Interactions of the Skin Pathogen Haemophilus ducreyi With the Human Host.

The obligate human pathogen Haemophilus ducreyi causes both cutaneous ulcers in children and sexually transmitted genital ulcers (chancroid) in adults. Pathogenesis is dependent on avoiding phagocytosis and exploiting the suppurative granuloma-like niche, which contains a myriad of innate immune cells and memory T cells. Despite this immune infiltrate, long-lived immune protection does not develop against repeated H. ducreyi infections-even with the same strain. Most of what we know about infectious skin diseases comes from naturally occurring infections and/or animal models; however, for H. ducreyi, this information comes from an experimental model of infection in human volunteers that was developed nearly three decades ago. The model mirrors the progression of natural disease and serves as a valuable tool to determine the composition of the immune cell infiltrate early in disease and to identify host and bacterial factors that are required for the establishment of infection and disease progression. Most recently, holistic investigation of the experimentally infected skin microenvironment using multiple "omics" techniques has revealed that non-canonical bacterial virulence factors, such as genes involved in central metabolism, may be relevant to disease progression. Thus, the immune system not only defends the host against H. ducreyi, but also dictates the nutrient availability for the invading bacteria, which must adapt their gene expression to exploit the inflammatory metabolic niche. These findings have broadened our view of the host-pathogen interaction network from considering only classical, effector-based virulence paradigms to include adaptations to the metabolic environment. How both host and bacterial factors interact to determine infection outcome is a current focus in the field. Here, we review what we have learned from experimental H. ducreyi infection about host-pathogen interactions, make comparisons to what is known for other skin pathogens, and discuss how novel technologies will deepen our understanding of this infection.

[Relationship between structure and function of cathelicidins and their molecular design: a review].

Cathelicidins play critical roles in mammalian innate immune defense against invasive bacterial infection. In addition to their broad-spectrum bactericidal effect, cathelicidins are interesting peptide-based drug templates because they have multiple functions including anti-inflammatory, wound healing, and angiogenesis promotion. This article summarizes the aim and method of cathelicidin molecular designs. Residue mutation, fragment assembly, chemical modification, and construction of conjugates and dimers are usually used to increase the biological activities. Addition or deletion of certain residues, disruption of leucine zipper and phenylalanine zipper are used to reduce the hemolysis and cytotoxicity. By substituting L-amino acids with D-amino acids, circular constructions and immobilization, cathelicidins' in vitro and in vivo stability could be greatly enhanced, especially their proteinase resistance.

Cathelicidins Inhibit Escherichia coli-Induced TLR2 and TLR4 Activation in a Viability-Dependent Manner.

Activation of the immune system needs to be tightly regulated to provide protection against infections and, at the same time, to prevent excessive inflammation to limit collateral damage to the host. This tight regulation includes regulating the activation of TLRs, which are key players in the recognition of invading microbes. A group of short cationic antimicrobial peptides, called cathelicidins, have previously been shown to modulate TLR activation by synthetic or purified TLR ligands and may play an important role in the regulation of inflammation during infections. However, little is known about how these cathelicidins affect TLR activation in the context of complete and viable bacteria. In this article, we show that chicken cathelicidin-2 kills Escherichia coli in an immunogenically silent fashion. Our results show that chicken cathelicidin-2 kills E. coli by permeabilizing the bacterial inner membrane and subsequently binds the outer membrane-derived lipoproteins and LPS to inhibit TLR2 and TLR4 activation, respectively. In addition, other cathelicidins, including human, mouse, pig, and dog cathelicidins, which lack antimicrobial activity under cell culture conditions, only inhibit macrophage activation by nonviable E. coli In total, this study shows that cathelicidins do not affect immune activation by viable bacteria and only inhibit inflammation when bacterial viability is lost. Therefore, cathelicidins provide a novel mechanism by which the immune system can discriminate between viable and nonviable Gram-negative bacteria to tune the immune response, thereby limiting collateral damage to the host and the risk for sepsis.

A potential contribution of antimicrobial peptide LL-37 to tissue fibrosis and vasculopathy in systemic sclerosis.

BACKGROUND: LL-37 is an antimicrobial peptide with pleiotropic effects on the immune system, angiogenesis and tissue remodelling. These are cardinal pathological events in systemic sclerosis (SSc). OBJECTIVES: To elucidate the potential role of LL-37 in SSc. METHODS: The expression of target molecules was evaluated by immunostaining and quantitative reverse-transcription real-time polymerase chain reaction in human and murine skin. The mechanisms regulating LL-37 expression in endothelial cells were examined by gene silencing and chromatin immunoprecipitation. Serum LL-37 levels were determined by enzyme-linked immunosorbent assay. RESULTS: In SSc lesional skin, LL-37 expression was increased in dermal fibroblasts, perivascular inflammatory cells, keratinocytes and, particularly, dermal small vessels. Expression positively correlated with interferon-α expression, possibly reflecting LL-37-dependent induction of interferon-α. In SSc animal models, bleomycin-treated skin exhibited the expression pattern of CRAMP, a murine homologue of LL-37, similar to that of LL-37 in SSc lesional skin. Furthermore, Fli1+/- mice showed upregulated expression of CRAMP in dermal small vessels. Fli1 binding to the CAMP (LL-37 gene) promoter and Fli1 deficiency-dependent induction of LL-37 were also confirmed in human dermal microvascular endothelial cells. In the analysis of sera, patients with SSc had serum LL-37 levels significantly higher than in healthy controls. Furthermore, serum LL-37 levels positively correlated with skin score and the activity of alveolitis and were significantly elevated in patients with digital ulcers compared with those without. CONCLUSIONS: LL-37 upregulation, induced by Fli1 deficiency at least in endothelial cells, potentially contributes to the development of skin sclerosis, interstitial lung disease and digital ulcers in SSc.

Amplifying renal immunity: the role of antimicrobial peptides in pyelonephritis.

Urinary tract infections (UTIs), including pyelonephritis, are among the most common and serious infections encountered in nephrology practice. UTI risk is increased in selected patient populations with renal and urinary tract disorders. As the prevalence of antibiotic-resistant uropathogens increases, novel and alternative treatment options will be needed to reduce UTI-associated morbidity. Discoveries over the past decade demonstrate a fundamental role for the innate immune system in protecting the urothelium from bacterial challenge. Antimicrobial peptides, an integral component of this urothelial innate immune system, demonstrate potent bactericidal activity toward uropathogens and might represent a novel class of UTI therapeutics. The urothelium of the bladder and the renal epithelium secrete antimicrobial peptides into the urinary stream. In the kidney, intercalated cells--a cell-type involved in acid-base homeostasis--have been shown to be an important source of antimicrobial peptides. Intercalated cells have therefore become the focus of new investigations to explore their function during pyelonephritis and their role in maintaining urinary tract sterility. This Review provides an overview of UTI pathogenesis in the upper and lower urinary tract. We describe the role of intercalated cells and the innate immune response in preventing UTI, specifically highlighting the role of antimicrobial peptides in maintaining urinary tract sterility.

The human antimicrobial peptide LL-37 binds directly to CsrS, a sensor histidine kinase of group A Streptococcus, to activate expression of virulence factors.

Group A Streptococcus (GAS) responds to subinhibitory concentrations of LL-37 by up-regulation of virulence factors through the CsrRS (CovRS) two-component system. The signaling mechanism, however, is unclear. To determine whether LL-37 signaling reflects specific binding to CsrS or rather a nonspecific response to LL-37-mediated membrane damage, we tested LL-37 fragments for CsrRS signaling and for GAS antimicrobial activity. We identified a 10-residue fragment (RI-10) of LL-37 as the minimal peptide that retains the ability to signal increased expression of GAS virulence factors, yet it has no detectable antimicrobial activity against GAS. Substitution of individual key amino acids in RI-10 reduced or abrogated signaling. These data do not support the hypothesis that CsrS detects LL-37-induced damage to the bacterial cell membrane but rather suggest that LL-37 signaling is mediated by a direct interaction with CsrS. To test whether LL-37 binds to CsrS, we used the purified CsrS extracellular domain to pull down LL-37 in vitro, a result that provides further evidence that LL-37 binds to CsrS. The dissociation of CsrS-mediated signaling from membrane damage by LL-37 fragments together with in vitro evidence for a direct LL-37-CsrS binding interaction constitute compelling evidence that signal transduction by LL-37 through CsrS reflects a direct ligand/receptor interaction.

Roles of cathelicidins in inflammation and bone loss.

Body surface tissues, such as the oral cavity, contact directly with the external environment and are continuously exposed to microbial insults. Cathelicidins are a family of antimicrobial peptides that are found in mammalian species. Humans and mice have only one cathelicidin. Cathelicidins are expressed in a variety of surface tissues. In addition, they are abundantly expressed in bone and bone marrow. Infectious stimuli upregulate the expression of cathelicidins, which play sentinel roles in allowing the tissues to fight against microbial challenges. Cathelicidins disrupt membranes of microorganisms and kill them. They also neutralize microbe-derived pathogens, such as lipopolysaccharide (LPS) and flagellin. Besides their antimicrobial functions, cathelicidins can also control actions of host cells, such as chemotaxis, proliferation, and cytokine production, through binding to the receptors expressed on them. LPS and flagellin induce osteoclastogenesis and the production of cathelicidins, which can in turn inhibit osteoclastogenesis. Thus, cathelicidins contribute to maintaining microbiota-host homeostasis and promoting repair responses to inflammatory insults. In this review, we describe recent findings on the multiple roles of cathelicidins in host defense. We also discuss the significance of the human cathelicidin, LL-37, as a pharmaceutical target for the treatment of inflammation and bone loss in infectious diseases, such as periodontitis.

Cathelicidin LL-37 induces time-resolved release of LTB4 and TXA2 by human macrophages and triggers eicosanoid generation in vivo.

In humans, LL-37 and eicosanoids are important mediators of inflammation and immune responses. Here we report that LL-37 promotes leukotriene B4 (LTB4) and thromboxane A2 (TXA2) generation by human monocyte-derived macrophages (HMDMs). LL-37 evokes calcium mobilization apparently via the P2X7 receptor (P2X7R), activation of ERK1/2 and p38 MAPKs, as well as cytosolic phospholipase A2 (cPLA2) and 5-lipoxygenase in HMDMs, leading to an early (1 h) release of LTB4. Similarly, TXA2 production at an early time involved the same signaling sequence along an LL-37-P2X7R-cPLA2-cyclooxygenase-1 (COX-1) axis. However, at later (6-8 h) time points, internalized LL-37 up-regulates COX-2 expression, promoting TXA2 production. Furthermore, intraperitoneal injection of mice with murine cathelicidin-related antimicrobial peptide (mCRAMP) induces significantly higher levels of LTB4 and TXA2 in mouse ascites rich in macrophages. Conversely, cathelicidin-deficient (Cnlp(-/-)) mice produce much less LTB4 and TXB2 in vivo in response to TNF-α compared with control mice. We conclude that LL-37 elicits a biphasic release of eicosanoids in macrophages with early, Ca(2+)-dependent formation of LTB4 and TXA2 followed by a late peak of TXA2, generated via induction of COX-2 by internalized LL-37, thus allowing eicosanoid production in a temporally controlled manner. Moreover, our findings provide evidence that LL-37 is an endogenous regulator of eicosanoid-dependent inflammatory responses in vivo.

Antimicrobial cathelicidin peptide LL-37 inhibits the LPS/ATP-induced pyroptosis of macrophages by dual mechanism.

Pyroptosis is a caspase-1 dependent cell death, associated with proinflammatory cytokine production, and is considered to play a crucial role in sepsis. Pyroptosis is induced by the two distinct stimuli, microbial PAMPs (pathogen associated molecular patterns) and endogenous DAMPs (damage associated molecular patterns). Importantly, cathelicidin-related AMPs (antimicrobial peptides) have a role in innate immune defense. Notably, human cathelicidin LL-37 exhibits the protective effect on the septic animal models. Thus, in this study, to elucidate the mechanism for the protective action of LL-37 on sepsis, we utilized LPS (lipopolysaccharide) and ATP (adenosine triphosphate) as a PAMP and a DAMP, respectively, and examined the effect of LL-37 on the LPS/ATP-induced pyroptosis of macrophage-like J774 cells. The data indicated that the stimulation of J774 cells with LPS and ATP induces the features of pyroptosis, including the expression of IL-1ß mRNA and protein, activation of caspase-1, inflammasome formation and cell death. Moreover, LL-37 inhibits the LPS/ATP-induced IL-1ß expression, caspase-1 activation, inflammasome formation, as well as cell death. Notably, LL-37 suppressed the LPS binding to target cells and ATP-induced/P2X7-mediated caspase-1 activation. Together these observations suggest that LL-37 potently inhibits the LPS/ATP-induced pyroptosis by both neutralizing the action of LPS and inhibiting the response of P2X7 to ATP. Thus, the present finding may provide a novel insight into the modulation of sepsis utilizing LL-37 with a dual action on the LPS binding and P2X7 activation.

Roles of cathelicidin-related antimicrobial peptide in murine osteoclastogenesis.

Cathelicidin-related antimicrobial peptide (CRAMP) not only kills bacteria but also binds to lipopolysaccharide (LPS) to neutralize its activity. CRAMP is highly expressed in bone marrow and its expression is reported to be up-regulated by inflammatory and infectious stimuli. Here, we examined the role of CRAMP in murine osteoclastogenesis. Osteoclasts were formed in co-cultures of osteoblasts and bone marrow cells in response to 1α,25-dihydroxyvitamin D3 [1α,25(OH)2 D3 ], prostaglandin E2 (PGE2 ), and Toll-like receptor (TLR) ligands such as LPS and flagellin through the induction of receptor activator of nuclear factor-κB ligand (RANKL) expression in osteoblasts. CRAMP inhibited the osteoclastogenesis in co-cultures treated with LPS and flagellin, but not in those treated with 1α,25(OH)2 D3 or PGE2 . Although bone marrow macrophages (BMMs) highly expressed formyl peptide receptor 2 (a receptor of CRAMP), CRAMP showed no inhibitory effect on osteoclastogenesis in BMM cultures treated with RANKL. CRAMP suppressed both LPS- and flagellin-induced RANKL expression in osteoblasts and tumour necrosis factor-α (TNF-α) expression in BMMs, suggesting that CRAMP neutralizes the actions of LPS and flagellin. LPS and flagellin enhanced the expression of CRAMP mRNA in osteoblasts. Extracellularly added CRAMP suppressed LPS- and flagellin-induced CRAMP expression. These results suggest that the production of CRAMP promoted by LPS and flagellin is inhibited by CRAMP released by osteoblasts through a feedback regulation. Even though CRAMP itself has no effect on osteoclastogenesis in mice, we propose that CRAMP is an osteoblast-derived protector in bacterial infection-induced osteoclastic bone resorption.

The human antimicrobial peptide LL-37, but not the mouse ortholog, mCRAMP, can stimulate signaling by poly(I:C) through a FPRL1-dependent pathway.

LL-37 is an antimicrobial peptide produced by human cells that can down-regulate the lipopolysaccharide-induced innate immune responses and up-regulate double-stranded (ds) RNA-induced innate responses through Toll-like receptor 3 (TLR3). The murine LL-37 ortholog, mCRAMP, also inhibited lipopolysaccharide-induced responses, but unlike LL-37, it inhibited viral-induced responses in mouse cells. A fluorescence polarization assay showed that LL-37 was able to bind dsRNA better than mCRAMP. In the human lung epithelial cell line BEAS-2B, LL-37, but not mCRAMP, colocalized with TLR3, and the colocalization was increased in the presence of dsRNA. The presence of poly(I:C) increased the accumulation of LL-37 in Rab5 endosomes. Signaling by cells induced with both LL-37 and poly(I:C) was sensitive to inhibitors that affect clathrin-independent trafficking, whereas signaling by poly(I:C) alone was not, suggesting that the LL-37-poly(I:C) complex trafficked to signaling endosomes by a different mechanism than poly(I:C) alone. siRNA knockdown of known LL-37 receptors identified that FPRL1 was responsible for TLR3 signaling induced by LL-37-poly(I:C). These results show that LL-37 and mCRAMP have different activities in TLR3 signaling and that LL-37 can redirect trafficking of poly(I:C) to effect signaling by TLR3 in early endosomes in a mechanism that involves FPRL1.

Cathelicidin-related antimicrobial peptide is required for effective lung mucosal immunity in Gram-negative bacterial pneumonia.

Cathelicidins are a family of endogenous antimicrobial peptides that exert diverse immune functions, including both direct bacterial killing and immunomodulatory effects. In this study, we examined the contribution of the murine cathelicidin, cathelicidin-related antimicrobial peptide (CRAMP), to innate mucosal immunity in a mouse model of Gram-negative pneumonia. CRAMP expression is induced in the lung in response to infection with Klebsiella pneumoniae. Mice deficient in the gene encoding CRAMP (Cnlp(-/-)) demonstrate impaired lung bacterial clearance, increased bacterial dissemination, and reduced survival in response to intratracheal K. pneumoniae administration. Neutrophil influx into the alveolar space during K. pneumoniae infection was delayed early but increased by 48 h in CRAMP-deficient mice, which was associated with enhanced expression of inflammatory cytokines and increased lung injury. Bone marrow chimera experiments indicated that CRAMP derived from bone marrow cells rather than structural cells was responsible for antimicrobial effects in the lung. Additionally, CRAMP exerted bactericidal activity against K. pneumoniae in vitro. Similar defects in lung bacterial clearance and delayed early neutrophil influx were observed in CRAMP-deficient mice infected with Pseudomonas aeruginosa, although this did not result in increased bacterial dissemination, increased lung injury, or changes in lethality. Taken together, our findings demonstrate that CRAMP is an important contributor to effective host mucosal immunity in the lung in response to Gram-negative bacterial pneumonia.

Antimicrobial peptides: agents of border protection for companion animals.

Over the past 20 years, there have been significant inroads into understanding the roles of antimicrobial peptides in homeostatic functions and their involvement in disease pathogenesis. In addition to direct antimicrobial activity, these peptides participate in many cellular functions, including chemotaxis, wound healing and even determination of canine coat colour. Various biological and genetic approaches have helped to elucidate the role of antimicrobial peptides with respect to innate immunity and host defense. Associations of antimicrobial peptides with various skin diseases, including psoriasis, rosacea and atopic dermatitis, have been documented in humans. In the longer term, therapeutic modulation of antimicrobial peptide expression may provide effective new treatments for disease. This review highlights current knowledge about antimicrobial peptides of the skin and circulating leukocytes, with particular focus on relevance to physiology and disease in companion animals.

Role of defensins and cathelicidin LL37 in auto-immune and auto-inflammatory diseases.

Defensins and cathelicidins are anti-microbial peptides (AMPs) that act as natural antibiotics and are part of the innate immune defence in many species. We consider human defensins and LL37, the only human member of the cathelicidin family. In particular, we refer to the human alpha-defensins called human neutrophil peptides (HNP1 through 4), which are produced by neutrophils, HD5 and HD6, mainly expressed in Paneth cells of intestine, the human beta-defensins HBD1, HBD2 and HBD3, synthesized by epithelial cells and LL37, which is located in granulocytes, but is also produced by epithelial cells of the skin, lungs, and gut. In the last years, the study of AMPs activity and regulation has allowed to understand the important role of these peptides not only in the innate defence mechanisms against bacteria, viruses, fungi, but also in the regulation of immune cell activation and migration. Complementary studies have disclosed a role for AMPs in modulating many physiological processes that involve non-immune cells, such as activation of wound healing, angiogenesis, cartilage remodeling. Due to the pleiotropic tasks of these peptides, many of them are now being discovered to contribute to immune pathology of chronic diseases that affect skin, gut, joints; this is supported by many examples of immune-mediated pathologies in which their expression is disregulated. In this article we review the current literature that suggests a role for human defensins and LL37 in pathogenic mechanisms of several chronic diseases that are considered of auto-immune or auto-inflammatory origin.

Susceptibility to vaccinia virus infection and spread in mice is determined by age at infection, allergen sensitization and mast cell status.

BACKGROUND: Patients, especially young children, with atopic dermatitis are at an increased risk of developing eczema vaccinatum, a severe reaction to the smallpox vaccine, either through direct vaccination or indirect contact with a person recently vaccinated. METHODS: Using a mouse model of infection, the severity of vaccinia-induced lesions was assessed from their appearance and viral DNA content. The response to vaccinia inoculation was assessed in young and adult mice, allergen-sensitized mice, and in mast cell-deficient mice. RESULTS: Young age, sensitization to an allergen prior to infection, and a mast cell deficit, accomplished by using mast cell-deficient mice, resulted in more severe viral lesions at the site of inoculation, according to lesion appearance and viral DNA content. All three factors combined demonstrated maximal susceptibility, characterized by the severity of primary lesions and the development of secondary (satellite) lesions, as occurs in eczema vaccinatum in humans. Resistance to the appearance of satellite lesions could be restored by adoptive transfer of bone marrow-derived mast cells from either wild-type or cathelicidin-related antimicrobial peptide-deficient mice. Primary lesions were more severe following the latter transfer, indicating that cathelicidin-related antimicrobial peptide does contribute to the protective activity of mast cells against infection. CONCLUSIONS: The combination of young age, allergen sensitization and a mast cell deficit resulted in the most severe lesions, including satellite lesions. Understanding the factors determining the relative resistance/sensitivity to vaccinia virus will aid in the development of strategies for preventing and treating adverse reactions which can occur after smallpox vaccination.

LL37 and hBD-3 elevate the ß-1,3-exoglucanase activity of Candida albicans Xog1p, resulting in reduced fungal adhesion to plastic.

The opportunistic fungus Candida albicans causes oral thrush and vaginal candidiasis, as well as candidaemia in immunocompromised patients including those undergoing cancer chemotherapy, organ transplant and those with AIDS. We previously found that the AMPs (antimicrobial peptides) LL37 and hBD-3 (human ß-defensin-3) inhibited C. albicans viability and its adhesion to plastic. For the present study, the mechanism by which LL37 and hBD-3 reduced C. albicans adhesion was investigated. After AMP treatment, C. albicans adhesion to plastic was reduced by up to ~60% and was dose-dependent. Our previous study indicated that LL37 might interact with the cell-wall ß-1,3-exoglucanase Xog1p, which is involved in cell-wall ß-glucan metabolism, and consequently the binding of LL37 or hBD-3 to Xog1p might cause the decrease in adhesion. For the present study, Xog1p(41-438)-6H, an N-terminally truncated, active, recombinant construct of Xog1p and Xog1p fragments were produced and used in pull-down assays and ELISA in vitro, which demonstrated that all constructs interacted with both AMPs. Enzymatic analyses showed that LL37 and hBD-3 enhanced the ß-1,3-exoglucanase activity of Xog1p(41-438)-6H approximately 2-fold. Therefore elevated Xog1p activity might compromise cell-wall integrity and decrease C. albicans adhesion. To test this hypothesis, C. albicans was treated with 1.3 µM Xog1p(41-438)-6H and C. albicans adhesion to plastic decreased 47.7%. Taken together, the evidence suggests that Xog1p is one of the LL37/hBD-3 targets, and elevated ß-1,3-exoglucanase activity reduces C. albicans adhesion to plastic.

LL37 and cationic peptides enhance TLR3 signaling by viral double-stranded RNAs.

BACKGROUND: Toll-like Receptor 3 (TLR3) detects viral dsRNA during viral infection. However, most natural viral dsRNAs are poor activators of TLR3 in cell-based systems, leading us to hypothesize that TLR3 needs additional factors to be activated by viral dsRNAs. The anti-microbial peptide LL37 is the only known human member of the cathelicidin family of anti-microbial peptides. LL37 complexes with bacterial lipopolysaccharide (LPS) to prevent activation of TLR4, binds to ssDNA to modulate TLR9 and ssRNA to modulate TLR7 and 8. It synergizes with TLR2/1, TLR3 and TLR5 agonists to increase IL8 and IL6 production. This work seeks to determine whether LL37 enhances viral dsRNA recognition by TLR3. METHODOLOGY/PRINCIPAL FINDINGS: Using a human bronchial epithelial cell line (BEAS2B) and human embryonic kidney cells (HEK 293T) transiently transfected with TLR3, we found that LL37 enhanced poly(I:C)-induced TLR3 signaling and enabled the recognition of viral dsRNAs by TLR3. The presence of LL37 also increased the cytokine response to rhinovirus infection in BEAS2B cells and in activated human peripheral blood mononuclear cells. Confocal microscopy determined that LL37 could co-localize with TLR3. Electron microscopy showed that LL37 and poly(I:C) individually formed globular structures, but a complex of the two formed filamentous structures. To separate the effects of LL37 on TLR3 and TLR4, other peptides that bind RNA and transport the complex into cells were tested and found to activate TLR3 signaling in response to dsRNAs, but had no effect on TLR4 signaling. This is the first demonstration that LL37 and other RNA-binding peptides with cell penetrating motifs can activate TLR3 signaling and facilitate the recognition of viral ligands. CONCLUSIONS/SIGNIFICANCE: LL37 and several cell-penetrating peptides can enhance signaling by TLR3 and enable TLR3 to respond to viral dsRNA.

[Structure, function and molecular design strategies of antibacterial peptide SMAP-29: a review].

Antibacterial peptides are a family of host-defense peptides most of which are gene-encoded and produced by living organisms of all types. Antibacterial peptides are small molecular proteins with broad antimicrobial spectrum against bacteria, viruses, fungi and sometimes even as anticancer peptide. SMAP-29, a cathelicidin-like peptide derived from sheep myeloid, line alpha-helical Structure, exerts a powerful broad antimicrobial activity against different pathogens including Gram-positive and Gram-negative bacteria, fungi, viruses, parasites, spirochaetes, chlamydia and antiendotoxin activity, and particular antibacterial mechanism, rapidly to permeabilize membranes of susceptible organisms. This paper summarizes the lately research progress of SMAP-29 and Variants including the characteristics of structure, structure-activity relationships, mode of action, diverse biological functions, gene recombinant and expression. We put emphasis on the necessity of molecular design, and primary and secondary structure-based modification, to provides a strong foundation for further drug development and design of SMAP-29.

Cathelicidin LL-37 increases lung epithelial cell stiffness, decreases transepithelial permeability, and prevents epithelial invasion by Pseudomonas aeruginosa.

In addition to its antibacterial activity, the cathelicidin-derived LL-37 peptide induces multiple immunomodulatory effects on host cells. Atomic force microscopy, F-actin staining with phalloidin, passage of FITC-conjugated dextran through a monolayer of lung epithelial cells, and assessment of bacterial outgrowth from cells subjected to Pseudomonas aeruginosa infection were used to determine LL-37's effect on epithelial cell mechanical properties, permeability, and bacteria uptake. A concentration-dependent increase in stiffness and F-actin content in the cortical region of A549 cells and primary human lung epithelial cells was observed after treatment with LL-37 (0.5-5 µM), sphingosine 1-phosphate (1 µM), or LPS (1 µg/ml) or infection with PAO1 bacteria. Other cationic peptides, such as RK-31, KR-20, or WLBU2, and the antibacterial cationic steroid CSA-13 did not reproduce the effect of LL-37. A549 cell pretreatment with WRW4, an antagonist of the transmembrane formyl peptide receptor-like 1 protein attenuated LL-37's ability to increase cell stiffness. The LL-37-mediated increase in cell stiffness was accompanied by a decrease in permeability and P. aeruginosa uptake by a confluent monolayer of polarized normal human bronchial epithelial cells. These results suggested that the antibacterial effect of LL-37 involves an LL-37-dependent increase in cell stiffness that prevents epithelial invasion by bacteria.