Defensins purified from human granulocytes bind C1q and activate the classical complement pathway like the transmembrane glycoprotein gp41 of HIV-1

Antimicrobial peptides´ immune modulation role in intracellular bacterial infection

Intracellular bacteria cause a wide range of diseases, and their intracellular lifestyle makes infections difficult to resolve. Furthermore, standard therapy antibiotics are often unable to eliminate the infection because they have poor cellular uptake and do not reach the concentrations needed to kill bacteria. In this context, antimicrobial peptides (AMPs) are a promising therapeutic approach. AMPs are short cationic peptides. They are essential components of the innate immune response and important candidates for therapy due to their bactericidal properties and ability to modulate host immune responses. AMPs control infections through their diverse immunomodulatory effects stimulating and/or boosting immune responses. This review focuses on AMPs described to treat intracellular bacterial infections and the known immune mechanisms they influence.

Role of Defensins in Tumor Biology

Defensins have long been considered as merely antimicrobial peptides. Throughout the years, more immune-related functions have been discovered for both the α-defensin and β-defensin subfamily. This review provides insights into the role of defensins in tumor immunity. Since defensins are present and differentially expressed in certain cancer types, researchers started to unravel their role in the tumor microenvironment. The human neutrophil peptides have been demonstrated to be directly oncolytic by permealizing the cell membrane. Further, defensins can inflict DNA damage and induce apoptosis of tumor cells. In the tumor microenvironment, defensins can act as chemoattractants for subsets of immune cells, such as T cells, immature dendritic cells, monocytes and mast cells. Additionally, by activating the targeted leukocytes, defensins generate pro-inflammatory signals. Moreover, immuno-adjuvant effects have been reported in a variety of models. Therefore, the action of defensins reaches beyond their direct antimicrobial effect, i.e., the lysis of microbes invading the mucosal surfaces. By causing an increase in pro-inflammatory signaling events, cell lysis (generating antigens) and attraction and activation of antigen presenting cells, defensins could have a relevant role in activating the adaptive immune system and generating anti-tumor immunity, and could thus contribute to the success of immune therapy.

Antimicrobial Peptide Arenicin-1 Derivative Ar-1-(C/A) as Complement System Modulator

Antimicrobial peptides (AMPs) are not only cytotoxic towards host pathogens or cancer cells but also are able to act as immunomodulators. It was shown that some human and non-human AMPs can interact with complement proteins and thereby modulate complement activity. Thus, AMPs could be considered as the base for complement-targeted therapeutics development. Arenicins from the sea polychaete Arenicola marina, the classical example of peptides with a β-hairpin structure stabilized by a disulfide bond, were shown earlier to be among the most prospective regulators. Here, we investigate the link between arenicins' structure and their antimicrobial, hemolytic and complement-modulating activities using the derivative Ar-1-(C/A) without a disulfide bond. Despite the absence of this bond, the peptide retains all important functional activities and also appears less hemolytic in comparison with the natural forms. These findings could help to investigate new complement drugs for regulation using arenicin derivatives.

Human antimicrobial peptides in autoimmunity

Antimicrobial peptides (AMPs) were firstly discovered as cytotoxic substances that killed bacteria. Later they were described as biologically active peptides that are able not only to kill invaders but also to modulate host immunity. In particular, it is shown that human antimicrobial peptides are able to influence the activity of different innate and adaptive immunity components, thus, obviously, they also participate in autoimmune processes. In this review we discuss the nature of human AMPs and analyze their role in such autoimmune disorders like type 1 diabetes mellitus, rheumatoid arthritis, systemic lupus erythematosus, psoriasis, Crohn's disease and sarcoidosis. These peptides were shown to have a "double-sided" influence on the autoimmune disease pathogenesis. Thus, described facts should be taken into account for the development of new pharmaceutical agents to cure patients with autoimmune disorders. These agents could derive from natural antimicrobial peptides that in some cases modulate immune response. For example, it was shown that human AMPs are able to modulate complement system dysregulation of which is known to be one of the most dangerous pathogenic factors during autoimmune processes.

HBD3 Induces PD-L1 Expression on Head and Neck Squamous Cell Carcinoma Cell Lines

Human β-defensin 3 (HBD3) is an antimicrobial peptide up-regulated in the oral tissues of individuals with head and neck squamous cell carcinomas (HNSCC) and oral squamous cell carcinomas (SCC) and present in high concentrations in their saliva. In this study, we determined if HBD3 contributes to HNSCC pathogenesis by inducing programmed death-ligand 1 (PD-L1) expression on HNSCC cell lines. For this, SCC cell lines SCC4, SCC15, SCC19, SCC25, and SCC99 (5.0 × 10⁴ viable cells) were used. Cells were incubated with IFNγ (0.6 µM) and HBD3 (0.2, 2.0, or 20.0 µM) for 24 h. Cells alone served as controls. Cells were then treated with anti-human APC-CD274 (PD-L1) and Live/Dead Fixable Green Dead Cell Stain. Cells treated with an isotype antibody and cells alone served as controls. All cell suspensions were analyzed in a LSR II Violet Flow Cytometer. Cytometric data was analyzed using FlowJo software. Treatment with IFNγ (0.6 µM) increased the number of cells expressing PD-L1 (p < 0.05) with respect to controls. Treatment with HBD3 (20.0 µM) also increased the number of cells expressing PD-L1 (p < 0.05) with respect to controls. However, treatment with IFNγ (0.6 µM) was not significantly different from treatment with HBD3 (20.0 µM) and the numbers of cells expressing PD-L1 were similar (p = 1). Thus, HBD3 increases the number of cells expressing PD-L1. This is a novel concept, but the role HBD3 contributes to HNSCC pathogenesis by inducing PD-L1 expression in tumors will have to be determined.

Human beta defensin 3 alters matrix metalloproteinase production in human dendritic cells exposed to Porphyromonas gingivalis hemagglutinin B

BACKGROUND

Matrix metalloproteinases (MMPs) are zinc- or calcium-dependent proteinases involved in normal maintenance of extracellular matrix. When elevated, they contribute to the tissue destruction seen in periodontal disease. Recently, we found that human beta defensin 3 (HBD3), a cationic antimicrobial peptide, alters chemokine and proinflammatory cytokine responses in human myeloid dendritic cells exposed to Porphyromonas gingivalis hemagglutinin B (HagB). In this study, the hypotheses that HagB induces MMP production in dendritic cells and that HBD3 mixed with HagB prior to treatment alters HagB-induced MMP profiles were tested.

METHODS

Dendritic cells were exposed to 0.2 μM HagB alone and HagB + HBD3 (0.2 or 2.0 μM) mixtures. After 16 hours, concentrations of MMPs in cell culture media were determined with commercial multiplex fluorescent bead-based immunoassays. An integrated cell network was used to identify potential HagB-induced signaling pathways in dendritic cells leading to the production of MMPs.

RESULTS

0.2 μM HagB induced MMP1, -2, -7, -9, and -12 responses in dendritic cells. 0.2 μM HBD3 enhanced the HagB-induced MMP7 response (P < 0.05) and 2.0 μM HBD3 attenuated HagB-induced MMP1, -7, and -9 responses (P < 0.05). The MMP12 response was not affected. In the predicted network, MMPs are produced via activation of multiple pathways. Signals converge to activate numerous transcription factors, which transcribe different MMPs.

CONCLUSION

HagB was an MMP stimulus and HBD3 was found to decrease HagB-induced MMP1, -7, and -9 responses in dendritic cells at 16 hours, an observation that suggests HBD3 can alter microbial antigen-induced production of MMPs.

Innate Immunity to Mucosal Candida Infections

Mucosal epithelial tissues are exposed to high numbers of microbes, including commensal fungi, and are able to distinguish between those that are avirulent and those that cause disease. Epithelial cells have evolved multiple mechanisms to defend against colonization and invasion by Candida species. The interplay between mucosal epithelial tissues and immune cells is key for control and clearance of fungal infections. Our understanding of the mucosal innate host defense system has expanded recently with new studies bringing to light the importance of epithelial cell responses, innate T cells, neutrophils, and other phagocytes during Candida infections. Epithelial tissues release cytokines, host defense peptides, and alarmins during Candida invasion that act in concert to limit fungal proliferation and recruit immune effector cells. The innate T cell/IL-17 axis and recruitment of neutrophils are of central importance in controlling mucosal fungal infections. Here, we review current knowledge of the innate immunity at sites of mucosal Candida infection, with a focus on infections caused by C. albicans.

[Interaction of Arenicin-1 with C1q Protein]

The interaction between arenicin-1, that is an antimicrobial peptide from polychaeta Arenicola marina, and human complement system protein C1q was studied using enzyme-linked receptor sorbent assay and ELISA. We revealed that arenicin-1 and C1q form complex that is stable in high ionic strength condition 0.5 M NaCl. The ability of C1q to interact with arenicin-1 is comparable with the binding activity of C1q towards another antimicrobial peptide, porcine cathelicidin protegrin-1, which has a similar spatial arrangement with arenicin-1. Namely, both arenicin-1 and protegrin-1 form cystine-stabilized antiparallel β-hairpin structure.

Cytotoxicity of HBD3 for dendritic cells, normal human epidermal keratinocytes, hTERT keratinocytes, and primary oral gingival epithelial keratinocytes in cell culture conditions

Human β-defensin 3 (HBD3) is a prominent host defense peptide. In our recent work, we observed that HBD3 modulates pro-inflammatory agonist-induced chemokine and cytokine responses in human myeloid dendritic cells (DCs), often at 20.0 μM concentrations. Since HBD3 can be cytotoxic in some circumstances, it is necessary to assess its cytotoxicity for DCs, normal human epidermal keratinocytes (NHEKs), human telomerase reverse transcriptase (hTERT) keratinocytes, and primary oral gingival epithelial (GE) keratinocytes in different cell culture conditions. Cells, in serum free media with resazurin and in complete media with 10% fetal bovine serum and resazurin, were incubated with 5, 10, 20, and 40 μM HBD3. Cytotoxicity was determined by measuring metabolic conversion of resazurin to resorufin. The lethal dose 50 (LD50, mean μM±Std Err) values were determined from the median fluorescent intensities of test concentrations compared to live and killed cell controls. The LD50 value range of HBD3 was 18.2-35.9 μM in serum-free media for DCs, NHEKs, hTERT keratinocytes, and GE keratinocytes, and >40.0 μM in complete media. Thus, HBD3 was cytotoxic at higher concentrations, which must be considered in future studies of HBD3-modulated chemokine and cytokine responses in vitro.

The overlapping roles of antimicrobial peptides and complement in recruitment and activation of tumor-associated inflammatory cells

Antimicrobial peptides (AMPs) represent a group of small (6-100 amino acids), biologically active molecules, which are produced by plants, mammals, and microorganisms (1). An important element of the innate immune response, AMP, possesses potent antibiotic, antifungal, and antiviral activities. Furthermore, AMP may be involved in a number of other processes such as angiogenesis and modulation of the immune response such as stimulation of chemokines and chemotaxis of leukocytes. AMPs have been proposed as alternative therapies for infectious diseases. AMP may also exert cytotoxic activity against tumor cells. Further understanding of the biological function of these peptides during tumor development and progression may aid in the development of novel anti-tumor therapies with refined application of innate molecules. AMP and complement have distinct roles to play in shaping the microenvironment (Table 1). Components of the complement system are integral contributors in responding to infection and sterile inflammation. Moreover, complement plays a role in the trafficking of cells in the tumor microenvironment, and thereby possibly in the immune response to cancer. This article will try to outline characteristics of AMP and complement in mobilization and recruitment of cells in tumor microenvironment.

2-Arachidonoyl-glycerol- and arachidonic acid-stimulated neutrophils release antimicrobial effectors against E. coli, S. aureus, HSV-1, and RSV

The endocannabinoid 2-AG is highly susceptible to its hydrolysis into AA, which activates neutrophils through de novo LTB(4) biosynthesis, independently of CB activation. In this study, we show that 2-AG and AA stimulate neutrophils to release antimicrobial effectors. Supernatants of neutrophils activated with nanomolar concentrations of 2-AG and AA indeed inhibited the infectivity of HSV-1 and RSV. Additionally, the supernatants of 2-AG- and AA-stimulated neutrophils strongly impaired the growth of Escherichia coli and Staphylococcus aureus. This correlated with the release of a large amount (micrograms) of α-defensins, as well as a limited amount (nanograms) of LL-37. All the effects of AA and 2-AG mentioned above were prevented by inhibiting LTB(4) biosynthesis or by blocking BLT(1). Importantly, neither CB(2) receptor agonists nor antagonists could mimic nor prevent the effects of 2-AG, respectively. In fact, qPCR data show that contaminating eosinophils express ∼100-fold more CB(2) receptor mRNA than purified neutrophils, suggesting that CB(2) receptor expression by human neutrophils is limited and that contaminating eosinophils are likely responsible for the previously documented CB(2) expression by freshly isolated human neutrophils. The rapid conversion of 2-AG to AA and their subsequent metabolism into LTB(4) promote 2-AG and AA as multifunctional activators of neutrophils, mainly exerting their effects by activating the BLT(1). Considering that nanomolar concentrations of AA or 2-AG were sufficient to impair viral infectivity, this suggests potential physiological roles for 2-AG and AA as regulators of host defense in vivo.

Antimicrobial-immunomodulatory activities of zebrafish phosvitin-derived peptide Pt5

A phosvitin (Pv)-derived peptide, Pt5, which consists of the C-terminal 55 residues of Pv in zebrafish, has been shown to function as an antimicrobial agent capable of killing microbes in vitro. However, its in vivo role in zebrafish remains unknown. In this study, we clearly demonstrated that Pt5 protected adult zebrafish from pathogenic Aeromonas hydrophila attack, capable of significantly enhancing the survival rate of zebrafish after the pathogenic challenge. Pt5 also caused a marked decrease in the numbers of A. hydrophila in the blood, spleen, kidney, liver and muscle, suggesting that Pt5 was able to block multiplication/dissemination of A. hydrophila in zebrafish. Additionally, Pt5 markedly suppressed the expression of the proinflammatory cytokine genes IL-1β, IL-6, TNF-α and IFN-γ in the spleen and head kidney of A. hydrophila-infected zebrafish, but it considerably enhanced the expressions of the antiinflammatory cytokine genes IL-10 and IL-4 in the same tissues. Taken together, these data indicate that Pt5 plays a dual role in zebrafish as an antimicrobial and immunomodulatory agent, capable of protecting zebrafish against pathogenic A. hydrophila through its antimicrobial activity as well as preventing zebrafish from the detrimental effects of an excessive inflammatory response via modulating immune functions.

The role of humoral innate immunity in hepatitis C virus infection

Infection with Hepatitis C Virus (HCV) causes chronic disease in approximately 80% of cases, resulting in chronic inflammation and cirrhosis. Current treatments are not completely effective, and a vaccine has yet to be developed. Spontaneous resolution of infection is associated with effective host adaptive immunity to HCV, including production of both HCV-specific T cells and neutralizing antibodies. However, the supporting role of soluble innate factors in protection against HCV is less well understood. The innate immune system provides an immediate line of defense against infections, triggering inflammation and playing a critical role in activating adaptive immunity. Innate immunity comprises both cellular and humoral components, the humoral arm consisting of pattern recognition molecules such as complement C1q, collectins and ficolins. These molecules activate the complement cascade, neutralize pathogens, and recruit antigen presenting cells. Here we review the current understanding of anti-viral components of the humoral innate immune system that play a similar role to antibodies, describing their role in immunity to HCV and their potential contribution to HCV pathogenesis.

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.

Gene expression profiles of acute exacerbations of idiopathic pulmonary fibrosis

RATIONALE

The molecular mechanisms underlying acute exacerbations of idiopathic pulmonary fibrosis (IPF) are poorly understood. We studied the global gene expression signature of acute exacerbations of IPF.

OBJECTIVES

To understand the gene expression patterns of acute exacerbations of IPF.

METHODS

RNA was extracted from 23 stable IPF lungs, 8 IPF lungs with acute exacerbation (IPF-AEx), and 15 control lungs and used for hybridization on Agilent gene expression microarrays. Functional analysis of genes was performed with Spotfire and Genomica. Gene validations for MMP1, MMP7, AGER, DEFA1-3, COL1A2, and CCNA2 were performed by real-time quantitative reverse transcription-polymerase chain reaction. Immunohistochemistry and in situ terminal deoxynucleotidyltransferase dUTP nick end-labeling assays were performed on the same tissues used for the microarray. ELISA for alpha-defensins was performed on plasma from control subjects, patients with stable IPF, and patients with IPF-AEx.

MEASUREMENTS AND MAIN RESULTS

Gene expression patterns in IPF-AEx and IPF samples were similar for the genes that distinguish IPF from control lungs. Five hundred and seventy-nine genes were differentially expressed (false discovery rate < 5%) between stable IPF and IPF-AEx. Functional analysis of these genes did not indicate any evidence of an infectious or overwhelming inflammatory etiology. CCNA2 and alpha-defensins were among the most up-regulated genes. CCNA2 and alpha-defensin protein levels were also higher and localized to the epithelium of IPF-AEx, where widespread apoptosis was also detected. alpha-Defensin protein levels were increased in the peripheral blood of patients with IPF-AEx.

CONCLUSIONS

Our results indicate that IPF-AEx is characterized by enhanced epithelial injury and proliferation, as reflected by increases in CCNA2 and alpha-defensins and apoptosis of epithelium. The concomitant increase in alpha-defensins in the peripheral blood and lungs may suggest their use as biomarkers for this disorder.

On the physiology and pathophysiology of antimicrobial peptides

Antimicrobial peptides (AMP) are a heterogeneous group of molecules involved in the nonspecific immune responses of a variety of organisms ranging from prokaryotes to mammals, including humans. AMP have various physical and biological properties, yet the most common feature is their antimicrobial effect. The majority of AMP disrupt the integrity of microbial cells by 1 of 3 known mechanisms--the barrel-stave pore model, the thoroidal pore model, or the carpet model. Results of growing numbers of descriptive and experimental studies show that altered expression of AMP in various tissues is important in the pathogenesis of several gastrointestinal, respiratory, and other diseases. We discuss novel approaches and strategies to further improve the promising future of therapeutic applications of AMP. The spread of antibiotic resistance increases the importance of developing a clinical role for AMP.

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 neutrophil peptide-1 inhibits both the classical and the lectin pathway of complement activation

Human neutrophil peptide-1 (HNP-1) is a member of the alpha-defensin family. Defensins are cationic antimicrobial peptides, which play an important role in the antimicrobial response to microorganisms. In addition, recent studies have revealed the involvement of defensins in inflammation, immunity and wound repair. Defensins are present in the azurophilic granules of neutrophils and are released upon neutrophil stimulation. Previous studies showed that HNP-1 binds to C1q and inhibits the classical complement pathway. In view of the structural and functional similarity between C1q and MBL, we have now examined the interactions between HNP-1 and MBL. We observed a dose-dependent binding of HNP-1 to MBL in calcium-free buffer, indicating that HNP-1 binds to MBL most likely via the collagenous domains. To identify the binding sites in HNP-1 involved in the binding to C1q and MBL, we used a series of overlapping synthetic linear peptides that spanned the entire HNP-1 sequence. Both MBL and C1q showed a dose-dependent binding to the same set of peptides, suggesting a similar binding site in HNP-1 for both MBL and C1q. Strongest binding was observed to peptides containing the C- or N-terminal part of the HNP-1 molecule. Using an ELISA based system, we demonstrated that HNP-1 inhibits activation of both the classical pathway and lectin pathway of complement. Furthermore, we demonstrated that C1q and MBL can form complexes with HNP-1 in solution. Together, the data indicate that HNP-1 interacts with both C1q and MBL efficiently resulting in inhibition of both the classical and the lectin pathway of complement. We conclude that HNP-1 may play a role in protection against tissue injury during inflammatory conditions by inhibiting the early phase of complement activation.

Importance of carbohydrate in the interaction of Tamm‐Horsfall protein with complement 1q and inhibition of classical complement activation

Tamm-Horsfall protein (THP) binds strongly to complement 1q (C1q), a key component of the classical complement pathway. The goals of this study were to determine whether THP altered the activation of the classical complement pathway and whether the carbohydrate portion of THP was involved in this glycoprotein's binding to C1q and alteration of complement activation. The ability of THP to prevent complement activation in diluted serum or plasma incubated at 37 degrees C was assessed using both a haemolytic assay with antibody-sensitized sheep RBC and a C4d ELISA. Both these methods showed that THP inhibited activation of the classical complement pathway in a dose-dependent manner. Glycosidases were used to remove most of the carbohydrate from THP. This partially deglycosylated THP bound human IgG with a higher affinity (KD1 = 1.4 nmol/L; KD2 = 0.31 micromol/L) than did intact THP (KD1 = 33.4 nmol/L; KD2 = 31.0 micromol/L). An ELISA showed that removal of carbohydrate from THP reduced, but did not eliminate, the ability of this protein to inhibit binding of C1q to intact THP. Haemolysis assays using antibody-sensitized sheep RBC showed that removal of THP carbohydrate eliminated the ability of THP to protect against complement activation. In conclusion, THP inhibited the activation of the classical complement pathway that occurred in diluted serum or plasma. The carbohydrate moieties of THP appeared to be important in this inhibitory activity.

Expression and regulation of antimicrobial peptides in articular joints

Articular joint infection is a surprisingly rare event considering the frequency of joint arthrocentesis and other invasive procedures applied to limb joints. This observation led us to the hypothesis that a local "chemical shield" in the form of antimicrobial proteins provides synovial membrane and articular cartilage with resistance to infection. We subsequently began a systematic analysis of in vitro and in vivo antimicrobially active proteins in healthy articular joints and in disease states such as pyogenic arthritis, rheumatoid arthritis, and osteoarthritis. An anatomical approach with systematic characterization combined with antimicrobial testing revealed expression and production of human antibiotic peptides and proteins. In this review, we focus on the most prominent antimicrobial proteins in articular joints, which we have identified as lysozyme, lactoferrin, secretory phospholipase A2, RNase 7, CAP37, the cathelicidin LL37, and especially the human beta-defensin-2 and -3 (HBD-2/-3). Activation pathways and possible antimicrobial functions are discussed and the involvement in non-antimicrobial processes such as tissue remodelling is also considered.

Antimicrobial peptides in the oral environment: expression and function in health and disease

The oral cavity is a unique environment in which antimicrobial peptides play a key role in maintaining health and may have future therapeutic applications. Present evidence suggests that alpha-defensins, beta-defensins, LL-37, histatin, and other antimicrobial peptides and proteins have distinct but overlapping roles in maintaining oral health and preventing bacterial, fungal, and viral adherence and infection. The expression of the inducible hBD-2 in normal oral epithelium, in contrast to other epithelia, and the apparent differential signaling in response to commensal and pathogenic organisms, provides new insights into innate immunity in this body site. Commensal bacteria are excellent inducers of hBD-2 in oral epithelial cells, suggesting that the commensal bacterial community acts in a manner to benefit the overall innate immune readiness of oral epithelia. This may have major significance for understanding host defense in the complex oral environment.

Tachyplesin activates the classic complement pathway to kill tumor cells

Tachyplesin is a small, cationic peptide that possesses antitumor properties. However, little is known about its action mechanism. We used phage display to identify a protein that interacted with tachyplesin and isolated a sequence corresponding to the collagen-like domain of C1q, a key component in the complement pathway. Their interaction was subsequently confirmed by both ELISA and affinity precipitation. Tachyplesin seemed to activate the classic complement cascade because it triggered several downstream events, including the cleavage and deposition of C4 and C3 and the formation of C5b-9. When TSU tumor cells were treated with tachyplesin in the presence of serum, activated C4b and C3b could be detected on tumor cells by flow cytometry, Western blotting, and confocal microscopy. However, this effect was blocked when the tumor cells were treated with hyaluronidase or a large excess of hyaluronan, indicating that hyaluronan or related glycosaminoglycans were involved in this process. Treatment of cells with tachyplesin and serum increased in membrane permeability as indicated by the ability of FITC-dextran to enter the cytoplasm. Finally, the combination of tachyplesin and human serum markedly inhibited the proliferation and caused death of TSU cells, and these effects were attenuated if the serum was heat-inactivated or if hyaluronidase was added. Taken together, these observations suggest that tachyplesin binds to both hyaluronan on the cell surface and C1q in the serum and activates the classic complement cascade, which damages the integrity of the membranes of the tumor cells resulting in their death.

Structural and functional anatomy of the globular domain of complement protein C1q

C1q is the first subcomponent of the classical pathway of the complement system and a major connecting link between innate and acquired immunity. As a versatile charge pattern recognition molecule, C1q is capable of engaging a broad range of ligands via its heterotrimeric globular domain (gC1q) which is composed of the C-terminal regions of its A (ghA), B (ghB) and C (ghC) chains. Recent studies using recombinant forms of ghA, ghB and ghC have suggested that the gC1q domain has a modular organization and each chain can have differential ligand specificity. The crystal structure of the gC1q, molecular modeling and protein engineering studies have combined to illustrate how modular organization, charge distribution and the spatial orientation of the heterotrimeric assembly offer versatility of ligand recognition to C1q. Although the biochemical and structural studies have provided novel insights into the structure-function relationships within the gC1q domain, they have also raised many unexpected issues for debate.

Primate defensins

Defensins are endogenous, cysteine-rich antimicrobial peptides that contribute to host defence against bacterial, fungal and viral infections. There are three subfamilies of defensins in primates: alpha-defensins are most common in neutrophils and Paneth cells of the small intestine; beta-defensins protect the skin and the mucous membranes of the respiratory, genitourinary and gastrointestinal tracts; and theta-defensins, which are expressed only in Old World monkeys, lesser apes and orangutans, are lectins with broad-spectrum antiviral efficacy. Here, their discovery and recent advances in understanding their properties and functions are described.

Defensins and Other Antimicrobial Peptides at the Ocular Surface

Although constantly exposed to the environment and "foreign bodies" such as contact lenses and unwashed fingertips, the ocular surface succumbs to infection relatively infrequently. This is, in large part, due to a very active and robust innate immune response mounted at the ocular surface. Studies over the past 20 years have revealed that small peptides with antimicrobial activity are a major component of the human innate immune response system. The ocular surface is no exception, with peptides of the defensin and cathelicidin families being detected in the tear film and secreted by corneal and conjunctival epithelial cells. There is also much evidence to suggest that the role of some antimicrobial peptides is not restricted to direct killing of pathogens, but, rather, that they function in various aspects of the immune response, including recruitment of immune cells, and through actions on dendritic cells provide a link to adaptive immunity. A role in wound healing is also supported. In this article, the properties, mechanisms of actions and functional roles of antimicrobial peptides are reviewed, with particular emphasis on the potential multifunctional roles of defensins and LL-37 (the only known human cathelicidin) at the ocular surface.

Multiple roles of antimicrobial defensins, cathelicidins, and eosinophil-derived neurotoxin in host defense

Mammals generate a diverse array of antimicrobial proteins, largely represented by defensins or cathelicidins. The direct in vitro microbicidal activity of antimicrobial proteins has long been considered an important innate immune defense, although the in vivo relevance has only very recently been established for certain defensins and cathelicidins. Mammalian defensins and cathelicidins have also been shown to have multiple receptor-mediated effects on immune cells. Beta-defensins interact with CCR6; murine beta-defensin-2 in addition activates TLR4. Cathelicidins act on FPRL1-expressing cells. Furthermore, several defensins have considerable immunoenhancing activity. Thus, it appears that mammalian antimicrobial proteins contribute to both innate and adaptive antimicrobial immunity.

Anti-complement effects of lactoferrin-derived peptides

Lactoferrin is an important biological molecule with many functions such as modulation of the inflammatory response, iron metabolism and antimicrobial defense. One effect of lactoferrin is the inhibition of the classical complement pathway. This study reports that antimicrobial peptides derived from the N-terminal region from both human and bovine lactoferrin, lactoferricin H and lactoferricin B, respectively, inhibit the classical complement pathway. No inhibitory effect of these peptides was observed on the alternative complement pathway in an AP50 assay. However, lactoferricin B reduced the inhibitory properties of serum against Escherichia coli in a concentration dependent manner. These results suggest that the N-terminal region of lactoferrin is the important part in the inhibition of complement activation and that these peptides possess other important properties than their antimicrobial effect.

Rat C-reactive protein activates the autologous complement system

Activation of complement is a biological function of human C-reactive protein (hCRP), whereas rat CRP (rCRP) has been claimed to be unable to activate complement. As important biological functions of proteins are probably conserved among species, we re-evaluated, using various ligands, the capability of rCRP to activate complement. The activation of complement by hCRP and rCRP was investigated in solid- and fluid-phase systems. In the solid-phase system, purified CRP was fixed to enzyme-linked immunosorbent assay (ELISA) plates and incubated with human or rat recalcified plasma. Dose-dependent binding of human and rat C3 and C4 was observed to human and rat CRP, respectively. In the fluid-phase system, recalcified rat plasma, which contains about 500 mg/l of CRP, or human plasma supplemented with hCRP, were incubated with lyso-phosphatidylcholine. A dose-dependent activation of complement was observed upon incubation with this ligand, as reflected by the generation of activated C4 as well as of CRP-complement complexes. This activation was, in both cases, inhibited by preincubation of plasma with p-aminophosphorylcholine, a specific inhibitor of the interaction of CRP with its ligands, or by chelation of calcium ions. We conclude that rat CRP, similarly to human CRP, can activate autologous complement. These results support the notion that opsonization of ligands with complement is an important biological function of CRP.

CAF-mediated human immunodeficiency virus (HIV) type 1 transcriptional inhibition is distinct from alpha-defensin-1 HIV inhibition

CD8(+) T lymphocytes can inhibit human immunodeficiency virus type 1 (HIV-1) replication by secreting a soluble factor(s) known as CD8(+) T-lymphocyte antiviral factor (CAF). One site of CAF action is inhibition of HIV-1 RNA transcription, particularly at the step of long terminal repeat (LTR)-driven gene expression. The inhibitory effect of CAF on HIV-1 LTR activation is mediated through STAT1 activation. A recent study reports that alpha-defensins 1 to 3 account for CAF activity against HIV-1. Here, we address whether alpha-defensins, particularly alpha-defensin-1, contribute to CAF-mediated inhibition of HIV-1 transcription. Both recombinant alpha-defensin-1 and CAF derived from herpesvirus saimiri (HVS)-transformed CD8(+) cells inhibited HIV-1 infection and gene expression. For both factors, the inhibition of HIV-1 infection did not occur at the level of viral entry. Pretreatment of cells with alpha-defensin-1 followed by a washing out prior to infection blocked infection by HIV-1, indicating that direct inactivation of virions was not required for its inhibitory effect. In contrast to CAF, alpha-defensin-1 did not inhibit phorbol myristate acetate- or Tat-mediated HIV-1 LTR activation in a transient transfection system, nor did it activate STAT1 tyrosine phosphorylation. Furthermore, alpha-defensins 1 to 3 were below the level of detection in a panel of HVS-transformed CD8(+) cells with potent HIV-1 inhibitory activity and a neutralizing antibody against alpha-defensins 1 to 3 did not reverse the inhibitory effect of CAF on HIV-1 gene expression in infected cells and on HIV-1 LTR activation in transfected cells. Taken together, our results suggest that alpha-defensin-1 inhibits HIV-1 infection following viral entry but that alpha-defensins 1 to 3 are not responsible for the HIV-1 transcriptional inhibition by CAF.

Antimicrobial peptides are expressed and produced in healthy and inflamed human synovial membranes

The objective of this study was to determine the expression and production of antimicrobial peptides by healthy and inflamed human synovial membranes. Deposition of the antimicrobial peptides lysozyme, lactoferrin, secretory phospholipase A(2) (sPA(2)), matrilysin (MMP7), human neutrophil alpha-defensins 1-3 (HNP 1-3), human beta-defensin 1 (HBD-1), and human beta-defensin 2 (HBD-2) was determined by immunohistochemistry. Expression of mRNA for the antimicrobial peptides bactericidal permeability-increasing protein (BPI), heparin binding protein (CAP37), human cationic antimicrobial protein (LL37), human alpha-defensin 5 (HD5), human alpha-defensin 6 (HD6), HBD-1, HBD-2, and human beta-defensin 3 (HBD-3) was analysed by reverse transcription polymerase chain reaction (RT-PCR). RT-PCR revealed CAP37 and HBD-1 mRNA in samples of healthy synovial membrane. Additionally, HBD-3 and/or LL37 mRNA was detected in synovial membrane samples from patients with pyogenic arthritis (PA), osteoarthritis (OA) or rheumatoid arthritis (RA). BPI, HD5, HD6, and HBD-2 mRNAs were absent from all samples investigated. Immunohistochemistry identified lysozyme, lactoferrin, sPA(2), and MMP7 in type A synoviocytes of all samples. HBD-1 was only present in type B synoviocytes of some of the samples. Immunoreactive HBD-2 peptide was only visible in some inflamed samples. HNP1-3 was detected in both healthy and inflamed synovial membranes. The data suggest that human synovial membranes produce a broad spectrum of antimicrobial peptides. Under inflammatory conditions, the expression pattern changes, with induction of HBD-3 in PA (LL37 in RA; HBD-3 and LL37 in OA) as well as down-regulation of HBD-1. HBD-3 holds therapeutic potential in PA as it has a broad spectrum of antimicrobial activity and accelerates epithelial healing. However, caution is appropriate since defensins also promote fibrin formation and cell proliferation - key elements in joint infection. Clarification of the role of antimicrobial peptides in OA and RA will require further investigation.

Considerations and development of topical microbicides to inhibit the sexual transmission of HIV

The increased incidence of HIV/AIDS disease in women aged 15 - 49 years has identified the urgent need for a female-controlled, efficacious and safe vaginal topical microbicide. To meet this challenge, new topical microbicide candidates consisting of molecules or formulations that modify the genital environment (BufferGel, engineered Lactobacillus, over-the-counter lubricants), surfactants (C31D/Savvy, sodium dodecyl sulfate, sodium lauryl sulfate), polyanionic polymers (PRO 2000, beta-cyclodextrin, Carraguard, CAP, D2S, SPL-7013), proteins (cyanovirin-N, monoclonal antibodies, thromspondin-1 peptides, Pokeweed antiviral protein and others), reverse transcription inhibitors (PMPA [Tenofovir ]), UC-781, SJ-3366, DABO and thiourea) and other molecules (NCp7-specific virucides, chemokine receptor agonists/antagonists, WHI-05 and WHI-07) are currently being investigated for activity, safety and efficacy. This review will assess the development of these molecules in the context of cervicovaginal defences and the clinical failure of nonoxynol-9.

Mammalian defensins in immunity: more than just microbicidal

Mammalian defensins are small, cationic, antimicrobial peptides encoded by the host that are considered to be important antibiotic-like effectors of innate immunity. By using chemokine receptors on dendritic cells and T cells, defensins might also contribute to the regulation of host adaptive immunity against microbial invasion. Defensins have considerable immunological adjuvant activity and linkage of beta-defensins or selected chemokines to an idiotypic lymphoma antigen has yielded potent antitumor vaccines. The functional overlap between defensins and chemokines is reinforced by reports that some chemokines have antimicrobial activities. Although showing similarity in activity and overall tertiary structure, the evolutionary relationship between defensins and chemokines remains to be determined.

[beta]-defensins in lung host defense

Host defenses at the mucosal surface of the airways evolved to present many layers of protection against inhaled microbes. Normally, the intrapulmonary airways are sterile. Airway secretions contain numerous factors with antimicrobial activity that contribute to innate defenses. Many protein and peptide components exert bacteriostatic or bacteriocidal effects against a wide variety of organisms and may act in synergistic or additive combinations. The beta-defensins are a relatively recently described family of peptide antimicrobials that are widely expressed at mucosal surfaces, including airway and submucosal gland epithelia. These small cationic peptides are products of individual genes that exhibit broad-spectrum activity against bacteria, fungi, and some enveloped viruses. Their expression in airway epithelia may be constitutive or inducible by bacterial products or pro-inflammatory cytokines. beta-defensins also act as chemokines for adaptive immune cells, including immature dendritic cells and T cells via the CCR6 receptor, and provide a link between innate and adaptive immunity. Alterations in the function of the beta-defensins may contribute to disease states. Here we review much of the biology of the beta-defensins, including gene discovery, genomic organization, molecular structure, regulation of expression, and function.

Improvement in burn wound infection and survival with antimicrobial peptide D2A21 (Demegel)

Naturally occurring antimicrobial peptides have been discovered in both plants and animals. Many of these peptides demonstrate impaired activity or cytotoxicity when applied exogenously. Synthetically engineered antimicrobial peptides have been designed to increase potency and activity against bacteria and fungus yet remain noncytotoxic. The antimicrobial peptide D2A21 (Demegel) has already demonstrated significant activity in vitro against many common hospital pathogens. The purpose of this study was to evaluate the effects of D2A21 in an in vivo infected burn-wound model, examining both quantitative cultures of the wound and survival of the animal. Forty-four Wistar rats were subjected to a 23 percent total body surface area scald burn. Pseudomonas aeruginosa was administered topically with 108 organisms and wounds were then evaluated at day 1, 2, or 3 for eschar and subeschar muscle quantitative culture. The experimental group was treated daily with 1.5% topical D2A21. The control group was treated with control gel. A second group of Wistar rats (n = 14) were burned and given a 107 inoculum of the same Pseudomonas and evaluated to 14 days for survival and weight changes. This group was subdivided into rats receiving either topical D2A21 or control base daily. The quantitative biopsy results demonstrated that D2A21-treated wounds had no bacterial growth in burn eschar at day 2 or 3, whereas control animals demonstrated growth at greater than 105 organisms by day 2. Subeschar muscle cultures also demonstrated significantly less bacterial invasion compared with controls on each day tested. D2A21-treated animals had an 85.7 percent survival compared with 0 percent survival in controls. Furthermore, the D2A21-treated groups demonstrated maintenance of body weights, whereas controls had significant weight loss with time. In conclusion, D2A21 demonstrates significant antibacterial activity against Pseudomonas, sterilizing burn eschar and decreasing subeschar bacterial load, allowing for a markedly significant improvement in survival in this infected burn-wound model.

Heat shock protein 70 is a potent activator of the human complement system

According to new hypotheses, extracellular heat shock proteins (Hsps) may represent an ancestral danger signal of cellular death or lysis-activating innate immunity. Recent studies demonstrating a dual role for Hsp70 as both a chaperone and cytokine, inducing potent proinflammatory response in human monocytes, provided support for the hypothesis that extracellular Hsp is a messenger of stress. Our previous work focused on the complement-activating ability of human Hsp60. We demonstrated that Hsp60 complexed with specific antibodies induces a strong classical pathway (CP) activation. Here, we show that another chaperone molecule also possesses complement-activating ability. Solid-phase enzyme-linked immunosorbent assay was applied for the experiments. Human Hsp70 activated the CP independently of antibodies. No complement activation was found in the case of human Hsp90. Our data further support the hypothesis that chaperones may messenger stress to other cells. Complement-like molecules and primitive immune cells appeared together early in evolution. A joint action of these arms of innate immunity in response to free chaperones, the most abundant cellular proteins displaying a stress signal, may further strengthen the effectiveness of immune reactions.

Induction of human β-defensin-2 expression in human astrocytes by lipopolysaccharide and cytokines

Defensins are cationic peptides with broad-spectrum antimicrobial activity. They are members of a supergene family consisting of alpha and beta subtypes and each subtype is comprised of a number of different isoforms. For example, human alpha-defensin (HAD) has six isoforms, which are expressed by polymorphonuclear leukocytes and Paneth cells. In contrast, human beta-defensin (HBD) has two isoforms that are expressed by epithelial cells of the skin, gut, respiratory and urogenital tracts. Recently, HBD-1 was detected in human brain biopsy tissue. However, little is known about the expression of HBD-1 or HBD-2 in the CNS and whether neural cells can secrete these peptides. For the present study, human astrocyte, microglial, meningeal fibroblast and neuronal cultures were probed for the expression of HBD-1 and HBD-2 mRNA and protein. Each cell type was either maintained in tissue culture medium alone or in medium containing lipopolysaccharide (LPS) at concentrations ranging from 0.1 to 1 microgram/mL, interleukin-1 beta (IL-1beta) at 1-50 ng/mL, or tumor necrosis factor alpha (TNF-alpha) at the same concentrations. The expression of HBD-1 and HBD-2 mRNAs was monitored by RT-PCR. The cDNA products were sequenced to characterize the gene product. HBD-2 protein was detected by immunoblot, immunoprecipitation and immunocytochemistry. Results of these studies showed that HBD-1 mRNA was detected in all cell cultures except in those enriched for neurons. In contrast, HBD-2 mRNA was detected only in astrocyte cultures that were treated with LPS, IL-1beta or TNF-alpha. The detection of the respective proteins correlated positively with the mRNA results. As such, these data represent the first demonstration of HBD-2 expression by astrocytes and suggest that this peptide may play a role in host defense against bacterial CNS pathogenesis.

Host defense in respiratory infections

Respiratory defenses against infection involve a diverse and complex system. Mechanical barriers limit exposure of the respiratory tract to potential pathogenic organisms, whereas the mucociliary apparatus and cough reflexes work to expel any microbes that may bypass the initial defenses. When microorganisms have gained entry to the lower respiratory tract, the alveolar macrophage and recruited phagocytes may eliminate the culprits before active infection can be established. Only after the failure of the innate immune defenses is a specific immune response mounted. Examination of clinical defects in host defense allows one to understand the importance of the multitude of components of the lung's immune defense system.

Animal antimicrobial peptides: an overview

Antibiotic peptides are a key component of the innate immune systems of most multicellular organisms. Despite broad divergences in sequence and taxonomy, most antibiotic peptides share a common mechanism of action, i.e., membrane permeabilization of the pathogen. This review provides a general introduction to the subject, with emphasis on aspects such as structural types, post-translational modifications, mode of action or mechanisms of resistance. Some of these questions are treated in depth in other reviews in this issue. The review also discusses the role of antimicrobial peptides in nature, including several pathological conditions, as well as recent accounts of their application at the preclinical level.

Defensins are dominant HLA-DR-associated self-peptides from CD34− peripheral blood mononuclear cells of different tumor patients (plasmacytoma, chronic myeloid leukemia)

The HLA-DR-associated peptides from peripheral blood mononuclear cells of 2 patients with plasmacytoma and 1 with chronic myeloid leukemia were isolated, identified, and compared. Several were identified as derivatives of the defensin family. Defensins (or human neutrophil peptides [HNP]) are antimicrobial, cationic peptides of 29 to 35 amino acids in length and are the major constituents of the azurophilic granules of human neutrophils. Using peripheral blood cells from leukapheresis, containing about 90% of polymorphonuclear cells, we could identify HNP-1, -2, and -4 and propeptides of up to 49 amino acids in length, eluted from HLA class II molecules. Binding of isolated and synthetic defensin peptides to various HLA-DR alleles using an in vitro binding/competition assay based on size exclusion chromatography revealed that defensin may bind into the peptide-binding groove. In a T-cell competition assay, defensins were able to reduce the proliferation of an HLA-DR-restricted T-cell line after preincubation of stimulating cells (CHO-DRB1*0401 transfectants) with defensin. Therefore, binding of defensins might prevent T-cell recognition of HLA class II molecules expressed on different blood precursor cells (all of which are “nonprofessional” antigen-presenting cells) by blocking the HLA peptide-binding groove or, alternatively, might protect defensin-expressing cells from self-destruction.

Beta-defensins: linking innate and adaptive immunity through dendritic and T cell CCR6

Defensins contribute to host defense by disrupting the cytoplasmic membrane of microorganisms. This report shows that human beta-defensins are also chemotactic for immature dendritic cells and memory T cells. Human beta-defensin was selectively chemotactic for cells stably transfected to express human CCR6, a chemokine receptor preferentially expressed by immature dendritic cells and memory T cells. The beta-defensin-induced chemotaxis was sensitive to pertussis toxin and inhibited by antibodies to CCR6. The binding of iodinated LARC, the chemokine ligand for CCR6, to CCR6-transfected cells was competitively displaced by beta-defensin. Thus, beta-defensins may promote adaptive immune responses by recruiting dendritic and T cells to the site of microbial invasion through interaction with CCR6.

Antibodies against human heat-shock protein (hsp) 60 and mycobacterial hsp65 differ in their antigen specificity and complement-activating ability

Although complement activation appears to have an important role both in the early and late phases of atherosclerosis, the exact mechanism of the initiation of this activation is still unknown. Since injuries of the endothelial cells are known to result in increased stress-protein expression we tested the complement-activating ability of recombinant human 60 kDa heat-shock protein (hsp60). Human hsp60 was found to activate the complement system in normal human serum in a dose-dependent manner. Activation took place through the classical pathway. The lack of complement activation in agammaglobulinemic serum indicates that the classical pathway is triggered by anti-hsp60 antibodies. Hsp60 activated complement in the sera of 74 patients with coronary heart disease as well, and a strong positive correlation (r = 0.459, P < 0.0001) was found between the extent of complement activation and the level of anti-hsp60 IgG antibodies but there was no correlation to the level of anti-hsp65 IgG antibodies. Further distinction between anti-hsp60 and anti-hsp65 antibodies was obtained from competitive ELISA experiments: binding of anti-hsp60 antibodies to hsp60-coated plates was inhibited only by recombinant hsp60 and vice versa. Our present findings indicate that anti-hsp60 and anti-hsp65 antibodies are distinct, showing only partial cross-reactivity. Since complement activation plays an important role in the development of atherosclerosis and the levels of complement-activating anti-hsp60 antibodies are elevated in atherosclerosis-related diseases, our present findings may have important pathological implications.

C1q-binding proteins and C1q receptors

Aggregated or immobilized complement C1q induces cellular responses in many different cell types. C1q-induced cellular responses may be involved in host defense and in protection against autoimmunity because C1q-deficient humans have infectious complications and a very high incidence of autoimmune disease. The search for the C1q receptor(s), which has been ongoing for 25 years, has led recently to the recognition that proteins identified as binding to C1q may be divided into two groups: C1q-binding molecules that are normally intracellular; and cell surface C1q receptors.

Inhibition of Activation of the Classical Pathway of Complement by Human Neutrophil Defensins

Defensins are small, cationic antimicrobial peptides that are present in the azurophilic granules of neutrophils. Earlier studies have shown that defensins may influence complement activation by specific interaction with activated C1, C1q, and C1-inhibitor. In the present study, we show that the defensin human neutrophil peptide-1 (HNP-1) is able to inhibit activation of the classical complement pathway by inhibition of C1q hemolytic activity. The binding site for HNP-1 on C1q is most likely located on the collagen-like stalks, as a clear, dose-dependent binding of HNP-1 to either intact C1q or to the collagen-like stalks of C1q was demonstrated using enzyme-linked immunosorbent assay (ELISA). Besides binding of HNP-1 to C1q, also a limited binding to C1 and to a mixture of C1r and C1s was observed, whereas no binding to C1-inhibitor was found. Because binding of HNP-1 to C1-inhibitor has been suggested in earlier studies, we also assessed the binding of HNP-1 to mixtures of C1-inhibitor with either C1r/ C1s or C1. No binding was found. Using a competition ELISA, it was found that HNP-1, but not protamine, inhibited binding of biotin-labeled HNP-1 to C1q in a dose-dependent fashion. In the fluid phase, preincubation of HNP-1 with C1q resulted in complex formation of HNP-1 and C1q and generation of stable complexes. In conclusion, HNP-1 is able to bind to C1q in the fluid phase and inhibits the classical complement pathway. This mechanism may be involved in the control of an inflammatory response in vivo.