Lactobacillus helveticus Prevents Periodontitis Induced by Aggregatibacter actinomycetemcomitans in Rats by Regulating β-Defensins

Objective

To study the preventive effect of Lactobacillus helveticus (L. helveticus) on periodontitis induced by Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) in rats.

Methods

Eighteen 8-week-old female rats were randomly divided into three groups: Sham group, Trehalose group, and L. helveticus SBT2171 (LH2171) group. We measured the distance of the cementoenamel junction-alveolar bone crest (CEJ-ABC) to evaluate alveolar bone resorption. Hematoxylin-eosin staining was used to observe the histopathological changes of rat hemimaxillary tissues. We detected the expression of β-defensins, tumor necrosis factor-α (TNF-α), interleukin- (IL-) 1β, and IL-6 and the number of A. actinomycetemcomitans in rat gingival tissues by quantitative reverse transcriptase polymerase chain reaction. The levels of IL-1β, IL-6, and TNF-α in rat gingival tissues were also measured by enzyme-linked immunosorbent assay.

Results

Compared with the Trehalose group, the distance of CEJ-ABC was prominently reduced and alveolar bone resorption was notably improved in the LH2171 group. And the infiltration of inflammatory cells in the hemimaxillary tissue decreased obviously, periodontal fibers were arranged neatly, connective tissue small blood vessels proliferated, and the number of A. actinomycetemcomitans reduced significantly in the LH2171 group. In addition, the mRNA expression and release of inflammatory factors in the gingival tissues in the LH2171 group were notably lower than those in the Trehalose group. On the 21st and 36th day, the expression of β-defensins in the gingival tissue of the LH2171 group increased significantly.

Conclusion

L. helveticus improves alveolar bone resorption and increases the expression of β-defensins thereby inhibiting the number of A. actinomycetemcomitans and thus prevents periodontitis.

Human β-defensin 1 Functions as a Tumor Suppressor via ER Stress-triggered JNK pathway in Hepatocellular Carcinoma

PURPOSE

Human β-defensin 1 (DEFB1) belongs to defensins family that contribute to innate immune responses and was recently found to downregulate a variety of cancers, including renal, prostatic, and oral squamous cell carcinoma, and therefore is considered as a potential tumor suppressor. However, the role of DEFB1 in hepatocellular carcinoma (HCC) still needs to be elucidated.

METHODS

Quantitative PCR and Western blot were used to measure the expression levels of interested proteins. CCK-8 and colony formation assays were performed to determine the ability of cell proliferation. Tumor formation experiments in nude mice were used to examine the tumor growth.

RESULTS

The expression level of DEFB1 was dramatically downregulated in human HCC. Quantitative PCR and Western blot results also showed a pronounced decrease of DEFB1 expression in the liver cancer cell lines. Rescuing the expression of DEFB1 in Huh7 cells effectively suppressed cell proliferation and reduced the colony forming ability, probably by inducing cell apoptosis and cell cycle arrest. Moreover, tumor formation experiments in nude mice also showed inhibition of tumor growth by DEFB1 expression in vivo. Furthermore, induction of DEFB1 expression induced degraded protein increase and endoplasmic reticulum (ER) stress, which subsequently activated JNK pathway. Pharmacologic inhibition of ER stress by 4-phenylbutyrate, a compound to alleviate ER stress, effectively eliminated DEFB1-induction inhibition of cell proliferation and migration.

CONCLUSION

DEFB1 functions as a tumor suppressor in HCC through activating ER stress and JNK pathway, which may provide a potential strategy for HCC treatment.

Functional Insights From the Evolutionary Diversification of Big Defensins

Big defensins are antimicrobial polypeptides believed to be the ancestors of β-defensins, the most evolutionary conserved family of host defense peptides (HDPs) in vertebrates. Nevertheless, big defensins underwent several independent gene loss events during animal evolution, being only retained in a limited number of phylogenetically distant invertebrates. Here, we explore the evolutionary history of this fascinating HDP family and investigate its patchy distribution in extant metazoans. We highlight the presence of big defensins in various classes of lophotrochozoans, as well as in a few arthropods and basal chordates (amphioxus), mostly adapted to life in marine environments. Bivalve mollusks often display an expanded repertoire of big defensin sequences, which appear to be the product of independent lineage-specific gene tandem duplications, followed by a rapid molecular diversification of newly acquired gene copies. This ongoing evolutionary process could underpin the simultaneous presence of canonical big defensins and non-canonical (β-defensin-like) sequences in some species. The big defensin genes of mussels and oysters, two species target of in-depth studies, are subjected to gene presence/absence variation (PAV), i.e., they can be present or absent in the genomes of different individuals. Moreover, big defensins follow different patterns of gene expression within a given species and respond differently to microbial challenges, suggesting functional divergence. Consistently, current structural data show that big defensin sequence diversity affects the 3D structure and biophysical properties of these polypeptides. We discuss here the role of the N-terminal hydrophobic domain, lost during evolution toward β-defensins, in the big defensin stability to high salt concentrations and its mechanism of action. Finally, we discuss the potential of big defensins as markers for animal health and for the nature-based design of novel therapeutics active at high salt concentrations.

Targeted inactivation of the mouse epididymal beta-defensin 41 alters sperm flagellar beat pattern and zona pellucida binding

During epididymal maturation, sperm acquire the ability to swim progressively by interacting with proteins secreted by the epididymal epithelium. Beta-defensin proteins, expressed in the epididymis, continue to regulate sperm motility during capacitation and hyperactivation in the female reproductive tract. We characterized the mouse beta-defensin 41 (DEFB41), by generating a mouse model with iCre recombinase inserted into the first exon of the gene. The homozygous Defb41(iCre/iCre) knock-in mice lacked Defb41 expression and displayed iCre recombinase activity in the principal cells of the proximal epididymis. Heterozygous Defb41(iCre/+) mice can be used to generate epididymis specific conditional knock-out mouse models. Homozygous Defb41(iCre/iCre) sperm displayed a defect in sperm motility with the flagella primarily bending in the pro-hook conformation while capacitated wild-type sperm more often displayed the anti-hook conformation. This led to a reduced straight line motility of Defb41(iCre/iCre) sperm and weaker binding to the oocyte. Thus, DEFB41 is required for proper sperm maturation.

Why do we study animal toxins?

Venom (toxins) is an important trait evolved along the evolutionary tree of animals. Our knowledges on venoms, such as their origins and loss, the biological relevance and the coevolutionary patterns with other organisms are greatly helpful in understanding many fundamental biological questions, i.e., the environmental adaptation and survival competition, the evolution shaped development and balance of venoms, and the sophisticated correlations among venom, immunity, body power, intelligence, their genetic basis, inherent association, as well as the cost-benefit and trade-offs of biological economy. Lethal animal envenomation can be found worldwide. However, from foe to friend, toxin studies have led lots of important discoveries and exciting avenues in deciphering and fighting human diseases, including the works awarded the Nobel Prize and lots of key clinic therapeutics. According to our survey, so far, only less than 0.1% of the toxins of the venomous animals in China have been explored. We emphasize on the similarities shared by venom and immune systems, as well as the studies of toxin knowledge-based physiological toxin-like proteins/peptides (TLPs). We propose the natural pairing hypothesis. Evolution links toxins with humans. Our mission is to find out the right natural pairings and interactions of our body elements with toxins, and with endogenous toxin-like molecules. Although, in nature, toxins may endanger human lives, but from a philosophical point of view, knowing them well is an effective way to better understand ourselves. So, this is why we study toxins.

Role of urinary cathelicidin LL-37 and human β-defensin 1 in uncomplicated Escherichia coli urinary tract infections

Cathelicidin (LL-37) and human β-defensin 1 (hBD-1) are important components of the innate defense in the urinary tract. The aim of this study was to characterize whether these peptides are important for developing uncomplicated Escherichia coli urinary tract infections (UTIs). This was investigated by comparing urinary peptide levels of UTI patients during and after infection to those of controls, as well as characterizing the fecal flora of participants with respect to susceptibility to LL-37 and in vivo virulence. Forty-seven UTI patients and 50 controls who had never had a UTI were included. Participants were otherwise healthy, premenopausal, adult women. LL-37 MIC levels were compared for fecal E. coli clones from patients and controls and were also compared based on phylotypes (A, B1, B2, and D). In vivo virulence was investigated in the murine UTI model by use of selected fecal isolates from patients and controls. On average, UTI patients had significantly more LL-37 in urine during infection than postinfection, and patient LL-37 levels postinfection were significantly lower than those of controls. hBD-1 showed similar urine levels for UTI patients and controls. Fecal E. coli isolates from controls had higher LL-37 susceptibility than fecal and UTI E. coli isolates from UTI patients. In vivo studies showed a high level of virulence of fecal E. coli isolates from both patients and controls and showed no difference in virulence correlated with the LL-37 MIC level. The results indicate that the concentration of LL-37 in the urinary tract and low susceptibility to LL-37 may increase the likelihood of UTI in a complex interplay between host and pathogen attributes.

Human beta-defensin-1 suppresses tumor migration and invasion and is an independent predictor for survival of oral squamous cell carcinoma patients

Background

Human beta-defensin-1 (hBD-1) has recently been considered as a candidate tumor suppressor in renal and prostate cancer. The aim of this study was to investigate the role of hBD-1 in the progression of oral squamous cell carcinoma (OSCC) and its potential as diagnostic/prognostic biomarker and therapeutic target for OSCC.

Methods

HBD-1 expression in tissues at different stages of oral carcinogenesis, as well as OSCC cell lines was examined. HBD-1 was overexpressed in HSC-3, UM1, SCC-9 and SCC-25 cells and subjected to cell growth, apoptosis, migration and invasion assays. Tissue microarray constructed with tissues from 175 patients was used to examine clinicopathological significance of hBD-1 expression in OSCC.

Results

HBD-1 expression decreased from oral precancerous lesions to OSCC and was lower in OSCC with lymph node metastasis than those without metastasis. In vitro, the expression of hBD-1 was related to the invasive potential of OSCC cell lines. Induction of exogenous expression of hBD-1 inhibited migration and invasion of OSCC cells, probably by regulation of RhoA, RhoC and MMP-2; but had no significant effect on proliferation or apoptosis. In a cohort of patients with primary OSCC, cases with no expression of hBD-1 had more chance to be involved in lymph node metastasis. Eventually, the positive expression of hBD-1 was associated with longer survival of patients with OSCC, and multivariate analysis and ROC curve analysis confirmed hBD-1 positivity to be an independent prognostic factor of OSCC, especially OSCC at early stage.

Conclusions

Overall, these data indicated that hBD-1 suppressed tumor migration and invasion of OSCC and was likely to be a prognostic biomarker and a potential target for treatment of OSCC.

Antiviral mechanisms of human defensins

Defensins are an effector component of the innate immune system with broad antimicrobial activity. Humans express two types of defensins, α- and β-defensins, which have antiviral activity against both enveloped and non-enveloped viruses. The diversity of defensin-sensitive viral species reflects a multitude of antiviral mechanisms. These include direct defensin targeting of viral envelopes, glycoproteins, and capsids in addition to inhibition of viral fusion and post-entry neutralization. Binding and modulation of host cell surface receptors and disruption of intracellular signaling by defensins can also inhibit viral replication. In addition, defensins can function as chemokines to augment and alter adaptive immune responses, revealing an indirect antiviral mechanism. Nonetheless, many questions regarding the antiviral activities of defensins remain. Although significant mechanistic data are known for α-defensins, molecular details for β-defensin inhibition are mostly lacking. Importantly, the role of defensin antiviral activity in vivo has not been addressed due to the lack of a complete defensin knockout model. Overall, the antiviral activity of defensins is well established as are the variety of mechanisms by which defensins achieve this inhibition; however, additional research is needed to fully understand the role of defensins in viral pathogenesis.

Innate immunity as orchestrator of bone marrow homing for hematopoietic stem/progenitor cells

The first step that precedes hematopoietic transplantation is elimination of pathological hematopoiesis by administration of myeloablative doses of radiochemotherapy. This eliminates hematolymphopoietic cells and at the same time damages hematopoietic microenvironment in bone marrow (BM). The damage of BM tissue leads to activation of complement cascade (CC), and bioactive CC cleavage fragments modulate several steps of BM recovery after transplantation of hematopoietic stem progenitor cells (HSPCs). Accordingly, C3 cleavage fragments (soluble C3a/desArgC3a and solid phase iC3b) and generation of soluble form of C5b-C9 also known as membrane attack complex (MAC) as well as release of antimicrobial cationic peptides from stromal cells (cathelicidin or LL-37 and beta-2 defensin) promote homing of HSPCs. To support this, C3 cleavage fragments and antimicrobial cationic peptides increase homing responsiveness of transplanted HSPCs to stroma-derived factor-1 (SDF-1) gradient. Furthermore, damaged BM cells release several other chemoattractants for HSPCs such as bioactive lipids sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P) and chemotactic purines (ATP and UTP). In this chapter, we will discuss the current view on homing of transplanted HSPCs into BM that in addition to SDF-1 is orchestrated by CC, antimicrobial cationic peptides, and several other prohoming factors. We also propose modulation of CC as a novel strategy to optimize/accelerate homing of HSPCs.

Human antimicrobial peptides LL-37 and human β-defensin-2 reduce viral replication in keratinocytes infected with varicella zoster virus

BACKGROUND

There is mounting evidence that antimicrobial peptides have an important role in cutaneous defence, but the expression of these antimicrobial peptides in atopic eczema (AE) is still unclear. There are several families of antimicrobial peptides, including cathelicidins and human β-defensins. Patients with AE are more susceptible to severe cutaneous viral infections, including varicella zoster virus (VZV).

AIM

To characterize the functional activity of the antimicrobial peptides LL-37 (human cathelicidin) and human β-defensin (hBD)-2 keratinocytes were infected with VZV, in a skin-infection model.

METHODS

Flow-cytometry analysis was used to investigate LL-37 expression in normal human keratinocytes, and quantitative PCR was used to determine viral loads in infected HaCaT keratinocytes and B cells, with and without exogenous LL-37 and hBD-2.

RESULTS

LL-37 expression was present in keratinocytes, and both exogenous LL-37 and hBD-2 significantly reduced VZV load in infected keratinocytes and B cells. Specific antibodies blocked the antiviral action exhibited by these antimicrobial peptides. Pre-incubation of VZV with LL-37, but not hBD-2, further reduced VZV load.

CONCLUSIONS

Both LL-37 and hBD-2 have an antiviral effect on VZV replication in the keratinocyte HaCaT cell line and in B cells, but their mechanism of action is different. Evidence of the relationship between antimicrobial peptide expression and higher susceptibility to infections in AE skin is still emerging. Developing novel antiviral therapies based on antimicrobial peptides may provide improved treatment options for patients with AE.

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.

Cationic amino acid transporters and beta-defensins in dry eye syndrome

Several diseases concomitant with L-arginine deficiency (diabetes, chronic kidney failure, psoriasis) are significantly associated with dry eye syndrome. One important factor that has so far been neglected is the y(+) transporter. In humans, y(+) accounts for nearly 80% of arginine transport, exclusively carrying the cationic amino acids L-arginine, L-lysine and L-ornithine. y(+) is represented by CAT(cationic amino acid transporter) proteins. L-arginine is a precursor of the moisturizer urea, which has been used in the treatment of dry skin diseases. Although urea has also been shown to be part of the tear film, little attention has been paid to it in this role. Moreover, L-arginine and L-lysine are major components contributing to synthesis of the antimicrobially active beta-defensins induced under dry eye conditions. The first results have demonstrated that transport of L-arginine and L-lysine into epithelial cells is limited by the y(+) transporter at the ocular surface.

The expression of human alpha and beta defensin in the endometrium and their effect on implantation

BACKGROUND

Alpha and beta defensins have been isolated from various human tissues and form an important part of the innate immune system. Their role in implantation of the embryo has not yet been studied. This study was designed to detect both alpha and beta defensins in the mid luteal phase endometrium and investigate the correlation between the defensin expression and implantation of the embryo.

METHOD AND RESULTS

An experimental study was designed to detect alpha defensin (HNP1-3) and beta defensin (HBD1) in midluteal phase endometrial samples obtained from women attending the IVF unit at the Liverpool Women's Hospital, UK. Samples were obtained at least two menstrual cycles before IVF treatment was commenced. Immunohistochemical staining was conducted to estimate defensin expression. Some endometrial stromal cells stained positive for HNP1-3 during the midluteal phase. HNP1-3 expression is significantly higher in cases presenting with female factor infertility as compared with purely male factor infertility. A significant increase was not observed in tubal factor or endometriosis when considered separately. Endometrial stromal neutrophils were shown to be the main source of endometrial HNP1-3. HBD1 was the only beta defensin detected by immunochemical staining in the midluteal phase endometrium. The intensity of staining was significantly different in the endometrial stroma, luminal and glandular epithelia. HBD1 expression is not significantly higher in female factor infertility.

CONCLUSION

The study confirmed secretion of HNP1-3 by endometrial stromal neutrophils. Glandular epithelium is the main source of HBD1 expression in the human endometrium. HNP1-3 shows increased expression in female factor infertility. HBD1 expression is not higher in female factor infertility. These defensins do not appear to influence implantation.

Innate Immune Defences in the Human Uterus during Pregnancy

The prevention of uterine infection is critical to appropriate fetal development and term delivery. The innate immune system is one component of the uterine environment and has a role in prevention of uterine infection. Natural antimicrobials are innate immune molecules with anti-bacterial, anti-viral and anti-fungal activity. We discuss two groups of natural antimicrobials in relation to pregnancy: (i) the defensins; and (ii) the whey acidic protein motif containing proteins, secretory leukocyte protease inhibitor (SLPI) and elafin. Human beta-defensins (HBD) 1-3 are expressed by placental and chorion trophoblast, amnion epithelium and decidua in term and preterm pregnancy. Elafin shows a similar pattern of localisation while SLPI is produced only by amnion epithelium and decidua. Evidence suggests that there is aberrant production of some natural antimicrobials in pathologic conditions of pregnancy. In preterm premature rupture of membranes (PPROM) levels of SLPI and elafin are reduced in amniotic fluid and fetal membranes, respectively. Elafin and HBD3 increase in chorioamnionitis and levels of the alpha-defensins, HNP1-3, increase in maternal plasma and amniotic fluid in women affected by microbial invasion of the uterus. In vitro culture studies have suggested a mechanism for increased production of natural antimicrobials in chorioamnionitis. Elafin, SLPI, HBD2 and 3 are all upregulated by inflammatory molecules in cells derived from gestational tissues. In summary, production of natural antimicrobials at key sites within the pregnant uterus suggests an important role in prevention of uterine infection during pregnancy and labour. Aberrant production of these molecules in PPROM and chorioamnionitis suggests that they also have a role in pathologic conditions. In particular, upregulation of these molecules by inflammatory molecules present in chorioamnionitis will ensure a robust response to infection.

Defensins in the immunology of bacterial infections

Defensins are a component of the host response against bacterial infections. Multiple studies suggest a linked upregulation of beta-defensins and pro-inflammatory cytokines expression in various tissues, as well as the possibility of mutual induction. Recent data demonstrate the importance of nucleotide-binding oligomerization proteins for the expression of defensins, and associate low levels of alpha-defensins expression by intestinal Paneth cells with susceptibility to Crohn's disease of the ileum. A novel anti-toxin activity has been identified for several alpha- and theta-defensins, expanding the repertoire of the antimicrobial functions of defensins. It has been shown that bacterial proteins can inactivate the action of defensins, and that pathogen type III secretion systems (T3SS) manipulate defensins expression via T3SS-mediated inhibition of the NF-kappaB pathway.

Characterization and functions of beta defensins in the epididymis

The epididymal beta-defensins have evolved by repeated gene duplication and divergence to encode a family of proteins that provide direct protection against pathogens and also support the male reproductive tract in its primary function. Male tract defensins also facilitate recovery from pathogen attack. The beta-defensins possess ancient conserved sequence and structural features widespread in multi-cellular organisms, suggesting fundamental roles in species survival. Primate SPAG11, the functional fusion of two ancestrally independent beta-defensin genes, produces a large family of alternatively spliced transcripts that are expressed according to tissue-specific and species-specific constraints. The complexity of SPAG11 varies in different branches of mammalian evolution. Interactions of human SPAG11D with host proteins indicate involvement in multiple signaling pathways.

Modification of chicken avian β-defensin-8 at positively selected amino acid sites enhances specific antimicrobial activity

Antimicrobial peptides (AMPs), essential components of innate immunity, are found in a range of phylogenetically diverse species and are thought to act by disrupting the membrane integrity of microbes. In this paper, we used evolutionary signatures to identify sites that are most relevant during the functional evolution of these molecules and introduced amino acid substitutions to improve activity. We first demonstrate that the anti-microbial activity of chicken avian beta-defensin-8, previously known as gallinacin-12, can be significantly increased against Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, Salmonella typhimurium phoP- mutant and Streptococcus pyogenes through targeted amino acid substitutions, which confer increased peptide charge. However, by increasing the AMP charge through amino acid substitutions at sites predicted to be subject to positive selection, antimicrobial activity against Escherichia coli was further increased. In contrast, no further increase in activity was observed against the remaining pathogens. This result suggests that charge-increasing modifications confer increased broad-spectrum activity to an AMP, whilst positive selection at particular sites is involved in directing the antimicrobial response against specific pathogens. Thus, there is potential for the rational design of novel therapeutics based on specifically targeted and modified AMPs.

The changing of the guard: Molecular diversity and rapid evolution of beta-defensins

Defensins are small cationic peptides involved in innate immunity and are components of the first line of defence against invading pathogens. beta-defensins are a subgroup of the defensin family that display a particular cysteine spacing and pattern of intramolecular bonding. These molecules are produced mostly by epithelia lining exposed surfaces and appear to have both antimicrobial and cell signalling functions. The unusually high degree of sequence variation in the mature peptide produced by the paralogous and in some cases orthologous genes implies extensive specialisation and species specific adaptation. Here we review recent functional data that are an important addition to our knowledge of the innate immune response and novel antibiotic design. We also consider the organisation and evolution of the genomic loci harbouring these genes where radical and rapid changes in beta-defensin sequences have been shown to result from the interplay of both positive and negative selection. Consequently these genes provide some unusually clear glimpses of the processes of duplication and specialisation that have shaped the mammalian genome.

Effect of corticosteroids and neuropeptides on the expression of defensins in bovine tracheal epithelial cells

Susceptibility to bacterial pneumonia in cattle is enhanced by stressors such as transportation, weaning, and commingling, which trigger a physiologic stress response resulting in elevated levels of endogenous corticosteroids and catecholamines. To determine the effect of neuroendocrine mediators on the expression of innate defense peptides in the lung, bovine tracheal epithelial cells were exposed to dexamethasone, catecholamines, acetylcholine, or substance P, and then beta-defensin expression was quantified using real-time reverse transcription-PCR. Basal expression of tracheal antimicrobial peptide (TAP) mRNA was not affected by any of the mediators tested. However, induction of TAP expression by lipopolysaccharide was significantly inhibited by pretreatment with dexamethasone. Bronchial biopsy specimens from dexamethasone-treated calves had significantly lower expression of TAP and lingual antimicrobial peptide (LAP) mRNA than saline-treated controls following 48 h of treatment. Lipopolysaccharide-elicited neutrophil recruitment was enhanced in the lungs of dexamethasone-treated calves compared to saline-treated controls. These findings indicate that modulation of epithelial antimicrobial peptide expression is one mechanism through which corticosteroids and stress may impair innate pulmonary defenses.

[Protective effect of recombinant beta-defensin-2 on acute lung injury induced by sepsis in rats]

OBJECTIVE

To explore the protective effect of recombinant beta-defensin-2 (BD2) on acute lung injury induced by sepsis in rats.

METHODS

Recombinant adenovirus carrying an expression cassette of rat BD2 (rBD2) or control adenovirus carrying empty vector was administered intratracheally to Sprague-Dawley rats 48 h before acute lung injury, which was induced by cecal ligation and double puncture (CLP). Histological changes of the lungs and 7-day survival rate were determined.

RESULT

The alveolar damage, interstitial edema, and infiltration of neutrophils were reduced and the survival rate was increased significantly in BD2 group than those in control group (P < 0.05). The CFU of abdominal bacteria was comparable to that in the control rats (P > 0.05).

CONCLUSION

The administration of recombinant BD2 protects lung injury and improves the survival of rats with induced sepsis.

[Effect of recombinant beta-defensin-2 peptide on apoptosis of pulmonary tissue in rats with sepsis]

OBJECTIVE

To investigate the effect of recombinant beta-defensin 2 (BD-2) on the apoptosis of pulmonary tissue in rats with sepsis.

METHODS

Forty-eight SD rats were randomly divided into defensin group and controls. In control group 24 rats received 10(7)PFU adenovirus via trachea intubation. In defensin group 24 rats received 10(7)PFU recombinant adenovirus carrying all expression cassette of rat BD-2 (Ad-rBD2). All rats received cecal ligation and puncture (CLP) to induce sepsis 48 h following the administration of adenovirus. Rats of both groups were sacrificed at 0, 12, 36 and 72 h after CLP; lungs were removed and fixed for Haematoxylin and Eosin (HE) stain. Apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) technique.

RESULT

The apoptosis index (AI) of lung cells increased significantly following CLP in control group,while it was significantly lower in defensin group than that of control group (P<0.05). In addition, a significant alveolar damage, interstitial edema, and infiltration of inflammatory cells were observed in control lungs, while it was less severe in defensin group.

CONCLUSION

Recombinant beta-defensin 2 may reduce the apoptosis of lung cells and attenuate lung injury.

Antimicrobial peptides human beta-defensins stimulate epidermal keratinocyte migration, proliferation and production of proinflammatory cytokines and chemokines

Besides their microbicidal functions, human beta-defensins (hBD) and LL-37 activate different immune and inflammatory cells, and their expression is enhanced in inflamed skin and cutaneous wound sites. To protect against pathogens, the skin produces antimicrobial peptides including hBDs and LL-37. Therefore, the aim of our study was to investigate whether hBDs participate in cutaneous inflammation and wound healing by inducing keratinocyte migration, proliferation, and production of proinflammatory cytokines/chemokines. We found that hBD-2, -3, and -4 but not hBD-1 stimulated human keratinocytes to increase their gene expression and protein production of IL-6, IL-10, IP-10, monocyte chemoattractant protein-1, macrophage inflammatory protein-3alpha, and RANTES. This stimulatory effect was markedly suppressed by pertussis toxin and U-73122, inhibitors for G protein and phospholipase C, respectively. We also demonstrated that hBDs elicited intracellular Ca2+ mobilization, and increased keratinocyte migration, and proliferation. In addition, these peptides induced phosphorylation of EGFR, signal transducer and activator of transcription (STAT)1, and STAT3, which are intracellular signaling molecules involved in keratinocyte migration and proliferation. In our study, inhibition of these molecules significantly reduced hBD-mediated keratinocyte migration and proliferation. In conclusion, this study provides evidence that human antimicrobial peptides may be involved in skin immunity through stimulating cytokine/chemokine production, and participate in wound healing by promoting keratinocyte migration and proliferation.

Cutting edge: human beta defensin 3--a novel antagonist of the HIV-1 coreceptor CXCR4

Previously, we showed that human epithelial cell-derived beta-defensins (hBD)-2 and -3 block HIV-1 replication via a direct interaction with virions and through modulation of the CXCR4 coreceptor on immunocompetent cells. In the present study, we show that hBD-3 promotes directly the internalization of CXCR4 yet does not induce calcium flux, ERK (ERK-1/2) phosphorylation, or chemotaxis. hBD-3 competes with stromal-derived factor 1 (SDF-1), the natural ligand for CXCR4, for cellular binding and blocks SDF-1-induced calcium flux, ERK-1/2 phosphorylation, and chemotaxis, without effects on other G protein-coupled receptors. The novel activity of this endogenous CXCR4 antagonist may provide a new strategy for HIV therapies or immunomodulation. Moreover, since the SDF-1/CXCR4 axis plays an important role in hemopoiesis, neurogenesis, cardiogenesis, and angiogenesis, endogenous agents such as hBD-3 or its derivatives offer a new paradigm in immunoregulatory therapeutics and provide the opportunity to enhance future drug design.

The human beta-defensin-3, an antibacterial peptide with multiple biological functions

A group of interesting molecules called defensins exhibit multiple functions but have been primarily recognized to possess a broad spectrum of antimicrobial activities. Studies have reported two different types of defensins (alpha and beta) from human and animals, a cyclic theta defensin from rhesus, and several defensin-like peptides from plants. There is no amino acid sequence homology between these peptides, but they all contain three Cys-Cys disulfide linkages while the connectivities are different. Human beta-defensin-3 (HbetaD-3) is the most recently discovered member of the host-defense peptide family that has attracted much attention. This molecule is expressed either constitutively or induced upon a challenge, and a growing evidence indicates the involvement of such molecules in adaptive immunity as well. It has been shown to exhibit antibacterial activities towards Gram-negative and Gram-positive bacteria as well as an ability to act as a chemo-attractant. Analysis of NMR structural data suggested a symmetrical dimeric form of this peptide in solution, which consists of three beta strands and a short helix in the N-terminal region. While the disulfide linkages are known to provide the structural stability and stability against proteases, the biological relevance of this dimeric form was contradicted by another biological study. Since there is considerable current interest in developing HbetaD-3 for possible pharmaceutical applications, studies to further our understanding on the determinants of antibacterial activities and immunomodulatory function of HbetaD-3 are considered to be highly significant. The knowledge of its biosynthetic regulation will also help in understanding the role of HbetaD-3 in immunity. This article presents an overview of the expression and regulation of HbetaD-3 in humans, and the structure-function correlations among HbetaD-3 and its modified peptides are discussed emphasizing the functional importance. The future scope for studies on HbetaD-3 and design of short potent antimicrobial peptides, based on the native HbetaD-3 molecule, that do not interfere in the immunomodulatory function is also outlined.

[Effect of human beta defensin 2 on Staphylococcus aureus infection: in vivo study with transgenic mice]

OBJECTIVE

To investigate the effect of human beta defensin 2 (HBD-2) on Staphylococcus aureus infection.

METHODS

A minigene of HBD-2 containing pCMV promoter, full length of HBD-2 cDNA, and BGH polyA tail was generated by PCR amplification and introduced into the fertilized oocytes of C57/ICR hybridized mouse by microinjection. After gestation of 3 - 4 weeks, immunohistochemistry was used to detect the expression of HBD-2 peptide in different tissues of the transgenic young mice. Staphylococcus aureus was cultured and injected intraperitoneally to wild type mice and transgenic mice to observe their surviving status.

RESULTS

PCR showed that the HBD-2 fragment had been successfully integrated into the chromosome of the mice. A widespread expression of HBD-2 gene was found in many tissues of the transgenic mice: trachea, lung, intestine, esophagus, testis, spleen, skin, endothelium, brain, etc. Four of the 7 transgenic mice survived the Staphylococcus aureus infection, and 10 wild type mice all died within 24 hours.

CONCLUSION

HBD-2 may play an important role ion the host defense against Staphylococcus aureus infection.

The novel beta-defensin DEFB123 prevents lipopolysaccharide-mediated effects in vitro and in vivo

Defensins are a family of secreted antimicrobial peptides proposed to directly interfere with bacterial membranes. Here we show a functional analysis of the novel beta-defensin DEFB123. A peptide comprising the beta-defensin core region was synthesized and used for our analysis. Like other beta-defensins, DEFB123 exerted antimicrobial activity against a broad spectrum of Gram-positive and Gram-negative bacteria, which was assessed by microbroth dilution assay and radial diffusion zone assay. In addition, the peptide showed lipopolysaccharide (LPS)-binding activity in a Limulus amoebocyte lysate (LAL) assay. Moreover, DEFB123 prevented LPS-induced tumor necrosis factor (TNF)-alpha secretion in a murine monocyte cell line (RAW264.7). Accordingly, DEFB123 abolished LPS-mediated MAPK induction in these cells. Protection against LPS-mediated effects was then investigated in a murine model of acute sepsis. Our experiments show that synthetic beta-defensin DEFB123 prevents LPS-induced mortality in C57BL/6 mice in a therapeutic approach. We propose that the physiological role of beta-defensins may include interference with LPS-action on macrophages, a function formerly thought to be restricted to the family of cathelicidins, a structurally unrelated group of antimicrobial peptides.

Innate immune defects in atopic dermatitis

Atopic dermatitis (AD) is a common, chronic inflammatory skin disease that becomes clinically apparent in the pediatric population. It is well recognized that subjects with AD have an increased susceptibility to cutaneous colonization and infection with bacteria, fungi, and viruses. The notion that subjects with AD have a cutaneous immune defect has received widespread acceptance, and several plausible explanations for this have been proposed. We will review the evidence that this susceptibility to cutaneous infection is at least in part due to a defect in the first line of defense against microbes, namely the innate immune system.

Contribution of alpha- and beta-defensins to lung function decline and infection in smokers: an association study

Background

Alpha-defensins, which are major constituents of neutrophil azurophilic granules, and beta-defensins, which are expressed in airway epithelial cells, could contribute to the pathogenesis of chronic obstructive pulmonary disease by amplifying cigarette smoke-induced and infection-induced inflammatory reactions leading to lung injury. In Japanese and Chinese populations, two different beta-defensin-1 polymorphisms have been associated with chronic obstructive pulmonary disease phenotypes. We conducted population-based association studies to test whether alpha-defensin and beta-defensin polymorphisms influenced smokers' susceptibility to lung function decline and susceptibility to lower respiratory infection in two groups of white participants in the Lung Health Study (275 = fast decline in lung function and 304 = no decline in lung function).

Methods

Subjects were genotyped for the alpha-defensin-1/alpha-defensin-3 copy number polymorphism and four beta-defensin-1 polymorphisms (G-20A, C-44G, G-52A and Val38Ile).

Results

There were no associations between individual polymorphisms or imputed haplotypes and rate of decline in lung function or susceptibility to infection.

Conclusion

These findings suggest that, in a white population, the defensin polymorphisms tested may not be of importance in determining who develops abnormally rapid lung function decline or is susceptible to developing lower respiratory infections.

The host defense peptide beta-defensin 1 confers protection against Bordetella pertussis in newborn piglets

Innate immunity plays an important role in protection against respiratory infections in humans and animals. Host defense peptides such as beta-defensins represent major components of innate immunity. We recently developed a novel porcine model of pertussis, an important respiratory disease of young children and infants worldwide. Here, we investigated the role of porcine beta-defensin 1 (pBD-1), a porcine defensin homologue of human beta-defensin 2, in conferring protection against respiratory infection with Bordetella pertussis. In this model, newborn piglets were fully susceptible to infection and developed severe bronchopneumonia. In contrast, piglets older than 4 weeks of age were protected against infection with B. pertussis. Protection was associated with the expression of pBD-1 in the upper respiratory tract. In fact, pBD-1 expression was developmentally regulated, and the absence of pBD-1 was thought to contribute to the increased susceptibility of newborn piglets to infection with B. pertussis. Bronchoalveolar lavage specimens collected from older animals as well as chemically synthesized pBD-1 displayed strong antimicrobial activity against B. pertussis in vitro. Furthermore, in vivo treatment of newborn piglets with only 500 mug pBD-1 at the time of challenge conferred protection against infection with B. pertussis. Interestingly, pBD-1 displayed no bactericidal activity in vitro against Bordetella bronchiseptica, a closely related natural pathogen of pigs. Our results demonstrate that host defense peptides play an important role in protection against pertussis and are essential in modulating innate immune responses against respiratory infections.

Lipid-Specific Membrane Activity of Human β-Defensin-3

Defensins represent a major component of innate host defense against bacteria, fungi, and enveloped viruses. One potent defensin found, e.g., in epithelia, is the polycationic human beta-defensin-3 (hBD3). We investigated the role of the lipid matrix composition, and in particular the presence of negatively charged lipopolysaccharides (LPS) from sensitive (Escherichia coli, Salmonella enterica serovar Minnesota) or resistant (Proteus mirabilis) Gram-negative bacteria or of the zwitterionic phospholipids of human cells, in determining the action of polycationic hBD3 on the different membranes, and related to their biological activity. The main focus was directed on data derived from electrical measurements on a reconstitution system of the OM as a planar asymmetric bilayer composed on one side of LPS and on the other of a phospholipid mixture. Our results demonstrate that the antimicrobial activity and the absence of cytotoxicity can be explained by the lipid-specificity of the peptide. A clear correlation between these aspects of the biological activity of hBD3 and its interaction with lipid matrices could be found. In particular, hBD3 could only induce lesions in those membranes resembling the lipid composition of the OM of sensitive bacterial strains. The permeation through the membrane is a decisive first step for the biological activity of many antimicrobial peptides. Therefore, we propose that the lipid-specificity of hBD3 as well as some other membrane-active antimicrobial peptides is important for their activity against bacteria or mammalian cells.

[Disturbances of antimicrobial lipids in atopic dermatitis]

Patients with atopic dermatitis exhibit an increased susceptibility to cutaneous infections, especially to pathological colonization with superantigen-secreting Staphylococcus aureus. Recent attention has been focused on antimicrobial peptides, especially on cathelicidin and human beta-defensin-2, which are under-expressed in atopic skin. Antimicrobial lipids from the stratum corneum are also major contributors to cutaneous antimicrobial defense. Current aspects of biochemistry and function of antimicrobial lipids in atopic dermatitis are reviewed in detail. The major classes of stratum corneum lipids with antimicrobial activity are free fatty acids, glucosylceramides, and free sphingosines. Diminished levels of free sphingosines in the stratum corneum have recently been detected in atopic dermatitis and have been associated with the pathological colonization of atopic skin with Staphylococcus aureus. The superantigen staphylococcal enterotoxin B has been shown to reduce the suppressive effect of regulatory T cells on T-cell proliferation, thus augmenting T-cell activation in patients with atopic dermatitis. The killing of superantigen-secreting bacterial strains with topically applied antimicrobial lipids offers new antiseptic and immunomodulatory options for the treatment and secondary prevention of atopic dermatitis.

Role of human beta-defensins in HIV infection

Mechanisms of resistance to HIV-1 infection in the human oral cavity are incompletely understood. While salivary components have been implicated in protection, there is growing evidence that human beta-defensins (hBDs), originating in oral epithelial cells, may be playing an important role in the prevention of HIV infection. New antiviral, chemotactic, and immunosurveillance properties are being attributed to hBDs, which are small cationic antimicrobial innate response molecules expressed in mucosal epithelium. Inducible hBDs are always expressed in normal oral epithelium, a property not shared by other mucosal barriers. Data reviewed in this paper demonstrate that: (1) HIV-1 X4 and R5 phenotypes induce hBD-2 and -3 mRNA in normal human oral epithelial cells; (2) hBD-2 and -3 inhibit HIV-1 infection by both viral strains, with greater activity against X4 viruses; and (3) this inhibition is due to a direct interaction with virions and through modulation of the CXCR4 co-receptor. These properties may be exploited as strategies for mucosal protection against HIV-1 transmission.

Peptides antimicrobiens naturels cutanés

Human skin is always in contact with the environment and is covered with a characteristic microflora, but it is usually not infected. Although desquamation and secretion of mucus lead to a permanent renewal of these body surfaces and simultaneous elimination of microorganisms adhering to these layers, another reason for this natural resistance might be the existence of a "chemical barrier" consisting in constitutively and inducibly produced antimicrobial peptides and proteins (AMPs), which include some ss-defensins, RNase 7, the S100-protein psoriasin and the cathelicidin LL-37. Most of these AMPs can be induced in vitro in epithelial cells by proinflammatory cytokines or bacteria. In vivo, AMPs are mainly expressed in uppermost and differentiated parts of inflammatory lesions and wounds, but some are also focally expressed in skin in the absence of inflammation, suggesting that apart from inflammatory mediators, also non-inflammatory stimuli of endogenous and/or exogenous origin can stimulate AMP-synthesis. Increased levels of AMPs in psoriatic lesions may explain why psoriasis patients rarely suffer from skin infections. Further, an increased infection rate in atopic dermatitis patients could be the consequence of decreased levels of AMPs in atopic lesions. These observations may indicate an important role of the "chemical skin barrier" in prevention of skin infection and suggest that artificial stimulation of this system, without inflammation, would be beneficial as "immune stimulus".

Toll-like receptor 2 (TLR2) mediates intracellular signalling in human keratinocytes in response to Malassezia furfur

Toll-like receptors (TLRs) are crucial players in the innate immune response to microbial invaders. The lipophilic yeast Malassezia furfur has been implicated in the triggering of scalp lesions in psoriasis. The aim of the present study was to assess the role of TLRs in the defence against M. furfur infection. The expression of the myeloid differentiation factor 88 (MyD88) gene, which is involved in the signalling pathway of many TLRs, was also analysed. In addition, a possible correlation of antimicrobial peptides of the beta-defensin family to TLRs was tested. Human keratinocytes infected with M. furfur and a variety of M. furfur-positive psoriatic skin biopsies were analysed by RT-PCR, for TLRs, MyD88, human beta-defensin 2 (HBD-2), HBD-3 and interleukin-8 (IL-8) mRNA expression. When keratinocytes were infected with M. furfur, an up-regulation for TLR2, MyD88, HBD-2, HBD-3 and IL-8 mRNA was demonstrated, compared to the untreated cells. The same results were obtained when psoriatic skin biopsies were analysed. The M. furfur-induced increase in HBD-2 and IL-8 gene expression is inhibited by anti-TLR2 neutralising antibodies, suggesting that TLR2 is involved in the M. furfur-induced expression of these molecules. These findings suggest the importance of TLRs in skin protection against fungi and the importance of keratinocytes as a component of innate immunity.

Human beta-defensins suppress human immunodeficiency virus infection: potential role in mucosal protection

Beta-defensins are small (3 to 5 kDa in size) secreted antimicrobial and antiviral proteins that are components of innate immunity. Beta-defensins are secreted by epithelial cells, and they are expressed at high levels in several mucosae, including the mouth, where the concentration of these proteins can reach 100 microg/ml. Because of these properties, we wondered whether they could be part of the defenses that lower oral transmission of human immunodeficiency virus (HIV) compared to other mucosal sites. Our data show that select beta-defensins, especially human beta-defensin 2 (hBD2) and hBD3, inhibit R5 and X4 HIV infection in a dose-dependent manner at doses that are compatible with or below those measured in the oral cavity. We observed that beta-defensin treatment inhibited accumulation of early products of reverse transcription, as detected by PCR. We could not, however, detect any reproducible inhibition of env-mediated fusion, and we did not observe any modulation of HIV coreceptors following treatment with hBD1 and hBD2, in both resting and phytohemagglutinin-activated cells. Our data instead suggest that, besides a direct inactivation of HIV virions, hBD2 inhibits HIV replication in the intracellular environment. Therefore, we speculate that beta-defensins mediate a novel antiretroviral mechanism that contributes to prevention of oral HIV transmission in the oral cavity. Immunohistochemical data on hBD2 expression in oral mucosal tissue shows that hBD2 is constitutively expressed, forming a barrier layer across the epithelium in healthy subjects, while in HIV-positive subjects levels of hBD2 expression are dramatically diminished. This may predispose HIV-positive subjects to increased incidence of oral complications associated with HIV infection.

Cross-species analysis of the mammalian β-defensin gene family: presence of syntenic gene clusters and preferential expression in the male reproductive tract

Mammalian β-defensins are an important family of innate host defense peptides with pleiotropic activities. As a first step to study the evolutionary relationship and biological role of the β-defensin family, we identified their complete repertoires in the human, chimpanzee, mouse, rat, and dog following systemic, genome-wide computational searches. Although most β-defensin genes are composed of two exons separated by an intron of variable length, some contain an additional one or two exons encoding an internal pro-sequence, a segment of carboxy-terminal mature sequences or untranslated regions. Alternatively, spliced isoforms have also been found with several β-defensins. Furthermore, all β-defensin genes are densely clustered in four to five syntenic chromosomal regions, with each cluster spanning <1.2 Mb across the five species. Phylogenetic analysis indicated that, although the majority of β-defensins are evolutionarily conserved across species, subgroups of gene lineages exist that are specific in certain species, implying that some β-defensins originated after divergence of these mammals from each other, while most others arose before the last common ancestor of mammals. Surprisingly, RT-PCR revealed that all but one rat β-defensin transcript are preferentially expressed in the male reproductive tract, particularly in epididymis and testis, except that Defb4, a human β-defensin-2 ortholog, is more restricted to the respiratory and upper gastrointestinal tracts. Moreover, most β-defensins expressed in the reproductive tract are developmentally regulated, with enhanced expression during sexual maturation. Existence of such a vast array of β-defensins in the male reproductive tract suggests that these genes may play a dual role in both fertility and host defense.

[Chronic inflammatory bowel diseases (IBD): novel pathophysiological concepts and their clinical relevance]

Despite many years of intensive research the pathogenesis of inflammatory bowel diseases is still enigmatic. All efforts to identify the cause of Crohn's disease and ulcerative colitis in a dysregulation of specific immune mechanisms have failed. This review presents a novel pathogenetic concept, based on the expression of natural mucosal antibiotic peptides. These so called defensins are part of innate immunity and defend the mucosa as antimicrobial peptides against intraluminal potentially pathogenic and invasive bacteria. In contrast to ulcerative colitis, Crohn's disease is characterised by a diminished defensin expression. This defect may represent the molecular pathogenesis of this disease.

Investigation of the possibility of human-beta defensin 2 (hBD2) as a molecular marker of gastric mucosal inflammation

BACKGROUND/AIMS

It has previously been reported that human-beta defensin 2 (hBD2) has a physiological role as a proinflammatory mediator in gastric mucosal inflammation as well as an antimicrobial peptide for Helicobacter pylori (Hp). The present study was conducted to evaluate the possibility of hBD2 as a molecular marker of gastric mucosal inflammation.

METHODOLOGY

The subjects were 40 A1 to S2 gastric ulcer patients, with or without Hp infection. Biopsy specimens of the mucosa were obtained endoscopically before and after the administration of lansoprazole (LPZ) (15mg/day) or famotidine (FAM) (40 mg/day or 20 mg/day), consecutively, and each set of samples was divided into two groups; one group was subjected to RT-PCR to assess the expression of hBD2, and the other was subjected to immunohistochemical analysis for evaluating the expression of CD68.

RESULTS

The expression of hBD2 was observed through the stage of gastric ulcer, from A1 to S1, regardless of the presence or absence of Hp infection, both before and after LPZ or FAM administration, and its intensity of expression decreasing as the number of CD68-positive cells decreased. The number of CD68-positive cells deceased as the severity of the ulcer increased from stage A1 to S2, regardless of the presence/absence of Hp infection. CD68-positive cells could hardly be observed in stage S2 gastric ulcers, in which hBD2 expression was also only scarcely noted.

CONCLUSIONS

These results suggested the possibility that hBD2 may be a molecular marker of gastric mucosal inflammation, irrespective of the presence/absence of Hp infection.

The Human β-Defensins (-1, -2, -3, -4) and Cathelicidin LL-37 Induce IL-18 Secretion through p38 and ERK MAPK Activation in Primary Human Keratinocytes

In addition to its physical barrier against invading microorganisms, the skin produces antimicrobial peptides, human beta-defensins (hBDs) and cathelicidin LL-37, that participate in the innate host defense. Because IL-18 is produced by keratinocytes and involved in skin diseases in which hBDs and LL-37 are highly expressed, we hypothesized that these peptides would activate keratinocytes to secrete IL-18. We found that hBD-2, -3, and -4 and LL-37, but not hBD-1, activated normal human keratinocytes to secrete IL-18; this secretion reached peak strength at 3 h. In addition, the combination of peptides resulted in a synergistic effect on IL-18 secretion. We also revealed that hBD-2, -3, and -4 and LL-37 increased IL-18 mRNA expression, and that IL-18 secretion was more enhanced in keratinocytes differentiated in vitro with high Ca2+-containing medium. Furthermore, because IL-18 secretion induced by hBDs and LL-37 could not be suppressed by caspase-1 or caspase family inhibitors, and because these peptides failed to increase caspase-1 activity, we suggest that hBD- and LL-37-induced IL-18 secretion is probably via a caspase-1-independent pathway. To determine the molecular mechanism involved, we demonstrated that IL-18 secretion was through p38 and ERK1/2 MAPK pathways, because the inhibitors of p38 and ERK1/2, but not JNK, almost completely nullified IL-18 secretion. Moreover, hBD-2, -3, and -4 and LL-37 could induce the phosphorylation of p38 and ERK1/2, but not JNK. Thus, the ability of hBDs and LL-37 to induce IL-18 secretion by keratinocytes provides a new mechanism for these peptides in innate immunity and an understanding of their role in the pathogenesis of skin disorders.

Enhanced human beta-defensin-2 (hBD-2) expression by corticosteroids is independent of NF-kappaB in colonic epithelial cells (CaCo2)

Beta-defensins are small cationic peptides with antimicrobial properties that contribute to innate host defense. Unlike human beta-defensin-1 (hBD-1), which is produced constitutively, human beta-defensin-2 (hBD-2) is expressed after adequate stimulation by cytokines and/or bacterial endotoxins in epithelial tissue and mononuclear phagocytes but may be deficient in patients with Crohn's disease. To further elucidate the role of the intestinal epithelium in antimicrobial host defense, gene regulation of hBD-2 and the interaction with NF-kappaB were analyzed in a cell culture model. Human colonic epithelial cells (CaCo2) were stimulated by pro-inflammatory cytokines (IL-1beta, TNF-alpha, IF-gamma) to induce hBD-2 mRNA transcription. Interactions with NF-kappaB were analyzed using specific inhibitors (sulfasalazine, gliotoxine, dexamethasone) at different concentrations. Defensin mRNA expression was quantified by competitive RT-PCR and antibacterial capacity of supernatants was determined by an antimicrobial assay. HBD-2 mRNA transcription and antimicrobial activity of CaCo2 cells were induced by stimulation with pro-inflammatory cytokines. Induction was not inhibited by sulfasalazine or gliotoxine, whereas dexamethasone further enhanced both gene transcription and antimicrobial capacity. The lack of inhibition of induced hBD-2 expression by specific NF-kappaB antagonists suggests an additional pathway of activation, independent of NF-kappaB. The induction of hBD-2 expression in cytokine-stimulated CaCo2 cells by corticosteroids indicates further immunomodulatory ability of steroid hormones not yet understood.

Distinct Strains of Propionibacterium acnes Induce Selective Human β-Defensin-2 and Interleukin-8 Expression in Human Keratinocytes Through Toll-Like Receptors

Acne is a chronic inflammatory disease of the pilosebaceous follicle. One of the main pathogenetic factors in acne is the increased proliferation of Propionibacterium acnes (P. acnes) in the pilosebaceous unit. We investigated whether direct interaction of P. acnes with keratinocytes might be involved in the inflammation and ductal hypercornification in acne. The capacities of different P. acnes strains to activate the innate immune response and the growth of cultured keratinocytes were investigated. We have found that two clinical isolates of P. acnes significantly induced human beta-defensin-2 (hBD2) messenger RNA (mRNA) expression; in contrast a third clinical isolate and the reference strain (ATCC11828) had no effect on hBD2 mRNA expression. In contrast, all four strains significantly induced the interleukin-8 (IL-8) mRNA expression. The P. acnes-induced increase in hBD2 and IL-8 gene expression could be inhibited by anti-Toll-like receptor 2 (TLR2) and anti-TLR4 neutralizing antibodies, suggesting that P. acnes-induced secretion of soluble factors in keratinocytes are both TLR2 and TLR4 dependent. In addition, the clinical isolate P. acnes (889) was capable of inducing keratinocyte cell growth in vitro. Our findings suggest that P. acnes modulates the antimicrobial peptide and chemokine expression of keratinocytes and thereby contributes to the recruitment of inflammatory cells to the sites of infections.

Resistance to human beta-defensins is common among oral treponemes

BACKGROUND/AIMS

Oral treponemes are implicated in the pathogenesis of periodontal disease. We have previously shown that Treponema denticola ATCC type strains and strain GM-1 are resistant to killing by human beta-defensins (hbetaD)-1 and -2. We hypothesize that resistance to beta-defensins is a common feature of oral treponemes, which allows colonization and persistence in the oral cavity. In this study, we tested additional isolates of T. denticola, as well as six other species of treponemes, for resistance to hbetaD-1, -2 and -3. We also examined the four ATCC strains of T. denticola and strain GM-1 for resistance to hbetaD-3.

METHODS

Resistance was determined by motility and Alamar Blue assays for metabolic activity.

RESULTS

All T. denticola strains tested were resistant to hbetaD-1, -2 and -3, with the exception of strain Ambigua, which was sensitive to hbetaD-2 and -3. All other treponemes except Treponema vincentii were resistant to hbetaD-1. Treponema pectinovorum was sensitive to hbetaD-2, while T. vincentii, T. pectinovorum and Treponema maltophilum were sensitive to hbetaD-3. Escherichia coli was used as a control organism and was killed by all three defensins.

CONCLUSION

Resistance to the constitutively expressed hbetaD-1 may assist treponemes in initial colonization of epithelial surfaces, while resistance to the inducible hbetaD-2 and -3 would allow some treponemes to survive in active periodontal lesions.

Activation of Toll-like receptor 2 on human tracheobronchial epithelial cells induces the antimicrobial peptide human beta defensin-2

As pattern recognition receptors capable of eliciting responses to a diverse array of microbial products, Toll-like receptors (TLRs) participate in the activation of host defense mechanisms that protect against infectious pathogens. Given that epithelial cells lie at the interface between the host and its environment, we designed experiments to determine whether human airway epithelial cells express TLRs and respond to TLR agonists. Immunohistochemical labeling of TLR2 in normal human airways revealed TLR2 expression throughout the epithelium, with an apparently higher level of expression on noncolumnar basal epithelial cells. Two-color immunofluorescent labeling of TLR2 and cytokeratins 8 and 15 revealed that TLR2 is coexpressed with the epithelial cell markers. In addition, airway epithelial cells grown at air-liquid interface responded to bacterial lipopeptide in a TLR2-dependent manner with induction of mRNA and protein of the antimicrobial peptide human beta defensin-2. Stimulation of epithelial cell cultures with lipopeptide resulted in a small and variable reduction of bacteria on the apical surface. Together, these data suggest that TLRs monitor epithelial surfaces to enhance host defense by inducing the production of an antimicrobial peptide.

Epithelial cell-derived antibacterial peptides human beta-defensins and cathelicidin: multifunctional activities on mast cells

Antibacterial peptides function as effectors for defense in innate immunity. In mammals, they are implicated in the barrier protection of epithelia where their expression can be induced during infection and inflammation. Over a dozen of antibacterial peptides have been identified in humans. Among these, defensins and cathelicidins have been well characterized. Two types of defensins (alpha- and beta-defensins) are recognized based on the presence of their conserved six cysteine residues, whereas cathelicidins are characterized by a homologous cathelin sequence in the pro-region and a variable antibacterial C-terminal sequence. Human beta-defensins and cathelicidin hCAP18/LL-37 are mainly expressed in epithelial tissues where mast cells are present. Here we review the structure of human beta-defensins and cathelicidin, and describe their multiple activities on mast cells to induce chemotaxis, degranulation and prostaglandin D(2) production, acting through receptors coupled to G-protein-phospholipase C pathway. Thus, in addition to their bactericidal activities, epithelial cell-derived antibacterial peptides may modulate the inflammatory responses by recruiting mast cells to inflammation foci and inducing the degranulation as well as prostaglandin production from this cell population.

ESP13.2, a member of the beta-defensin family, is a macaque sperm surface-coating protein involved in the capacitation process

Female macaques produced isoantibodies to a limited number of sperm surface proteins following immunization with sperm components released by phosphatidylinositol-specific phospholipase C (PI-PLC). Washed, acrosome-intact, fixed sperm injected into rabbits elicited a major immune response to one of the same PI-PLC-released proteins, which was shown to be a sperm surface-coating protein. After purification and digestion of the glycoprotein, four peptides were analyzed for amino acid sequence, and all had 100% homology with an epididymal secretory protein, ESP13.2, reported previously to be a small, cationic-rich peptide and a member of the beta-defensin family. Antibodies to purified ESP13.2 recognized a number of protein bands on Western blots of nonreduced PI-PLC-released sperm components and nonreduced whole-sperm extracts. After chemical disulfide reduction, only a single, broad band from 31 to 35 kDa was recognized by anti-ESP13.2 antibodies. Indirect immunofluorescence showed ESP13.2 over the entire surface of ejaculated macaque sperm. Fluorescence was only slightly reduced after sperm were washed through 80% Percoll. A 24-h incubation in capacitating medium significantly reduced the amount of ESP13.2 over the head and midpiece, whereas exposure of the incubated sperm to dbcAMP and caffeine (capacitation activators) resulted in almost complete loss of ESP13.2 from the sperm surface. After activation, ESP13.2 was the primary component released into the medium as judged electrophoretically. Lignosulfonic acid, a potent inhibitor of macaque fertilization in vitro, completely blocked release of ESP13.2 from the sperm surface, even following treatment with activators. These findings suggest that the beta-defensin, ESP13.2, has a function in the capacitation of macaque spermatozoa and may modulate sperm surface-receptor presentation at the time of fertilization.

Engineering disulfide bridges to dissect antimicrobial and chemotactic activities of human beta-defensin 3

Human defensins form a family of small, cationic, and Cys-rich antimicrobial proteins that play important roles in innate immunity against invading microbes. They also function as effective immune modulators in adaptive immunity by selectively chemoattracting T lymphocytes and immature dendritic cells. On the basis of sequence homology and the connectivity of six conserved Cys residues, human defensins are classified into alpha and beta families. Structures of several beta-defensins have recently been characterized, confirming the disulfide connectivity conserved within the family, i.e., Cys1-Cys5, Cys2-Cys4, and Cys3-Cys6. We found that human beta-defensin 3 (hBD3), a recently described member of the growing beta family, did not fold preferentially into a native conformation in vitro under various oxidative conditions. Using the orthogonal protection of Cys1-Cys5 and of Cys1-Cys6, we chemically synthesized six topological analogs of hBD3 with predefined disulfide connectivities, including the (presumably) native beta pairing. Unexpectedly, all differently folded hBD3 species exhibited similar antimicrobial activity against Escherichia coli, whereas a wide range of chemotactic activities was observed with these analogs for monocytes and cells transfected by the chemokine receptor CCR6. Furthermore, whereas substitution of all Cys residues by alpha-aminobutyric acid completely abolished the chemotactic activity of hBD3, the bactericidal activity remained unaffected in the absence of any disulfide bridge. Our findings demonstrate that disulfide bonding in hBD3, although required for binding and activation of receptors for chemotaxis, is fully dispensable for its antimicrobial function, thus shedding light on the mechanisms of action for human beta-defensins and the design of novel peptide antibiotics.