cells. These results demonstrate that myeloid cells of patients with SCN can produce pro-LL-37, suggesting that other pathways are impaired.

Stimulus-dependent impairment of the neutrophil oxidative burst response in lactoferrin-deficient mice

Lactoferrin (LF) is an iron-binding protein found in milk, mucosal secretions, and the secondary granules of neutrophils in which it is considered to be an important factor in the innate immune response against microbial infections. Moreover, LF deficiency in the secondary granules of neutrophils has long been speculated to contribute directly to the hypersusceptibility of specific granule deficiency (SGD) patients to severe, life-threatening bacterial infections. However, the exact physiological significance of LF in neutrophil-mediated host defense mechanisms remains controversial and has not yet been clearly established in vivo using relevant animal models. In this study, we used lactoferrin knockout (LFKO) mice to directly address the selective role of LF in the host defense response of neutrophils and to determine its contribution, if any, to the phenotype of SGD. Neutrophil maturation, migration, phagocytosis, granule release, and antimicrobial response to bacterial challenge were unaffected in LFKO mice. Interestingly, a stimulus-dependent defect in the oxidative burst response of LFKO neutrophils was observed in that normal activation was seen in response to opsonized bacteria whereas an impaired response was evident after phorbol myristate-13-acetate stimulation. Taken together, these results indicate that although LF deficiency alone is not a primary cause of the defects associated with SGD, this protein does play an immunomodulatory role in the oxidative burst response of neutrophils.

The PhoQ-activating potential of antimicrobial peptides contributes to antimicrobial efficacy and is predictive of the induction of bacterial resistance

Antimicrobial peptides (AMPs) are among the leading candidates to replace antibiotics which have been rendered ineffective by the evolution of resistant bacterial strains. Concerns do exist, however, that the therapeutic administration of AMPs may also select for resistant strains but with much more dire consequences, as these peptides represent an endogenous and essential component of host immune defense. The recent demonstration that AMPs function as ligands for the bacterial sensory kinase PhoQ for the initiation of virulence and adaptive responses lends credence to these concerns. While the ability to serve as PhoQ ligands suggests that the therapeutic administration of AMPs could (i) exacerbate infections by promoting bacterial virulence and (ii) select resistant mutants by encouraging adaptive behaviors, it also provides a rational basis for AMP selection and optimization. Here, we demonstrate that derivatives of a representative AMP have differential abilities to serve as PhoQ ligands and that this correlates with the ability to induce bacterial adaptive responses. We propose that PhoQ-activating potential is a logical parameter for AMP optimization and introduce a novel strategy for the treatment of minimal bactericidal concentration data that permits the discrimination and quantification of the contributions of PhoQ-activating potential and direct antimicrobial activity to net antimicrobial efficiency.

Biosynthesis of defensins and other antimicrobial peptides

Defensins are small (about 30 amino acid residues) cationic antimicrobial peptides with a conserved framework of six disulphide-linked cysteines. Human defensin HNP-1 and the closely related HNP-3 are amphiphilic dimers that act in part by permeabilizing cell membranes. Defensin mRNAs, abundant in neutrophilic promyelocytes, certain non-human macrophages and Paneth cells, encode 94-100 amino acid prepropeptides. PreproHNP-1 is post-translationally processed to inactive proHNP-1 then to mature HNP-1 stored in granules. Bactenecin Bac-5 and perhaps other related neutrophil peptides are also synthesized as prepropeptides but are stored in granules as inactive propeptides. Their conserved cathelin-like propiece inhibits the cysteine protease, cathepsin L, and is removed only during granule release. Charge neutralization of mature peptide by the propiece is seen in both probactenecins and prodefensins. In contrast the propiece of cecropins is very short and proceropins are microbicidal. The pathways that convert myeloid preprodefensins to defensins are specific to myeloid cells but the signal for targeting to granules also functions in non-myeloid granulated cells. The truncation of the anionic propiece by deletion mutagenesis dramatically reduces defensin synthesis, suggesting that the propiece may assist in peptide stabilization, folding or subcellular transport. Despite some similarities in the mechanism of action of the various families of antimicrobial peptides, their precursors differ greatly, presumably owing to differing functions of the propieces.

Multifunctional antimicrobial peptides: therapeutic targets in several human diseases

Antimicrobial peptides have emerged as promising agents against antibiotic-resistant pathogens. They represent essential components of the innate immunity and permit humans to resist infection by microbes. These gene-encoded peptides are found mainly in phagocytes and epithelial cells, showing a direct activity against a wide range of microorganisms. Their role has now broadened from that of simply endogenous antibiotics to multifunctional mediators, and their antimicrobial activity is probably not the only primary function. Although antimicrobial peptide deficiency, dysregulation, or overproduction is not known to be a direct cause of any single human disease, numerous studies have now provided compelling evidence for their involvement in the complex network of immune responses and inflammatory diseases, thereby influencing diverse processes including cytokine release, chemotaxis, angiogenesis, wound repair, and adaptive immune induction. The purpose of this review is to highlight recent literature, showing that antimicrobial peptides are associated with several human conditions including infectious and inflammatory diseases, and to discuss current clinical development of peptide-based therapeutics for future use.

Elevated plasma interleukin-6 levels in trained male triathletes following an acute period of intense interval training

The aim of the present study was to investigate possible changes in the plasma IL-6 levels, subjective reporting of sources and symptoms of stress and the innate immune system in response to an acute period of intensified run training in highly trained endurance athletes. Eight healthy endurance trained male subjects (mean +/- SD age 23 +/- 2 years, VO(2max) 64.8 +/- 2.6 ml kg(-1) min(-1), mass 77.1 +/- 2.9 kg) completed the study which took place over a 4 week period. In weeks 2 and 3, in addition to their normal endurance training, subjects completed interval-training run sessions on three successive days. Saliva and venous blood samples were taken at the end of each week. Blood samples were analysed for leukocyte counts; neutrophil function; plasma IL-6; creatine kinase activity; and cortisol. Symptoms and sources of stress were assessed by questionnaire. Plasma IL-6 and creatine kinase activity were elevated following intensified training. Neutrophil function was reduced but total leukocyte and neutrophil counts, plasma cortisol and salivary IgA remained unchanged. There was a worsening in symptoms of stress despite there being no significant change in the sources of stress during intensified training. In conclusion, an acute period of intensified training can induce a suppression of the innate immune system and a chronic elevation in IL-6. This was associated with an increase in fatigue and generalised malaise which lends support to the recent cytokine theories of unexplained, underperformance syndrome.

Arginase 1 is expressed in myelocytes/metamyelocytes and localized in gelatinase granules of human neutrophils

Arginase 1 (ARG1) metabolizes arginine, thus reducing the availability of arginine as a substrate for nitric oxide synthase (NOS). The decreased production of nitric oxide (NO) by NOS and the production of ornithine by ARG1 affect immune responses and tissue regeneration at sites of infection, respectively. We here demonstrate that ARG1 is synthesized in myelocytes/metamyelocytes and is stored in gelatinase granules. In accordance with this, activated neutrophils coreleased ARG1 and gelatinase to the extracellular environment on stimulation with phorbol-12-myristate 13-acetate (PMA), formyl-methionyl-leucyl-phenylalanine (fMLP), or tumor necrosis factor α (TNF-α). Overall, these findings define ARG1 as a genuine gelatinase granule protein and support a model in which activated neutrophils release ARG1 at sites of infection to modulate immune responses and promote tissue regeneration.

[A mixture of antimicrobial peptides and fibrin glue in treatment of partial-thickness burn wounds]

BACKGROUND

Antimicrobial peptides are naturally occurring cationic peptides. The first-line of defense in infected burns is the innate immune system, of which antimicrobial peptides are essential parts. To facilitate their topical use in infected partial-thickness burns, the efficacy of a mixture with fibrin glue in vitro and in vivo was tested.

METHODS

After in vitro tests, 15 male Sprague-Dawley rats received partial-thickness burns. Afterwards, the wounds were infected with multiresistant Pseudomonas aeruginosa. The animals received PG-1 (100 microg/ml, n=5), fibrin glue (n=5), or a mixture of both (n=5) topically. The efficacy of the materials was previously proven by radial diffusion assay. After 24 h, the infected and burned skin was harvested and quantitative bacterial counts per gram of skin performed.

RESULTS

The biologic effect of the peptides was confirmed in vitro. The PG-1 and fibrin glue groups did not show significant differences in bacterial numbers, whereas the mixture group showed significant reduction in Pseudomonas in vivo (P<0.04 and P<0.01).

CONCLUSION

A mixture of an antimicrobial peptide and commercially available fibrin glue is capable of significantly reducing bacteria in infected partial thickness burns in vivo compared to controls.

Antimicrobial peptides versus invasive infections

It has been estimated that there are more microorganisms within and upon the human body than there are human cells. By necessity, every accessible niche must be defended by innate mechanisms to prevent invasive infection, and ideally that precludes the need for robust inflammatory responses. Yet the potential for pathogens to transcend the integument actively or passively and access the bloodstream emphasizes the need for rapid and potent antimicrobial defense mechanisms within the vascular compartment. Antimicrobial peptides from leukocytes have long been contemplated as being integral to defense against these infections. Recently, platelets are increasingly recognized for their likely multiple roles in antimicrobial host defense. Platelets and leukocytes share many structural and functional archetypes. Once activated, both cell types respond in specific ways that emphasize key roles for their antimicrobial peptides in host defense efficacy: (a) targeted accumulation at sites of tissue injury or infection; (b) direct interaction with pathogens; and (c) deployment of intracellular (leukocyte phagosomes) or extracellular (platelet secretion) antimicrobial peptides. Antimicrobial peptides from these cells exert rapid, potent, and direct antimicrobial effects against organisms that commonly access the bloodstream. Experimental models in vitro and in vivo show that antimicrobial peptides from these cells significantly contribute to prevent or limit infection. Moreover, certain platelet antimicrobial proteins are multifunctional kinocidins (microbicidal chemokines) that recruit leukocytes to sites of infection, and potentiate the antimicrobial mechanisms of these cells. In turn, pathogens pre-decorated by kinocidins may be more efficiently phagocytosed and killed by leukocytes and their antimicrobial peptide arsenal. Hence, multiple and relevant interactions between platelets and leukocytes have immunologic functions yet to be fully understood. A clearer definition of these interactions, and the antimicrobial peptide effectors contributing to these functions, will significantly advance our understanding of antimicrobial host defense against invasive infection. In addition, this knowledge may accelerate development of novel anti-infective agents and strategies against pathogens that have become refractory to conventional antimicrobials.

Host antimicrobial defence peptides in human disease

Antimicrobial peptides or host defence peptides are endogenous peptide antibiotics, which have been confirmed as an essential part of the immune system. Apart from direct killing of bacteria, a role for the peptides in antiviral and immunomodulatory functions has recently been claimed. In this chapter we have focused on the host contact with microbes, where these host defence peptides are key players. The interplay with commensals and pathogens in relation to antimicrobial peptide expression is discussed, with specific emphasis on the respiratory and the alimentary systems. A possible novel difference in epithelial interactions between commensals and pathogens is considered in relation to disease.

Immunomodulatory properties of defensins and cathelicidins

Host defence peptides are a conserved component of the innate immune response in all complex life forms. In humans, the major classes of host defence peptides include the α- and β-defensins and the cathelicidin, hCAP-18/LL-37. These peptides are expressed in the granules of neutrophils and by a wide variety of tissue types. They have many roles in the immune response including both indirect and direct antimicrobial activity, the ability to act as chemokines as well as induce chemokine production leading to recruitment of leukocytes to the site of infection, the promotion of wound healing and an ability to modulate adaptive immunity. It appears that many of these properties are mediated though direct interaction of peptides with the cells of the innate immune response including monocytes, dendritic cells, T cells and epithelial cells. The importance of these peptides in immune responses has been demonstrated since animals defective in the expression of certain host defence peptides showgreater susceptibility to bacterial infections. In the very few instances in which human patients have been demonstrated to have defective host defence peptide expression, these individuals suffer from frequent infections. Although studies of the immunomodulatory properties of these peptides are in their infancy, there is a growing body of evidence suggesting that the immunomodulatory properties of these small, naturally occurring molecules might be harnessed for development as novel therapeutic agents.

The human cationic host defense peptide LL-37 mediates contrasting effects on apoptotic pathways in different primary cells of the innate immune system

The human cathelicidin LL-37 is a cationic host defense peptide (antimicrobial peptide) expressed primarily by neutrophils and epithelial cells. This peptide, up-regulated under conditions of inflammation, has immunomodulatory and antimicrobial functions. We demonstrate that LL-37 is a potent inhibitor of human neutrophil apoptosis, signaling through P2X(7) receptors and G-protein-coupled receptors other than the formyl peptide receptor-like-1 molecule. This process involved modulation of Mcl-1 expression, inhibition of BID and procaspase-3 cleavage, and the activation of phosphatidylinositol-3 kinase but not the extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase pathway. In contrast to the inhibition of neutrophil apoptosis, LL-37 induced apoptosis in primary airway epithelial cells, demonstrating alternate consequences of LL-37-mediated modulation of apoptotic pathways in different human primary cells. We propose that these novel immunomodulatory properties of LL-37 contribute to peptide-mediated enhancement of innate host defenses against acute infection and are of considerable significance in the development of such peptides and their synthetic analogs as potential therapeutics for use against multiple antibiotic-resistant infectious diseases.

Cationic host defense (antimicrobial) peptides

Members of the cationic host defense (antimicrobial) peptide family are widely distributed in nature, existing in organisms from insects to plants to mammals and non-mammalian vertebrates. Although many demonstrate direct antimicrobial activity against bacteria, fungi, eukaryotic parasites and/or viruses, it has been established that cationic peptides have a key modulatory role in the innate immune response. More recent evidence suggests that host defense peptides are effective adjuvants, are synergistic with other immune effectors, polarize the adaptive response, and support wound healing. In addition, the mechanisms of action are being unraveled, which support more effective implementation of derivatives of these endogenous peptides as therapeutic agents.

Neutrophil-Mediated Maturation of Chemerin: A Link between Innate and Adaptive Immunity

Dendritic cells and macrophages are professional APCs that play a central role in initiating immune responses, linking innate and adaptive immunity. Chemerin is a novel chemoattractant factor that specifically attracts APCs through its receptor ChemR23. Interestingly, chemerin is secreted as a precursor of low biological activity, prochemerin, which upon proteolytic removal of a C-terminal peptide, is converted into a potent and highly specific agonist of its receptor. Given the fact that APCs are often preceded by polymorphonuclear cells (PMN) in inflammatory infiltrates, we hypothesized that PMN could mediate chemerin generation. We demonstrate here that human degranulated PMNs release proteases that efficiently convert prochemerin into active chemerin. The use of specific protease inhibitors allowed us to identify the neutrophil serine proteases cathepsin G and elastase as responsible for this process. Mass spectrometry analysis of processed prochemerin showed that each protease generates specifically a distinct form of active chemerin, differing in their C terminus and initially identified in human inflammatory fluids. These findings strongly suggest that bioactive chemerin generation takes place during the early stages of inflammation, underscoring the functional contribution of chemerin as a bridge between innate and adaptive immunity.