Dual role of alpha-defensin-1 in anti-HIV-1 innate immunity

UFFizi: a generic platform for ranking informative features

Background

Feature selection is an important pre-processing task in the analysis of complex data. Selecting an appropriate subset of features can improve classification or clustering and lead to better understanding of the data. An important example is that of finding an informative group of genes out of thousands that appear in gene-expression analysis. Numerous supervised methods have been suggested but only a few unsupervised ones exist. Unsupervised Feature Filtering (UFF) is such a method, based on an entropy measure of Singular Value Decomposition (SVD), ranking features and selecting a group of preferred ones.

Results

We analyze the statistical properties of UFF and present an efficient approximation for the calculation of its entropy measure. This allows us to develop a web-tool that implements the UFF algorithm. We propose novel criteria to indicate whether a considered dataset is amenable to feature selection by UFF. Relying on formalism similar to UFF we propose also an Unsupervised Detection of Outliers (UDO) method, providing a novel definition of outliers and producing a measure to rank the "outlier-degree" of an instance.

Our methods are demonstrated on gene and microRNA expression datasets, covering viral infection disease and cancer. We apply UFFizi to select genes from these datasets and discuss their biological and medical relevance.

Conclusions

Statistical properties extracted from the UFF algorithm can distinguish selected features from others. UFFizi is a framework that is based on the UFF algorithm and it is applicable for a wide range of diseases. The framework is also implemented as a web-tool.

The web-tool is available at: http://adios.tau.ac.il/UFFizi

Both copy number and sequence variations affect expression of human DEFB4

Copy number variations (CNVs) were found to contribute massively to the variability of genomes. One of the best studied CNV region is the beta-defensin cluster (DEFB) on 8p23.1. Individual DEFFB copy numbers (CNs) between 2 and 12 were found, whereas low CNs predispose for Crohn's disease. A further level of complexity is represented by sequence variations between copies (multisite variations, MSVs). To address the relation of DEFB CN and MSV to the expression of beta-defensin genes, we analyzed DEFB4 expression in B-lymphoblastoid cell lines (LCLs) and primary keratinocytes (normal human epidermal keratinocyte, NHEK) before and after stimulation with lipopolysaccharide, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). Moreover, we quantified one DEFB4 MSV in DNA and mRNA as a marker for variant-specific expression (VSE) and resequenced a region of approximately 2 kb upstream of DEFB4 in LCLs. We found a strong correlation of DEFB CN and DEFB4 expression in 16 LCLs, although several LCLs with very different CNs exhibit similar expression levels. Quantification of the MSV revealed VSE with consistently lower expression of one variant. Costimulation of NHEKs with TNF-alpha/IFN-gamma leads to a synergistic increase in total DEFB4 expression and suppresses VSE. Analysis of the DEFB4 promoter region showed remarkably high density of sequence variabilities (approximately 1 MSV/41 bp).

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.

Recombinant mouse beta-defensin 2 inhibits infection by influenza A virus by blocking its entry

Human influenza A virus (IAV) is a major cause of life-threatening respiratory tract disease worldwide. Defensins are small cationic peptides of about 2-6 kDa that are known for their broad-spectrum antimicrobial activity. Here, we focused on the anti-influenza A activity of mouse beta-defensin 2 (mBD2). The prokaryotic expression plasmid pET32a-mBD2 was constructed and introduced into Escherichia coli Rosseta gami (2) to produce recombinant mBD2 (rmBD2). Purified rmBD2 showed strong antiviral activity against IAV in vitro. The protective rate for Madin-Darby canine kidney cells was 93.86% at an rmBD2 concentration of 100 microg/ml. Further studies demonstrated that rmBD2 prevents IAV infection by inhibiting viral entry. In addition, both pretreatment and postinfection treatment with rmBD2 provided protection against lethal virus challenge with IAV in experimental mice, with protection rates of 70 and 30%, respectively. These results suggest that the mBD2 might have important effects on influenza A virus invasion.

Increased alpha-defensins 1-3 production by dendritic cells in HIV-infected individuals is associated with slower disease progression

Background

Defensins are natural endogenous antimicrobial peptides with potent anti-HIV activity and immuno-modulatory effects. We recently demonstrated that immature dendritic cells (DC) produce α-defensins1-3 and that α-defensins1-3 modulate DC generation and maturation. Since DC-HIV interaction plays a critical role during the first steps of HIV infection, we investigated the possible impact of α-defensins1-3 production by DC on disease progression.

Methodology/Principal Findings

Monocyte-derived DC (MDDC) were analyzed comparatively in healthy controls (HC) and HIV-infected patients, including untreated “elite” and “viremic” controllers, untreated viremic non-controllers and antiretroviral-treated patients. We found that production of α-defensins1-3 was significantly increased in MDDC from HIV-infected patients versus HC, and this increase was mainly due to that observed in controllers, while in non-controllers the increase was not statistically significant (controllers vs. HC, p<0.005; controllers vs. non-controllers p<0.05). Secreted α-defensins1-3 by immature MDDC positively correlated with CD4 T cell counts in controllers, but not in non-controllers. Moreover, independently of their clinical classification, HIV-infected patients with higher α-defensins1-3 secretion by immature MDDC showed slower disease progression, measured as no decrease in the number of CD4+ T-cells below 350 cell/mm³, lower increase of plasma viral load and no initiation of treatment over time. Plasma alpha-defensins1-3 levels lacked any relationship with immunologic and virologic parameters.

Conclusions/Significance

High production of α-defensins1-3 by immature DCs appears as a host protective factor against progression of HIV-1infection, suggesting potential diagnostic, therapeutic and preventive implications. This protective effect may arise from the activity of α-defensins1-3 to damage the virions prior and/or after their internalization by immature DC, and hence favoring a more efficient viral processing and presentation to HIV-specific CD4+ T cells, without or with a minor rate of transmission of infectious HIV-1 virions.

Therapeutic approaches using host defence peptides to tackle herpes virus infections

One of the most common viral infections in humans is caused by herpes simplex virus (HSV). It can easily be treated with nucleoside analogues (e.g., acyclovir), but resistant strains are on the rise. Naturally occurring antimicrobial peptides have been demonstrated to possess antiviral activity against HSV. New evidence has also indicated that these host defence peptides are able to selectively stimulate the innate immune system to fight of infections. This review will focus on the anti-HSV activity of such peptides (both natural and synthetic), describe their mode of action and their clinical potential.

Multifunctional host defense peptides: antimicrobial peptides, the small yet big players in innate and adaptive immunity

The term 'antimicrobial peptides' refers to a large number of peptides first characterized on the basis of their antibiotic and antifungal activities. In addition to their role as endogenous antibiotics, antimicrobial peptides, also called host defense peptides, participate in multiple aspects of immunity (inflammation, wound repair, and regulation of the adaptive immune system) as well as in maintaining homeostasis. The possibility of utilizing these multifunctional molecules to effectively combat the ever-growing group of antibiotic-resistant pathogens has intensified research aimed at improving their antibiotic activity and therapeutic potential, without the burden of an exacerbated inflammatory response, but conserving their immunomodulatory potential. In this minireview, we focus on the contribution of small cationic antimicrobial peptides - particularly human cathelicidins and defensins - to the immune response and disease, highlighting recent advances in our understanding of the roles of these multifunctional molecules.

Through the looking glass, mechanistic insights from enantiomeric human defensins

Despite the small size and conserved tertiary structure of defensins, little is known at a molecular level about the basis of their functional versatility. For insight into the mechanism(s) of defensin function, we prepared enantiomeric pairs of four human defensins, HNP1, HNP4, HD5, and HBD2, and studied their killing of bacteria, inhibition of anthrax lethal factor, and binding to HIV-1 gp120. Unstructured HNP1, HD5, and HBD3 and several other human alpha- and beta-defensins were also examined. Crystallographic analysis showed a plane of symmetry that related (L)HNP1 and (D)HNP1 to each other. Either d-enantiomerization or linearization significantly impaired the ability of HNP1 and HD5 to kill Staphylococcus aureus but not Escherichia coli. In contrast, (L)HNP4 and (D)HNP4 were equally bactericidal against both bacteria. d-Enantiomers were generally weaker inhibitors or binders of lethal factor and gp120 than their respective native, all-l forms, although activity differences were modest, particularly for HNP4. A strong correlation existed among these different functions. Our data indicate: (a) that HNP1 and HD5 kill E. coli by a process that is mechanistically distinct from their actions that kill S. aureus and (b) that chiral molecular recognition is not a stringent prerequisite for other functions of these defensins, including their ability to inhibit lethal factor and bind gp120 of HIV-1.

Defensins in viral infections

Defensins are antimicrobial peptides important to innate host defense. In addition to their direct antimicrobial effect, defensins modulate immune responses. Increasing evidence indicates that defensins exhibit complex functions by positively or negatively modulating infections of both enveloped and non-enveloped viruses. The effects of defensins on viral infections appear to be specific to the defensin, virus and target cell. Regulation of viral infection by defensins is achieved by multiple mechanisms. This review focuses on the interplay between defensins and viral infections, the mechanisms of action of defensins and the in vivo studies of the role of defensins in viral infections.

Comprehensive proteomic analysis of human cervical-vaginal fluid using colposcopy samples

Background

Cervical-vaginal fluid (CVF) plays an important role in the prevention of gynecological infections, although little is known about the contribution of CVF proteins to the immunity of the lower female genital tract. In order to analyze the protein composition of human CVF, we used CVF samples that are routinely collected during colposcopy, but are usually discarded. Since these samples are available in large quantities we aimed to analyze their usefulness for proteomics experiments. The samples were analyzed using different prefractionation techniques (ultrafiltration and C₄(RP)-LC protein separation) followed by C₁₈(RP)-LC peptide separation and identification by MALDI-TOF-TOF mass spectrometry. To determine the reproducibility of this proteomics platform we analyzed three technical replicates. Using spectral counting, protein abundances were estimated in a semiquantitative way. We also compared the results obtained in this study with those from previous studies derived from patients with different physiological conditions in order to determine an overlapping protein set.

Results

In total, we were able to identify 339 proteins in human CVF of which 151 proteins were not identified in any other proteomics study on human CVF so far. Those included antimicrobial peptides, such as human beta-defensin 2 and cathelicidin, which were known to be present in CVF, and endometrial proteins such as glycodelin and ribonucleoprotein A. Comparison of our results with previously published data led to the identification of a common protein set of 136 proteins. This overlapping protein set shows increased fractions of immunological and extracellular proteins, confirming the extracellular immunological role of CVF.

Conclusion

We demonstrated here that CVF colposcopy samples can be used in proteomics experiments and hence are applicable for biomarker discovery experiments. The delineation of an overlapping set of proteins that is identified in most proteomics studies on CVF may help in the description of a reference proteome when performing proteomics studies on human CVF.

Impact of alpha-defensins1-3 on the maturation and differentiation of human monocyte-derived DCs. Concentration-dependent opposite dual effects

alpha-defensins1-3 are potent antimicrobial molecules that also link innate and adaptive immunity, depending on the concentration range. However, their effects on the biology of human DCs remain largely unknown. We analyzed the impact of different concentrations of alpha-defensins1-3 on the maturation and differentiation of monocyte-derived DCs (MDDCs). Low doses of alpha-defensins1-3 up-regulated CD83, CD86 and HLA-DR expression, increased TNF-alpha, IL-1beta, IL-12p40, IL-10 and IL-8 secretion, and slightly augmented allostimulatory capacity. By contrast, high doses down-regulated CD86 and HLA-DR expression, TNF-alpha, IL-1beta, IL-12p40 and IL-10 secretion and allostimulatory capacity, whereas strongly up-regulated IL-8. Furthermore, during the MDDC differentiation process, high doses of alpha-defensins1-3 affected CD14, CD11c and CD86 expression and strongly up-regulated IL-8. Results suggest that alpha-defensins1-3 might modulate the maturation and differentiation of MDDCs in vivo and therefore could be of special interest in the field of vaccine development.

Levels of innate immune factors in genital fluids: association of alpha defensins and LL-37 with genital infections and increased HIV acquisition

BACKGROUND

Several mucosal innate immune proteins exhibit HIV inhibitory activity and their analogues are potential microbicide candidates. However, their clinical associations and in-vivo role in cervicovaginal host defense against HIV acquisition are poorly defined.

METHODS

Cervicovaginal secretions (CVSs) were collected from HIV uninfected Kenyan sex workers at enrolment into an HIV prevention trial. After trial completion, CVS from participants acquiring HIV (cases) and matched controls were assessed for levels of innate immune factors and HIV neutralizing capacity, by blinded investigators. Cross-sectional and prospective associations of innate immune factors were examined.

RESULTS

CVS contained high levels of defensins (human neutrophil peptide-1-3 and human beta defensin-2-3), LL-37 and secretory leukocyte protease inhibitor. Regulated upon activation normal T-cell expressed and secreted levels were lower, and IFNalpha was undetectable. CVS from 20% of participants neutralized a clade A primary HIV isolate, and 12% neutralized both clade A and C isolates. HIV neutralization was correlated with human neutrophil peptide-1-3 (alpha-defensins) and LL-37 levels. However, alpha-defensin and LL-37 levels were increased in participants with bacterial sexually transmitted infections and were independently associated with increased HIV acquisition in multivariate analysis.

CONCLUSIONS

Despite significant HIV inhibitory activity, cervicovaginal levels of alpha-defensins and LL-37 were associated with increased HIV acquisition, perhaps due to their association with bacterial sexually transmitted infections.

Human defensins as cancer biomarkers and antitumour molecules

Human defensins, which are small cationic peptides produced by neutrophils and epithelial cells, form two genetically distinct alpha and beta subfamilies. They are involved in innate immunity through killing microbial pathogens or neutralizing bacterial toxins and in adaptive immunity by serving as chemoattractants and activators of immune cells. alpha-defensins are mainly packaged in neutrophil granules (HNP1, HNP2, HNP3) or secreted by intestinal Paneth cells (HD5, HD6), while beta-defensins are expressed in mucosa and epithelial cells. Using surface enhanced laser desorption/ionisation time-of-flight (SELDI-TOF) mass spectrometry (MS), alpha-defensins were found to be expressed in a variety of human tumours, either in tumour cells or at their surface. HNP1-3 peptides are also secreted and their accumulation in biological fluids was proposed as a tumour biomarker. Conversely, beta-defensin-1 (HBD-1) is down-regulated in some tumour types in which it could behave as a tumour suppressor protein. Alpha-defensins promote tumour cell growth or, at higher concentration, provoke cell death. These peptides also inhibit angiogenesis, which, in addition to immunomodulation, indicates a complex role in tumour development. This review summarizes current knowledge of defensins to discuss their role in tumour growth, tumour monitoring and cancer treatment.

Antimicrobial peptides, skin infections, and atopic dermatitis

The innate immune system evolved more than 2 billion years ago to first recognize pathogens then eradicate them. Several distinct defects in this ancient but rapidly responsive element of human immune defense account for the increased incidence of skin infections in atopics. These defects include abnormalities in the physical barrier of the epidermis, alterations in microbial pattern recognition receptors such as toll receptors and nucleotide binding oligomerization domains, and a diminished capacity to increase the expression of antimicrobial peptides during inflammation. Several antimicrobial peptides are affected including; cathelicidin, HBD-2, and HBD-3, which are lower in lesional skin of atopics compared with other inflammatory skin diseases, and dermcidin, which is decreased in sweat. Other defects in the immune defense barrier of atopics include a relative deficiency in plasmacytoid dendritic cells. In the future, understanding the cause of these defects may allow therapeutic intervention to reduce the incidence of infection in atopic individuals and potentially decrease the severity of this disorder.

High-resolution mapping of the 8p23.1 beta-defensin cluster reveals strictly concordant copy number variation of all genes

One unexpected feature of the human genome is the high structural variability across individuals. Frequently, large regions of the genome show structural polymorphisms and many vary in their abundance. However, accurate methods for the characterization and typing of such copy number variations (CNV) are needed. The defensin cluster at the human region 8p23.1 is one of the best studied CNV regions due to its potential clinical relevance for innate immunity, inflammation, and cancer. The region can be divided into two subclusters, which harbor predominantly either alpha- or beta-defensin genes. Previous studies assessing individual copy numbers gave different results regarding whether the complete beta-defensin cluster varies or only particular genes therein. We applied multiplex ligation-dependent probe amplification (MLPA) to measure defensin locus copy numbers in 42 samples. The data show strict copy number concordance of all 10 loci typed within the beta-defensin cluster in each individual, while seven loci within the alpha-defensin cluster are consistently found as single copies per chromosome. The exception is DEFA3, which is located within the alpha-defensin cluster and was found to also differ in copy number interindividually. Absolute copy numbers ranged from two to nine for the beta-defensin cluster and zero to four for DEFA3. The CNV-typed individuals, including HapMap samples, are publicly available and may serve as a universal reference for absolute copy number determination. On this basis, MLPA represents a reliable technique for medium- to high-throughput typing of 8p23.1 defensin CNV in association studies for diverse clinical phenotypes.

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.

Human alpha-defensins inhibit BK virus infection by aggregating virions and blocking binding to host cells

BK virus (BKV) is a polyomavirus that establishes a lifelong persistence in most humans and is a major impediment to success of kidney grafts. The function of the innate immune system in BKV infection and pathology has not been investigated. Here we examine the role of antimicrobial defensins in BKV infection of Vero cells. Our data show that alpha-defensin human neutrophil protein 1 (HNP1) and human alpha-defensin 5 (HD5) inhibit BKV infection by targeting an early event in the viral lifecycle. HD5 treatment of BKV reduced viral attachment to cells, whereas cellular treatment with HD5 did not. Colocalization studies indicated that HD5 interacts directly with BKV. Ultrastructural analysis revealed HD5-induced aggregation of virions. HD5 also inhibited infection of cells by other related polyomaviruses. This is the first study to demonstrate polyomavirus sensitivity to defensins. We also show a novel mechanism whereby HD5 binds to BKV leading to aggregation of virion particles preventing normal virus binding to the cell surface and uptake into cells.

Neisseria gonorrhoeae-induced human defensins 5 and 6 increase HIV infectivity: role in enhanced transmission

Sexually transmitted infections (STIs) increase the likelihood of HIV transmission. Defensins are part of the innate mucosal immune response to STIs and therefore we investigated their role in HIV infection. We found that human defensins 5 and 6 (HD5 and HD6) promoted HIV infection, and this effect was primarily during viral entry. Enhancement was seen with primary viral isolates in primary CD4(+) T cells and the effect was more pronounced with R5 virus compared with X4 virus. HD5 and HD6 promoted HIV reporter viruses pseudotyped with vesicular stomatitis virus and murine leukemia virus envelopes, indicating that defensin-mediated enhancement was not dependent on CD4 and coreceptors. Enhancement of HIV by HD5 and HD6 was influenced by the structure of the peptides, as loss of the intramolecular cysteine bonds was associated with loss of the HIV-enhancing effect. Pro-HD5, the precursor and intracellular form of HD5, also exhibited HIV-enhancing effect. Using a cervicovaginal tissue culture system, we found that expression of HD5 and HD6 was induced in response to Neisseria gonorrhoeae (GC, for gonococcus) infection and that conditioned medium from GC-exposed cervicovaginal epithelial cells with elevated levels of HD5 also enhanced HIV infection. Introduction of small interfering RNAs for HD5 or HD6 abolished the HIV-enhancing effect mediated by GC. Thus, the induction of these defensins in the mucosa in the setting of GC infection could facilitate HIV infection. Furthermore, this study demonstrates the complexity of defensins as innate immune mediators in HIV transmission and warrants further investigation of the mechanism by which defensins modulate HIV infection.

Antimicrobial polypeptides are key anti-HIV-1 effector molecules of cervicovaginal host defense

Mucosal surfaces of the cervix and vagina are portals for heterosexual transmission of human immunodeficiency virus type 1 (HIV-1) and, therefore, play a fundamental role in the pathogenesis of primary infection. Cationic antimicrobial polypeptides including defensins are the principal effector molecules of mucosal innate immunity against microbes and viruses such as HIV. In cervicovaginal secretions, antimicrobial polypeptides constitute the majority of the intrinsic anti-HIV-1 activity, synergism between cationic polypeptides is complex, and full anti-HIV-1 activity involves the complete complement of cationic polypeptides. Periods in which cationic antimicrobial polypeptide expression is reduced are likely associated with increased susceptibility to HIV-1 infection. This review provides an overview of the role of cationic antimicrobial polypeptides in innate cervicovaginal anti-HIV-1 host defense, and discusses how hormones and bacterial infections can regulate their expression. Emphasis is placed on the theta-defensin (retrocyclin) class of anti-HIV-1 peptides and their potential for development as topical microbicides to prevent HIV-1 transmission.

Defensins' offensive play: exploiting a viral achilles' heel

Vertebrates rely on antimicrobial peptides as a front-line defense against invading pathogens. Certain cationic antimicrobial peptides, such as human alpha-defensins, have traditionally been thought to destroy invading microbes by disrupting their lipid membranes. In this issue of Cell Host & Microbe, Smith and Nemerow reveal that alpha-defensins can inactivate adenoviruses, which lack lipid membranes, through direct binding of the defensin to the virus's naked protein shell.

Mechanism of adenovirus neutralization by Human alpha-defensins

Defensins are naturally occurring antimicrobial peptides that disrupt bacterial membranes and prevent bacterial invasion of the host. Emerging studies indicate that certain defensins also block virus infection; however, the mechanism(s) involved are poorly understood. We demonstrate that human alpha-defensins inhibit adenovirus infection at low micromolar concentrations, and this requires direct association of the defensin with the virus. Moreover, defensins inhibit virus disassembly at the vertex region, thereby restricting the release of an internal capsid protein, pVI, which is required for endosomal membrane penetration during cell entry. As a consequence, defensins hamper the release of adenovirus particles from endocytic vesicles, resulting in virion accumulation in early endosomes and lysosomes. Thus, defensins possess remarkably distinct modes of activity against bacteria and viruses, and their function may provide insights for the development of new antiviral strategies.

Inhibitory function of adapter-related protein complex 2 alpha 1 subunit in the process of nuclear translocation of human immunodeficiency virus type 1 genome

The transfection of human cells with siRNA against adapter-related protein complex 2 alpha 1 subunit (AP2alpha) was revealed to significantly up-regulate the replication of human immunodeficiency virus type 1 (HIV-1). This effect was confirmed by cell infection with vesicular stomatitis virus G protein-pseudotyped HIV-1 as well as CXCR4-tropic and CCR5-tropic HIV-1. Viral adsorption, viral entry and reverse transcription processes were not affected by cell transfection with siRNA against AP2alpha. In contrast, viral nuclear translocation as well as the integration process was significantly up-regulated in cells transfected with siRNA against AP2alpha. Confocal fluorescence microscopy revealed that a subpopulation of AP2alpha was not only localized in the cytoplasm but was also partly co-localized with lamin B, importin beta and Nup153, implying that AP2alpha negatively regulates HIV-1 replication in the process of nuclear translocation of viral DNA in the cytoplasm or the perinuclear region. We propose that AP2alpha may be a novel target for disrupting HIV-1 replication in the early stage of the viral life cycle.

Antimicrobial peptides in human skin disease

The skin continuously encounters microbial pathogens. To defend against this, cells of the epidermis and dermis have evolved several innate strategies to prevent infection. Antimicrobial peptides are one of the primary mechanisms used by the skin in the early stages of immune defense. In general, antimicrobial peptides have broad antibacterial activity against gram-positive and negative bacteria and also show antifungal and antiviral activity. The antimicrobial activity of most peptides occurs as a result of unique structural characteristics that enable them to disrupt the microbial membrane while leaving human cell membranes intact. However, antimicrobial peptides also act on host cells to stimulate cytokine production, cell migration, proliferation, maturation, and extracellular matrix synthesis. The production by human skin of antimicrobial peptides such as defensins and cathelicidins occurs constitutively but also greatly increases after infection, inflammation or injury. Some skin diseases show altered expression of antimicrobial peptides, partially explaining the pathophysiology of these diseases. Thus, current research suggests that understanding how antimicrobial peptides modify susceptibility to microbes, influence skin inflammation, and modify wound healing, provides greater insight into the pathophysiology of skin disorders and offers new therapeutic opportunities.

SAMMA, a mandelic acid condensation polymer, inhibits dendritic cell-mediated HIV transmission

SAMMA, a mandelic acid condensation polymer, exhibits a broad antimicrobial activity against several sexually transmitted pathogens including human immunodeficiency virus (HIV). Here we demonstrated that SAMMA suppressed HIV transmission by dendritic cells (DCs), one of the first target cells for primary infection. The greatest inhibitory effect was achieved when SAMMA was present during the co-culture with target cells. The inhibitory effect of SAMMA on DC-mediated HIV transmission was not due to cytotoxicity. Analysis of the level of DC-associated HIV p24 antigen revealed that SAMMA prevented HIV internalization by DCs when the virus was pre-incubated with the compound. In contrast, pre-incubation of DCs with SAMMA followed by wash-off did not affect the amount of cell-associated HIV p24 antigen. In addition, SAMMA blocked HIV glycoprotein-mediated cell-cell fusion. This study suggests that SAMMA prevents HIV infection through multiple mechanisms.

Human immature monocyte-derived dendritic cells produce and secrete α-defensins 1-3

Defensins are effector molecules of the innate immunity with a broad antimicrobial spectrum, including HIV. They also link innate and adaptive immunity, displaying chemotactic activity for monocytes, T cells, and dendritic cells (DCs). alpha-Defensins 1-3 are mainly produced by neutrophils, but their production by other leukocyte subsets has also been reported. Herein, we studied whether monocyte-derived DCs (MDDCs), which are regarded as a model for myeloid DCs, produce alpha-defensins 1-3. We found that immature MDDCs (imMDDCs) produce alpha-defensins 1-3 mRNA, but this production is undetectable or barely detectable following 48 h of maturation with the proinflammatory cytokine cocktail (IL-1beta+IL-6+TNF-alpha) or LPS. It is surprising that alpha-defensins 1-3 production was up-regulated when exposed to each one of the proinflammatory cytokines alone, especially IL-1beta. alpha-Defensins 1-3 produced by imMDDCs were mainly secreted peptides. Production and secretion of alpha-defensins 1-3 by imMDDCs can have biological relevance for the antigen processing of pathogens and can contribute to understanding differences in susceptibility to infections, an issue of special interest in the field of HIV infection.

Host factors influencing susceptibility to HIV infection and AIDS progression

Transmission of HIV first results in an acute infection, followed by an apparently asymptomatic period that averages ten years. In the absence of antiretroviral treatment, most patients progress into a generalized immune dysfunction that culminates in death. The length of the asymptomatic period varies, and in rare cases infected individuals never progress to AIDS. Other individuals whose behavioral traits put them at high-risk of HIV transmission, surprisingly appear resistant and never succumb to infection. These unique cases highlight the fact that susceptibility to HIV infection and progression to disease are complex traits modulated by environmental and genetic factors. Recent evidence has indicated that natural variations in host genes can influence the outcome of HIV infection and its transmission. In this review we summarize the available literature on the roles of cellular factors and their genetic variation in modulating HIV infection and disease progression.

Dual antiviral activity of human alpha-defensin-1 against viral haemorrhagic septicaemia rhabdovirus (VHSV): inactivation of virus particles and induction of a type I interferon-related response

It is well known that human alpha-defensin-1, also designated as human neutrophil peptide 1 (HNP1), is a potent inhibitor towards several enveloped virus infecting mammals. In this report, we analyzed the mechanism of the antiviral action of this antimicrobial peptide (AMP) on viral haemorrhagic septicaemia virus (VHSV), a salmonid rhabdovirus. Against VHSV, synthetic HNP1 possesses two antiviral activities. The inactivation of VHSV particles probably through interfering with VHSV-G protein-dependent fusion and the inhibition of VHSV replication in target cells by up-regulating genes related to the type I interferon (IFN) response, such as Mx. Neither induction of IFN-stimulated genes (ISGs) by HNP1 nor their antiviral activity against fish rhabovirus has been previously reported. Therefore, we can conclude that besides to acting as direct effector, HNP1 acts across species and can elicit one of the strongest antiviral responses mediated by innate immune system. Since the application of vaccine-based immunization strategies is very limited, the used of chemicals is restricted because of their potential harmful impact on the environment and no antimicrobial peptides from fish that exhibit both antiviral and immunoenhancing capabilities have been described so far, HNP1 could be a model molecule for the development of antiviral agents for fish. In addition, these results further confirm that molecules that mediate the innate resistance of animals to virus may prove useful as templates for new antivirals in both human and animal health.

Breast milk alpha-defensins are associated with HIV type 1 RNA and CC chemokines in breast milk but not vertical HIV type 1 transmission

Alpha-defensins are proteins exhibiting in vitro anti-HIV-1 activity that may protect against mother-to-child transmission of HIV-1 via breast milk. Correlates of alpha-defensins in breast milk and transmission risk were determined in a cohort of HIV-1-infected pregnant women in Nairobi followed for 12 months postpartum with their infants. Maternal blood was collected antenatally and at delivery for HIV-1 viral load and infant HIV-1 infection status was determined < 48 h after birth and at months 1, 3, 6, 9, and 12. Breast milk specimens collected at month 1 were assayed for alpha-defensins, HIV-1 RNA, subclinical mastitis, and CC and CXC chemokines. We detected alpha-defensins in breast milk specimens from 108 (42%) of 260 HIV-1-infected women. Women with detectable alpha-defensins (> or =50 pg/ml) had a median concentration of 320 pg/ml and significantly higher mean breast milk HIV-1 RNA levels than women with undetectable alpha-defensins (2.9 log(10) copies/ml versus 2.5 log(10) copies/ml, p = 0.003). Increased alpha-defensins concentrations in breast milk were also associated with subclinical mastitis (Na (+)/K(+) ratio > 1) and increased breast milk chemokine levels. Overall, 40 (15%) infants were HIV-1 uninfected at birth and subsequently acquired HIV-1. There was no significant association between month 1 alpha-defensins and risk of HIV-1 transmission. In conclusion, alpha-defensins were associated with breast milk HIV-1 viral load, chemokine levels, and subclinical mastitis, all of which may alter risk of infant HIV-1 acquisition. Despite these associations there was no significant relationship between breast milk alpha-defensins and mother-to-child transmission, suggesting a complex interplay between breast milk HIV-1, inflammation, and antiinfective factors.

Characterization of alpha-defensins plasma levels in Macaca fascicularis and correlations with virological parameters during SHIV89.6Pcy11 experimental infection

Alpha-defensins have been shown to inhibit HIV-1 replication in vitro and may contribute to the overall control of viral replication in vivo. In the present work, we quantitatively measured the levels of alpha-defensins in the plasma of healthy and experimentally SHIV-infected Macaca fascicularis (cynomolgus monkeys), an animal model of AIDS pathogenesis and vaccine development. Characterization of physiological plasma alpha-defensins levels was performed in 12 healthy monkeys following longitudinal analysis using an alpha-defensins ELISA kit currently validated for macaque use. Subsequently, alpha-defensins levels were quantitatively measured in 23 cynomolgus monkeys during titration protocols following both the mucosal and systemic routes of infection with the pathogenic SHIV89.6P(cy11). A significant increase in plasma alpha-defensins levels was consistently observed at early time points in all infected animals, regardless of the infection route. Moreover, a positive correlation was observed between viral replication and levels of alpha-defensins during the acute phase of infection. Interestingly, in the animals infected through the mucosal route, alpha-defensins levels remained significantly higher at later time points, up to 19 weeks from the infection, while in cynomolgus infected intravenously, alpha-defensins levels returned to baseline levels by 4 weeks from infection, suggesting that the different route of infection may differently activate the innate immune response.

Serpin A1 and CD91 as host instruments against HIV-1 infection: are extracellular antiviral peptides acting as intracellular messengers?

Serpin A1 (alpha1-antitrypsin, alpha1-proteinase inhibitor) has been shown to be a non-cytolytic antiviral factor present in blood and effective against HIV infection. The best known physiological role of serpin A1 is to inhibit neutrophil elastase, a proteinase which is secreted by neutrophils at sites of infection and inflammation. Decreased HIV-infectivity is associated with decreased density of membrane-associated elastase. The enzyme may facilitate binding of the HIV membrane protein gp120 to host cells, and it specifically cleaves SDF-1, the physiological ligand of the HIV-1 co-receptor CXCR4. It has been suggested that one of the actions of serpin A1 as antiviral agent is to reduce HIV infectivity, and this property could be due to elastase inhibition. However, the most dramatic effect of serpin A1 is inhibition of HIV production. In vitro experiments indicate that the C-terminal peptide of serpin A1, produced during the formation of the complex of serpin with serine proteinases, may be responsible for the inhibition of HIV-1 expression in infected cells. This peptide, an integral part of the serpin-enzyme complex, is internalized by several scavenger receptors. Peptides corresponding to the C-terminal section of serpin A1 inhibit HIV-1 long-terminal-repeat-driven transcription and interact with nuclear proteins, such as alpha1-fetoprotein transcription factor. LDL-receptor-related protein 1 (LRP1/CD91), the best known receptor for serpin-enzyme complexes, is up-regulated in monocytes of HIV-1-infected true non-progressors. CD91 could be one of the major players in host resistance against HIV-1. It has the capacity of internalizing antiviral peptides such as serpin C-terminal fragments and alpha-defensins, and is at the same time the receptor for heat-shock proteins in antigen-presenting cells, in which chaperoned viral peptides could lead to the induction of cytotoxic T-cell responses.

Multispecific myeloid defensins

PURPOSE OF REVIEW

This review describes recent progress in our understanding of defensins and their contributions to innate immunity. Defensins are small, cysteine-rich endogenous antibiotic peptides. Human neutrophils contain large amounts of three alpha-defensins (HNP-1-HNP-3), and smaller amounts of a fourth, HNP-4. Monocytes and macrophages generally lack defensins, but they release messengers that induce the synthesis of beta-defensins in epithelial cells.

RECENT FINDINGS

In addition to their antimicrobial and immunomodulatory effects, HNP-1-HNP-3 possess antiviral and toxin-neutralizing properties. Induction of beta-defensins in epithelial cells is mediated by cell-surface Toll-like receptors or cytoplasmic peptidoglycan receptors that can recognize pathogen-associated molecules. Mutations in Nod2, a cytoplasmic peptidoglycan receptor, are associated with reduced levels of intestinal alpha-defensins and ileal Crohn's disease. Human defensin genes show marked copy-number polymorphism. High level constitutive expression of defensins may afford protection against HIV-1 and other defensin-sensitive pathogens. Theta-defensins (cyclic octadecapeptides found in nonhuman primates) have impressive antiviral and antitoxic properties.

SUMMARY

The multiple properties of defensins contribute to human innate immunity against bacteria, bacterial toxins, and viruses.

In Vitro Discriminative Antipseudomonal Properties Resulting from Acyl Substitution of N-Terminal Sequence of Dermaseptin S4 Derivatives

Truncation and acylation were combined to investigate the broad-spectrum bactericidal and hemolytic peptide S4(1-15). Substitution of up to seven residues with dodecanoic acid (C(12)) gradually led to specific antipseudomonal activity: out of 40 bacterial strains tested in vitro, C(12)-S4(8-15) displayed similar minimal inhibitory concentrations (MICs) as S4(1-15) against Pseudomonas aeruginosa sp. (identical MIC(90)) but was practically inactive against most other bacteria or erythrocytes. Surface plasmon resonance and isothermal titration calorimetry experiments revealed the binding properties of S4(1-15) to be consistent with its nonselective activities, while discriminative activities of C(12)-S4(8-15) correlated with high binding affinity to a membrane containing pseudomonal lipopolysaccharides and with lower affinities to membranes containing nonpseudomonal lipopolysaccharides or cholesterol. Various mechanistic studies failed to detect significant differences in secondary structure, bactericidal kinetics, or ability to perturb the cytoplasmic membrane, pointing to a similar mode of action.

Characterization of the antiviral effects of interferon-alpha against a SARS-like coronoavirus infection in vitro

Interferon (IFN)-αs bind to and activate their cognate cell surface receptor to invoke an antiviral response in target cells. Well-described receptor-mediated signaling events result in transcriptional regulation of IFN sensitive genes, effectors of this antiviral response. Results from a pilot study to evaluate the clinical efficacy of IFN-α treatment of SARS patients provided evidence for IFN-inducible resolution of disease. In this report we examined the contribution of IFN-inducible phosphorylation-activation of specific signaling effectors to protection from infection by a SARS-related murine coronavirus, MHV-1. As anticipated, the earliest receptor-activation event, Jak1 phosphorylation, is critical for IFN-inducible protection from MHV-1 infection. Additionally, we provide evidence for the contribution of two kinases, the MAP kinase p38MAPK, and protein kinase C (PKC) δ to antiviral protection from MHV-1 infection. Notably, our data suggest that MHV-1 infection, as for the Urbani SARS coronoavirus, inhibits an IFN response, inferred from the lack of activation of pkr and 2′5′-oas, genes associated with mediating the antiviral activities of IFN-αs. To identify potential target genes that are activated downstream of the IFN-inducible signaling effectors we identified, and that mediate protection from coronavirus infection, we examined the gene expression profiles in the peripheral blood mononuclear cells of SARS patients who received IFN treatment. A subset of differentially regulated genes were distinguished with functional properties associated with antimicrobial activities.

Stable expression of soluble therapeutic peptides in eukaryotic cells by multimerisation: application to the HIV-1 fusion inhibitory peptide C46

A major drawback of therapeutic peptides is their short half-life, which results in the need for multiple applications and high synthesis costs. To overcome this, we established a eukaryotic expression system that allows the stable expression of small therapeutic peptides by multimerisation. By inserting the sequence encoding the therapeutic peptide between a signal peptide and the multimerising domain of the alpha-chain from the human C4bp plasma protein, therapeutic peptides as small as 5 kDa are secreted as multimers from transfected cells; this allows easy purification. As proof of principle, we show that the T20-derived HIV-1 fusion inhibitory peptide C46 in its multimeric form: i) was efficiently secreted, ii) was more stable than the current antiviral drug T20 in vitro and in vivo, and iii) inihibited HIV-1 entry with similar efficiency in vitro. Besides the gain in stability, multimerisation also leads to increased valency and allows the combination of several therapeutic functions. Furthermore, by expressing the multimers from cells, post-translational modifications could easily be introduced.

Pentraxin 3 protects from MCMV infection and reactivation through TLR sensing pathways leading to IRF3 activation

Reactivation of latent human cytomegalovirus (HCMV) following allogeneic transplantation is a major cause of morbidity and mortality and predisposes to severe complications, including superinfection by Aspergillus species (spp). Antimicrobial polypeptides, including defensins and mannan-binding lectin, are known to block viral fusion by cross-linking sugars on cell surface. Pentraxin 3 (PTX3), a member of the long pentraxin family, successfully restored antifungal immunity in experimental hematopoietic transplantation. We assessed here whether PTX3 binds HCMV and murine virus (MCMV) and the impact on viral infectivity and superinfection in vivo. We found that PTX3 bound both viruses, reduced viral entry and infectivity in vitro, and protected from MCMV primary infection and reactivation as well as Aspergillus superinfection. This occurred through the activation of interferon (IFN) regulatory factor 3 (IRF3) in dendritic cells via the TLR9/MyD88-independent viral recognition sensing and the promotion of the interleukin-12 (IL-12)/IFN-γ–dependent effector pathway.

Acyl-substituted dermaseptin S4 derivatives with improved bactericidal properties, including on oral microflora

The 15-mer dermaseptin S4 derivative S4(1-15) was recently shown to exhibit potent activity against oral pathogens associated with caries and periodontitis. Here, we investigated possible modes for improving the peptide's properties through systematic replacement of an N-terminal amino acid(s) with various fatty acids that modulate the peptide's hydrophobicity and/or charge. Deletion of 1 to 3 residues led to progressive loss of potency as assessed by MIC experiments performed on four test bacteria. Replacing the deleted amino acids with fatty acids most often resulted in potency recovery or improvement, as evidenced by lower MICs and faster bactericidal kinetics in culture media. Best results were obtained after replacement of the N-terminal dipeptide alanine-leucine with heptanoic (C7) or aminododecanoic (NC12) acid. Circular dichroism analysis correlated antibacterial properties to the peptide's secondary structure. MIC experiments and confocal laser scanning microscopy results indicated that C7-S4(3-15) and NC12-S4(3-15) were bactericidal to various oral pathogens, including those which are immobilized in a biofilm. C7-S4(3-15) performed similarly to or better than (depending on growth medium) IB-367, a peptide assessed in clinical trials for treatment of oral mucositis, reducing CFU counts by >3 log units within 2 min of incubation. Collectively, the data indicate that substitution of fatty acids for amino acids may be a useful strategy in revealing improved derivatives of known antimicrobial peptides and suggest the suitability of such compounds for controlling pathogens associated with oral diseases.

Host antimicrobial defence peptides in human disease

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

Effects of prostratin on Cyclin T1/P-TEFb function and the gene expression profile in primary resting CD4+ T cells

Background

The latent reservoir of human immunodeficiency virus type 1 (HIV-1) in resting CD4⁺ T cells is a major obstacle to the clearance of infection by highly active antiretroviral therapy (HAART). Recent studies have focused on searches for adjuvant therapies to activate this reservoir under conditions of HAART. Prostratin, a non tumor-promoting phorbol ester, is a candidate for such a strategy. Prostratin has been shown to reactivate latent HIV-1 and Tat-mediated transactivation may play an important role in this process. We examined resting CD4⁺ T cells from healthy donors to determine if prostratin induces Cyclin T1/P-TEFb, a cellular kinase composed of Cyclin T1 and Cyclin-dependent kinase-9 (CDK9) that mediates Tat function. We also examined effects of prostratin on Cyclin T2a, an alternative regulatory subunit for CDK9, and 7SK snRNA and the HEXIM1 protein, two factors that associate with P-TEFb and repress its kinase activity.

Results

Prostratin up-regulated Cyclin T1 protein expression, modestly induced CDK9 protein expression, and did not affect Cyclin T2a protein expression. Although the kinase activity of CDK9 in vitro was up-regulated by prostratin, we observed a large increase in the association of 7SK snRNA and the HEXIM1 protein with CDK9. Using HIV-1 reporter viruses with and without a functional Tat protein, we found that prostratin stimulation of HIV-1 gene expression appears to require a functional Tat protein. Microarray analyses were performed and several genes related to HIV biology, including APOBEC3B, DEFA1, and S100 calcium-binding protein genes, were found to be regulated by prostratin.

Conclusion

Prostratin induces Cyclin T1 expression and P-TEFb function and this is likely to be involved in prostratin reactivation of latent HIV-1 proviruses. The large increase in association of 7SK and HEXIM1 with P-TEFb following prostratin treatment may reflect a requirement in CD4⁺ T cells for a precise balance between active and catalytically inactive P-TEFb. Additionally, genes regulated by prostratin were identified that have the potential to regulate HIV-1 replication both positively and negatively.

High level expression of human epithelial beta-defensins (hBD-1, 2 and 3) in papillomavirus induced lesions

Background

Epithelial defensins including human β-defensins (hBDs) and α-defensins (HDs) are antimicrobial peptides that play important roles in the mucosal defense system. However, the role of defensins in papillomavirus induced epithelial lesions is unknown.

Results

Papilloma tissues were prospectively collected from 15 patients with recurrent respiratory papillomatosis (RRP) and analyzed for defensins and chemokine IL-8 expression by quantitative, reverse-transcriptase polymerase chain reaction (RT-PCR) assays. HBD-1, -2 and -3 mRNAs were detectable in papilloma samples from all RRP patients and the levels were higher than in normal oral mucosal tissues from healthy individuals. Immunohistochemical analysis showed that both hBD-1 and 2 were localized in the upper epithelial layers of papilloma tissues. Expression of hBD-2 and hBD-3 appeared to be correlated as indicated by scatter plot analysis (r = 0.837, p < 0.01) suggesting that they were co-inducible in papillomavirus induced lesions. Unlike hBDs, only low levels of HD5 and HD6 were detectable in papillomas and in oral mucosa.

Conclusion

Human β-defensins are upregulated in respiratory papillomas. This novel finding suggests that hBDs might contribute to innate and adaptive immune responses targeted against papillomavirus-induced epithelial lesions.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

α-Defensins 1, 2, and 3 Are Expressed by Granulocytes in Lymphoid Tissues of HIV-1-Seropositive and -Seronegative Individuals

alpha-Defensins 1, 2, and 3 exert antiretroviral activity in vitro, but their role in controlling HIV-1 replication in vivo and the cells that produce them are controversial. This study sought to determine whether alpha-defensins are present in HIV-1-infected individuals' lymphoid tissues, the major site of HIV-1 replication, and to identify the cells that express them. alpha-Defensin expression was evaluated by immunostaining inguinal lymph node sections from 19 untreated HIV-1-infected individuals and 8 individuals at low risk or seronegative for HIV-1 infection. Percentages of tissue sections that stained positively for alpha-defensins were not significantly different between HIV-seropositive (median, 7.6%) and -seronegative (median, 5.5%) individuals. Conditions that could have produced lymph node inflammation were present in most seronegative subjects, and their lymph node weights correlated with alpha-defensin expression (Spearman rho = 0.833; P = 0.010). A median of 100% (range, 95%-100%) of alpha-defensin-expressing lymph node cells from 8 subjects coexpressed the granulocyte marker, CD15. CD15 and alpha-defensin staining correlated (Spearman rho = 0.622; P < 0.001). These data suggest that alpha-defensins within lymphoid tissue are expressed by granulocytes and are prevalent in HIV-1-seronegative individuals with inflammatory processes as well as HIV-1-infected individuals. The role of alpha-defensins in controlling HIV-1 replication merits further investigation.

Defensin: a multifunctional molecule lives up to its versatile name

Human neutrophil proteins 1, 2 and 3 (HNP1-3) were originally identified as endogenous antibiotics that can kill microbial pathogens immediately after the onset of the host innate immune response. Recent studies revealed that these peptides perform additional, previously unexpected functions, notably the neutralization of certain secreted bacterial toxins. In this Opinion article, a brief overview of the well-established functions of HNP1-3 is given and novel biological activities of HNP1-3 are described, with emphasis on neutralization of secreted bacterial toxins. We propose that toxin neutralization represents a novel biological function of HNP1-3 in host defense.

The role of defensins in virus-induced asthma

Respiratory viruses appear to play a central role in asthma pathogenesis. In addition to a major role in triggering asthma exacerbations, viral infections early in life may play a role in disease development. Although defensins were initially identified as antimicrobial peptides, recent studies have demonstrated that they have a much broader range of actions that are of relevance to virally induced asthma. Defensins are not only induced during viral infections, they exert direct antiviral actions against some enveloped viruses, and also can impair viral infection of cells. In addition, defensins modulate the activity of several cell types that contribute to innate immunity, including mast cells, epithelial cells, natural killer cells, and dendritic cells. They also have the capacity to modulate adaptive immunity and to contribute to airway remodeling. In this article, recent advances in these areas are reviewed in the context of the potential role of defensins in virus-induced asthma.

Defensins in innate antiviral immunity

Defensins are small antimicrobial peptides that are produced by leukocytes and epithelial cells, and that have an important role in innate immunity. Recent advances in understanding the mechanisms of the antiviral action(s) of defensins indicate that they have a dual role in antiviral defence, acting directly on the virion and on the host cell. This Review focuses on the antiviral activities and mechanisms of action of mammalian defensins, and on the clinical relevance of these activities. Understanding the complex function of defensins in innate immunity against viral infection has implications for the prevention and treatment of viral disease.

Expression and purification of recombinant human alpha-defensins in Escherichia coli

Different strategies have been developed to produce small antimicrobial peptides (AMPs) using recombinant techniques. Up to now, all efforts to obtain larger quantities of active recombinant human alpha-defensins have been only moderately successful. Here we report an effective method of biosynthesis of human alpha-defensins (hNP-1 to hNP-3 and hD-5 and hD-6) in the Escherichia coli. All the peptides, expressed as insoluble fusions with the peptide encoded by a portion of E. coli tryptophan operon (trp DeltaLE 1413 polypeptide), were isolated from the inclusion bodies by immobilized metal affinity chromatography (IMAC) and separated from the fusion leader by chemical cleavage. Fully reduced peptides that were purified according to a straightforward protocol were subsequently folded, oxidized, and subjected to functional and structural analyses. With the exception of hD-6, all recombinant alpha-defensins exhibit expected anti-E. coli activity, as measured by the colony counting method. The method described in this report is a low-cost, efficient way of generating alpha-defensins in quantities ranging from milligrams to grams.