Defensins

Antimicrobial defensin peptides of the human nasal mucosa

Defensins, a prominent group of antimicrobial peptides, are an important component of the innate immune response, particularly at mucosal surfaces that are vulnerable to colonization by potential pathogens. The present study was undertaken to investigate the expression of defensins in inferior turbinate mucosa of normal subjects and inferior turbinate mucosa and nasal polyps of patients with chronic sinusitis. Expression of beta-defensin 1 and 2 and alpha-defensin 5 and 6 messenger RNAs (mRNAs) was investigated by reverse transcriptase-polymerase chain reaction, and their expression level was semiquantitatively evaluated by dot blot hybridization. Immunohistochemical analysis was used for detection of alpha-defensins 1, 2, and 3 in tissue sections. Beta-defensin 1 mRNA was expressed in all tissue samples, at levels that did not differ significantly. Beta-defensin 2 mRNA was detected in the turbinate mucosa and nasal polyps of patients with chronic sinusitis, but not in normal mucosa. Its expression level was significantly higher in nasal polyps than in turbinate mucosa. Alpha-defensin 5 and 6 mRNAs were not expressed in any tissues, but alpha-defensins 1, 2, and 3 were detected in all tissue samples obtained from patients with chronic sinusitis. These results suggest that beta-defensin 1 may play a constitutive role in nasal defenses, whereas alpha-defensins 1, 2, and 3 and beta-defensin 2 may be induced in response to local infection or inflammation.

Antibacterial peptides in stimulated human granulocytes: characterization of ubiquitinated histone H1A

Antibacterial peptides were isolated from human peripheral granulocytes of a healthy donor who had been treated with granulocyte-colony stimulating factor (G-CSF) and cortisol. Peptides were solubilized in acidified chloroform/methanol, and partitioned in chloroform/methanol/water. Water- soluble polypeptides were separated by cation-exchange and reversed-phase chromatography. Several previously characterized antibacterial polypeptides were identified; defensins 1-3, defensin 4, lysozyme, eosinophil cationic protein, and calgranulin A. In addition, several histone fragments were isolated and exhibited activity against the Gram- positive bacterium Bacillus megaterium strain Bm11. These fragments included two C-terminal fragments of histone H1A, three C-terminal fragments of histone H1D, one fragment of histone H1B, and two fragments of histone H4. The molecular masses of both histone H1A fragments, as determined by electrospray (ES) MS, were 270 Da higher than those calculated from their amino acid sequences. The two histone H1A fragments corresponded to Lys152-Lys222 (7527 +/- 1 Da) and Lys167-Lys222 (6023 +/- 1 Da). Tandem MS (MS/MS) of the 7.5 kDa and 6.0 kDa fragments indicated that the post-translational modification is on Lys222, the epsilon-amino group of which was conjugated with the alpha-carboxyl group of the tripeptide Arg-Gly-Gly. This finding was substantiated by digestion of the 7.5-kDa polypeptide with trypsin and analysis of the resulting peptides by ES MS and MS/MS. The tripeptide Arg-Gly-Gly corresponded uniquely to the three C-terminal residues of ubiquitin, demonstrating the presence of ubiquitinated histone H1A.

Immunohistochemical study on expression of alpha-defensin and beta-defensin-2 in human buccal epithelia with candidiasis

OBJECTIVES AND DESIGN

It has been previously reported that alpha-defensin (HNPs) and beta-defensin-2 (HBD-2) peptides with antifungal and cytotoxic activities can be detected in oral carcinomas and the saliva of patients with oral carcinomas. The present study investigated the presence of HNPs and HBD-2 in oral epithelia with candidiasis.

MATERIALS AND METHODS

Tissue sections (4 microm) were prepared from biopsy and surgically removed specimens diagnosed as oral candidiasis (n = 10). The sections were examined immunohistochemically with antibodies directed against HNPs and HBD-2.

RESULTS

Tissue sections of oral candidiasis were immunostained with antidefensin antibodies. Neutrophils in the inflamed lamina propria were positively immunostained with anti-HNPs antibody. The cytoplasm of cells in the upper spinous layer, in the lower spinous layer and in the parakeratinized layer of buccal epithelia with candidiasis was immunostained intensely with anti-HBD-2 antibody. In contrast, the expression of HBD-2 in the normal spinous layer was much weaker than that in oral candidiasis. No signals of HNPs were found in normal buccal epithelium.

CONCLUSION

Buccal specimens from individuals with oral candidiasis show greater levels of expression of both HNPs and HBD-2. There might be a dual protection manner by defensins against fungal inflammation in infected buccal epithelia locally. Generally, HBD-2 signals have been found everywhere in the buccal epithelium; however, in an infected area, the signal intensity of HBD-2 has increased. HNPs signals have not been found in the normal buccal epithelium; however, HNPs signals have increased when the infection occurred.

Plasma concentrations of defensins and lactoferrin in children with severe sepsis

BACKGROUND

We hypothesized that systemic release of endogenous leukocyte-derived polypeptide antimicrobial defensins (polymorphonuclear leukocyte-specific) and lactoferrin (polymorphonuclear leukocyte and epithelial cell derived) occurs in nonneutropenic children with severe sepsis.

METHODS

We performed a prospective cross-sectional and longitudinal study in a university children's hospital pediatric intensive care unit. Ninety-two consecutive children meeting criteria for sepsis and 14 critically ill children without sepsis (controls) were enrolled, and plasma defensins and lactoferrin concentrations were measured on Days 1 and 3 of sepsis.

RESULTS

Nonneutropenic sepsis patients (n = 71) had increased defensins and lactoferrin plasma concentrations compared with critically ill control patients [defensins, 450 ng/ml vs. 150 ng/ml; lactoferrin, 332 ng/ml vs. 176 ng/ml (median values); P < 0.05] and neutropenic sepsis patients [n = 21; defensins, 450 ng/ml vs. 50 ng/ml; lactoferrin, 332 ng/ml vs. 20 ng/ml (median values); P < 0.05]. Neutropenic sepsis patients had similar plasma defensin concentrations and a decrease in plasma lactoferrin concentrations compared with control patients (P < 0.05). Defensins and lactoferrin plasma concentrations correlated to total white blood cell and absolute neutrophil count (P < 0.05). There was no association between plasma defensin concentration and organ failure or outcome; however, increased plasma lactoferrin concentrations were observed with the development of organ failure (P < 0.05).

CONCLUSION

These data suggest that increased circulating defensins and lactoferrin release are dependent in part on neutrophil count and might play a role in host defense in children with severe sepsis.

Structure determination of human and murine beta-defensins reveals structural conservation in the absence of significant sequence similarity

Defensins are cationic and cysteine-rich peptides that play a crucial role in the host defense against microorganisms of many organisms by their capability to permeabilize bacterial membranes. The low sequence similarity among the members of the large mammalian beta-defensin family suggests that their antimicrobial activity is largely independent of their primary structure. To investigate to what extent these defensins share a similar fold, the structures of the two human beta-defensins, hBD-1 and hBD-2, as well as those of two novel murine defensins, termed mBD-7 and mBD-8, were determined by nuclear magnetic resonance spectroscopy. All four defensins investigated share a striking similarity on the level of secondary and tertiary structure including the lack of a distinct hydrophobic core, suggesting that the fold is mainly stabilized by the presence of three disulfide bonds. In addition to the overall shape of the molecules, the ratio of solvent-exposed polar and hydrophobic side chains is also very similar among the four defensins investigated. It is significant that beta-defensins do not exhibit a common pattern of charged and hydrophobic residues on the protein surface and that the beta-defensin-specific fold appears to accommodate a wide range of different amino acids at most sequence positions. In addition to the implications for the mode of biological defensin actions, these findings are of particular interest because beta-defensins have been suggested as lead compounds for the development of novel peptide antibiotics for the therapy of infectious diseases.

Granulysin blocks replication of varicella-zoster virus and triggers apoptosis of infected cells

Granulysin, a lytic protein present in cytolytic granules of human natural killer and cytotoxic T cells, entered cells infected with varicella-zoster virus (VZV). Exposure to granulysin accelerated death of infected cells as assessed by apoptosis markers. The functional domain of granulysin that mediated its antiviral effects was amino acid 23-51; this domain also mediates the additional antitumor cell effects of granulysin. Because granulysin is a product of natural killer cells and T lymphocytes, it is possible that its antiviral activity may act as a mediator of innate and adaptive immune mechanisms.

An in vitro study of antibacterial properties of the cervical mucus plug in pregnancy

OBJECTIVE

To evaluate whether cervical mucus plugs are antibacterial in vitro.

STUDY DESIGN

Cervical mucus plugs from 56 healthy women in labor were studied by 2 different antimicrobial assays: (1) analysis of the inhibition by the cervical mucus plug of several gram-positive and gram-negative bacteria by overlaying the cervical mucus plug onto an agar plate with imbedded bacteria, and (2) determination of the antibacterial property of the cervical mucus plug material by radial diffusion assay with group B Streptococcus and Escherichia coli.

RESULTS

In the agar overlay assay, there was complete inhibition of clinical isolates of Staphylococcus saprophyticus, E coli, and Pseudomonas aeruginosa and patient-variable partial-to-complete inhibition of Enterococcus faecium, Staphylococcus aureus, Streptococcus pyogenes, and Streptococcus agalactiae. In the radial diffusion assay, cervical mucus plugs had activity toward group B Streptococcus equivalent to 0.075 microg/mL of gentamicin and toward E coli equivalent to 0.5 microg/mL of gentamicin.

CONCLUSION

A low-molecular substance with antibacterial activity in the cervical mucus plug may protect the fetus against ascending infections.

Defensins -- innate immunity at the epithelial frontier

Physical barrier function was formerly believed to play the major role in mucosal protection against luminal bacteria. This view has now been challenged by the discovery of specialized molecules that possess antimicrobial activity. More than 100 peptides have been identified so far, and the number is still growing. These peptides are distributed widely and conserved throughout phylogeny. The epithelial expression of antimicrobial peptides is of particular interest as many pathogens adhere to epithelial surfaces and may eventually invade the host. This rapidly acting defence system of innate immunity is already engaged before adoptive immune interactions take place. These antimicrobial peptides consist of constitutive and inducible forms, potentiating this barrier function in terms of an inflammatory response. One important subgroup of antimicrobial peptides is the family of defensins, which are classified as alpha (alpha-) and beta (beta-) defensins. Eight different peptides with varying antimicrobial properties have been identified. They are distributed widely in humans, and organ-specific expression patterns have been observed. Homologous peptides have been found in other mammals, vertebrates, invertebrates, insects and plants. The identification of alpha-defensins and their murine counterparts, cryptdins, in the small intestine prompted intensive research into epithelial antimicrobial defence.

Antimicrobial peptides: properties and applicability

All organisms need protection against microorganisms, e. g. bacteria, viruses and fungi. For many years, attention has been focused on adaptive immunity as the main antimicrobial defense system. However, the adaptive immune system, with its network of humoral and cellular responses is only found in higher animals, while innate immunity is encountered in all living creatures. The turning point in the appreciation of the innate immunity was the discovery of antimicrobial peptides in the early eighties. In general these peptides act by disrupting the structural integrity of the microbial membranes. It has become clear that membrane-active peptides and proteins play a crucial role in both the innate and the adaptive immune system as antimicrobial agents. This review is focused on the functional and structural features of the naturally occurring antimicrobial peptides, and discusses their potential as therapeutics.

Antimycobacterial agent based on mRNA encoding human beta-defensin 2 enables primary macrophages to restrict growth of Mycobacterium tuberculosis

Human macrophages are hosts for Mycobacterium tuberculosis, the causative agent of tuberculosis, which killed approximately 1.87 million people in 1997. Human alveolar macrophages do not express alpha- or beta-defensins, broad-spectrum antimicrobial peptides which are expressed in macrophages from other species more resistant to infection with M. tuberculosis. It has been previously reported that M. tuberculosis is susceptible to killing by defensins, which may explain the difference in resistance. Defensin peptides have been suggested as a possible therapeutic strategy for a variety of infectious diseases, but development has been hampered by difficulties in their large-scale production. Here we report the cellular synthesis of human beta-defensin 2 via highly efficient mRNA transfection of human macrophages. This enabled mycobactericidal and mycobacteristatic activity by the macrophages. Although human macrophages are difficult to transfect with plasmid vectors, these studies illustrate that primary macrophages are permissive for mRNA transfection, which enabled expression of a potentially therapeutic protein.

Rhesus monkey (Macaca mulatta) mucosal antimicrobial peptides are close homologues of human molecules

One component of host defense at mucosal surfaces appears to be epithelium-derived antimicrobial peptides. Molecules of the defensin and cathelicidin families have been studied in several species, including human and mouse. We describe in this report the identification and characterization of rhesus monkey homologues of human mucosal antimicrobial peptides. Using reverse transcriptase PCR methodology, we cloned the cDNAs of rhesus monkey beta-defensin 1 and 2 (rhBD-1 and rhBD-2) and rhesus monkey LL-37/CAP-18 (rhLL-37/rhCAP-18). The predicted amino acid sequences showed a high degree of homology to the human molecules. The expression of the monkey antimicrobial peptides was analyzed using immunohistochemistry with three polyclonal antibodies to the human molecules. As in humans, rhesus monkey antimicrobial peptides are expressed in epithelia of various organs. The present study demonstrates that beta-defensins and cathelicidins of rhesus monkeys are close homologues to the human molecules and indicate that nonhuman primates represent valid model organisms to study innate immune functions.

Bogorol A produced in culture by a marine Bacillus sp. reveals a novel template for cationic peptide antibiotics

[figure: see text] Bogorol A (1), a novel peptide antibiotic active against MRSA and VRE, has been isolated from cultures of a marine Bacillus sp. collected in Papua New Guinea. The structure of bogorol A was elucidated by a combination of spectroscopic analyses and chemical degradation. Bogorol A illustrates a new structural template for "cationic peptide antibiotics".

Bacterial infections and inflammation in the lungs of cystic fibrosis patients

The aim of this review is to describe the role of respiratory epithelial cells in processes that contribute to the pathogenesis of lung disease in patients with cystic fibrosis.

Human beta defensin is absent in burn blister fluid

Defensins are a family of cationic antimicrobial peptides that participate in innate host defence. Human beta defensin-2 (HBD-2) is produced by human keratinocytes, and has a potent bactericidal activity against a wide spectrum of microorganisms. We have recently shown that expression of HBD-2 is present in normal skin and lost in the full-thickness burn wound. Defensins have been found in the blister fluid of chronic wounds. Our study was designed to examine blister fluid from partial-thickness burns for defensin content. Fluid from five patients was collected from partial-thickness burn blisters, and then analysed by sandwich Enzyme-Linked Immunosorbent Assay (ELISA) with a monoclonal antibody and rabbit polyclonal antibody to HBD-2. The assay was validated against a Western blot assay for HBD-2 in samples of bronchoalveolar lavage fluid from patients with inflammatory lung disease. No HBD-2 was detectable in any of the burn blister fluids analysed. HBD-2 is lost in the full-thickness burn wound, and we have now demonstrated its absence in burn blister fluid. This finding represents evidence of a host defence defect within the burn wound and suggests a possible therapeutic role for antimicrobial peptides in the management of burn wounds.

An essential amino acid induces epithelial beta -defensin expression

Antimicrobial peptides constitute an important component of the mammalian innate immune response. Several types of antimicrobial peptides, including the beta-defensins, are produced at epithelial surfaces in response to infectious threats. Here we show that a class of small molecules, including l-isoleucine and several of its analogs, can specifically induce epithelial beta-defensin expression. This induction is transcriptional in nature and involves activation of the NF-kappaB/rel family of trans-activating factors. We hypothesize that these substances represent unique markers for the presence of pathogens and are recognized by innate immune pattern recognition receptors. Isoleucine or its analogs ultimately may have clinical utility as novel immunostimulants that could bolster the barrier defenses of mucosal surfaces.

Characterization of luminal paneth cell alpha-defensins in mouse small intestine. Attenuated antimicrobial activities of peptides with truncated amino termini

Paneth cells at the base of small intestinal crypts secrete apical granules that contain antimicrobial peptides including alpha-defensins, termed cryptdins. Using an antibody specific for mouse cryptdin-1, -2, -3, and -6, immunogold-localization studies demonstrated that cryptdins are constituents of mouse Paneth cell secretory granules. Several cryptdin peptides have been purified from rinses of adult mouse small intestine by gel filtration and reverse-phase high performance liquid chromatography. Their primary structures were determined by peptide sequencing, and their antimicrobial activities were compared with those of the corresponding tissue forms. The isolated luminal cryptdins included peptides identical to the tissue forms of cryptdin-2, -4, and -6 as well as variants of cryptdin-1, -4, and -6 that have N termini truncated by one or two residues. In assays of antimicrobial activity against Staphylococcus aureus, Escherichia coli, and the defensin-sensitive Salmonella typhimurium phoP(-) mutant, full-length cryptdins had the same in vitro antibacterial activities whether isolated from tissue or from the lumen. In contrast, the N-terminal-truncated (des-Leu), (des-Leu-Arg)-cryptdin-6, and (des-Gly)-cryptdin-4 peptides were markedly less active. The microbicidal activities of recombinant cryptdin-4 and (des-Gly)-cryptdin-4 peptides against E. coli, and S. typhimurium showed that the N-terminal Gly residue or the length of the cryptdin-4 N terminus are determinants of microbicidal activity. Innate immunity in the crypt lumen may be modulated by aminopeptidase modification of alpha-defensins after peptide secretion.

Structural features and biological activities of the cathelicidin-derived antimicrobial peptides

Cathelicidins are a numerous group of mammalian proteins that carry diverse antimicrobial peptides at the C-terminus of a highly conserved preproregion. These peptides, which become active when released from the proregion, display a remarkable variety of sizes, sequences, and structures, and in fact comprise representatives of all the structural groups in which the known antimicrobial peptides have been classified. Most of the cathelicidin-derived peptides exert a broad spectrum and potent antimicrobial activity and also bind to lipopolysaccharide and neutralize its effects. In addition, some of them have recently been shown to exert other activities and might participate in host defense also by virtue of their ability to induce expression of molecules involved in a variety of biological processes. This review is aimed at providing a general overview of the cathelicidins and of the peptides derived therefrom, with emphasis on aspects such as structure, biological activities in vitro and in vivo, and structure/activity relationship studies.

LEAP-1, a novel highly disulfide-bonded human peptide, exhibits antimicrobial activity

We report the isolation and characterization of a novel human peptide with antimicrobial activity, termed LEAP-1 (liver-expressed antimicrobial peptide). Using a mass spectrometric assay detecting cysteine-rich peptides, a 25-residue peptide containing four disulfide bonds was identified in human blood ultrafiltrate. LEAP-1 expression was predominantly detected in the liver, and, to a much lower extent, in the heart. In radial diffusion assays, Gram-positive Bacillus megaterium, Bacillus subtilis, Micrococcus luteus, Staphylococcus carnosus, and Gram-negative Neisseria cinerea as well as the yeast Saccharomyces cerevisiae dose-dependently exhibited sensitivity upon treatment with synthetic LEAP-1. The discovery of LEAP-1 extends the known families of mammalian peptides with antimicrobial activity by its novel disulfide motif and distinct expression pattern.

The role of cationic antimicrobial peptides in innate host defences

Cationic antimicrobial peptides are found in all living species. A single animal can contain >24 different antimicrobial peptides, which fall into four structural classes. These peptides are produced in large quantities at sites of infection and/or inflammation and can have broad-spectrum antibacterial, antifungal, antiviral, antiprotozoan and antisepsis properties. In addition, they interact directly with host cells to modulate the inflammatory process and innate defences.

Differential expression of human alpha- and beta-defensins mRNA in gastrointestinal epithelia

BACKGROUND

While defensins have received great attention for their role in bronchial innate immune defence, little is known about the expression levels of the four human epithelial defensins (HD5, HD6, hBD1 and hBD2) in the digestive tract. In this study we quantified the alpha- and beta-defensins mRNA in biopsies obtained from the gastrointestinal mucosa and identified the cells expressing the beta-defensin hBD1 mRNA in ileal mucosa.

MATERIAL AND METHODS

Biopsies from human stomach (corpus and antrum), duodenum, jejunum, ileum and colon were analysed for their expression of alpha- and beta-defensins. The mRNA of defensins was quantified by semiquantitative reverse transcription-polymerase chain reaction. Cells expressing beta-defensin hBD1 mRNA were identified by in situ hybridization with 35S-labelled RNA probes in tissue sections of human ileum.

RESULTS

The hBD1 mRNA was expressed at low levels with little variability throughout the gastrointestinal tract and was detected in all epithelial cells of ileal mucosa. HD5 and HD6 mRNA expression was restricted to the intestine and displayed high interindividual variability. The highest expression levels were observed in jejunum and ileum. Biopsies obtained from duodenum displayed low levels or no expression of HD5 and HD6. The expression level increased considerably in a biopsy obtained from a patient with acute coeliac sprue. In contrast, low levels were observed in a biopsy from a patient with coeliac sprue in remission.

CONCLUSIONS

The expression levels of hBD1, HD5 and HD6 throughout the gastrointestinal tract are tissue and peptide specific and these defensins are expressed with high interindividual variability.

Microanalysis of antimicrobial properties of human fluids

Host defense responses of animals and plants to pathogenic microbes are mediated in part by the release of antimicrobial substances into tissue fluids. Exploration of the antimicrobial properties of tissue fluids is often limited by their small quantity. We have developed assays of antimicrobial activity that require only 1 microl of fluid. Using normal nasal secretions as a model mucosal fluid we demonstrated that the kinetics of the 1 microl colony-forming unit (CFU) assays were equivalent to the larger CFU assays. The handling of viscous mucin-containing fluids was facilitated by pretreatment with N-acetylcysteine (NAC), a treatment that did not alter the performance of the assay. This low-volume assay will facilitate studies of the antimicrobial properties of scarce biological fluids.

Bactericidal activity of mammalian cathelicidin-derived peptides

Endogenous antimicrobial peptides of the cathelicidin family contribute to innate immunity. The emergence of widespread antibiotic resistance in many commonly encountered bacteria requires the search for new bactericidal agents with therapeutic potential. Solid-phase synthesis was employed to prepare linear antimicrobial peptides found in cathelicidins of five mammals: human (FALL39/LL37), rabbit (CAP18), mouse (mCRAMP), rat (rCRAMP), and sheep (SMAP29 and SMAP34). These peptides were tested at ionic strengths of 25 and 175 mM against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus. Each peptide manifested activity against P. aeruginosa irrespective of the NaCl concentration. CAP18 and SMAP29 were the most effective peptides of the group against all test organisms under both low- and high-salt conditions. Select peptides of 15 to 21 residues, modeled on CAP18 (37 residues), retained activity against the gram-negative bacteria and methicillin-sensitive S. aureus, although the bactericidal activity was reduced compared to that of the parent peptide. In accordance with the behavior of the parent molecule, the truncated peptides adopted an alpha-helical structure in the presence of trifluoroethanol or lipopolysaccharide. The relationship between the bactericidal activity and several physiochemical properties of the cathelicidins was examined. The activities of the full-length peptides correlated positively with a predicted gradient of hydrophobicity along the peptide backbone and with net positive charge; they correlated inversely with relative abundance of anionic residues. The salt-resistant, antimicrobial properties of CAP18 and SMAP29 suggest that these peptides or congeneric structures have potential for the treatment of bacterial infections in normal and immunocompromised persons and individuals with cystic fibrosis.

Mucosal barrier injury: biology, pathology, clinical counterparts and consequences of intensive treatment for haematological malignancy: an overview

Mucositis is an inevitable side-effect of the conditioning regimens used for haematopoietic stem cell transplantation. The condition is better referred to as mucosal barrier injury (MBI) since it is primarily the result of toxicity and is a complex and dynamic pathobiological process manifested not only in the mouth but also throughout the entire digestive tract. A model has been proposed for oral MBI and consists of four phases, namely inflammatory, epithelial, ulcerative and healing phases. A variety of factors are involved in causing and modulating MBI including the nature of the conditioning regimen, the elaboration of pro-inflammatory and other cytokines, translocation of the resident microflora and their products, for example, endotoxins across the mucosal barrier, exposure to antimicrobial agents and whether or not the haematopoietic stem cell graft is from a donor. Neutropenic typhlitis is the most severe gastrointestinal manifestation of MBI, but it also influences the occurrence of other major transplant-related complications including acute GVHD, veno-occlusive disease and systemic infections. The pathobiology, clinical counterparts and the means of measuring MBI are discussed together with potential approaches for prevention, amelioration and, perhaps, even cure. Bone Marrow Transplantation (2000) 25, 1269-1278.

Salivary MUC5B-mediated adherence (ex vivo) of Helicobacter pylori during acute stress

OBJECTIVE

Biochemical host defenses at mucosal sites, such as the oral cavity, play a key role in the regulation of microbial ecology and the prevention of infectious disease. These biochemical factors have distinct features, some of which benefit the host and some that benefit bacteria. We investigated the effects of acute stress on the salivary levels of the carbohydrate structure sulfo-Lewis (sulfo-Le), which is linked to the mucosal glycoprotein MUC5B. Sulfo-Le was recently identified as an adhesion molecule for Helicobacter pylori; therefore, we also measured saliva-mediated adherence (ex vivo) of H. pylori. The oral cavity is suspected to be involved in the transmission of H. pylori.

METHODS

Saliva was collected from 17 undergraduates before (baseline), during (stress), and after (recovery) exposure to a video showing surgical procedures. In addition, blood pressure, an impedance cardiogram, and an electrocardiogram were recorded.

RESULTS

During stressor exposure, participants reported increased state anxiety. In addition, stroke volume increased and heart rate decreased. The stressor induced a strong increase in salivary sulfo-Le concentration (U/ml), sulfo-Le output (U/min), sulfo-Le/total protein ratio (U/mg protein), and saliva-mediated adherence (ex vivo) of H. pylori. As expected, sulfo-Le concentration correlated with the adherence of H. pylori (r = 0.72, p < .05). It was demonstrated that the observed adherence was induced by MUC5B and that the carbohydrate structure sulfo-Le contributed to this process.

CONCLUSIONS

Our study demonstrated a direct link between stress-mediated biochemical changes and altered host-microbe interactions in humans. Increased bacterial adherence may be a contributing factor in the observed relationship between stress and susceptibility to infectious disease.

Regulation of intestinal alpha-defensin activation by the metalloproteinase matrilysin in innate host defense

Precursors of alpha-defensin peptides require activation for bactericidal activity. In mouse small intestine, matrilysin colocalized with alpha-defensins (cryptdins) in Paneth cell granules, and in vitro it cleaved the pro segment from cryptdin precursors. Matrilysin-deficient (MAT-/-) mice lacked mature cryptdins and accumulated precursor molecules. Intestinal peptide preparations from MAT-/- mice had decreased antimicrobial activity. Orally administered bacteria survived in greater numbers and were more virulent in MAT-/- mice than in MAT+/+ mice. Thus, matrilysin functions in intestinal mucosal defense by regulating the activity of defensins, which may be a common role for this metalloproteinase in its numerous epithelial sites of expression.

Molecular cloning and characterization of rat genes encoding homologues of human beta-defensins

beta-Defensins are cationic peptides with broad-spectrum antimicrobial activity that may play a role in mucosal defenses of several organs. They have been isolated in several species, and in humans, two beta-defensins have been identified. Here, we report the identification of two genes encoding beta-defensin homologues in the rat. Partial cDNAs were found by searching the expressed-sequence-tag database, and primers were designed to generate full-length mRNA coding sequences. One gene was highly similar to the human beta-defensin-1 (HBD-1) gene and mouse beta-defensin-1 gene at both the nucleic acid and amino acid levels and was termed rat beta-defensin-1 (RBD-1). The other gene, named RBD-2, was homologous to the HBD-2 and bovine tracheal antimicrobial peptide (TAP) genes. The predicted prepropeptides were strongly cationic, were 69 and 63 residues in length for RBD-1 and RBD-2, respectively, and contained the six-cysteine motif characteristic of beta-defensins. The beta-defensin genes mapped closely on rat chromosome 16 and were closely linked to the alpha-defensins genes, suggesting that they are part of a gene cluster, similar to the organization reported for humans. Northern blot analysis showed that both RBD-1 and RBD-2 mRNA transcripts were approximately 0.5 kb in length; RBD-1 mRNA was abundantly transcribed in the rat kidney, while RBD-2 was prevalent in the lung. Reverse transcription-PCR indicated that RBD-1 and RBD-2 mRNAs were distributed in a variety of other tissues. In the lung, RBD-1 mRNA expression localized to the tracheal epithelium while RBD-2 was expressed in alveolar type II cells. In conclusion, we characterized two novel beta-defensin homologues in the rat. The rat may be a useful model to investigate the function and contribution of beta-defensins to host defense in the lung, kidney, and other tissues.

Oxygen-independent microbicidal mechanisms of phagocytes

The principal biological function of phagocytic cells is the destruction of invading microorganisms. Following phagocytosis, microbes are exposed to multiple antimicrobial substances ranging in complexity from simple oxygen radicals to large proteins. These substances disrupt various microbial structures and eventually kill and digest most of the invaders. This review is focused on oxygen-independent microbicidal mechanisms in granulocytes and macrophages.

Reduced antimicrobial peptide expression in human burn wounds

Severely burned skin ceases to perform its natural protective role and surrenders itself as a nidus and portal for bacterial invasion. Antimicrobial peptides are part of a non-specific chemical defence system, separate from cellular and humoral immunity. Two of these peptides, human beta-defensins 1 and 2 have been recently found in skin and are produced by keratinocytes. Beta defensins have potent bactericidal activity against a wide spectrum of bacterial and fungal organisms commonly responsible for burn wound infections. To date, expression of beta defensins has not been examined in the human burn wound. Our findings demonstrate that expression of hBD-2 is greatly decreased in the burn wound whereas hBD-1 appears to be preserved. These results may have important implications in the pathogenesis and treatment of invasive burn sepsis.

Mouse beta-defensin 3 is an inducible antimicrobial peptide expressed in the epithelia of multiple organs

One component of host defense at mucosal surfaces is epithelium-derived peptides with antimicrobial activity called defensins. We describe in this report the isolation and characterization of a murine homologue of human beta-defensin 2 (hBD-2) called mouse beta-defensin 3 (mBD-3). The predicted amino acid sequence shows the hallmark features of other known epithelial defensins, including the ordered array of six cysteine residues. Analysis of a genomic clone of mBD-3 revealed two exons separated by a 1.7-kb intron. The mBD-3 gene is localized at the proximal portion of chromosome 8, the site where genes for mouse alpha- and beta-defensins are found. Under basal condition, mBD-3 transcripts were detected at low levels in epithelial cells of surface organs, such as the intestine and lung. After instillation of Pseudomonas aeruginosa PAO1 into mouse airways, mBD-3-specific mRNA was upregulated significantly not only in large airways but also in the small bowel and liver. Recombinant mBD-3 peptide, produced from a baculovirus expression system, showed antimicrobial activity against P. aeruginosa PAO1 (MIC of 8 micrograms/ml) and Escherichia coli D31 (MIC of 16 micrograms/ml) in a salt-dependent manner. This study demonstrates that a murine homologue of hBD-2 is present in the respiratory system and other mucosal surfaces. These similarities between murine and human host defense apparatus provide further impetus to evaluate the mouse as a model for studying the human innate host defense system.

Antibiotic peptides from higher eukaryotes: biology and applications

Gene-encoded antibiotic peptides are increasingly being recognized as effector molecules of host defense in plants and animals. Studies of antimicrobial peptides are providing new insights into the dynamic interactions between microbes and their hosts, and are generating new paradigms for the pathogenesis and treatment of diseases. Because antimicrobial peptides of higher eukaryotes differ structurally from conventional antibiotics produced by bacteria and fungi, they offer novel templates for pharmaceutical compounds that could be effective against increasingly resistant microbes.

A 450-kb contig of defensin genes on human chromosome 8p23

Defensins are a large family of host defense peptides expressed in leukocytes and epithelia. Using P1 and BAC clones, we have determined the organization of the human alpha-defensin genes and the beta-defensin gene HDEFB1 on chromosome 8p23. From the telomere, the order of the genes (with encoded peptides in parentheses) is HDEFA5 (HD-5), HDEFA1/1A (HNP-1/3), HDEFA4 (HNP-4), HDEFA6 (HD-6), and HDEFB1 (HBD-1). These genes span a region of approximately 450kb. Genes encoding intestinal Paneth cell defensins (HDEFA5 and HDEFA6) flank the myeloid defensin gene cluster (HDEFA1, HDEFA1A, HDEFA4). Based on our previous studies, the remaining known defensin gene, HDEFB2 (HBD-2), is about 400kb centromeric to HDEFB1. This map supports the hypothesis, originally proposed because of sequence similarities, that myeloid alpha-defensin genes evolved by reduplication and divergence from Paneth cell defensin genes, and identifies regions and clones, which should be useful in the search for new defensin genes.

Immunomagnetic recovery of human neutrophil defensins from the human gingival crevice

The human neutrophilic protein defensins are cationic, antimicrobial, cytotoxic, corticostatic chemotactic, opsonic peptides found in azurophilic granules and constitute about 5% of the total protein in human neutrophils. In the present study, defensins were recovered from the human gingival crevice using paramagnetic microspheres (beads), coated with anti-defensin antibodies. The bead-bound defensins were assayed using an enzyme-linked immunosorbent assay developed in this laboratory. Twenty sites were sampled; defensin was found in 100% of the sites and ranged in amount from 270-2000 ng/site. The large local concentrations of defensins, estimated in the mg/ml range, may have major effects on the microbiology of the gingival crevice.

Production of beta-defensin antimicrobial peptides by the oral mucosa and salivary glands

beta-Defensins are cationic peptides with broad-spectrum antimicrobial activity that are produced by epithelia at mucosal surfaces. Two human beta-defensins, HBD-1 and HBD-2, were discovered in 1995 and 1997, respectively. However, little is known about the expression of HBD-1 or HBD-2 in tissues of the oral cavity and whether these proteins are secreted. In this study, we characterized the expression of HBD-1 and HBD-2 mRNAs within the major salivary glands, tongue, gingiva, and buccal mucosa and detected beta-defensin peptides in salivary secretions. Defensin mRNA expression was quantitated by RNase protection assays. HBD-1 mRNA expression was detected in the gingiva, parotid gland, buccal mucosa, and tongue. Expression of HBD-2 mRNA was detected only in the gingival mucosa and was most abundant in tissues with associated inflammation. To test whether beta-defensin expression was inducible, gingival keratinocyte cell cultures were treated with interleukin-1beta (IL-1beta) or bacterial lipopolysaccharide (LPS) for 24 h. HBD-2 expression increased approximately 16-fold with IL-1beta treatment and approximately 5-fold in the presence of LPS. Western immunoblotting, liquid chromatography, and mass spectrometry were used to identify the HBD-1 and HBD-2 peptides in human saliva. Human beta-defensins are expressed in oral tissues, and the proteins are secreted in saliva; HBD-1 expression was constitutive, while HBD-2 expression was induced by IL-1beta and LPS. Human beta-defensins may play an important role in the innate defenses against oral microorganisms.

Antimicrobial defensin peptides of the human ocular surface

BACKGROUND/AIMS

The antimicrobial activity of the tear film exceeds the activity of its known constituents. The authors postulate that this excess activity is the result of antimicrobial peptides called defensins, and they aimed to look for defensins in the human eye.

METHODS

Evidence of defensin production was sought by reverse transcriptase polymerase chain reaction (RT-PCR). Intron spanning primers were designed for beta defensins 1 and 2, and alpha defensins 5 and 6. RT-PCR was performed on cornea, conjunctiva, and lacrimal gland samples, and reaction products were size fractionated and sequenced to confirm their identity. A monoclonal antibody was utilised for the detection of alpha defensins 1, 2, and 3 in tissue sections and in immunoblots of tears.

RESULTS

RT-PCR revealed beta defensin 1 message in samples of conjunctiva, cornea, and lacrimal gland. beta Defensin 2 message was detected in the conjunctiva and cornea but was absent from the lacrimal gland. alpha Defensin 5 and 6 message was absent in these tissues but alpha defensins 1, 2, and 3 were detected in normal tears, lacrimal gland, and inflamed conjunctiva by immunochemistry.

CONCLUSION

The data suggest the human eye innately produces a spectrum of antimicrobial defensin peptides. Defensins hold therapeutic potential in ocular infections as they have a broad spectrum of antimicrobial activity (bacteria fungi and viruses ) and accelerate epithelial healing.

Antimicrobial peptides in insects; structure and function

Antimicrobial peptides appear to be ubiquitous and multipotent components of the innate immune defense arsenal used by both prokaryotic and eukaryotic organisms. During the past 15 years a multitude of these peptides have been isolated largely from insects. In spite of great differences in size, amino acid composition and structure, most of the antimicrobial peptides from insects can be grouped into one of three categories. The largest category in number contains peptides with intramolecular disulfide bonds forming hairpin-like beta-sheets or alpha-helical-beta-sheet mixed structures. The second most important group is composed of peptides forming amphipathic alpha-helices. The third group comprises peptides with an overrepresentation in proline and/or glycine residues. In general, the insect antimicrobial peptides have a broad range of activity and are not cytotoxic. Despite a wealth of information on structural requirements for their antimicrobial activity, the mode of action of these peptides is not yet fully understood. However, some data suggest the existence of two types of mode of action: 1. through peptide-lipid interaction or 2. through receptor-mediated recognition processes. This review presents the main results obtained during the last four years in the field of antimicrobial peptides from insects with a special focus on the proline-rich and cysteine-rich peptides.

Activity of abundant antimicrobials of the human airway

Human airways produce several antimicrobial factors; the most abundant are lysozyme and lactoferrin. Despite their likely importance in preventing infection, and their possible key role in the pathogenesis of cystic fibrosis (CF), we know little about their antibacterial activity in the context of the CF airway. We found that abundant airway antimicrobial factors kill common CF pathogens, although Burkholderia was relatively resistant. To study the antibacterial activity, we developed a rapid, sensitive, and quantitative in vitro luminescence assay. Because NaCl concentrations may be elevated in CF airway surface liquid, we tested the effect of salt on antibacterial activity. Activity of individual factors and of airway lavage fluid was inhibited by high ionic strength, and it was particularly sensitive to divalent cations. However, it was not inhibited by nonionic osmolytes and thus did not require hypotonic liquid. The inhibition by ionic strength could be partially compensated by increased concentrations of antibacterial factors, thus there was no one unique salt concentration for inhibition. CF airway secretions also contain abundant mucin and elastase; however, these had no effect on antibacterial activity of lysozyme, lactoferrin, or airway lavage fluids. When studied at low NaCl concentrations, CF and non-CF airway lavage fluids contained similar levels of antibacterial activity. These results suggest approaches toward developing treatments aimed at preventing or reducing airway infections in individuals with CF.

Levels of antimicrobial molecules defensin and lactoferrin are elevated in the cerebrospinal fluid of children with meningitis

OBJECTIVE

To measure levels of defensins and lactoferrin in the cerebrospinal fluid (CSF) of children with meningitis. STUDY DESIGN. Prospective descriptive study involving children undergoing lumbar puncture during evaluation for meningitis.

METHODS

CSF concentrations of defensins and lactoferrin were determined using enzyme-linked immunosorbent assays on 19 children with bacterial meningitis, 31 children with aseptic meningitis, and 32 control children found to have normal CSF during evaluation for meningitis. Pertinent clinical and laboratory data were gathered on all children.

RESULTS

CSF concentrations of both defensins and lactoferrin were elevated markedly in children with bacterial and aseptic meningitis, compared with control children. No control subject had detectable levels of defensins in the CSF. Lactoferrin was undetectable in the CSF of 31 of 32 control subjects. Defensin and lactoferrin levels were significantly higher in the CSF of children with bacterial meningitis than in those with aseptic meningitis. Defensin levels in the CSF of children with bacterial meningitis ranged from 128 ng/mL to 99 430 ng/mL with a mean of 30 311 ng/mL (SD +/- 28 865) and a median of 23 042 ng/mL. Defensin levels in the CSF of children with aseptic meningitis ranged from 0 ng/mL to 1675 ng/mL with a mean of 227 ng/mL (SD +/- 433) and a median of 23 ng/mL. A significant correlation was found between defensin levels in the CSF and the total leukocyte count and the absolute neutrophil count in the CSF of children with bacterial meningitis. Lactoferrin levels in the CSF of children with bacterial meningitis ranged from 184 ng/mL to 31 412 ng/mL with a mean of 13 209 ng/mL (SD +/- 9644) and a median of 10 382 ng/mL. Lactoferrin levels in the CSF of children with aseptic meningitis ranged from 0 ng/mL to 2715 ng/mL with a mean of 1042 ng/mL (SD +/- 878) and a median of 852 ng/mL. No correlation was found between lactoferrin level in the CSF and the total leukocyte count or the absolute neutrophil count in the CSF of children with bacterial meningitis. In our study population, the sum total of CSF defensins and lactoferrin was found to be highly sensitive and specific in delineating bacterial from aseptic meningitis when compared with standard CSF studies.

CONCLUSIONS

Significant elevations of defensins and lactoferrin, indicative of endogenous local antimicrobial peptide and polypeptide release, are found in the CSF of children with meningitis. We speculate that elevations in these antimicrobial molecules may reflect the intensity of the host response. Defensins seem to parallel neutrophil activation more closely than lactoferrin. Cumulative levels of CSF defensins and lactoferrin clearly distinguished bacterial meningitis from aseptic meningitis and control patients. Further investigation is warranted to determine the usefulness of measuring defensins and lactoferrin as a diagnostic tool and therapeutic monitor in the evaluation of children with meningitis.

Defensins impair phagocytic killing by neutrophils in biomaterial-related infection

The implantation of foreign material carries a risk of infection which frequently is resistant to all treatment short of removing the implant. We have previously shown that these materials activate neutrophils by contact, leading to production of oxygen free radicals accompanied by release of granule products. Such activation further results in depletion of local host defenses, including the capacity of biomaterial-activated neutrophils to kill bacteria. Among the granule products released from neutrophils are small cationic antibacterial peptides (human neutrophil peptides [HNP]) known as defensins. Here we tested the hypothesis that defensins, released from activated neutrophils onto the surface of biomaterials, might play a role in the deactivation of subsequent neutrophil populations. Incubation of neutrophils with purified HNP resulted in a dose-related impairment of stimulus-induced oxygen radical production and of phagocytic killing. Furthermore, fresh neutrophils added to biomaterial-associated neutrophils exhibited impaired phagocytic killing. This impairment could be abrogated by antibody to HNP but not by an irrelevant antibody. Taken together, these observations support the idea that neutrophils activated at a material surface can create, by means of HNP release, an environment hostile to their microbicidal function and that of their infiltrating brethren.