Human beta-defensin-2 functions as a chemotactic agent for tumour necrosis factor-alpha-treated human neutrophils

Emergency and therapeutic vaccination--is stimulating innate immunity an option?

There is increasing evidence that activation of innate immunity, in animals and man, by live vaccines, sub-unit vaccines or synthetic or non-synthetic stimulants can induce a profound and rapidly induced resistance to pathogens, including infectious agents that are unrelated to the stimulating antigen or agent. We review the evidence for this phenomenon and present the proposition that this approach might be used to stimulate immunity during the life of the animal when susceptibility to infection is high and when normal vaccination procedures may be inappropriate.

The synthetic peptides bovine enteric β-defensin (EBD), bovine neutrophil β-defensin (BNBD) 9 and BNBD 3 are chemotactic for immature bovine dendritic cells

Human and murine immature DCs (iDCs) are highly efficient in antigen capture and processing, while as mature cells they present antigen and are potent initiators of cell-mediated immune responses. Consequently, iDCs are logical targets for vaccine antigens. Originally discovered for their antimicrobial activity, and thought of as strictly part of the innate immune system, studies with defensins such as human β (beta)-defensin 2 (hBD2) and murine β-defensin 2 (mBD2) have shown that they can function as chemo-attractant for iDCs and, in vaccination strategies, can enhance antigen-specific adaptive immune responses. Most studies to date have been conducted in mice. In contrast, little is known about defensins in cattle. To expand our understanding of the role of defensins in modulating immune responses in cattle, DCs were generated from bovine monocytes and the immature state of these bovine DCs was characterized phenotypically and through functional assays. By day 3 (DC3), bovine monocyte-derived DCs stained positively for DC-specific receptors CD1, CD80/86, CD205, DC-Lamp and MMR. When compared to conventional 6-day DC cultures or DCs cultured for 10 days with and without maturation factors, these DC3 were functionally at their most immature stage. Fourteen of the 16 known bovine β-defensins were synthesized and the synthetic peptides were screened for their ability to attract bovine iDCs. Bovine DC3 were consistently attracted to BNBD3, an analog of BNBD3 (aBNBD3), BNBD9 and bovine EBD in vitro and to aBNBD3 in vivo. These results are the first to describe chemotactic ability of synthetic bovine β-defensins for immature bovine monocyte-derived DCs.

Effects on antigen-presenting cells of short-term interaction with the human host defence peptide β-defensin 2

β-Defensins are antimicrobial peptides that exert their host-defence functions at the interface between the host and microbial biota. They display a direct, salt- and medium-sensitive cidal activity, in vitro, against a broad spectrum of bacteria and fungi, and there is increasing evidence that they also play a role in alerting and enhancing cellular components of innate and adaptive immunity. Their interaction with biological membranes plays a central role in both of these types of activities. In the present study, we have investigated the interaction of fluorescently labelled hBD2 (human β-defensin 2) with monocytes, macrophages and iDCs (immature dendritic cells), observing a differential capacity to be rapidly internalized into these cells. Complementary microscopy techniques [TEM (transmission electron microscopy), optical microscopy and IR microspectroscopy] were used to explore the functional and biological implications of these interactions on iDCs. Short-term exposure to the peptide resulted in significant alterations in membrane composition and re-organization of the endomembrane system, with the induction of degranulation. These events may be associated with the antigen-presenting activities or the chemotaxis of iDCs, which appears to occur via both CCR6 (CC chemokine receptor 6)-dependent and -independent mechanisms.

Protecting the boundary: the sentinel role of host defense peptides in the skin

The skin is our primary shield against microbial pathogens and has evolved innate and adaptive strategies to enhance immunity in response to injury or microbial insult. The study of antimicrobial peptide (AMP) production in mammalian skin has revealed several of the elegant strategies that AMPs use to prevent infection. AMPs are inducible by both infection and injury and protect the host by directly killing pathogens and/or acting as multifunctional effector molecules that trigger cellular responses to aid in the anti-infective and repair response. Depending on the specific AMP, these molecules can influence cytokine production, cell migration, cell proliferation, differentiation, angiogenesis and wound healing. Abnormal production of AMPs has been associated with the pathogenesis of several cutaneous diseases and plays a role in determining a patient's susceptibility to pathogens. This review will discuss current research on the regulation and function of AMPs in the skin and in skin disorders.

A worldwide analysis of beta-defensin copy number variation suggests recent selection of a high-expressing DEFB103 gene copy in East Asia

Beta-defensins are a family of multifunctional genes with roles in defense against pathogens, reproduction, and pigmentation. In humans, six beta-defensin genes are clustered in a repeated region which is copy-number variable (CNV) as a block, with a diploid copy number between 1 and 12. The role in host defense makes the evolutionary history of this CNV particularly interesting, because morbidity due to infectious disease is likely to have been an important selective force in human evolution, and to have varied between geographical locations. Here, we show CNV of the beta-defensin region in chimpanzees, and identify a beta-defensin block in the human lineage that contains rapidly evolving noncoding regulatory sequences. We also show that variation at one of these rapidly evolving sequences affects expression levels and cytokine responsiveness of DEFB103, a key inhibitor of influenza virus fusion at the cell surface. A worldwide analysis of beta-defensin CNV in 67 populations shows an unusually high frequency of high-DEFB103-expressing copies in East Asia, the geographical origin of historical and modern influenza epidemics, possibly as a result of selection for increased resistance to influenza in this region. Hum Mutat 32:743–750, 2011. © 2011 Wiley-Liss, Inc.

Bioactive coating of titanium surfaces with recombinant human β-defensin-2 (rHuβD2) may prevent bacterial colonization in orthopaedic surgery

BACKGROUND

A promising strategy to prevent infections around orthopaedic titanium implants is to use naturally occurring cationic antimicrobial peptides (CAMPs) such as the human β-defensin-2 as antibacterial coatings. Human antimicrobial peptides represent a part of the innate immune system and have a broad antimicrobial spectrum against bacteria, fungi, and viruses.

METHODS

In the present study, titanium surfaces were functionalized by four different self-assembled monolayers (SAMs) forming methoxy silanes: (1) hexadecyltrimethoxysilane, (2) dimethoxymethyloctylsilane, (3) allyltrimethylsilane, and (4) 3-aminopropyltrimethoxysilane. In addition, calf skin type-I collagen was cross-linked to the SAM surface 3-aminopropyltrimethoxysilane by means of two different treatments: (1) N-hydroxysuccinimide and (2) glutaraldehyde. The functionalized titanium surfaces were coated with recombinant human β-defensin-2 (rHuβD2), an antimicrobial peptide, and were tested for antibacterial activity against Escherichia coli. The release of rHuβD2 was quantified by means of enzyme-linked immunosorbent assay (ELISA).

RESULTS

The coating of functionalized titanium surfaces with rHuβD2 was successful. Recombinant HuβD2 was eluted from the titanium surfaces continuously, yielding antimicrobial activity up to several hours. Antimicrobial activity with a killing rate of 100% was observed for all functionalized titanium surfaces after two hours of incubation. The dimethoxymethyloctylsilane-functionalized titanium surface delivered 0.65 μg of rHuβD2 after six hours with a 60% bacterial killing rate. The silane-functionalized surfaces exhibited a faster release of antimicrobially active rHuβD2 compared with collagen modifications.

CONCLUSIONS

Natural antibiotics such as rHuβD2 integrated into the metal surface of titanium implants may be a promising tool to prevent and control infections around orthopaedic implants.

Anti-bacterial effects of poly-N-acetyl-glucosamine nanofibers in cutaneous wound healing: requirement for Akt1

Background

Treatment of cutaneous wounds with poly-N-acetyl-glucosamine nanofibers (sNAG) results in increased kinetics of wound closure in diabetic animal models, which is due in part to increased expression of several cytokines, growth factors, and innate immune activation. Defensins are also important for wound healing and anti-microbial activities. Therefore, we tested whether sNAG nanofibers induce defensin expression resulting in bacterial clearance.

Methodology

The role of sNAG in defensin expression was examined using immunofluoresence microscopy, pharmacological inhibition, and shRNA knockdown in vitro. The ability of sNAG treatment to induce defensin expression and bacterial clearance in WT and AKT1−/− mice was carried out using immunofluoresent microscopy and tissue gram staining. Neutralization, using an antibody directed against β-defensin 3, was utilized to determine if the antimicrobial properties of sNAG are dependent on the induction of defensin expression.

Conclusions/Findings

sNAG treatment causes increased expression of both α- and β-type defensins in endothelial cells and β-type defensins in keratinocytes. Pharmacological inhibition and shRNA knockdown implicates Akt1 in sNAG-dependent defensin expression in vitro, an activity also shown in an in vivo wound healing model. Importantly, sNAG treatment results in increased kinetics of wound closure in wild type animals. sNAG treatment decreases bacterial infection of cutaneous wounds infected with Staphylococcus aureus in wild type control animals but not in similarly treated Akt1 null animals. Furthermore, sNAG treatment of S. aureus infected wounds show an increased expression of β-defensin 3 which is required for sNAG-dependent bacterial clearance. Our findings suggest that Akt1 is involved in the regulation of defensin expression and the innate immune response important for bacterial clearance. Moreover, these findings support the use of sNAG nanofibers as a novel method for enhancing wound closure while simultaneously decreasing wound infection.

Innate antimicrobial immunity in inflammatory bowel diseases

Inflammatory bowel diseases are characterized by chronic intestinal inflammation at different sites. Data from animal models as well as human patients including gene-association studies suggest that different components of the innate barrier function are primarily defective. These recent advances support the evolving hypothesis that intestinal bacteria induce inflammation predominantly as a result of a weakened innate mucosal barrier in genetically predisposed individuals. This article discusses our current understanding of the primary events of disease. Together, these findings should result in new therapeutic avenues aimed at restoring antimicrobial barrier function to prevent a bacterial-triggered inflammatory response.

Beta-defensins: what are they really doing in the oral cavity?

Initially identified as broad-spectrum antimicrobial peptides, the members of the β-defensin family have increasingly been observed to exhibit numerous other activities, both in vitro and in vivo, that do not always relate directly to host defense. Much research has been carried out in the oral cavity, where the presence of commensal bacteria further complicates the definition of their role. In addition to direct antimicrobial activity, β-defensins exhibit potent chemotactic activity for a variety of innate immune cells, as well as stimulating other cells to secrete cytokines. They can also inhibit the inflammatory response, however, by the specific binding of microbe-associated molecular patterns. These patterns are also able to induce the expression of β-defensins in gingival epithelial cells, although significant differences are observed between different species of bacteria. Together these results suggest a complex model of a host-defense related function in maintenance of bacterial homeostasis and response to pathogens. This model is complicated, however, by numerous other observations of β-defensin involvement in cell proliferation, wound healing and cancer. Together, the in vitro, in vivo and human studies suggest that these peptides are important in the biology of the oral cavity; exactly how is still subject to speculation.

CCL20 and β-defensin-2 induce arrest of human Th17 cells on inflamed endothelium in vitro under flow conditions

CCR6 is a chemokine receptor that is expressed at the cell surface of Th17 cells, an IL-17- and IL-22-secreting population of CD4(+) T cells with antipathogenic, as well as inflammatory, properties. In the current study, we have determined the involvement of CCR6 in human Th17 lymphocyte migration toward inflamed tissue by analyzing the capacity of its ligands to induce arrest of these cells onto inflamed endothelium in vitro under flow conditions. We show that polarized, in situ-differentiated, skin-derived Th17 clones activated via the TCR-CD3 complex produce CCL20 in addition to IL-17 and IL-22. The latter cytokines induce, in a synergic fashion, the production of human β-defensin (hBD)-2, but neither hBD-1 nor hBD-3, by epidermal keratinocytes. Both CCL20 and hBD-2 are capable of inducing the arrest of Th17 cells, but not Th1 or Th2 cells, on HUVEC in an CD54-dependent manner that is CCR6 specific and independent from the expression of CXCR4, reported to be an alternative receptor for hBD-2. In addition, Ag-specific activation induces a transient loss of CCR6 expression, both at the transcriptional and protein level, which occurs with slow kinetics and is not due to endogenous CCL20-mediated internalization of CCR6. Together, these results indicate that Ag-specific activation will initially contribute to CCR6-mediated Th17 cell trafficking toward and sequestration in inflamed tissue, but that it eventually results in a transitory state of nonresponsiveness to further stimulation of these cells with CCR6 ligands, thus permitting their subsequent migration out of the inflamed site.

Antimicrobial peptides in gastrointestinal inflammation

Acute and chronic inflammations of mucosal surfaces are complex events in which the effector mechanisms of innate and adaptive immune systems interact with pathogenic and commensal bacteria. The role of constitutive and inducible antimicrobial peptides in intestinal inflammation has been investigated thoroughly over the recent years, and their involvement in various disease states is expanded ever more. Especially in the intestines, a critical balance between luminal bacteria and the antimicrobial peptides is essential, and a breakdown in barrier function by impaired production of defensins is already implicated in Crohn's disease. In this paper, we focus on the role of antimicrobial peptides in inflammatory processes along the gastrointestinal tract, while considering the resident and pathogenic flora encountered at the specific sites. The role of antimicrobial peptides in the primary events of inflammatory bowel diseases receives special attention.

TLR4 upregulation underpins airway neutrophilia in smokers with chronic obstructive pulmonary disease and acute respiratory failure

Activation of Toll-like receptors (TLR) seems to be involved in the pathogenesis of chronic obstructive pulmonary disease (COPD). Upon TLR activation the release of defensins, including human beta defensin 2 (HBD-2), may occur. In this study, we explored the innate responses in patients with respiratory failure, with and without COPD, requiring intubation and mechanical ventilation. Mini-bronchoalveolar lavage (mini-BAL) samples were collected from nonsmoker subjects without COPD (n = 10), smokers without COPD (n = 6), and smokers with COPD (n = 15). TLR4, TLR2, and HBD-2 expression was evaluated by immunocytochemistry; interleukin (IL)-8, IP-10, and HBD-2 concentrations were evaluated by enzyme-linked immunosorbent assay; chemotactic activity toward neutrophils and lymphocytes; and cell apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling [TUNEL] and by flow cytometry with anti-TLR4 and with HBD-2 depleted and not depleted mini-BAL). COPD mini-BAL showed increased neutrophil numbers, reduced neutrophil apoptosis, increased TLR4 and HBD-2 expression, increased neutrophil chemotactic activity, reduced IP-10 concentrations, and reduced lymphocyte chemotactic activity compared with those in nonsmoker subjects without COPD. In the smokers without COPD the mini-BAL showed reduced TLR4 and HBD-2 expression, higher IP-10 concentrations, and higher chemotactic activity than in patients with COPD. The blocking of TLR4 activation and HBD-2 depletion increased neutrophil apoptosis. No differences were observed for TLR2 expression and IL-8 concentrations. This study strengthens the contribution of TLR4 to promoting airway neutrophilia in COPD.

Measurement methods and accuracy in copy number variation: failure to replicate associations of beta-defensin copy number with Crohn's disease

The copy number variation in beta-defensin genes on human chromosome 8 has been proposed to underlie susceptibility to inflammatory disorders, but presents considerable challenges for accurate typing on the scale required for adequately powered case-control studies. In this work, we have used accurate methods of copy number typing based on the paralogue ratio test (PRT) to assess beta-defensin copy number in more than 1500 UK DNA samples including more than 1000 cases of Crohn's disease. A subset of 625 samples was typed using both PRT-based methods and standard real-time PCR methods, from which direct comparisons highlight potentially serious shortcomings of a real-time PCR assay for typing this variant. Comparing our PRT-based results with two previous studies based only on real-time PCR, we find no evidence to support the reported association of Crohn's disease with either low or high beta-defensin copy number; furthermore, it is noteworthy that there are disagreements between different studies on the observed frequency distribution of copy number states among European controls. We suggest safeguards to be adopted in assessing and reporting the accuracy of copy number measurement, with particular emphasis on integer clustering of results, to avoid reporting of spurious associations in future case-control studies.

CCR6 as a possible therapeutic target in psoriasis

IMPORTANCE OF THE FIELD

Psoriasis is a common, chronic autoimmune disease of the skin. Despite a number of effective treatments, new therapies are needed with enhanced efficacy, safety and convenience. Chemokine receptors are GPCRs that control leukocyte trafficking, and like other GPCRs, are good potential drug targets. The chemokine receptor CCR6 is expressed on the T(H)17 subset of CD4(+) T cells, which produces IL-17A/F, IL-22, TNF-alpha and other cytokines, and which has been implicated in the pathogenesis of psoriasis. CCR6 and its ligand, CCL20/MIP-3alpha, are highly expressed in psoriatic skin and CCR6 is necessary for the pathology induced in a mouse model of psoriasis-like inflammation.

AREAS COVERED IN THIS REVIEW

This review summarizes the evidence for the importance of the IL-23/T(H)17 axis, and in particular CCR6 and CCL20 in psoriasis, dating from 2000 to the present, and discusses the possibility of inhibiting CCR6 as a treatment for the disease.

WHAT THE READER WILL GAIN

The review informs the reader of the current thinking on the mechanisms of inflammation in psoriasis and the possible roles for CCR6 (and CCL20) in disease pathogenesis.

TAKE HOME MESSAGE

We conclude that CCR6 should be investigated as a potential therapeutic target in psoriasis.

Defensins in innate immunity

The innate immune system is the first line of defense against many common microorganisms, which can initiate adaptive immune responses to provide increased protection against subsequent re-infection by the same pathogen. As a major family of antimicrobial peptides, defensins are widely expressed in a variety of epithelial cells and sometimes in leukocytes, playing an important role in the innate immune system due to their antimicrobial, chemotactic and regulatory activities. This review introduces their structure, classification, distribution, synthesis, and focuses on their biological activities and mechanisms, as well as clinical relevance. These studies of defensins in the innate immune system have implications for the prevention and treatment of a variety of infectious diseases, including bacterial ocular disease.

Copy number variation in chemokine superfamily: the complex scene of CCL3L-CCL4L genes in health and disease

Genome copy number changes (copy number variations: CNVs) include inherited, de novo and somatically acquired deviations from a diploid state within a particular chromosomal segment. CNVs are frequent in higher eukaryotes and associated with a substantial portion of inherited and acquired risk for various human diseases. CNVs are distributed widely in the genomes of apparently healthy individuals and thus constitute significant amounts of population-based genomic variation. Human CNV loci are enriched for immune genes and one of the most striking examples of CNV in humans involves a genomic region containing the chemokine genes CCL3L and CCL4L. The CCL3L-CCL4L copy number variable region (CNVR) shows extensive architectural complexity, with smaller CNVs within the larger ones and with interindividual variation in breakpoints. Furthermore, the individual genes embedded in this CNVR account for an additional level of genetic and mRNA complexity: CCL4L1 and CCL4L2 have identical exonic sequences but produce a different pattern of mRNAs. CCL3L2 was considered previously as a CCL3L1 pseudogene, but is actually transcribed. Since 2005, CCL3L-CCL4L CNV has been associated extensively with various human immunodeficiency virus-related outcomes, but some recent studies called these associations into question. This controversy may be due in part to the differences in alternative methods for quantifying gene copy number and differentiating the individual genes. This review summarizes and discusses the current knowledge about CCL3L-CCL4L CNV and points out that elucidating their complete phenotypic impact requires dissecting the combinatorial genomic complexity posed by various proportions of distinct CCL3L and CCL4L genes among individuals.

Inducible expression of human β-defensin 2 by Chlamydophila pneumoniae in brain capillary endothelial cells

Defensins are an important family of natural antimicrobial peptides. Chlamydophila pneumoniae, a common cause of acute respiratory infection, has a tendency to cause persistent inflammatory diseases such as atherosclerosis, which may lead to cardiovascular disease or stroke. As endothelial cells are related to the physiopathology of stroke, the effects of in vitro C. pneumoniae infection on the expression of human β-defensin 2 (HBD-2) in brain capillary endothelial cells (BB19) was investigated. A time-dependent increase in HBD-2 mRNA was observed by means of real-time reverse transcription PCR (RT-PCR) in BB19 cells following C. pneumoniae infection, with a maximum increase at 24 h. A gradual induction of HBD-2 protein in the C. pneumoniae-infected endothelial cells was detected by immunoblotting. Immunofluorescence revealed the staining of HBD-2 in the cytoplasm of endothelial cells following C. pneumoniae infection. The secretion of HBD-2 (confirmed by ELISA) was significantly elevated 24 h after C. pneumoniae infection. These novel results indicate that HBD-2 is expressed and produced in the human brain capillary endothelial cells upon infection with C. pneumoniae, and provide evidence that HBD-2 plays a role in the early immune responses to C. pneumoniae and probably in the immunopathogenesis of atherosclerosis.

Administration of nonviral gene vector encoding rat beta-defensin-2 ameliorates chronic Pseudomonas aeruginosa lung infection in rats

BACKGROUND

Beta-defensin-2 (BD-2) plays an important role in host defense against pathogenic microbe challenge by its direct antimicrobial activity and immunomodulatory functions. The present study aimed to determine whether genetic up-regulation of rat BD-2 (rBD-2) could ameliorate chronic Pseudomonas aeruginosa lung infection in rats.

METHODS

Plasmid-encoding rBD-2 was delivered to lungs in vivo using linear polyethylenimine at 48 h before challenging with seaweed alginate beads containing P. aeruginosa. Macroscopic and histopathological changes of the lungs, bacterial loads, inflammatory infiltration, and the levels of cytokines/chemokines [interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, kertinocyte-derived chemokine (KC), macrophage inflammatory protein-2 (MIP-2)] were measured at 3 and 7 days post-infection (p.i.).

RESULTS

The overexpression of rBD-2 resulted in a significant increase in animal survival rate (at 3 days p.i.), a significant decrease in bacterial loads in the lungs (at 3 and 7 days p.i.), and significantly milder lung pathology. In addition, the overexpression of rBD-2 led to increased infiltration of polymorphonuclear neutrophils (PMN), and elevated protein expression of cytokines/chemokines (IL-1beta, TNF-alpha, KC and MIP-2) at the early stage of infection (at 3 days p.i.), at the same time as being dramatically decreased at the later stage of infection (at 7 days p.i.).

CONCLUSIONS

Genetic up-regulation of rBD-2 increased animal survival rate, and reduced bacterial loads in lungs after bacterial infection. The overexpression of rBD-2 also modulated the production of several cytokines/chemokines and increased PMN recruitment at the early stage of infection. Our findings indicate that the enhancement of BD-2 may be an efficacious intervention for chronic P. aeruginosa lung infection.

Vitamin D and molecular actions on the immune system: modulation of innate and autoimmunity

Vitamin D has received increased attention recently for its pleiotropic actions on many chronic diseases. The importance of vitamin D on the regulation of cells of the immune system has gained increased appreciation over the past decade with the discovery of the vitamin D receptor (VDR) and key vitamin D metabolizing enzymes expressed by cells of the immune system. Animal studies, early epidemiologic and clinical studies have supported a potential role for vitamin D in maintaining immune system balance. The hormonal form of vitamin D up-regulates anti-microbial peptides, namely cathelicidin, to enhance clearance of bacteria at various barrier sites and in immune cells. Vitamin D modulates the adaptive immune system by direct effects on T cell activation and on the phenotype and function of antigen-presenting cells (APCs), particularly of DCs. The purpose of this manuscript is to review the molecular and clinical evidence for vitamin D as a modulator of the innate and adaptive immune system.

Novel synthetic, salt-resistant analogs of human beta-defensins 1 and 3 endowed with enhanced antimicrobial activity

Human beta-defensins (hBDs) are antimicrobial peptides of human innate immunity. The antibacterial activities of hBDs 1, 2, and 4 but not the activity of hBD3 are impaired by high salt levels. We have designed and synthesized seven novel hBD analogs, constituted by different domains of hBD1 (which is constitutively expressed in humans) and of hBD3 (which is induced by microorganisms and inflammatory factors in humans), that would maintain and potentially increase the wild-type antimicrobial activities and be salt resistant. We have compared the antibacterial, antiviral, and chemotactic activities of the analogs with those of hBD1 and hBD3. We show that the hBD1 internal region and the hBD3 C-terminal region are critical for antibacterial activity also at high salt concentrations, whereas deletion of the N-terminal region of hBD3 results in an increase in antibacterial activity. All analogs inhibited herpes simplex virus; antiviral activity was enhanced by the hBD1 internal region and the hBD3 C-terminal region. Wild-type and analog peptides were chemotactic for granulocytes and monocytes, irrespective of the salt concentrations. These new peptides may have therapeutic potential.

Cyclic and acyclic defensins inhibit human immunodeficiency virus type-1 replication by different mechanisms

Defensins are antimicrobial peptides expressed by plants and animals. In mammals there are three subfamilies of defensins, distinguished by structural features: α, β and θ. Alpha and β-defensins are linear peptides with broad anti-microbial activity that are expressed by many mammals including humans. In contrast, θ-defensins are cyclic anti-microbial peptides made by several non-human primates but not humans. All three defensin types have anti-HIV-1 activity, but their mechanisms of action differ. We studied the anti-HIV-1 activity of one defensin from each group, HNP-1 (α), HBD-2 (β) and RTD-1 (θ). We examined how each defensin affected HIV-1 infection and demonstrated that the cyclic defensin RTD-1 inhibited HIV-1 entry, while acyclic HNP-1 and HBD-2 inhibited HIV-1 replication even when added 12 hours post-infection and blocked viral replication after HIV-1 cDNA formation. We further found that all three defensins downmodulated CXCR4. Moreover, RTD-1 inactivated X4 HIV-1, while HNP-1 and HBD-2 inactivated both X4 and R5 HIV-1. The data presented here show that acyclic and cyclic defensins block HIV-1 replication by shared and diverse mechanisms. Moreover, we found that HNP-1 and RTD-1 directly inhibited firefly luciferase enzymatic activity, which may affect the interpretation of previously published data.

The potent adjuvant effects of chicken beta-defensin-1 when genetically fused with infectious bursal disease virus VP2 gene

Defensins are fundamental components of innate immune response. Current data favor that defensins play vital roles on both innate and adaptive immune responses. The aim of the present study was to investigate whether the chicken beta-defensin-1 (also named avian beta-defensin-1, AvBD1) has the potent adjuvant effects on DNA vaccine encoding IBDV VP2 gene, when genetically fused with VP2 gene. The recombinant vectors pcDNA3.1(+)-VP2 and pcDNA3.1(+)-AvBD1-VP2 were constructed as the DNA vaccines. Four groups of 14-day-old chickens were intramuscularly injected with PBS buffer, empty vector pcDNA3.1(+), recombinant pcDNA3.1(+)-VP2 and pcDNA3.1(+)-AvBD1-VP2. Results showed that VP2-specific antibody levels significantly increased following two recombinant DNA vaccine administrations (p<0.05), compared with the group of PBS and empty vector. The antibody level of group immunized with pcDNA3.1(+)-AvBD1-VP2 was significantly higher than that of group immunized with pcDNA3.1(+)-VP2 after second vaccination (p<0.05). The percentages of CD3+, CD4+ and CD8+ T-cell subtypes between groups of pcDNA3.1(+)-VP2 and pcDNA3.1(+)-AvBD1-VP2 obtained significantly different (p<0.05), the latter was higher, at 7 days post-booster. The protection from IBD challenged by immunized chickens with DNA vaccines encoding IBDV VP2 gene alone was lower than that by immunized IBDV VP2 gene together with AvBD1 gene. The results indicated that AvBD1 has an adjuvant effects on improvement the IBDV VP2-DNA vaccine effectiveness.

Haemophilus ducreyi SapA contributes to cathelicidin resistance and virulence in humans

Haemophilus ducreyi is an extracellular pathogen of human epithelial surfaces that resists human antimicrobial peptides (APs). The organism's genome contains homologs of genes sensitive to antimicrobial peptides (sap operon) in nontypeable Haemophilus influenzae. In this study, we characterized the sap-containing loci of H. ducreyi 35000HP and demonstrated that sapA is expressed in broth cultures and H. ducreyi-infected tissue; sapA is also conserved among both class I and class II H. ducreyi strains. We constructed a nonpolar sapA mutant of H. ducreyi 35000HP, designated 35000HPsapA, and compared the percent survival of wild-type 35000HP and 35000HPsapA exposed to several human APs, including alpha-defensins, beta-defensins, and the cathelicidin LL-37. Unlike an H. influenzae sapA mutant, strain 35000HPsapA was not more susceptible to defensins than strain 35000HP was. However, we observed a significant decrease in the survival of strain 35000HPsapA after exposure to LL-37, which was complemented by introducing sapA in trans. Thus, the Sap transporter plays a role in resistance of H. ducreyi to LL-37. We next compared mutant strain 35000HPsapA with strain 35000HP for their ability to cause disease in human volunteers. Although both strains caused papules to form at similar rates, the pustule formation rate at sites inoculated with 35000HPsapA was significantly lower than that of sites inoculated with 35000HP (33.3% versus 66.7%; P = 0.007). Together, these data establish that SapA acts as a virulence factor and as one mechanism for H. ducreyi to resist killing by antimicrobial peptides. To our knowledge, this is the first demonstration that an antimicrobial peptide resistance mechanism contributes to bacterial virulence in humans.

CCR6 ligands inhibit HIV by inducing APOBEC3G

We have identified a post-entry CCR6-dependent mechanism of inhibition of HIV occurring at an early stage of infection mediated by the induction of the host restriction factor apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G). We observed induction of APOBEC3G expression only in CCR6(+) cells but not in cells treated with the G inhibitory (Gi) pathway inhibitor pertussis toxin. CCR6 is highly expressed on peripheral blood CD4(+)CCR5(+) memory T cells and by 2 populations of CD4(+) T cells within the gut, alpha4beta7(+) and T helper type 17, that have been implicated in cell-to-cell spread of HIV and enhanced restoration of CD4(+) T cells within gut-associated lymphoid tissue, respectively. This novel CCR6-mediated mechanism of inhibition allows the identification of pathways that induce intrinsic immunity to HIV, which could be useful in devising novel therapeutics that selectively target CCR6(+) cells.

The roles of antimicrobial peptides in innate host defense

Antimicrobial peptides (AMPs) are multi-functional peptides whose fundamental biological role in vivo has been proposed to be the elimination of pathogenic microorganisms, including Gram-positive and -negative bacteria, fungi, and viruses. Genes encoding these peptides are expressed in a variety of cells in the host, including circulating phagocytic cells and mucosal epithelial cells, demonstrating a wide range of utility in the innate immune system. Expression of these genes is tightly regulated; they are induced by pathogens and cytokines as part of the host defense response, and they can be suppressed by bacterial virulence factors and environmental factors which can lead to increased susceptibility to infection. New research has also cast light on alternative functionalities, including immunomodulatory activities, which are related to their unique structural characteristics. These peptides represent not only an important component of innate host defense against microbial colonization and a link between innate and adaptive immunity, but also form a foundation for the development of new therapeutic agents.

Genomic copy number variation, human health, and disease

Despite the long recognised effects of chromosomal structural abnormalities and completion of the Human Genome Project, much of the structural variation in the genome has gone unrecognised until recently. Deletions and duplications of DNA strands of between a few hundred bp and several million bp-collectively referred to as copy number variants-are now known to be widespread. Since 2007, rigorous and adequately powered genome-wide association studies based on single nucleotide polymorphisms have yielded replicated associations to several common diseases. Some copy number variants explain rare, previously uncharacterised disorders, and they are now expected to explain some of the genetic contribution to common diseases. We review efforts to map copy number variants and discuss present and future prospects for assessment of their relation to human health and disease.

Defensin-related peptide 1 (Defr1) is allelic to Defb8 and chemoattracts immature DC and CD4+ T cells independently of CCR6

β-Defensins comprise a family of cationic, antimicrobial and chemoattractant peptides. The six cysteine canonical motif is retained throughout evolution and the disulphide connectivities stabilise the conserved monomer structure. A murine β-defensin gene (Defr1) present in the main defensin cluster of C57B1/6 mice, encodes a peptide with only five of the canonical six cysteine residues. In other inbred strains of mice, the allele encodes Defb8, which has the six cysteine motif. We show here that in common with six cysteine β-defensins, defensin-related peptide 1 (Defr1) displays chemoattractant activity for CD4⁺ T cells and immature DC (iDC), but not mature DC cells or neutrophils. Murine Defb2 replicates this pattern of attraction. Defb8 is also able to attract iDC but not mature DC. Synthetic analogues of Defr1 with the six cysteines restored (Defr1 Y5C) or with only a single cysteine (Defr1-1c^V) chemoattract CD4⁺ T cells with reduced activity, but do not chemoattract DC. β-Defensins have previously been shown to attract iDC through CC receptor 6 (CCR6) but neither Defr1 or its related peptides nor Defb8, chemoattract cells overexpressing CCR6. Thus, we demonstrate that the canonical six cysteines of β-defensins are not required for the chemoattractant activity of Defr1 and that neither Defr1 nor the six cysteine polymorphic variant allele Defb8, act through CCR6.

Novel partners of SPAG11B isoform D in the human male reproductive tract

Human sperm-associated antigen 11 (SPAG11) is closely related to beta-defensins in structure, expression, and function. Like the beta-defensins, SPAG11 proteins are predominantly expressed in the male reproductive tract, where their best-known major roles are in innate host defense and reproduction. Although several hypotheses have emerged to describe the evolution of beta-defensin and SPAG11 multifunctionality, few describe these multiple functions in terms of defensin interactions with specific proteins. To gain insight into the protein interaction potentials of SPAG11 and the signaling pathways that SPAG11 may influence, we used a yeast two-hybrid screening of a human testis-epididymis library. The results reveal human SPAG11B isoform D (SPAG11B/D) interactions with tryptase alpha/beta 1 (TPSAB1), tetraspanin 7 (TSPAN7), and attractin (ATRN). These interactions were confirmed by coimmunoprecipitation and glutathione S-transferase affinity matrix binding. SPAG11B/D and the three interacting proteins are expressed in the proximal epididymis, and all function in immunity and fertility pathways. We analyzed the functional consequences of SPAG11B/D interaction with TPSAB1 and showed that SPAG11B/D is both a substrate and a potent inhibitor of TPSAB1 activity. Furthermore, we show that (like SPAG11B/D) TSPAN7 and ATRN are associated with spermatozoa.

Beta-defensin-2 protein is a serum biomarker for disease activity in psoriasis and reaches biologically relevant concentrations in lesional skin

BACKGROUND

Previous studies have extensively documented antimicrobial and chemotactic activities of beta-defensins. Human beta-defensin-2 (hBD-2) is strongly expressed in lesional psoriatic epidermis, and recently we have shown that high beta-defensin genomic copy number is associated with psoriasis susceptibility. It is not known, however, if biologically and pathophysiologically relevant concentrations of hBD-2 protein are present in vivo, which could support an antimicrobial and proinflammatory role of beta-defensins in lesional psoriatic epidermis.

METHODOLOGY/PRINCIPAL FINDINGS

We found that systemic levels of hBD-2 showed a weak but significant correlation with beta defensin copy number in healthy controls but not in psoriasis patients with active disease. In psoriasis patients but not in atopic dermatitis patients, we found high systemic hBD-2 levels that strongly correlated with disease activity as assessed by the PASI score. Our findings suggest that systemic levels in psoriasis are largely determined by secretion from involved skin and not by genomic copy number. Modelling of the in vivo epidermal hBD-2 concentration based on the secretion rate in a reconstructed skin model for psoriatic epidermis provides evidence that epidermal hBD-2 levels in vivo are probably well above the concentrations required for in vitro antimicrobial and chemokine-like effects.

CONCLUSIONS/SIGNIFICANCE

Serum hBD-2 appears to be a useful surrogate marker for disease activity in psoriasis. The discrepancy between hBD-2 levels in psoriasis and atopic dermatitis could explain the well known differences in infection rate between these two diseases.

Alarmins and antimicrobial immunity

Alarmins are endogenous mediators capable of enhancing innate and adaptive immune response through induction of concomitant recruitment and activation of antigen-presenting cells. Here we provide a brief overview of various alarmins, highlight their critical roles in innate and adaptive antimicrobial immunity, and speculate on potential usage of alarmins in combating aspergillosis.

CCR6 regulation of the actin cytoskeleton orchestrates human beta defensin-2- and CCL20-mediated restitution of colonic epithelial cells

Intestinal inflammation is exacerbated by defects in the epithelial barrier and subsequent infiltration of microbes and toxins into the underlying mucosa. Production of chemokines and antimicrobial peptides by an intact epithelium provide the first line of defense against invading organisms. In addition to its antimicrobial actions, human beta defensin-2 (HBD2) may also stimulate the migration of dendritic cells through binding the chemokine receptor CCR6. As human colonic epithelium expresses CCR6, we investigated the potential of HBD2 to stimulate intestinal epithelial migration. Using polarized human intestinal Caco2 and T84 cells and non-transformed IEC6 cells, HBD2 was equipotent to CCL20 in stimulating migration. Neutralizing antibodies confirmed HBD2 and CCL20 engagement to CCR6 were sufficient to induce epithelial cell migration. Consistent with restitution, motogenic concentrations of HBD2 and CCL20 did not induce proliferation. Stimulation with those CCR6 ligands leads to calcium mobilization and elevated active RhoA, phosphorylated myosin light chain, and F-actin accumulation. HBD2 and CCL20 were unable to stimulate migration in the presence of either Rho-kinase or phosphoinositide 3-kinase inhibitors or an intracellular calcium chelator. Together, these data indicate that the canonical wound healing regulatory pathway, along with calcium mobilization, regulates CCR6-directed epithelial cell migration. These findings expand the mechanistic role for chemokines and HBD2 in mucosal inflammation to include immunocyte trafficking and killing of microbes with the concomitant activation of restitutive migration and barrier repair.

Antimicrobial human beta-defensin-2 stimulates migration, proliferation and tube formation of human umbilical vein endothelial cells

Human beta-defensin-2 (hBD-2) is an antimicrobial peptide which is released upon microbial invasion and contributes to mucosal and epithelial defense modulating both innate and adaptive immunity. We found that hBD-2 stimulates chemotaxis of human endothelial cells with an extent similar to that exerted by the vascular endothelial growth factor (VEGF). The hBD-2-dependent chemotaxis is dose-dependent, maximal effect being reached at 500 ng/ml concentration. In the absence of any growth factor, hBD-2 favors wound healing of endothelial cells, causing an about 2-fold increase in the speed of wound closure with respect to the control. Furthermore, hBD-2 promotes endothelial cell proliferation, although at a minor extent as compared to VEGF. When plated on matrigel enriched with angiogenic factors, endothelial cells form a three-dimensional network of tubes that gives rise to capillary-like structures. Similarly to VEGF, hBD-2 promotes capillary-like tube formation of human endothelial cells. Pro-angiogenic effect promoted by hBD-2 is dose-dependent, peaks at a 500 ng/ml hBD-2 concentration and is prevented by blocking anti-alphavbeta3 monoclonal antibody. However, hBD-2-induced pro-angiogenic activity is not due to endogenously produced VEGF because it is not prevented by neutralizing anti-VEGF antibodies. Overall, our findings suggest that hBD-2 could link inflammation and the host defense through its pro-angiogenic activity.

Allelic recombination between distinct genomic locations generates copy number diversity in human beta-defensins

Beta-defensins are small secreted antimicrobial and signaling peptides involved in the innate immune response of vertebrates. In humans, a cluster of at least 7 of these genes shows extensive copy number variation, with a diploid copy number commonly ranging between 2 and 7. Using a genetic mapping approach, we show that this cluster is at not 1 but 2 distinct genomic loci approximately 5 Mb apart on chromosome band 8p23.1, contradicting the most recent genome assembly. We also demonstrate that the predominant mechanism of change in beta-defensin copy number is simple allelic recombination occurring in the interval between the 2 distinct genomic loci for these genes. In 416 meiotic transmissions, we observe 3 events creating a haplotype copy number not found in the parent, equivalent to a germ-line rate of copy number change of approximately 0.7% per gamete. This places it among the fastest-changing copy number variants currently known.

The role of antimicrobial peptides at the ocular surface

Antimicrobial peptides (AMPs) such as defensins and cathelicidins are small peptides with broad-spectrum activity against bacteria, fungi and viruses. In addition, several AMPs modulate mammalian cell behaviours including migration, proliferation and cytokine production. This review describes findings from recent studies showing the presence of various AMPs at the human ocular surface and discusses their mechanism of antimicrobial action and potential non-microbicidal roles. Corneal and conjunctival epithelial cells produce beta-defensins and the cathelicidin LL-37, whereas neutrophils, infiltrating in response to a specific stimulus, supply additional LL-37 as well as alpha-defensins. In vitro studies suggest that LL-37 and human beta-defensin-3 are the most likely to have significant independent antimicrobial activity, while other AMPs may act synergistically to help protect the ocular surface from invading pathogens. Current evidence also supports a role for some AMPs in modulating wound healing responses. Although yet to be brought to fruition, AMPs hold significant potential as therapeutic agents for the prophylaxis and treatment of infection, promotion of wound healing and immune modulation.

Human beta defensin 2 promotes intestinal wound healing in vitro

Limiting microbial threats, maintenance and re-establishment of the mucosal barrier are vital for intestinal homeostasis. Antimicrobial peptides have been recognized as essential defence molecules and decreased expression of these peptides has been attributed to chronic inflammation of the human intestinal mucosa. Recently, pluripotent properties, including stimulation of proliferation and migration have been suggested for a number of antimicrobial peptides. However, it is currently unknown, whether the human beta-defensin 2 (hBD-2) in addition to its known antimicrobial properties has further effects on healing and protection of the intestinal epithelial barrier. Caco-2 and HT-29 cells were stimulated with 0.1-10 microg/ml hBD-2 for 6-72 h. Effects on cell viability and apoptosis were monitored and proliferation was quantified by bromo-deoxyuridine incorporation. Migration was quantified in wounding assays and characterized by immunohistochemistry. Expression of mucins was determined by quantitative PCR and slot-blot analysis. Furthermore, anti-apoptotic capacities of hBD-2 were studied. Over a broad range of concentrations and stimulation periods, hBD-2 was well tolerated by IECs and did not induce apoptosis. hBD-2 significantly increased migration but not proliferation of intestinal epithelial cells. Furthermore, hBD-2 induced cell line specific the expression of mucins 2 and 3 and ameliorated TNF-related apoptosis-inducing ligand (TRAIL) induced apoptosis. In addition to its known antimicrobial properties, hBD-2 might have further protective effects on the intestinal epithelium. Results of this in vitro study suggest, that hBD-2 expression may play a dual role in vivo, i.e. in impaired intestinal barrier function observed in patients with inflammatory bowel disease.

Skin peptides: biological activity and therapeutic opportunities

The skin provides an effective barrier to the loss of body fluids and environmental assault. In addition to the physical barrier provided by the stratum corneum, the skin also contains a chemical barrier consisting of antimicrobial peptides (AMPs), which control microbial growth on the surface. These AMPs also have multiple roles as mediators of inflammation with effects on epithelial and inflammatory cells, influencing cell proliferation, wound healing, cytokine/chemokine production and chemotaxis. This review describes the range of peptides found in the skin, both constitutive and those induced in response to injury. The role these peptides play in normal skin function and in various skin conditions is described. A better understanding of their role in normal and skin disease may offer new strategies in skin disease, dermatology and as cosmeceuticals.

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.