Human cathelicidin (LL-37), a multifunctional peptide, is expressed by ocular surface epithelia and has potent antibacterial and antiviral activity

The corneal expression of antimicrobial peptides during experimental fungal keratitis

PURPOSE/AIM OF STUDY: To investigate the expression of endogenous antimicrobial peptides within the murine cornea during the onset and progression of posttraumatic keratomycosis caused by Candida albicans.

MATERIALS AND METHODS

Scarified corneas of BALB/c mice were topically inoculated with C. albicans and monitored for one week. A murine gene microarray compared the relative expression of 36 antimicrobial peptide genes in infected corneas to controls. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) determined gene expression levels for murine cathelicidin and β-defensins in normal corneas, scarified corneas, and C. albicans-infected corneas. Immunofluorescent staining localized the expression of cathelicidin in corneal sections.

RESULTS

Traumatized eyes exposed to C. albicans developed progressive corneal inflammation, with a fungal inoculum of 10(6) colony-forming units (CFU) bringing about significantly (P < 0.05) more severe corneal inflammatory disease than a 10(5) CFU inoculum. Camp, encoding a murine cathelicidin-related antimicrobial peptide, was significantly upregulated 45-fold by microarray (P = 0.0007) and 36-fold by real-time RT-PCR (P = 0.0009). Camp increased significantly (P = 0.002) more in corneas receiving the higher than the lower fungal inoculum. Cathelicidin was preferentially expressed within the stroma on the first day after fungal inoculation, and Camp expression progressively declined over one week as the amount of recoverable fungi decreased. The genetic expression of β-defensin 1 and β-defensin 2 was initially downregulated (P ≤ 0.01) at the onset of fungal keratitis then returned toward normal levels.

CONCLUSIONS

The antimicrobial peptide cathelicidin rapidly increases within the inflamed murine corneal stroma after the initiation of fungal keratitis and may play a role in the host responses that follow corneal trauma and infection.

Vitamin D and the anti-viral state

Vitamin D has long been recognized as essential to the skeletal system. Newer evidence suggests that it also plays a major role regulating the immune system, perhaps including immune responses to viral infection. Interventional and observational epidemiological studies provide evidence that vitamin D deficiency may confer increased risk of influenza and respiratory tract infection. Vitamin D deficiency is also prevalent among patients with HIV infection. Cell culture experiments support the thesis that vitamin D has direct anti-viral effects particularly against enveloped viruses. Though vitamin D's anti-viral mechanism has not been fully established, it may be linked to vitamin D's ability to up-regulate the anti-microbial peptides LL-37 and human beta defensin 2. Additional studies are necessary to fully elucidate the efficacy and mechanism of vitamin D as an anti-viral agent.

Toll-like receptor activation modulates antimicrobial peptide expression by ocular surface cells

The ability of the ocular surface to respond to pathogens is in part attributed to toll-like receptors (TLRs) that recognize conserved motifs on various microbes. This study examines TLR expression on various ocular surface cells, if TLR agonists can modulate the expression of antimicrobial peptides (AMPs), human beta defensins (hBD) and cathelicidin (hCAP-18/LL-37) which maybe functionally active against Pseudomonas aeruginosa (PA) and if TLR agonists or AMPs can modulate TLR mRNA expression. TLR1-10 mRNA expression was examined in corneal epithelial, corneal stromal cells and conjunctival epithelial cells by RT-PCR. To confirm protein expression flow cytometry or immunostaining was performed for selected TLRs on some cell cultures. Ocular surface cells were cultured with a range of TLR agonists and then hBD-1, 2, 3, or hCAP-18 mRNA and protein expression was determined by RT-PCR and immunoblotting. In some experiments, cells were cultured with a cocktail of agonists for TLR3, 5 and 6/2 and the antimicrobial activity of the culture media was tested against PA. TLR mRNA expression was also examined in primary human corneal epithelial cells (HCEC) treated with either 3 μg/ml of hBD-2, 5 μg/ml of LL-37 or TLR4, 5 and 9 agonists. Overall, the ocular surface cells expressed mRNA for most of the TLRs but some differences were found. TLR2 was not detected in corneal fibroblasts, TLR4 was not detected in primary cultured or freshly isolated HCEC, TLR5 was not detected in conjunctival epithelial cells (IOBA-NHC) and corneal fibroblasts, TLR7 was not detected in freshly isolated HCEC and TLR10 was not detected in HCEC and IOBA-NHC. TLR8 mRNA was not expressed by any of the samples tested. Immunostaining of cadaver corneas revealed TLR5 and 9 expression throughout the cornea while TLR3 was significantly expressed only in the epithelium. Flow cytometry and immunostaining revealed cultured fibroblasts expressed TLR9 but had no significant TLR3 expression. hBD-2 expression was upregulated by TLR1/2, 3, 4, 5 and 6/2 agonists depending on the cell type, whereas only the TLR3 agonist upregulated the expression of hCAP-18 in primary HCEC. The combination of TLR3, 5 and 6/2 agonists in primary HCEC, upregulated hBD-2 and hCAP-18 mRNA and peptide expression and secretion into the culture media, which significantly killed PA. This antimicrobial activity was primarily attributed to LL-37. TLR agonists did not modulate TLR expression itself, however, LL-37 or hBD-2 downregulated TLR5, 7 and/or 9 mRNA depending on the cell type. TLRs are expressed on the ocular surface and TLR agonists trigger the production of LL-37 and hBD-2, with LL-37 being particularly important for protecting the ocular surface against PA infection.

Chemokine gene expression in lung CD8 T cells correlates with protective immunity in mice immunized intra-nasally with Adenovirus-85A

Background

Immunization of BALB/c mice with a recombinant adenovirus expressing Mycobacterium tuberculosis (M. tuberculosis) antigen 85A (Ad85A) protects against aerosol challenge with M. tuberculosis only when it is administered intra-nasally (i.n.). Immunization with Ad85A induces a lung-resident population of activated CD8 T cells that is antigen dependent, highly activated and mediates protection by early inhibition of M. tuberculosis growth. In order to determine why the i.n. route is so effective compared to parenteral immunization, we used microarray analysis to compare gene expression profiles of pulmonary and splenic CD8 T cells after i.n. or intra-dermal (i.d.) immunization.

Method

Total RNA from CD8 T cells was isolated from lungs or spleens of mice immunized with Ad85A by the i.n. or i.d. route. The gene profiles generated from each condition were compared. Statistically significant (p ≤ 0.05) differentially expressed genes were analyzed to determine if they mapped to particular molecular functions, biological processes or pathways using Gene Ontology and Panther DB mapping tools.

Results

CD8 T cells from lungs of i.n. immunized mice expressed a large number of chemokines chemotactic for resting and activated T cells as well as activation and survival genes. Lung lymphocytes from i.n. immunized mice also express the chemokine receptor gene Cxcr6, which is thought to aid long-term retention of antigen-responding T cells in the lungs. Expression of CXCR6 on CD8 T cells was confirmed by flow cytometry.

Conclusions

Our microarray analysis represents the first ex vivo study comparing gene expression profiles of CD8 T cells isolated from distinct sites after immunization with an adenoviral vector by different routes. It confirms earlier phenotypic data indicating that lung i.n. cells are more activated than lung i.d. CD8 T cells. The sustained expression of chemokines and activation genes enables CD8 T cells to remain in the lungs for extended periods after i.n. immunization. This may account for the early inhibition of M. tuberculosis growth observed in Ad85A i.n. immunized mice and explain the effectiveness of i.n. compared to parenteral immunization with this viral vector.

Topical flagellin protects the injured corneas from Pseudomonas aeruginosa infection

Among bacterial pathogens, Pseudomonas (P.) aeruginosa infection is the most sight threatening. The corneal innate immune responses are key mediators of the host's defense to P. aeruginosa. Using a mouse model of Pseudomonas keratitis, we evaluated the protective effects of topical application of flagellin, a ligand for Toll-Like receptor 5 (TLR5), on the development of Pseudomonas keratitis and elucidated the underlying mechanisms. Topical application of purified flagellin 6 and 24 h prior to P. aeruginosa inoculation on injured mouse corneas significantly attenuated clinical symptoms of P. aeruginosa keratitis, decreased bacterial burden, and suppressed infection induced inflammation in the B6 mouse cornea. Topical application of flagellin on wounded cornea induced PMN infiltration and markedly upregulated cathelicidin-related antimicrobial peptide (CRAMP) expression. In PMN depleted mice, flagellin promoted bacterial clearance in the cornea compared to that of the PBS treated mice, but was unable to prevent corneal perforation and systemic bacterial dissemination and sepses. Deletion of CRAMP increased corneal susceptibility to P. aeruginosa and abolished flagellin-induced protection in B6 mice. Our findings illustrate the profound protective effect of flagellin on the cornea innate defense, a response that can be exploited for prophylactic purposes to prevent contact lens associated Pseudomonas keratitis.

Antimicrobial and antibiofilm activity of cathelicidins and short, synthetic peptides against Francisella

Francisella infects the lungs causing pneumonic tularemia. Focusing on the lung's host defense, we have examined antimicrobial peptides as part of the innate immune response to Francisella infection. Interest in antimicrobial peptides, such as the cathelicidins, has grown due their potential therapeutic applications and the increasing problem of bacterial resistance to commonly used antibiotics. Only one human cathelicidin, LL-37, has been characterized. Helical cathelicidins have also been discovered in snakes including the Chinese King Cobra, Naja atra (NA-CATH). Four synthetic 11-residue peptides (ATRA-1, -2, -1A and -1P) containing variations of a repeated motif within NA-CATH were designed. We hypothesized that these smaller synthetic peptides could have excellent antimicrobial effectiveness with shorter length (and less cost), making them strong potential candidates for development into broad-spectrum antimicrobial compounds. We tested the susceptibility of F. novicida to four ATRA peptides, LL-37, and NA-CATH. Two of the ATRA peptides had high antimicrobial activity (microM), while the two proline-containing ATRA peptides had low activity. The ATRA peptides did not show significant hemolytic activity even at high peptide concentration, indicating low cytotoxicity against host cells. NA-CATH killed Francisella bacteria more quickly than LL-37. However, LL-37 was the most effective peptide against F. novicida (EC50=50 nM). LL-37 mRNA was induced in A549 cells by Francisella infection. We recently demonstrated that F. novicida forms in vitro biofilms. LL-37 inhibited F. novicida biofilm formation at sub-antimicrobial concentrations. Understanding the properties of these peptides, and their endogenous expression in the lung could lead to potential future therapeutic interventions for this lung infection.

Immunobiology of herpes simplex virus and cytomegalovirus infections of the fetus and newborn

Immunologic "immaturity" is often blamed for the increased susceptibility of newborn humans to infection, but the precise mechanisms and details of immunologic development remain somewhat obscure. Herpes simplex virus (HSV) and cytomegalovirus (CMV) are two of the more common severe infectious agents of the fetal and newborn periods. HSV infection in the newborn most commonly occurs after exposure to the virus during delivery, and can lead to a spectrum of clinical disease ranging from isolated skin-eye-mucous membrane infection to severe disseminated multiorgan disease, often including encephalitis. In contrast to HSV, clinically severe CMV infections early in life are usually acquired during the intrauterine period. These infections can result in a range of clinical disease, including hearing loss and neurodevelopmental delay. However, term newborns infected with CMV after delivery are generally asymptomatic, and older children and adults often acquire infection with HSV or CMV with either no or mild clinical symptoms. The reasons for these widely variable clinical presentations are not completely understood, but likely relate to developmental differences in immune responses.This review summarizes recent human and animal studies of the immunologic response of the fetus and newborn to these two infections, in comparison to the responses of older children and adults. The immunologic defense of the newborn against each virus is considered under the broader categories of (i) the placental barrier to infection, (ii) skin and mucosal barriers (including antimicrobial peptides), (iii) innate responses, (iv) humoral responses, and (v) cellular responses. A specific focus is made on recent studies of innate and cellular immunity to HSV and CMV.

Antibacterial activity and cytotoxicity of PEGylated poly(amidoamine) dendrimers

We have investigated the antibacterial activity and cytotoxicity of a series of amino-terminated poly(amidoamine) (PAMAM) dendrimers modified with poly(ethylene glycol) (PEG) groups. The antibacterial activity of the PAMAM dendrimers and their derivatives against the common ocular pathogens, Pseudomonas aeruginosa and Staphylococcus aureus, was evaluated by their minimum inhibitory concentrations (MICs). For the unmodified third and fifth generation (G3 and G5) amino-terminated dendrimers, the MICs against both P. aeruginosa and S. aureus were in the range of 6.3-12.5 microg mL(-1), comparable to that of the antimicrobial peptide LL-37 (1.3-12.5 microg mL(-1)) and within the wide range of 0.047-128 microg mL(-1) for the fluoroquinolone antibiotics. PEGylation of the dendrimers decreased their antibacterial activities, especially for the Gram-positive bacteria (S. aureus). The reduction in potency is likely due to the decrease in the number of protonated amino groups and shielding of the positive charges by the PEG chains, thus decreasing the electrostatic interactions of the dendrimers with the negatively-charged bacterial surface. Interestingly, localization of a greater number of amino groups on G5 vs. G3 dendrimers did not improve the potency. Significantly, even a low degree of PEGylation, e.g. 6% with EG(11) on G3 dendrimer, greatly reduced the cytotoxicity towards human corneal epithelial cells while maintaining a high potency against P. aeruginosa. The cytotoxicity of the PEGylated dendrimers to host cells is much lower than that reported for antimicrobial peptides. Furthermore, the MICs of these dendrimers against P. aeruginosa are more than two orders of magnitude lower than other antimicrobial polymers reported to date. These results motivate further exploration of the potential of cationic dendrimers as a new class of antimicrobial agents that may be less likely to induce bacterial resistance than standard antibiotics.

Antimicrobial host defense peptides in an arteriviral infection: differential peptide expression and virus inactivation

Antimicrobial host defense peptides (AHDPs) are effective against a wide range of microbes, including viruses. The arteriviral infection caused by porcine reproductive and respiratory syndrome virus (PRRSV) is a devastating pandemic that causes the most economically significant disease of swine. We sought to determine if the expression of AHDPs was influenced by infection with PRRSV, and if porcine AHDPs have direct antiviral activity against PRRSV. Because pulmonary alveolar macrophages (PAMs) are primary targets of PRRSV infection, gene expression of porcine AHDPs was evaluated in lungs from fetal and 2-wk-old congenitally infected pigs. In PRRSV-positive lungs and PAMs, gene expression of most porcine AHDPs showed little upregulation. However, gene expression of porcine beta-defensin-1 (pBD-1), pBD-4, pBD-104, pBD-123, and pBD-125 were downregulated more than threefold in 2-wk-old congenitally infected pig lungs. Incubation of PRRSV with pBD-3 or PG-4 significantly inhibited viral infectivity in MARC-145 cells. Using nine protegrin or protegrin-derived peptides, we determined that a cyclic analog of PG-4 increased anti-PRRSV activity, and that substitution of phenylalanine with valine eliminated most PG-4 antiviral activity. In PAMs, pBD-3 and PG-4 at 5-40 microg/mL consistently suppressed PRRSV titers. Collectively, these findings suggest a potential role for some porcine AHDPs as innate antiviral effectors in PRRSV infection. Moreover, modulation of porcine innate immune mechanisms with AHDPs may be one means of limiting the impact of this costly pandemic viral disease.

Growth factors and corneal epithelial wound healing

In this article, we briefly review recent findings in the effects of growth factors including the EGF family, KGF, HGF, IGF, insulin, and TGF-beta on corneal epithelial wound healing. We discuss the essential role of EGFR in inter-receptor cross-talk in response to wounding in corneal epithelium and bring forward a concept of "alarmins" to the field of wound healing research.

A novel antimicrobial peptidoglycan recognition protein in the cornea

PURPOSE

In an earlier gene expression study, the authors identified a novel antimicrobial gene, Peptidoglycan recognition protein 1 (Pglyrp1), in the mouse cornea. Here the expression of the Pglyrp1 transcript and the encoded protein, PGLYRP1, in the cornea was investigated. The role of PGLYRP1 in the cornea was further investigated using wild-type and Pglyrp1-deficient mice. This is the first report of this antimicrobial protein in the cornea.

METHODS

PGLYRP1 was detected in the cornea and was further localized to the epithelium by immunohistology, confocal microscopy, immunoblotting, and real-time PCR. The role of PGLYRP1 in the cornea was investigated by comparing the response of wild-type and Pglyrp1(-/-) mice to corneal epithelial wounds and Pseudomonas aeruginosa-mediated corneal infections. The antibacterial effects of corneal PGLYRP1 were assayed by measuring bacterial growth in vitro, in the presence of wild-type corneal epithelial extracts, before and after antibody-mediated blocking of PGLYRP1.

RESULTS

PGLYRP1 is expressed at high levels in the mouse corneal epithelium. PGLYRP1 was localized to the mouse corneal epithelium and the human corneal epithelium. The Pglyrp1(-/-) mouse shows delayed healing and poor clearing of bacterial keratitis; in vitro its epithelial protein extract shows reduced bacteriostatic activity compared with wild-type mice.

CONCLUSIONS

PGLYRP1 is a novel antimicrobial protein of the corneal epithelium and protects the ocular surface from bacterial infections.

LL-37 complexation with glycosaminoglycans in cystic fibrosis lungs inhibits antimicrobial activity, which can be restored by hypertonic saline

There is an abundance of antimicrobial peptides in cystic fibrosis (CF) lungs. Despite this, individuals with CF are susceptible to microbial colonization and infection. In this study, we investigated the antimicrobial response within the CF lung, focusing on the human cathelicidin LL-37. We demonstrate the presence of the LL-37 precursor, human cathelicidin precursor protein designated 18-kDa cationic antimicrobial protein, in the CF lung along with evidence that it is processed to active LL-37 by proteinase-3. We demonstrate that despite supranormal levels of LL-37, the lung fluid from CF patients exhibits no demonstrable antimicrobial activity. Furthermore Pseudomonas killing by physiological concentrations of exogenous LL-37 is inhibited by CF bronchoalveolar lavage (BAL) fluid due to proteolytic degradation of LL-37 by neutrophil elastase and cathepsin D. The endogenous LL-37 in CF BAL fluid is protected from this proteolysis by interactions with glycosaminoglycans, but while this protects LL-37 from proteolysis it results in inactivation of LL-37 antimicrobial activity. By digesting glycosaminoglycans in CF BAL fluid, endogenous LL-37 is liberated and the antimicrobial properties of CF BAL fluid restored. High sodium concentrations also liberate LL-37 in CF BAL fluid in vitro. This is also seen in vivo in CF sputum where LL-37 is complexed to glycosaminoglycans but is liberated following nebulized hypertonic saline resulting in increased antimicrobial effect. These data suggest glycosaminoglycan-LL-37 complexes to be potential therapeutic targets. Factors that disrupt glycosaminoglycan-LL-37 aggregates promote the antimicrobial effects of LL-37 with the caveat that concomitant administration of antiproteases may be needed to protect the now liberated LL-37 from proteolytic cleavage.

cAMP stringently regulates human cathelicidin antimicrobial peptide expression in the mucosal epithelial cells by activating cAMP-response element-binding protein, AP-1, and inducible cAMP early repressor

Little is known about the regulation of the innate host defense peptide cathelicidin at the mucosal surfaces. Expression is believed to be transcriptionally regulated, and several cis-acting elements have been identified in the cathelicidin putative promoter. However, the trans-acting factors have not been clearly defined. We have recently reported that bacterial exotoxins suppress cathelicidin expression in sodium butyrate-differentiated intestinal epithelial cells (ECs), and this may be mediated through inducible cAMP early repressor. Here we have shown that cAMP-signaling pathways transcriptionally regulate cathelicidin expression in various ECs. cAMP-response element-binding protein (CREB) and AP-1 (activator protein-1) bind to the cathelicidin putative promoter in vitro. Additionally, transcriptional complexes containing CREB, AP-1, and cathelicidin upstream regulatory sequences are formed within ECs. We have also shown that these complexes may activate cathelicidin promoter and are required for its inducible expression in ECs. This is underscored by the fact that silencing of CREB and AP-1 results in failure of ECs to up-regulate cathelicidin, and hepatitis B virus X protein may use CREB to induce cathelicidin. On the other hand, inducible cAMP early repressor competes with CREB and AP-1 for binding to the cathelicidin promoter and represses transcription, thus functioning as a counter-regulatory mechanism. Finally, both CREB and AP-1 were shown to play major roles in the regulation of cathelicidin in sodium butyrate-differentiated HT-29 cells. This is the first report of a detailed mechanistic study of inducible cathelicidin expression in the mucosal ECs. At the same time, it describes a novel immunomodulatory function of cAMP.

Phenotype of atopic dermatitis subjects with a history of eczema herpeticum

BACKGROUND

A subset of subjects with atopic dermatitis (AD) are susceptible to serious infections with herpes simplex virus, called eczema herpeticum, or vaccina virus, called eczema vaccinatum.

OBJECTIVE

This National Institute of Allergy and Infectious Diseases-funded multicenter study was performed to establish a database of clinical information and biologic samples on subjects with AD with and without a history of eczema herpeticum (ADEH(+) and ADEH(-) subjects, respectively) and healthy control subjects. Careful phenotyping of AD subsets might suggest mechanisms responsible for disseminated viral infections and help identify at-risk individuals.

METHODS

We analyzed the data from 901 subjects (ADEH(+) subjects, n = 134; ADEH(-) subjects, n = 419; healthy control subjects, n = 348) enrolled between May 11, 2006, and September 16, 2008, at 7 US medical centers.

RESULTS

ADEH(+) subjects had more severe disease based on scoring systems (Eczema Area and Severity Index and Rajka-Langeland score), body surface area affected, and biomarkers (circulating eosinophil counts and serum IgE, thymus and activation-regulated chemokine, and cutaneous T cell-attracting chemokine) than ADEH(-) subjects (P < .001). ADEH(+) subjects were also more likely to have a history of food allergy (69% vs 40%, P < .001) or asthma (64% vs 44%, P < .001) and were more commonly sensitized to many common allergens (P < .001). Cutaneous infections with Staphylococcus aureus or molluscum contagiosum virus were more common in ADEH(+) subjects (78% and 8%, respectively) than in ADEH(-) subjects (29% and 2%, respectively; P < .001).

CONCLUSION

Subjects with AD in whom eczema herpeticum develops have more severe T(H)2-polarized disease with greater allergen sensitization and more commonly have a history of food allergy, asthma, or both. They are also much more likely to experience cutaneous infections with S. aureus or molluscum contagiosum.

CAP37-derived antimicrobial peptides have in vitro antiviral activity against adenovirus and herpes simplex virus type 1

PURPOSE

The antiviral activity of an established antibacterial CAP37 domain and its extracellular mechanism of action were investigated.

METHODS

CAP37-derived peptides modified to assess the importance of disulfide bonds were evaluated in cytotoxicity and antiviral assays (direct time kill, dose dependency, and TOTO-1) for adenovirus (Ad) and herpes simplex virus type 1 (HSV-1).

RESULTS

Variable virus, adenovirus serotype-dependent, and dose-dependent inhibition were demonstrated without cytotoxicity. For peptide A (CAP37(20-44)), TOTO-1 dye uptake was demonstrated for Ad5 and HSV-1.

CONCLUSIONS

Unlike the antibacterial activity of this CAP37 domain, its antiviral activity is not fully dependent upon disulfide bond formation. Viral inhibition appears to result, in part, from disruption of the envelope and/or capsid.

Systems biology evaluation of immune responses induced by human host defence peptide LL-37 in mononuclear cells

The immune system is very complex, it involves the integrated regulation and expression of hundreds of proteins. To understand in greater detail how the human host defence immunomodulatory peptide LL-37 interacts with innate immunity, a systems approach was pursued. Polychromatic flow cytometry was employed to demonstrate that within human peripheral blood mononuclear cells, CD14+ monocytes, myeloid and plasmocytoid dendritic cells and T- and B-lymphocytes, all responded to LL-37, with the differential production of intracellular cytokines. Microarray analyses with CD14+ monocytes indicated the differential expression of 475 genes in response to stimulation with LL-37. To understand this complex response, bioinformatic interrogation, using InnateDB, of the gene ontology, signalling pathways and transcription factor binding sites was undertaken. Activation of the IkappaBalpha/NFkappaB, mitogen-activated protein kinases p38, ERK1/2 and JNK, and PI3K signalling pathways in response to LL-37 was demonstrated by pathway and ontology over-representation analyses, and confirmed experimentally by inhibitor studies. Computational analysis of the predicted transcription factor binding sites upstream of the genes that were regulated by LL-37 predicted the involvement of several transcription factors including NFkappaB and five novel factors, AP-1, AP-2, SP-1, E2F1, and EGR, which were experimentally confirmed to respond to LL-37 by performing transcription factor array studies on nuclear extracts from LL-37 treated mononuclear cells. These data are discussed as reflecting the integration of several responsive signalling pathways through the involvement of transcription factor complexes in gene expression activated by LL-37 in human mononuclear cells.

Vitamin D beyond bones in chronic obstructive pulmonary disease: time to act

The discovery that the vitamin D endocrine system regulates a very large number of genes and their associated biological processes improves our insight into the fundamental role of vitamin D and sun exposure for human health. Accumulating epidemiological data are linking a low vitamin D nutritional status to highly prevalent diseases such as cancer, autoimmune diseases, and chronic infections. Approximately half of the world's elderly, and to a lesser extent the adult population, have insufficient to deficient 25-hydroxyvitamin D (25-OHD) serum levels, and several intervention studies are being undertaken to study the impact of adequate vitamin D supplementation in chronic diseases. In this perspective we claim that chronic obstructive pulmonary disease (COPD) is a candidate disease for which vitamin D supplementation might be beneficial. Epidemiological studies revealed a dose-dependent association between serum 25-OHD levels and pulmonary function so that adequate vitamin D supplementation may extend beyond its protection against osteoporotic fractures. In line with the novel insights on its immune function, it is tempting to speculate that vitamin D may down-regulate the inflammatory immune response in the airways while boosting innate immune defense against different microorganisms. Apart from its affects on osteoporosis, vitamin D may also interfere with other comorbidities of COPD such as skeletal muscle weakness, cardiovascular disease, and cancer. Because respiratory treatments in COPD fail to reverse disease progression, interventional trials that may exploit the broader potential of vitamin D are warranted. A further challenge of such studies is to define optimal serum 25-OHD levels for such noncalcemic endpoints.

The role of antimicrobial peptides at the ocular surface

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

Human 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.

Hypothesis--ultraviolet-B irradiance and vitamin D reduce the risk of viral infections and thus their sequelae, including autoimmune diseases and some cancers

Many viral infections reach clinical significance in winter, when it is cold, relative humidity is lowest and vitamin D production from solar ultraviolet-B irradiation is at its nadir. Several autoimmune diseases, such as multiple sclerosis, type 1 diabetes mellitus and asthma, are linked to viral infections. Vitamin D, through induction of cathelicidin, which effectively combats both bacterial and viral infections, may reduce the risk of several autoimmune diseases and cancers by reducing the development of viral infections. Some types of cancer are also linked to viral infections. The cancers with seemingly important risk from viral infections important in winter, based on correlations with increasing latitude in the United States, an index of wintertime solar ultraviolet-B dose and vitamin D, are bladder, prostate, testicular and thyroid cancer, Hodgkin's and non-Hodgkin's lymphoma, and, perhaps, gastric cancer. The evidence examined includes the role of viruses in the etiology of these diseases, the geographic and seasonal variation of these diseases, and the time of life when vitamin D is effective in reducing the risk of disease. In general, the evidence supports the hypothesis. However, further work is required to evaluate this hypothesis.

Cathelicidin-deficient (Cnlp -/- ) mice show increased susceptibility to Pseudomonas aeruginosa keratitis

PURPOSE

To examine the clinical progression and innate immune responses during Pseudomonas aeruginosa (PA) keratitis in cathelicidin-deficient (KO) mice.

METHODS

PA (ATCC 19660) keratitis was induced in KO mice and wild-type (WT) littermates generated on a 129/SVJ background. Clinical score and histopathology were used to monitor the progression of infection at postinfection (PI) days 1, 3, 7, 14, and 21. Mouse corneas were harvested for viable bacteria quantitation, and myeloperoxidase (MPO) assays were performed to determine the number of infiltrating neutrophils. ELISA was used to quantitate interleukin (IL)-1beta, IL-6, macrophage inflammatory peptide (MIP)-2, keratinocyte-derived chemokine (KC), tumor necrosis factor (TNF)-alpha, and vascular endothelial growth factor (VEGF) levels in the corneas.

RESULTS

WT mice were resistant (cornea healed), whereas KO mice showed increased susceptibility (corneas failed to recover by 21 days or perforated) to PA infection. Clinical scores were significantly elevated in the infected corneas of KO mice versus WT mice at 7, 14, and 21 days PI. Absence of cathelicidin resulted in significantly delayed clearance of PA in the cornea and an increased number of infiltrating neutrophils at 1, 3, 7, and 14 days PI. KO mice also exhibited differential expression of protein levels for IL-1beta, IL-6, MIP-2, KC, TNF-alpha, and VEGF up to day 21 PI compared with the WT mice.

CONCLUSIONS

Cathelicidin-deficient mice showed considerable susceptibility to PA keratitis. The present study demonstrates direct in vivo evidence that endogenous expression of cathelicidin provides defense against corneal PA infection indicating its importance in host innate immunity at the ocular surface.

Ocular surface expression and in vitro activity of antimicrobial peptides

PURPOSE

Human ocular surface epithelia express four antimicrobial peptides (APs): beta -defensin (hBD) 1-3 and LL-37. Here the expression of additional APs (hBD 4-6, HE2beta 1; histatin-1, -3; liver expressed antimicrobial peptide-1, -2; macrophage inflammatory protein (MIP)-3alpha, and thymosin (T)beta -4) was sought and activity against common ocular pathogens studied.

METHODS

AP expression was determined in human corneal and conjunctival epithelial cells (HCEC, HCjEC) by RT-PCR and in corneal sections by immunostaining. Antimicrobial assays were performed to assess peptide (hBD 1-3, LL-37, MIP-3alpha, and Tbeta 4) activity against Pseudomonas aeruginosa (PA), Staphylococcus aureus (SA), and Staphylococcus epidermidis (SE) in the presence of NaCl or tears.

RESULTS

HCEC and HCjEC expressed MIP-3alpha and Tbeta 4. hBD 1-3, MIP-3alpha, and Tbeta 4 showed activity against PA. hBD-3 had potent activity against SA and SE, whereas hBD-2, MIP-3alpha and Tbeta 4 had moderate activity and hBD-1 had none. NaCl markedly attenuated, and tears almost completely inhibited the activity of hBD 1-2 and Tbeta 4, but not that of hBD-3.

CONCLUSIONS

The ocular surface epithelia additionally express MIP-3alpha and Tbeta 4 which have moderate antimicrobial activity. The current data support a role for hBD-3 as an antimicrobial peptide in vivo, but call in to question the effectiveness of some other APs. However, further study is required to conclusively elucidate the physiological role of each AP.

Lactoferrin Glu561Asp polymorphism is associated with susceptibility to herpes simplex keratitis

Lactoferrin plays an important role in the defense against infections, including herpes simplex virus (HSV) keratitis. We studied the impact of three single nucleotide polymorphisms in the human lactoferrin gene on the susceptibility to HSV infections of the eye and the severity of such infections. Lactoferrin gene polymorphisms were determined by PCR combined with restriction fragment length analysis in 105 HSV keratitis patients and 145 control subjects. Bilateral tear samples were harvested from 50 patients and 40 healthy controls and tear lactoferrin concentrations were determined by ELISA. Patients' records were used to acquire information about the severity of the HSV keratitis. The frequencies of the Glu561Asp polymorphism, but not those of the Ala11Thr and Lys29Arg polymorphisms, differed significantly between patients and control subjects with an under-representation of the Asp561 allele in the patient group. Furthermore, the values for best corrected visual acuity, frequency of recurrences since onset, and average duration of clinical episodes did not differ among patients with various lactoferrin genotypes. In addition, tear lactoferrin concentrations were the same in patients with HSV keratitis and healthy controls and also did not differ among patients with various lactoferrin genotypes. Lactoferrin Glu561Asp polymorphism is associated with the susceptibility to HSV keratitis with a protective role for lactoferrin variants comprising Asp561. However, no beneficial effects of this lactoferrin variant on the clinical outcome of ocular HSV keratitis were noted.

In vitro activity of human beta-defensin 2 against Pseudomonas aeruginosa in the presence of tear fluid

Pseudomonas aeruginosa causes vision-threatening keratitis and is difficult to treat due to emerging resistance. Human beta-defensin 2 (hBD-2) is an antimicrobial peptide expressed by ocular surface epithelia with broad-spectrum activity against various pathogens, including P. aeruginosa. The activity of hBD-2 against P. aeruginosa in the presence of human tears or NaCl was studied. In some experiments, tears were heat-inactivated, filtered, and separated into cationic/anionic fractions or mucin MUC5AC was removed by immunoprecipitation before use. Immunoprecipitation was performed to study the interaction between hBD-2 and MUC5AC. hBD-2 activity was reduced by 40 to 90% in the presence of 17.5 to 70% (vol/vol) tears. NaCl reduced hBD-2 activity, but at most it could account for only 36% of the inhibitory effect of tears. Heat inactivation and filtration attenuated the ability of tears to inhibit hBD-2 activity by 65 and 68%, respectively. Anionic tear fractions significantly reduced (86%) the activity of hBD-2, whereas only a 22% reduction was observed with the cationic fractions. In the absence of MUC5AC, the activity of hBD-2 was restored by 64%. Immunoprecipitation studies suggested that the loss of hBD-2 activity in tears is due to a direct binding interaction with MUC5AC. Our data showed that the antimicrobial activity of hBD-2 is sensitive to the presence of human tears and that this is partly due to the salt content and also the presence of MUC5AC. These data cast doubt on the effectiveness of hBD-2 as an antimicrobial peptide, and additional studies are required to conclusively elucidate its role in innate immunity at the ocular surface in vivo.

Gene expression and localization of the epinecidin-1 antimicrobial peptide in the grouper (Epinephelus coioides), and its role in protecting fish against pathogenic infection

Epinecidin-1 is an antimicrobial peptide and plays a vital role in protecting fish against pathogenic infection. As a mimic of a grouper epinecidin-1 peptide, it has tertiary structures that closely resemble those of pleurocidin found in the winter flounder (Pleuronectes americanus). The tissue-specific, lipopolysaccharide (LPS)-stimulation-specific, and poly(I):poly(C)-stimulation-specific expressions of the grouper (Epinephelus coioides) epinecidin-1 antimicrobial peptide were determined using a comparative reverse-transcription polymerase chain reaction. Results of the tissue distribution analysis revealed high levels of epinecidin-1 messenger RNA (mRNA) in the head kidneys, intestines, and skin. Expression of epinecidin-1 mRNA was dose-dependently stimulated by both LPS and poly(I):poly(C). Immunohistochemical analysis with the polyclonal antiserum of a grouper epinecidin-1 peptide (rabbit polyclonal antibody) showed that the peptide was localized with the epinecidin-1 antibody in the gills and intestines. Two synthetic peptides of the grouper epinecidin-1 peptide (g-ple 22-51 and g-ple 22-42) and one winter flounder pleurocidin as a control exhibited high antimicrobial activities against gram-negative or gram-positive bacteria. In addition, peptide treatment was effective in promoting a significant increase in fish survival after the injection of Vibrio vulnificus in tilapia (Oreochromis mossambicus) and grouper. These results are relevant to the design of prophylactic and therapeutic strategies to counter bacterial infections, especially for preventing or ameliorating immune defects in fish during bacterial infections.

Life at the front: dissecting bacterial-host interactions at the ocular surface

The ocular surface usually looks quiet, presenting a general impression of biological inactivity. Yet, the ability of the cornea to maintain health while continually exposed to environmental insults, and in the relative absence of immune strategies afforded by other body sites, reflects its complexity. Because it is critical for transparency and, therefore, our survival, the fine structure of the cornea has likely provided the driving force for the evolution of what appears to be a truly remarkable system. While several molecules are now known to participate, we are only beginning to obtain the knowledge to fully explain the mechanisms involved in corneal resistance to infection. Full explanation will require a better understanding of the interplay between microbes and various components of the ocular surface, and of the critical factors determining health as the usual outcome. To understand infectious disease, we need to consider how the scenario changes in conditions associated with susceptibility. What we learn in the process could yield a wealth of potential therapies for a wide variety of diseases of the eye and of other sites.

Antibacterial activities of poly(amidoamine) dendrimers terminated with amino and poly(ethylene glycol) groups

Poly(amidoamine) (PAMAM) dendrimer derivatives have been investigated for their biological applications, especially for delivery of drugs, including antimicrobial drugs to eukaryotic cells, but their effects on bacterial cells are largely unexplored. Herein we report that amino-terminated PAMAM dendrimers are highly toxic to the common Gram-negative pathogen Pseudomonas aeruginosa. The concentration that kills 50% of the bacteria (EC50) was in the range of approximately 0.9-1.5 microg/mL for the generation 5, amino-terminated dendrimers with or without partial (43%) coating of poly(ethylene glycol) (PEG). These EC50 values were lower than that ( approximately 1.9-2.8 microg/mL) for LL-37, a potent antimicrobial peptide expressed in a variety of epithelia. On the contrary, the dendrimers were far less toxic (EC50 > 21 microg/mL) to the Gram-positive pathogen Staphylococcus aureus than LL-37 (EC50 = approximately 1.9 microg/mL). In agreement with the previous studies on other cell types, the dendrimers were not cytotoxic to human corneal epithelial cells at the concentrations that were toxic to P. aeruginosa. Our findings indicate that amino-terminated PAMAM dendrimers and their partially PEG-coated derivatives possess attractive antimicrobial properties, particularly against Gram-negative bacteria, thus expanding the potential biological application of the dendrimers.

Insight into the host-parasite interplay by proteomic study of host proteins copurified with the human parasite, Schistosoma japonicum

The tegument proteins of schistosome have attracted the most attention in studies of host-parasite interplay, while the host proteins acting at the host-parasite interface remained largely elusive. Here, we undertook a high-throughput proteomic approach to characterize the schistosome-adsorbed host proteins. Fifty five distinct host proteins were confidently identified in S. japonicum samples, including cercaria, schistosomula, adults, eggs, and miracidia, together with tegument and eggshell preparations, of which 23 and 38 host proteins were identified in adult worms and eggs, respectively. Among the schistosome-adsorbed host proteins, host neutrophil elastases were found in the granuloma initiated by schistosome egg deposition, implying that the host innate immune molecules could participate in the granuloma formation for fighting against schistosome invasion, except for the adaptive immune system. In addition, some host proteins, such as proteinase inhibitor and superoxide dismutase, might be utilized by schistosome to counteract or attenuate the host attacks. These parasite-adsorbed host proteins will provide new insights into the host immune responses against schistosome infection, the evasive behavior of the adult worms, and the granuloma formation, which could render an in-depth understanding for the host-parasite interplay.

Antimicrobial peptides and proteins, exercise and innate mucosal immunity

This review examines the question of whether exercise can be used as an experimental model to further our understanding of innate antimicrobial peptides and proteins (AMPs) and their role in susceptibility to infection at mucosal surfaces. There is strong evidence to suggest that AMPs, in combination with cellular and physical factors, play an important role in preventing infection. Although AMPs act directly on microorganisms, there is increasing recognition that they also exert their protective effect via immunomodulatory mechanisms, especially in noninflammatory conditions. Further studies that manipulate physiologically relevant concentrations of AMPs are required to shed light on the role they play in reducing susceptibility to infection. Evidence shows that in various form prolonged and/or exhaustive exercise is a potent modulator of the immune system, which can either sharpen or blunt the immune response to pathogens. The intensity and duration of exercise can be readily controlled in experimental settings to manipulate the degree of physical stress. This would allow for an investigation into a potential dose–response effect between exercise and AMPs. In addition, the use of controlled exercise could provide an experimental model by which to examine whether changes in the concentration of AMPs alters susceptibility to illness.

Antimicrobial peptides as new recognition molecules for screening challenging species

The goal of this study was to evaluate binding of four targets of biodefense interest to immobilized antimicrobial peptides (AMPs) in biosensor assays. Polymyxins B and E, melittin, cecropins A, B, and P, parasin, bactenecin and magainin-1, as well as control antibodies, were used as capture molecules for detection of Cy3-labeled Venezuelan equine encephalitis virus (VEE), vaccinia virus, C. burnetti and B. melitensis. Although VEE, vaccinia virus and C. burnetti did not show any binding activity to their corresponding capture antibodies, B. melitensis bound to immobilized anti-Brucella monoclonal antibodies. The majority of the immobilized AMPs included in this study bound labeled VEE, vaccinia virus and C. burnetti in a concentration-dependent manner, and B. melitensis bound to polymyxin B, polymyxin E, and bactenecin. No binding was observed on immobilized magainin-1. In contrast to all bacterial targets tested to date, VEE and vaccinia virus demonstrated similar patterns of binding to all peptides. While the direct assay is generally replaced by a sandwich assay for analysis of real-world samples, direct binding experiments are commonly used to characterize specificity and sensitivity of binding molecules. In this case, they clearly demonstrate the capability of AMPs as recognition molecules for four biothreat agents.

Antimicrobial peptides: therapeutic potential

A significant component of the innate immune system of a wide variety of animals and plants is arbitrated by cationic host defence peptides. In man, these peptides, in addition to exhibiting a direct antimicrobial activity, seems to provide a range of non-antimicrobial bioactivities related to defence, inflammation and wound healing. Despite the fact that such peptides have so far failed to reach the market, there are continued initiatives to advance such potential therapeutics to, and through, the clinic. The reasons behind such initiatives include: reduced manufacturing costs for peptides; allowing entry into therapeutic areas previously inaccessible due to cost; the continued identification of previously unknown bioactivities of such peptides; and the resurgence of interest in peptide therapeutics. As a result, clinical programmes based on cationic host defence peptides exist in the areas of infection, dermatology, cancer and inflammation. The probability of clinical success for host defence peptide-based therapeutics is on the rise as options for a wider range of clinical indications emerge.

Antiviral therapy for adenovirus infections

The treatment of severe adenovirus keratoconjunctivitis and life-threatening adenovirus infections in immunocompromised patients is still unsatisfactory. We here review the mode of action and antiviral data for cidofovir and ribavirin, obtained in cell culture, animal models or patients. Several nucleoside or nucleotide analogues have been described that target the adenovirus polymerase, whereas other antiviral targets have been poorly investigated. Furthermore, optimal therapeutic response may be achieved by combining antiviral therapy with immunotherapeutic approaches, as currently being explored.

LL-37, the only human member of the cathelicidin family of antimicrobial peptides

Antimicrobial peptides and their precursor molecules form a central part of human and mammalian innate immunity. The underlying genes have been thoroughly investigated and compared for a considerable number of species, allowing for phylogenetic characterization. On the phenotypical side, an ever-increasing number of very varied and distinctive influences of antimicrobial peptides on the innate immune system are reported. The basic biophysical understanding of mammalian antimicrobial peptides, however, is still very limited. This is especially unsatisfactory since knowledge of structural properties will greatly help in the understanding of their immunomodulatory functions. The focus of this review article will be on LL-37, the only cathelicidin-derived antimicrobial peptide found in humans. LL-37 is a 37-residue, amphipathic, helical peptide found throughout the body and has been shown to exhibit a broad spectrum of antimicrobial activity. It is expressed in epithelial cells of the testis, skin, the gastrointestinal tract, and the respiratory tract, and in leukocytes such as monocytes, neutrophils, T cells, NK cells, and B cells. It has been found to have additional defensive roles such as regulating the inflammatory response and chemo-attracting cells of the adaptive immune system to wound or infection sites, binding and neutralizing LPS, and promoting re-epthelialization and wound closure. The article aims to report the known biophysical facts, with an emphasis on structural evidence, and to set them into relation with insights gained on phylogenetically related antimicrobial peptides in other species. The multitude of immuno-functional roles is only outlined. We believe that this review will aid the future work on the biophysical, biochemical and immunological investigations of this highly intriguing molecule.

Cathelicidin deficiency predisposes to eczema herpeticum

BACKGROUND

The cathelicidin family of antimicrobial peptides is an integral component of the innate immune response that exhibits activity against bacterial, fungal, and viral pathogens. Eczema herpeticum (ADEH) develops in a subset of patients with atopic dermatitis (AD) because of disseminated infection with herpes simplex virus (HSV).

OBJECTIVE

This study investigated the potential role of cathelicidins in host susceptibility to HSV infection.

METHODS

Glycoprotein D was measured by means of real-time RT-PCR as a marker of HSV replication in skin biopsy specimens and human keratinocyte cultures. Cathelicidin expression was evaluated in skin biopsy specimens from patients with AD (n = 10) without a history of HSV skin infection and from patients with ADEH (n = 10).

RESULTS

The cathelicidin peptide LL-37 (human cathelicidin) exhibited activity against HSV in an antiviral assay, with significant killing (P < .001) within the physiologic range. The importance of cathelicidins in antiviral skin host defense was confirmed by the observation of higher levels of HSV-2 replication in cathelicidin-deficient (Cnlp-/-) mouse skin (2.6 +/- 0.5 pg HSV/pg GAPDH, P < .05) compared with that seen in skin from their wild-type counterparts (0.9 +/- 0.3). Skin from patients with ADEH exhibited significantly (P < .05) lower levels of cathelicidin protein expression than skin from patients with AD. We also found a significant inverse correlation between cathelicidin expression and serum IgE levels (r2 = 0.46, P < .05) in patients with AD and patients with ADEH.

CONCLUSION

This study demonstrates that the cathelicidin peptide LL-37 possesses antiviral activity against HSV and demonstrates the importance of variable skin expression of cathelicidins in controlling susceptibility to ADEH. Additionally, serum IgE levels might be a surrogate marker for innate immune function and serve as a biomarker for which patients with AD are susceptible to ADEH.

CLINICAL IMPLICATIONS

A deficiency of LL-37 might render patients with AD susceptible to ADEH. Therefore increasing production of skin LL-37 might prevent herpes infection in patients with AD.

A review of antimicrobial peptides and their therapeutic potential as anti-infective drugs

PURPOSE

Antimicrobial peptides (AMPs) are an essential part of innate immunity that evolved in most living organisms over 2.6 billion years to combat microbial challenge. These small cationic peptides are multifunctional as effectors of innate immunity on skin and mucosal surfaces and have demonstrated direct antimicrobial activity against various bacteria, viruses, fungi, and parasites. This review summarizes their progress to date as commercial antimicrobial drugs for topical and systemic indications.

METHODS

Literature review.

RESULTS

Despite numerous clinical trials, no modified AMP has obtained Food & Drug Administration approval yet for any topical or systemic medical indications.

CONCLUSIONS

While AMPs are recognized as essential components of natural host innate immunity against microbial challenge, their usefulness as a new class of antimicrobial drugs still remains to be proven.