The human antibacterial cathelicidin, hCAP-18, is bound to lipoproteins in plasma

Host heterogeneity in humoral bactericidal activity can be complement independent

Background

Humoral bactericidal activity was first recognized nearly a century ago. However, the extent of inter-individual heterogeneity and the mechanisms underlying such heterogeneity beyond antibody or complement systems have not been well studied.

Methods

The plasma bactericidal activity of five healthy volunteers were tested against 30 strains of Gram-negative uropathogens, Klebsiella pneumoniae and Escherichia coli, associated with bloodstream infections. IgG and IgM titers specific to K. pneumoniae strains KP13883 and KPB1 were measured by ELISA, and complement inhibitor was used to measure the contribution of complement-induced killing. Furthermore, MALDI-TOF mass spectrometry was conducted to determine the metabolomic components of plasma with bactericidal properties in 25 healthy individuals using Bayesian inference of Pearson correlation between peak intensity and colony counts of surviving bacteria.

Results

Plasma bactericidal activity varied widely between individuals against various bacterial strains. While individual plasma with higher IgM titers specific to K. pneumoniae strain KP13883 showed more efficient killing of the strain, both IgM and IgG titers for K. pneumoniae strain KPB1 did not correlate well with the killing activity. Complement inhibition assays elucidated that the complement-mediated killing was not responsible for the inter-individual heterogeneity in either isolate. Subsequently, using MALDI-TOF mass spectrometry on plasmas of 25 healthy individuals, we identified several small molecules including gangliosides, pediocins, or saponins as candidates that showed negative correlation between peak intensities and colony forming units of the test bacteria.

Conclusion

This is the first study to demonstrate the inter-individual heterogeneity of constitutive innate humoral bactericidal function quantitatively and that the heterogeneity can be independent of antibody or the complement system.

A Novel Pathway of Platelet Activation in ACS Mediated by LL-37 Immunoglobulin G Autoantibody Immune Complexes

The cathelicidin antimicrobial peptide LL-37 is a self-antigen in neutrophil extracellular traps that provokes autoantibody responses in autoimmune/autoinflammatory conditions. LL-37 immunoglobulin (Ig) G autoantibody levels were measured in subjects with and without atherosclerotic cardiovascular disease assessed using the coronary artery calcium score, in patients who had a future myocardial infarction and in a cohort of acute coronary syndrome (ACS) patients. LL-37 IgG levels were not associated with coronary artery calcium score, but future myocardial infarction patients had significantly higher LL-37 IgG at baseline. Reduced LL-37 IgG in ACS was associated with increased LL-37 IgG-immune complex. ACS plasma increased activated CD62P+ platelets from healthy donors mediated in part by LL-37 IgG-immune complexes and platelet Fc gamma receptor 2a.

Increased LL37 in psoriasis and other inflammatory disorders promotes LDL uptake and atherosclerosis

Patients with chronic inflammatory disorders such as psoriasis have an increased risk of cardiovascular disease and elevated levels of LL37, a cathelicidin host defense peptide that has both antimicrobial and proinflammatory properties. To explore whether LL37 could contribute to the risk of heart disease, we examined its effects on lipoprotein metabolism and show that LL37 enhanced LDL uptake in macrophages through the LDL receptor (LDLR), scavenger receptor class B member 1 (SR-B1), and CD36. This interaction led to increased cytosolic cholesterol in macrophages and changes in expression of lipid metabolism genes consistent with increased cholesterol uptake. Structure-function analysis and synchrotron small-angle x-ray scattering showed structural determinants of the LL37-LDL complex that underlie its ability to bind its receptors and promote uptake. This function of LDL uptake is unique to cathelicidins from humans and some primates and was not observed with cathelicidins from mice or rabbits. Notably, Apoe-/- mice expressing LL37 developed larger atheroma plaques than did control mice, and a positive correlation between plasma LL37 and oxidized phospholipid on apolipoprotein B (OxPL-apoB) levels was observed in individuals with cardiovascular disease. These findings provide evidence that LDL uptake can be increased via interaction with LL37 and may explain the increased risk of cardiovascular disease associated with chronic inflammatory disorders.

Protein Corona of Anionic Fluid-Phase Liposomes Compromises Their Integrity Rather than Uptake by Cells

Despite the undisputable role of the protein corona in the biointeractions of liposome drug carriers, the field suffers from a lack of knowledge regarding the patterns of protein deposition on lipid surfaces with different compositions. Here, we investigated the protein coronas formed on liposomes of basic compositions containing combinations of egg phosphatidylcholine (PC), palmitoyloleoyl phosphatidylglycerol (POPG), and cholesterol. Liposome-protein complexes isolated by size-exclusion chromatography were delipidated and analyzed using label-free LC-MS/MS. The addition of the anionic lipid and cholesterol both affected the relative protein abundances (and not the total bound proteins) in the coronas. Highly anionic liposomes, namely those containing 40% POPG, carried corona enriched with cationic proteins (apolipoprotein C1, beta-2-glycoprotein 1, and cathelicidins) and were the least stable in the calcein release assay. Cholesterol improved the liposome stability in the plasma. However, the differences in the corona compositions had little effect on the liposome uptake by endothelial (EA.hy926) and phagocytic cells in the culture (U937) or ex vivo (blood-derived monocytes and neutrophils). The findings emphasize that the effect of protein corona on the performance of the liposomes as drug carriers occurs through compromising particle stability rather than interfering with cellular uptake.

Sub-acute and sub-chronic toxicity assessment of the antimicrobial peptide Dermaseptin B2 on biochemical, haematological and histopathological parameters in BALB/c mice and Albino Wistar rats

Background

Dermaseptins (Drs) are peptides found in the skin secretions of a variety of Hylid frogs, particularly those belonging to the Agalychnis and Phyllomedusa families. Dermaseptin B2 (Drs B2), an amphipathic, α-helical polypeptide was reported as the most active of the Dermaseptin B family. We have previously shown that Drs B2 has strong anti-proliferative activities against RD cells in vitro and thus required further evaluations for future medical applications.

Aim

The aim the study was to evaluate the 14-day sub-acute and 90-day sub-chronic toxicities Drs B2 in vivo.

Materials and Methods

BALB/c mice were treated with increasing concentrations of 5-25 mg/kg of Drs B2. Rats were treated with 2, 4 and 10-fold concentrations of the calculated LD₅₀ of Drs B2 following OECD recommendations. At the end of the experimentation periods, the animals were sacrificed and dissected to collect blood and selected organs for analysis of any effects caused by Drs B2 treatment on the biochemical, haematological, and histological parameters.

Results

The 14-day sub-acute toxicity tests did not cause significant alteration in the biochemical, hematological and histological parameters. The 90-day sub-chronic toxicity study showed lower ALT and AST than control at doses 1.9 mg/kg and 4.6 mg/kg, respectively. Their haematology results also showed higher platelet count than the controls but the differences were not statistically significant. Histological analysis showed increased megakaryocytes in the spleen for both the mice and the rats.

Conclusion

The results of this study indicate that short term treatment of Drs B2 could be safe to the animals, however, long-term treatment can have mild effects on the liver parameters and cause an inflammatory response in the spleen.

Prognostic Impacts of LL-37 in Relation to Lipid Profiles of Patients with Myocardial Infarction: A Prospective Cohort Study

Background. In vivo studies show that LL-37 inhibits the progression of atherosclerosis and predicts a lower risk of recurrent ischemia in patients with acute myocardial infarction (AMI), which could be mediated by the modulation of lipid metabolism. The current study aimed to investigate the effects of various lipid contents on the prognostic impacts of LL-37 in patients with AMI. Methods. A total of 1567 consecutive AMI patients were prospectively recruited from March 2017 to January 2020. Patients were firstly stratified into two groups by the median level of LL-37 and then stratified by levels of various lipid contents and proprotein convertase subtilisin/kexin type 9 (PCSK9). Cox regression with multiple adjustments was performed to analyze associations between LL-37, lipid profiles, PCSK9, and various outcomes. The primary outcome was major adverse cardiovascular event (MACE), a composite of all-cause death, recurrent MI, and ischemic stroke. Results. During a median follow-up of 786 (726−1107) days, a total of 252 MACEs occurred. A high level of LL-37 was associated with lower risk of MACE in patients with elevated lipoprotein(a) (≥300 mg/L, hazard ratio (HR): 0.49, 95% confidence interval (CI): 0.29−0.86, p = 0.012) or PCSK9 levels above the median (≥47.4 ng/mL, HR: 0.57, 95% CI: 0.39−0.82, p < 0.001), which was not observed for those without elevated lp(a) (<300 mg/L, HR: 0.96, 95% CI: 0.70−1.31, p = 0.781, pinteraction = 0.035) or PCSK9 (<47.4 ng/mL, HR: 1.02, 95% CI: 0.68−1.54, p = 0.905, pinteraction = 0.032). Conclusions. For patients with AMI, a high level of LL-37 was associated with lower ischemic risk among patients with elevated lp(a) and PCSK9.

Characterization of Recombinant Antimicrobial Peptide BMGlv2 Heterologously Expressed in Trichoderma reesei

Antimicrobial peptides (AMPs) serve as alternative candidates for antibiotics and have attracted the attention of a wide range of industries for various purposes, including the prevention and treatment of piglet diarrhea in the swine industry. Escherichia coli, Salmonella, and Clostridium perfringens are the most common pathogens causing piglet diarrhea. In this study, the antimicrobial peptide gloverin2 (BMGlv2), derived from Bombyx mandarina, was explored to determine the efficient prevention effect on bacterial piglet diarrhea. BMGlv2 was heterologously expressed in Trichoderma reesei Tu6, and its antimicrobial properties against the three bacteria were characterized. The results showed that the minimum inhibitory concentrations of the peptide against E. coli ATCC 25922, S. derby ATCC 13076, and C. perfringens CVCC 2032 were 43.75, 43.75, and 21.86 μg/mL, respectively. The antimicrobial activity of BMGlv2 was not severely affected by high temperature, salt ions, and digestive enzymes. It had low hemolytic activity against rabbit red blood cells, indicating its safety for use as a feed additive. Furthermore, the measurements of the leakage of bacterial cell contents and scanning electron microscopy of C. perfringens CVCC 2032 indicated that BMGlv2 exerted antimicrobial activity by destroying the cell membrane. Overall, this study showed the heterologous expression of the antimicrobial peptide BMGlv2 in T. reesei and verified its antimicrobial properties against three common pathogenic bacteria associated with piglet diarrhea, which can provide a reference for the applications of AMPs as an alternative product in industrial agriculture.

The ratio of serum LL-37 levels to blood leucocyte count correlates with COVID-19 severity

Beneficial effects of vitamin D on COVID-19 progression have been discussed in several studies. Vitamin D stimulates the expression of the antimicrobial peptide LL-37, and evidence shows that LL-37 can antagonize SARS-CoV-2. Therefore, we investigated the association between LL-37 and vitamin D serum levels and the severity of COVID-19. To this end, 78 COVID-19 patients were divided into 5 groups according to disease severity. We determined serum levels of LL-37, vitamin D, and routine laboratory parameters. We demonstrated a correlation of CRP, IL-6, PCT, leukocyte count, and LDH with the severity of COVID-19. Our study did not demonstrate a direct relationship between serum levels of LL-37 and vitamin D and the severity of COVID-19. LL-37 is produced by granulocytes and released at the site of inflammation. Therefore, the analysis of LL-37 in broncho-alvelolar lavage rather than in patient serum seems critical. However, since LL-37 is produced by granulocytes, we determined serum LL-37 levels as a function of leukocyte count. The LL-37/leukocyte count ratio correlates highly significantly inversely proportional with COVID-19 severity. Our results indicate that the LL-37/leukocyte count ratio could be used to assess the risk of COVID-19 progression as early as hospital admission.

The blood protein hCAP-18 in neutropenia: An 18-month experience of a new ELISA for clinical use

Neutropenia as an isolated clinical finding may include aetiologies ranging from severe disease to a transient condition, and differential diagnosis may be challenging. Previous data and clinical experience suggest that low levels of the neutrophil-derived protein human 18 kDa cathelicidin antimicrobial protein (hCAP-18) in the blood are predictive of more severe forms of neutropenia. The objective of this study was to present the results from a newly developed ELISA method that has been used in clinical routine in Sweden since 2018 for quantification of hCAP-18 in blood plasma. Using this method, we report that patients with severe disease analysed during the study period presented with low or undetectable levels of blood plasma hCAP-18, validating its use as screening tool for severe neutropenia. Furthermore, neutropenic patients as a group displayed lower levels of hCAP-18 as compared to blood donors. Within the group of neutropenic patients, those with neutrophil antibodies displayed significantly higher hCAP-18 levels compared to patients with idiopathic neutropenia. By including an analysis of hCAP-18 in the primary investigation of neutropenia, an increased accuracy in differential diagnosis is achieved, thus contributing to reduced costs of neutropenia management.

Romo1-Derived Antimicrobial Peptide Is a New Antimicrobial Agent against Multidrug-Resistant Bacteria in a Murine Model of Sepsis

Abuse of antibiotics often leads to increase of multidrug-resistant (MDR) bacteria, which threatens the life of human beings. To overcome threat of antibiotic resistance, scientists are developing a novel class of antibiotics, antimicrobial peptides, that can eradicate MDR bacteria. Unfortunately, these antibiotics have mainly been developed to cure bacterial skin infections rather than others, such as life-threatening sepsis. Major pharmaceutical companies have tried to develop antiseptic drugs; however, they have not been successful. Here, we report that AMPR-11, the antimicrobial peptide (AMP) derived from mitochondrial nonselective channel Romo1, has antimicrobial activity against Gram-positive and Gram-negative bacteria comprising many clinically isolated MDR strains. Moreover, AMPR-11 increased the survival rate in a murine model of sepsis caused by MDR bacteria. We propose that AMPR-11 could be a novel antiseptic drug candidate with a broad antimicrobial spectrum to overcome MDR bacterial infection.

To overcome increasing bacterial resistance to conventional antibiotics, many antimicrobial peptides (AMPs) derived from host defense proteins have been developed. However, there are considerable obstacles to their application to systemic infections because of their low bioavailability. In the present study, we developed an AMP derived from Romo1 (AMPR-11) that exhibits a broad spectrum of antimicrobial activity. AMPR-11 showed remarkable efficacy against sepsis-causing bacteria, including multidrug-resistant strains, with low toxicity in a murine model of sepsis after intravenous administration. It seems that AMPR-11 disrupts bacterial membranes by interacting with cardiolipin and lipid A. From the results of this study, we suggest that AMPR-11 is a new class of agent for overcoming low efficacy in the intravenous application of AMPs and is a promising candidate to overcome multidrug resistance.

A mouse model for vitamin D-induced human cathelicidin antimicrobial peptide gene expression

In humans and other primates, 1,25(OH)2vitamin D3 regulates the expression of the cathelicidin antimicrobial peptide (CAMP) gene via toll-like receptor (TLR) signaling that activates the vitamin D pathway. Mice and other mammals lack the vitamin D response element (VDRE) in their CAMP promoters. To elucidate the biological importance of this pathway, we generated transgenic mice that carry a genomic DNA fragment encompassing the entire human CAMP gene and crossed them with Camp knockout (KO) mice. We observed expression of the human transgene in various tissues and innate immune cells. However, in mouse CAMP transgenic macrophages, TLR activation in the presence of 25(OH)D3 did not induce expression of either CAMP or CYP27B1 as would normally occur in human macrophages, reinforcing important species differences in the actions of vitamin D. Transgenic mice did show increased resistance to colonization by Salmonella typhimurium in the gut. Furthermore, the human CAMP gene restored wound healing in the skin of Camp KO mice. Topical application of 1,25(OH)2vitamin D3 to the skin of CAMP transgenic mice induced CAMP expression and increased killing of Staphylococcus aureus in a wound infection model. Our model can help elucidate the biological importance of the vitamin D-cathelicidin pathway in both pathogenic and non-pathogenic states.

Profiling antimicrobial peptides from the medical maggot Lucilia sericata as potential antibiotics for MDR Gram-negative bacteria

Background

The ability of MDR Gram-negative bacteria to evade even antibiotics of last resort is a severe global challenge. The development pipeline for conventional antibiotics cannot address this issue, but antimicrobial peptides (AMPs) offer an alternative solution.

Objectives

Two insect-derived AMPs (LS-sarcotoxin and LS-stomoxyn) were profiled to assess their suitability for systemic application in humans.

Methods

The peptides were tested against an extended panel of 114 clinical MDR Gram-negative bacterial isolates followed by time–kill analysis, interaction studies and assays to determine the likelihood of emerging resistance. In further in vitro studies we addressed cytotoxicity, cardiotoxicity and off-target interactions. In addition, an in vivo tolerability and pharmacokinetic study in mice was performed.

Results

LS-sarcotoxin and LS-stomoxyn showed potent and selective activity against Gram-negative bacteria and no cross-resistance with carbapenems, fluoroquinolones or aminoglycosides. Peptide concentrations of 4 or 8 mg/L inhibited 90% of the clinical MDR isolates of Escherichia coli, Enterobacter cloacae, Acinetobacter baumannii and Salmonella enterica isolates tested. The ‘all-d’ homologues of the peptides displayed markedly reduced activity, indicating a chiral target. Pharmacological profiling revealed a good in vitro therapeutic index, no cytotoxicity or cardiotoxicity, an inconspicuous broad-panel off-target profile, and no acute toxicity in mice at 10 mg/kg. In mouse pharmacokinetic experiments LS-sarcotoxin and LS-stomoxyn plasma levels above the lower limit of quantification (1 and 0.25 mg/mL, respectively) were detected after 5 and 15 min, respectively.

Conclusions

LS-sarcotoxin and LS-stomoxyn are suitable as lead candidates for the development of novel antibiotics; however, their pharmacokinetic properties need to be improved for systemic administration.

Decoding the human serum interactome of snake-derived antimicrobial peptide Ctn[15-34]: Toward an explanation for unusually long half-life

The inherent propensity to enzymatic degradation of most peptides remains a bottleneck in their therapeutic development. Efficient, early screening methods are necessary for in vitro characterization of the molecular events occurring when peptides get in contact with biological fluids such us plasma. Herein we present an affinity purification/MS approach for mapping peptide serum interactors. We have applied this methodology to identify the serum partners of antibiotic peptide Ctn [15-34], aiming to ascertain the molecular interactions underlying its unusually long half-life (~ 12 h) in human serum. From 42 proteins captured in pull-downs with biotinylated Ctn [15-34] as bait, five are of special interest for their transport/binding properties hence alleged peptide arresting potential. The subset contains two members of the albumin superfamily, two apolipoproteins and a globulin. All five share a binding ability for hydrophobic species, and also bind Ctn [15-34], presumably via its C-terminal hydrophobic section, with affinities in the μM range as shown by surface plasmon resonance. Additionally, our functional enrichment reveals several significant immune-related processes suggesting an immunomodulatory role of Ctn [15-34]. Taken together, this study exemplifies how pharmacoproteomics can be used to analyze bioavailability issues and shed light on the serum interactors ultimately conferring protection to Ctn [15-34] against proteolytic events. SIGNIFICANCE: The affinity purification/MS identification methodology reported here can be viewed as a routine pharmacoproteomic approach to investigate the serum interactome of peptide drugs, identifying proteins affecting bioavailability and thus assisting the peptide drug development process. The specific results described here enlighten the serum stability issues of peptide Ctn [15-34] and ratify its promising future as an anti-infective lead.

HCV Pit Stop at the Lipid Droplet: Refuel Lipids and Put on a Lipoprotein Coat before Exit

The replication cycle of the liver-tropic hepatitis C virus (HCV) is tightly connected to the host lipid metabolism, during the virus entry, replication, assembly and egress stages, but also while the virus circulates in the bloodstream. This interplay coins viral particle properties, governs viral cell tropism, and facilitates immune evasion. This review summarizes our knowledge of these interactions focusing on the late steps of the virus replication cycle. It builds on our understanding of the cell biology of lipid droplets and the biosynthesis of liver lipoproteins and attempts to explain how HCV hijacks these organelles and pathways to assemble its lipo-viro-particles. In particular, this review describes (i) the mechanisms of viral protein translocation to and from the lipid droplet surface and the orchestration of an interface between replication and assembly complexes, (ii) the importance of the triglyceride mobilization from the lipid droplets for HCV assembly, (iii) the interplay between HCV and the lipoprotein synthesis pathway including the role played by apolipoproteins in virion assembly, and finally (iv) the consequences of these complex virus–host interactions on the virion composition and its biophysical properties. The wealth of data accumulated in the past years on the role of the lipid metabolism in HCV assembly and its imprint on the virion properties will guide vaccine design efforts and reinforce our understanding of the hepatic lipid metabolism in health and disease.

Plasma proteome correlates of lipid and lipoprotein: biomarkers of metabolic diversity and inflammation in children of rural Nepal

Proteins involved in lipoprotein metabolism can modulate cardiovascular health. While often measured to assess adult metabolic diseases, little is known about the proteomes of lipoproteins and their relation to metabolic dysregulation and underlying inflammation in undernourished child populations. The objective of this population study was to globally characterize plasma proteins systemically associated with HDL, LDL, and triglycerides in 500 Nepalese children. Abnormal lipid profiles characterized by elevated plasma triglycerides and low HDL-cholesterol (HDL-C) concentrations were common, especially in children with subclinical inflammation. Among 982 proteins analyzed, the relative abundance of 11, 12, and 52 plasma proteins was correlated with LDL-cholesterol (r = −0.43∼0.70), triglycerides (r = −0.39∼0.53), and HDL-C (r = −0.49∼0.79) concentrations, respectively. These proteins included apolipoproteins and numerous unexpected intracellular and extracellular matrix binding proteins, likely originating in hepatic and peripheral tissues. Relative abundance of two-thirds of the HDL proteome varied with inflammation, with acute phase reactants higher by 4∼40%, and proteins involved in HDL biosynthesis, cholesterol efflux, vitamin transport, angiogenesis, and tissue repair lower by 3∼20%. Untargeted plasma proteomics detects comprehensive sets of both known and novel lipoprotein-associated proteins likely reflecting systemic regulation of lipoprotein metabolism and vascular homeostasis. Inflammation-altered distributions of the HDL proteome may be predisposing undernourished populations to early chronic disease.

Variation, Indispensability, and Masking in the M protein

The M protein is the major surface-associated virulence factor of group A Streptococcus (GAS) and an antigenically variable target of host immunity. How selection pressures to escape immune recognition, maintain indispensable functions, and mask vulnerabilities have shaped the sequences of the >220M protein types is unclear. Recent experiments have shed light on this question by showing that, hidden within the antigenic variability of many M protein types, are sequence patterns conserved for recruiting human C4b-binding protein (C4BP). Other host factors may be recruited in a similar manner by conserved but hidden sequence patterns in the M protein. The identification of such patterns may be applicable to the development of a GAS vaccine.

Human Cathelicidin Compensates for the Role of Apolipoproteins in Hepatitis C Virus Infectious Particle Formation

Exchangeable apolipoproteins (ApoA, -C, and -E) have been shown to redundantly participate in the formation of infectious hepatitis C virus (HCV) particles during the assembly process, although their precise role in the viral life cycle is not well understood. Recently, it was shown that the exogenous expression of only short sequences containing amphipathic α-helices from various apolipoproteins is sufficient to restore the formation of infectious HCV particles in ApoB and ApoE double-gene-knockout Huh7 (BE-KO) cells. In this study, through the expression of a small library of human secretory proteins containing amphipathic α-helix structures, we identified the human cathelicidin antimicrobial peptide (CAMP), the only known member of the cathelicidin family of antimicrobial peptides (AMPs) in humans and expressed mainly in bone marrow and leukocytes. We showed that CAMP is able to rescue HCV infectious particle formation in BE-KO cells. In addition, we revealed that the LL-37 domain in CAMP containing amphipathic α-helices is crucial for the compensation of infectivity in BE-KO cells, and the expression of CAMP in nonhepatic 293T cells expressing claudin 1 and microRNA miR-122 confers complete propagation of HCV. These results suggest the possibility of extrahepatic propagation of HCV in cells with low-level or no expression of apolipoproteins but expressing secretory proteins containing amphipathic α-helices such as CAMP.

IMPORTANCE

Various exchangeable apolipoproteins play a pivotal role in the formation of infectious HCV during the assembly of viral particles, and amphipathic α-helix motifs in the apolipoproteins have been shown to be a key factor. To the best of our knowledge, we have identified for the first time the human cathelicidin CAMP as a cellular protein that can compensate for the role of apolipoproteins in the life cycle of HCV. We have also identified the domain in CAMP that contains amphipathic α-helices crucial for compensation and show that the expression of CAMP in nonhepatic cells expressing claudin 1 and miR-122 confers complete propagation of HCV. We speculate that low levels of HCV propagation might be possible in extrahepatic tissues expressing secretory proteins containing amphipathic α-helices without the expression of apolipoproteins.

The Roles of Cathelicidin LL-37 in Inflammatory Bowel Disease

Human cathelicidin LL-37, the only member of the cathelicidin family of host defense peptides expressed in humans, plays a crucial role in host defense against pathogen invasion, as well as in regulating the functions of anti-inflammation, antitumorigenesis, and tissue repair. It is primarily produced by phagocytic leukocytes and epithelial cells, and mediates a wide range of biological responses. Emerging evidence from several studies indicates that LL-37 plays a prominent and complex role in inflammatory bowel disease (IBD). Although overexpression of LL-37 has been implicated in the inflamed and noninflamed colon mucosa in patients with ulcerative colitis, LL-37 expression was not changed in the inflamed or noninflamed colon or ileal mucosa in patients with Crohn's disease. Furthermore, studies in animal models and human patients further characterized the protective effect of cathelicidins both in ulcerative colitis and Crohn's disease. These data suggest the intricate functions of LL-37 in IBD. They will also create many strategies and opportunities for therapeutic intervention in IBD in the future. This review aims to elucidate the structure and bioactivity of LL-37 and also discuss the recent progress in understanding the relationship between LL-37 and IBD.

Carbamylated LL-37 as a modulator of the immune response

Carbamylation of lysine residues and protein N-termini is an ubiquitous, non-enzymatic post-translational modification. Carbamylation at sites of inflammation is due to cyanate formation during the neutrophil oxidative burst and may target lysine residues within the antimicrobial peptide LL-37. The bactericidal and immunomodulatory properties of LL-37 depend on its secondary structure and cationic nature, which are conferred by arginine and lysine residues. Therefore, carbamylation may affect the biological functions of LL-37. The present study examined the kinetics and pattern of LL-37 carbamylation to investigate how this modification affects the bactericidal, cytotoxic and immunomodulatory function of the peptide. The results indicated that LL-37 undergoes rapid modification in the presence of physiological concentrations of cyanate, yielding a spectrum of diverse carbamylated peptides. Mass spectrometry analyses revealed that theN-terminal amino group of Leu-1 was highly reactive and was modified almost instantly by cyanate to generate the predominant form of the modified peptide, named LL-37(C1) This was followed by the sequential carbamylation of Lys-8, Lys-12, and Lys-15 to yield LL-37(C8), and Lys-15 to yield LL-37(C12,15) Carbamylation had profound and diverse effects on the structure and biological properties of LL-37. In some cases, anti-inflammatory LL-37 was rapidly converted to pro-inflammatory LL-37.

Dynamic capsule restructuring by the main pneumococcal autolysin LytA in response to the epithelium

Bacterial pathogens produce complex carbohydrate capsules to protect against bactericidal immune molecules. Paradoxically, the pneumococcal capsule sensitizes the bacterium to antimicrobial peptides found on epithelial surfaces. Here we show that upon interaction with antimicrobial peptides, encapsulated pneumococci survive by removing capsule from the cell surface within minutes in a process dependent on the suicidal amidase autolysin LytA. In contrast to classical bacterial autolysis, during capsule shedding, LytA promotes bacterial survival and is dispersed circumferentially around the cell. However, both autolysis and capsule shedding depend on the cell wall hydrolytic activity of LytA. Capsule shedding drastically increases invasion of epithelial cells and is the main pathway by which pneumococci reduce surface bound capsule during early acute lung infection of mice. The previously unrecognized role of LytA in removing capsule to combat antimicrobial peptides may explain why nearly all clinical isolates of pneumococci conserve this enzyme despite the lethal selective pressure of antibiotics.

Pneumococci produce a carbohydrate capsule that protects them against components of the host immune system but sensitizes them to host antimicrobial peptides. Here, Kietzman et al. show that pneumococci respond to antimicrobial peptides by capsule shedding, which requires the main autolysin LytA.

Effect of Cholecalciferol Supplementation on Vitamin D Status and Cathelicidin Levels in Sepsis: A Randomized, Placebo-Controlled Trial

OBJECTIVES

To compare changes in vitamin D status and cathelicidin (LL-37) levels in septic ICU patients treated with placebo versus cholecalciferol.

DESIGN

Randomized, placebo-controlled, trial.

SETTING

Medical and surgical ICUs of a single teaching hospital in Boston, MA.

PATIENTS

Thirty adult ICU patients.

INTERVENTIONS

Placebo (n = 10) versus 200,000 IU cholecalciferol (n = 10) versus 400,000 IU cholecalciferol (n = 10), within 24 hours of new-onset severe sepsis or septic shock.

MEASUREMENTS AND MAIN RESULTS

Blood samples were obtained at baseline (day 1) and on days 3, 5, and 7, to assess total 25-hydroxyvitamin D, as well as vitamin D-binding protein and albumin to calculate bioavailable 25-hydroxyvitamin D. Plasma LL-37 and high-sensitivity C-reactive protein levels were also measured. At baseline, median (interquartile range) plasma 25-hydroxyvitamin D was 17 ng/mL (13-22 ng/mL) and peaked by day 5 in both intervention groups. Groups were compared using Kruskal-Wallis tests. Relative to baseline, on day 5, median change in biomarkers for placebo, 200,000 IU cholecalciferol, and 400,000 IU cholecalciferol groups, respectively, were as follows: 1) total 25-hydroxyvitamin D, 3% (-3% to 8%), 49% (30-82%), and 69% (55-106%) (p < 0.001); 2) bioavailable 25-hydroxyvitamin D, 4% (-8% to 7%), 45% (40-70%), and 96% (58-136%) (p < 0.01); and 3) LL-37: -17% (-9% to -23%), 4% (-10% to 14%), and 30% (23-48%) (p = 0.04). Change in high-sensitivity C-reactive protein levels did not differ between groups. A positive correlation was observed between bioavailable 25-hydroxyvitamin D and LL-37 (Spearman ρ = 0.44; p = 0.03) but not for total 25-hydroxyvitamin D and LL-37.

CONCLUSIONS

High-dose cholecalciferol supplementation rapidly and safely improves 25-hydroxyvitamin D and bioavailable 25-hydroxyvitamin D levels in patients with severe sepsis or septic shock. Changes in bioavailable 25-hydroxyvitamin D are associated with concomitant increases in circulating LL-37 levels. Larger trials are needed to verify these findings and to assess whether optimizing vitamin D status improves sepsis-related clinical outcomes.

Group A Streptococcal M1 Protein Sequesters Cathelicidin to Evade Innate Immune Killing

The antimicrobial peptide LL-37 is generated upon proteolytic cleavage of cathelicidin and limits invading pathogens by directly targeting microbial membranes as well as stimulating innate immune cell function. However, some microbes evade LL-37-mediated defense. Notably, group A Streptococcus (GAS) strains belonging to the hypervirulent M1T1 serogroup are more resistant to human LL-37 than other GAS serogroups. We show that the GAS surface-associated M1 protein sequesters and neutralizes LL-37 antimicrobial activity through its N-terminal domain. M1 protein also binds the cathelicidin precursor hCAP-18, preventing its proteolytic maturation into antimicrobial forms. Exogenous M1 protein rescues M1-deficient GAS from killing by neutrophils and within neutrophil extracellular traps and neutralizes LL-37 chemotactic properties. M1 also binds murine cathelicidin, and its virulence contribution in a murine model of necrotizing skin infection is largely driven by its ability to neutralize this host defense peptide. Thus, cathelicidin resistance is essential for the pathogenesis of hyperinvasive M1T1 GAS.

The antimicrobial propeptide hCAP-18 plasma levels in neutropenia of various aetiologies: a prospective study

The underlying cause of neutropenia may be difficult to determine due to similar clinical presentation in many neutropenic conditions. The neutrophil protein hCAP-18 (pro-LL-37) is a major component of neutrophil secondary granules and in this prospective study we assessed the use of hCAP-18 levels in blood plasma for differential diagnosis of neutropenic patients (n = 133) of various aetiologies. Plasma levels of hCAP-18 were determined using immunoblot and ELISA. Patients with severe congenital neutropenia (n = 23) presented with the lowest levels of plasma hCAP-18 and differential diagnostic accuracy revealed high sensitivity (100%) and specificity (98.8%) for hCAP-18 ELISA. The correlation coefficient of the hCAP-18 ELISA versus immunoblotting was (R = 0.831) and that of the peptide LL-37 ELISA versus immunoblotting was (R = 0.405) (P < 0.001). Plasma hCAP-18 levels thus displayed high diagnostic value in differential diagnosis of chronic neutropenia. Neutropenic patients with Shwachman-Diamond syndrome, Barth syndrome, Cohen syndrome, acute myeloid leukaemia and specific granule deficiency presented with reduced plasma hCAP-18 levels as well. The blood plasma level of hCAP-18 was thus low in conditions in which the neutrophil antibacterial propeptide hCAP-18 is deficient, i.e. severe congenital neutropenia and neutrophil-specific granule deficiency, and in conditions in which bone marrow myelopoiesis is negatively affected.

Characterization of antimicrobial activity and mechanisms of low amphipathic peptides with different α-helical propensity

Antimicrobial peptides (AMPs) serve as a defense mechanism within multicellular organisms and are attracting increasing attention because of their potential application in the treatment of multidrug-resistant infections. Amphipathicity has long been believed to be the most important consideration for the structural modification and design of both naturally occurring and synthetic AMPs. Previous studies indicated that disruptive amphipathicity formed by replacing the paired charged amino acid residues on the polar face of an amphipathic helix with tryptophan residues linked with hydrogen bonds on the basis of α-helical protein folding principles endowed the AMPs with increased cell selectivity. In an attempt to augment and hone this strategy further, we designed a series of imperfect amphipathic peptides by placing different types of amino acid residues at the hydrogen bond linked positions of α-helix structures to characterize their antimicrobial properties and mechanism of action. The d-Trp-substituted sequence (PRW4-d) showed greater antimicrobial potency than Cys-(C4), Asp-(D4), Ile-(I4), and Pro-(P4) substituted sequences, comparable to the l-Trp-substituted parent sequence (PRW4). Furthermore, the total replacement of Lys residues with Arg residues along the peptide sequence (PRW4-R) exhibited enhanced antimicrobial activity and cell selectivity. In addition, no cytotoxicity was observed among these synthetic peptides. PRW4-d and PRW4-R maintained their activities in the presence of physiological salts and human serum. The fluorescence spectroscopy, flow cytometry, and electron microscopy observations indicated that the optimized sequences exhibited excellent antimicrobial potency by inducing cytoplasmic membrane potential loss, membrane permeabilization and disruption. Collectively, the results could be useful for designing short AMPs with great antimicrobial activity and cell selectivity.

Neutrophil extracellular traps as a new paradigm in innate immunity: friend or foe?

The discovery of neutrophil extracellular traps in 2004 opened a fascinating new chapter in immune-mediated microbial killing. Brinkman et al. demonstrated that neutrophils, when catastrophically stimulated, undergo a novel form of programmed cell death (neutrophil extracellular trap formation) whereby they decondense their entire nuclear chromatin/DNA and release the resulting structure into the cytoplasm to mix with granule-derived antimicrobial peptides before extruding these web-like structures into the extracellular environment. The process requires the activation of the granule enzyme peptidyl arginine deiminase-4, the formation of reactive oxygen species (in particular hypochlorous acid), the neutrophil microtubular system and the actin cytoskeleton. Recent work by Yousefi et al. demonstrated that exposure to different agents for shorter stimulation periods resulted in neutrophil extracellular trap release from viable granulocytes, and that such neutrophil extracellular traps comprised mitochondrial DNA rather than nuclear DNA and were also capable of microbial entrapment and destruction. Deficiency in NADPH-oxidase production (as found in patients with chronic granulomatous disease) results in an inability to produce neutrophil extracellular traps and, along with their failure to produce antimicrobial reactive oxygen species, these patients suffer from severe, and sometimes life-threatening, infections. However, conversely the release of nuclear chromatin into tissues is also potentially autoimmunogenic and is now associated with the generation of anti-citrullinated protein antibodies in seropositive rheumatoid arthritis. Other neutrophil-derived nuclear and cytoplasmic contents are also pathogenic, either through direct effects on tissues or via autoimmune processes (e.g. autoimmune vasculitis). In this review, we discuss the plant origins of a highly conserved innate immune method of microbial killing, the history and biology of neutrophil extracellular traps and their role in defence and in human diseases. We attempt to resolve areas of controversy and propose roles for excess neutrophil extracellular trap release from hyperactive/reactive neutrophils and for the unique peptidyl arginine deiminase enzyme of Porphyromonas gingivalis in the pathogenesis of periodontitis, and subsequently a role for periodontitis/the peptidyl arginine deiminase enzyme of P. gingivalis in the causal pathway of autoimmune diseases such as rheumatoid arthritis. We propose that neutrophil extracellular trap and peptidyl arginine deiminase release may propagate tissue-destructive mechanisms rather than provide protection in susceptible individuals and that release of host-derived DNase may play an important role in the digestion and removal of neutrophil extracellular traps within tissues.

Vesicular LL-37 contributes to inflammation of the lesional skin of palmoplantar pustulosis

“Pustulosis palmaris et plantaris”, or palmoplantar pustulosis (PPP), is a chronic pustular dermatitis characterized by intraepidermal palmoplantar pustules. Although early stage vesicles (preceding the pustular phase) formed in the acrosyringium contain the antimicrobial peptides cathelicidin (hCAP-18/LL-37) and dermcidin, the details of hCAP-18/LL-37 expression in such vesicles remain unclear. The principal aim of the present study was to clarify the manner of hCAP-18/LL-37 expression in PPP vesicles and to determine whether this material contributed to subsequent inflammation of lesional skin. PPP vesicle fluid (PPP-VF) induced the expression of mRNAs encoding IL-17C, IL-8, IL-1α, and IL-1β in living skin equivalents, but the level of only IL-8 mRNA decreased significantly upon stimulation of PPP vesicle with depletion of endogenous hCAP-18/LL-37 by affinity chromatography (dep-PPP-VF). Semi-quantitative dot-blot analysis revealed higher concentrations of hCAP-18/LL-37 in PPP-VF compared to healthy sweat (2.87±0.93 µM vs. 0.09±0.09 µM). This concentration of hCAP-18/LL-37 in PPP-VF could upregulate expression of IL-17C, IL-8, IL-1α, and IL-1β at both the mRNA and protein levels. Recombinant hCAP-18 was incubated with dep-PPP-VF. Proteinase 3, which converts hCAP-18 to the active form (LL-37), was present in PPP-VF. Histopathological and immunohistochemical examination revealed that early stage vesicles contained many mononuclear cells but no polymorphonuclear cells, and the mononuclear cells were CD68-positive. The epidermis surrounding the vesicle expresses monocyte chemotactic chemokine, CCL2. In conclusion, PPP-VF contains the proteinase required for LL-37 processing and also may directly upregulate IL-8 in lesional keratinocytes, in turn contributing to the subsequent inflammation of PPP lesional skin.

Structural and functional analysis of the pro-domain of human cathelicidin, LL-37

Cathelicidins form a family of small host defense peptides distinct from another class of cationic antimicrobial peptides, the defensins. They are expressed as large precursor molecules with a highly conserved pro-domain known as the cathelin-like domain (CLD). CLDs have high degrees of sequence homology to cathelin, a protein isolated from pig leukocytes and belonging to the cystatin family of cysteine protease inhibitors. In this report, we describe for the first time the X-ray crystal structure of the human CLD (hCLD) of the sole human cathelicidin, LL-37. The structure of the hCLD, determined at 1.93 Å resolution, shows the cystatin-like fold and is highly similar to the structure of the CLD of the pig cathelicidin, protegrin-3. We assayed the in vitro antibacterial activities of the hCLD, LL-37, and the precursor form, pro-cathelicidin (also known as hCAP18), and we found that the unprocessed protein inhibited the growth of Gram-negative bacteria with efficiencies comparable to that of the mature peptide, LL-37. In addition, the antibacterial activity of LL-37 was not inhibited by the hCLD intermolecularly, because exogenously added hCLD had no effect on the bactericidal activity of the mature peptide. The hCLD itself lacked antimicrobial function and did not inhibit the cysteine protease, cathepsin L. Our results contrast with previous reports of hCLD activity. A comparative structural analysis between the hCLD and the cysteine protease inhibitor stefin A showed why the hCLD is unable to function as an inhibitor of cysteine proteases. In this respect, the cystatin scaffold represents an ancestral structural platform from which proteins evolved divergently, with some losing inhibitory functions.

Human cathelicidin LL-37 prevents bacterial biofilm formation

Human pathogens often colonize their host by the formation of biofilms. These surface-attached aggregates of bacteria are characterized by a self-produced extracellular matrix, which makes them highly resistant towards antibiotic treatment. Their abilities to adhere to abiotic surfaces (e.g., catheters and other medical devices) also makes bacterial biofilm formation a challenge in modern medicine. Antimicrobial peptides have lately been introduced as a potential class of drug molecules for combating severe hospital-acquired infections. One of these peptides, human cathelicidin LL-37, has recently been demonstrated to bridge innate and adaptive host defence, in addition to facilitating a robust antibiofilm effect at sub-inhibitory concentrations. In this review we will discuss the evidence, potential and challenges for LL-37 as a candidate molecule for therapeutic use.

Modification of a novel angiogenic peptide, AG30, for the development of novel therapeutic agents

We previously identified a novel angiogenic peptide, AG30, with antibacterial effects that could serve as a foundation molecule for the design of wound-healing drugs. Toward clinical application, in this study we have developed a modified version of the AG30 peptide characterized by improved antibacterial and angiogenic action, thus establishing a lead compound for a feasibility study. Because AG30 has an α-helix structure with a number of hydrophobic and cationic amino acids, we designed a modified AG30 peptide by replacing several of the amino acids. The replacement of cationic amino acids (yielding a new molecule, AG30/5C), but not hydrophobic amino acids, increased both the angiogenic and the antimicrobial properties of the peptide. AG30/5C was also effective against methicillin-resistant Staphylococcus aureus (MRSA) and antibiotic-resistant Pseudomonas aeruginosa. In a diabetic mouse wound-healing model, the topical application of AG30/5C accelerated wound healing with increased angiogenesis and attenuated MRSA infection. To facilitate the eventual clinical investigation/application of these compounds, we developed a large-scale procedure for the synthesis of AG30/5C that employed the conventional solution method and met Good Manufacturing Practice guidelines. In the evaluation of stability of this peptide in saline solution, RP-HPLC analysis revealed that AG30/5C was fairly stable under 5°C for 12 months. Therefore, we propose the use of AG30/5C as a wound-healing drug with antibacterial and angiogenic actions.

Neutrophils, from marrow to microbes

Neutrophils are produced in the bone marrow from stem cells that proliferate and differentiate to mature neutrophils fully equipped with an armory of granules. These contain proteins that enable the neutrophil to deliver lethal hits against microorganisms, but also to cause great tissue damage. Neutrophils circulate in the blood as dormant cells. At sites of infection, endothelial cells capture bypassing neutrophils and guide them through the endothelial cell lining whereby the neutrophils are activated and tuned for the subsequent interaction with microbes. Once in tissues, neutrophils kill microorganisms by microbicidal agents liberated from granules or generated by metabolic activation. As a final act, neutrophils can extrude stands of DNA with bactericidal proteins attached that act as extracellular traps for microorganisms.

Generation of novel bone forming cells (monoosteophils) from the cathelicidin-derived peptide LL-37 treated monocytes

Background

Bone generation and maintenance involve osteoblasts, osteoclasts, and osteocytes which originate from unique precursors and rely on key growth factors for differentiation. However, an incomplete understanding of bone forming cells during wound healing has led to an unfilled clinical need such as nonunion of bone fractures. Since circulating monocytes are often recruited to sites of injury and may differentiate into various cell types including osteoclasts, we investigated the possibility that circulating monocytes in the context of tissue injury may also contribute to bone repair. In particular, we hypothesized that LL-37 (produced from hCAP-18, cathelicidin), which recruits circulating monocytes during injury, may play a role in bone repair.

Methods and Findings

Treatment of monocytes from blood with LL-37 for 6 days resulted in their differentiation to large adherent cells. Growth of LL-37-differentiated monocytes on osteologic discs reveals bone-like nodule formation by scanning electron microscopy (SEM). In vivo transplantation studies in NOD/SCID mice show that LL-37-differentiated monocytes form bone-like structures similar to endochondral bone formation. Importantly, LL-37-differentiated monocytes are distinct from conventional monocyte-derived osteoclasts, macrophages, and dendritic cells and do not express markers of the mesenchymal stem cells (MSC) lineage, distinguishing them from the conventional precursors of osteoblasts. Furthermore, LL-37 differentiated monocytes express intracellular proteins of both the osteoblast and osteoclast lineage including osteocalcin (OC), osteonectin (ON), bone sialoprotein II (BSP II), osteopontin (OP), RANK, RANKL, MMP-9, tartrate resistant acid phosphatase (TRAP), and cathepsin K (CK).

Conclusion

Blood derived monocytes treated with LL-37 can be differentiated into a novel bone forming cell that functions both in vitro and in vivo. We propose the name monoosteophil to indicate their monocyte derived lineage and their bone forming phenotype. These cells may have wide ranging implications in the clinic including repair of broken bones and treatment of osteoporosis.

Spotlight on Human LL-37, an Immunomodulatory Peptide with Promising Cell-Penetrating Properties

Cationic antimicrobial peptides are major components of innate immunity and help control the initial steps of the infectious process. They are expressed not only by immunocytes, but also by epithelial cells. They share an amphipathic secondary structure with a polar cationic site, which explains their tropism for prokaryote membranes and their hydrophobic site contributing to the destructuration of these membranes. LL-37 is the only cationic antimicrobial peptide derived from human cathelicidin. LL-37 can also cross the plasma membrane of eukaryotic cells, probably through special domains of this membrane called lipid rafts. This transfer could be beneficial in the context of vaccination: the activation of intracellular toll-like receptors by a complex formed between CpG oligonucleotides and LL-37 could conceivably play a major role in the building of a cellular immunity involving NK cells.

Lipopolysaccharide (LPS) detoxification of analogue peptides derived from limulus anti-LPS factor

Lipopolysaccharide (LPS) plays a critical role in the pathogenesis of sepsis due to gram-negative bacterial infections. Therefore, LPS-neutralizing molecules could have important clinical applications. Our previous work showed, CLP19, an analogue peptide derived from limulus anti-LPS factor (LALF), possessed the capacity to neutralize LPS and thereby inhibit the LPS-induced responses. However, potential cytotoxicity of CLP19 was also found, especially when added to human red blood cells. Accordingly we further developed two peptides (designated as CLP19-1 and CLP19-2) by single- and double-point amino acid substitution of CLP19, respectively, in order to reduce its toxicity and meanwhile retain the anti-LPS activity. In this study, the LPS-detoxifying effectiveness of these peptides was evaluated both in vitro and in vivo. CLP19-1 was found to dose-dependently neutralize LPS in vitro, with significantly lower hemolysis of red blood cells as compared with CLP19. Further in vivo tests verified that CLP19-1 exerted significant protective effects on mice against LPS, characterized by significantly improved survival, decreasing of tumor necrosis factor alpha (TNF-α) serum level and alleviation of tissue injury. Our work indicates that CLP19-1 is worthy of further study as potential anti-LPS agents for the management of sepsis.

The human cathelicidin hCAP18/LL-37: a multifunctional peptide involved in mycobacterial infections

Antimicrobial peptides are predominantly small cationic polypeptides that are classified together on the basis of these molecules to directly kill or inhibit the growth of microorganisms including mycobacteria, and to activate mechanisms of cellular and adaptive immunity. Various families of antimicrobial peptides have been identified, including the cathelicidins. The cathelicidin family is characterised by a conserved N-terminal cathelin domain and a variable C-terminal antimicrobial domain that can be released from the precursor protein after cleavage by proteinases. LL-37 is the C-terminal part of the only human cathelicidin identified to date called human cationic antimicrobial protein (hCAP18), which is mainly expressed by neutrophils and epithelial cells. The cathelicidin hCAP18/LL-37 is a multifunctional molecule that may mediate various host responses, including bactericidal action, chemotaxis, epithelial cell activation, angiogenesis, epithelial wound repair and activation of chemokine secretion. The antimicrobial peptide LL-37 is produced from human cells during infection of mycobacteria and exerts a microbicidal effect. The discussion will (1) describe recent work on the antimicrobial and immunomodulatory functions of the cathelicidin hCAP18/LL-37, (2) highlight the effectiveness of the cathelicidin hCAP18/LL-37 as a potent component in antimycobacterial immune responses and (3) summarise current progress in the understanding of the therapeutic application of hCAP18/LL-37 and its derivates antimicrobial peptides in mycobacterial infection.

Ficolin-1 is present in a highly mobilizable subset of human neutrophil granules and associates with the cell surface after stimulation with fMLP

Ficolins are soluble molecules that bind carbohydrate present on the surface of microorganisms and function as recognition molecules in the lectin complement pathway. Three ficolins have been identified in humans: ficolin-1, ficolin-2, and ficolin-3. Ficolin-1 is synthesized in monocytes and type II alveolar epithelial cells. Ficolin-1 has been shown to be present in secretory granules of human neutrophils, but it is not known which subset of the neutrophils' secretory granules harbors ficolin-1. To determine the exact subcellular localization of ficolin-1 in neutrophils, recombinant ficolin-1 was expressed in Chinese hamster ovary cells and used for generation of polyclonal antibodies. This allowed detection of ficolin-1 in subcellular fractions of human neutrophils by ELISA, by Western blotting, and by immunohistochemistry. Real-time PCR examination of normal human bone marrow showed FCN1 gene expression largely in myelocytes, metamyelocytes, and band cells with a profile quite similar to that of gelatinase. In accordance with this, biosynthesis studies of neutrophils precursor cells showed that ficolin-1 was primarily synthesized in myelocytes, metamyelocytes, and band cells. Immunohistochemistry and subcellular fractionation demonstrated that ficolin-1 is primarily localized in gelatinase granules but also in highly exocytosable gelatinase-poor granules, not described previously. Ficolin-1 is released from neutrophil granules by stimulation with fMLP or PMA, and the majority becomes associated with the surface membrane of the cells and can be detected by flow cytometry. Our studies show that neutrophils are a major source of ficolin-1, which can be readily exocytosed by stimulation.

AMPed up immunity: how antimicrobial peptides have multiple roles in immune defense

Antimicrobial peptides (AMPs) are widely expressed and rapidly induced at epithelial surfaces to repel assault from diverse infectious agents including bacteria, viruses, fungi and parasites. Much information suggests that AMPs act by mechanisms that extend beyond their capacity to serve as gene-encoded antibiotics. For example, some AMPs alter the properties of the mammalian membrane or interact with its receptors to influence diverse cellular processes including cytokine release, chemotaxis, antigen presentation, angiogenesis and wound healing. These functions complement their antimicrobial action and favor resolution of infection and repair of damaged epithelia. Opposing this, some microbes have evolved mechanisms to inactivate or avoid AMPs and subsequently become pathogens. Thus, AMPs are multifunctional molecules that have a central role in infection and inflammation.

Lipids including cholesteryl linoleate and cholesteryl arachidonate contribute to the inherent antibacterial activity of human nasal fluid

Mucosal surfaces provide first-line defense against microbial invasion through their complex secretions. The antimicrobial activities of proteins in these secretions have been well delineated, but the contributions of lipids to mucosal defense have not been defined. We found that normal human nasal fluid contains all major lipid classes (in micrograms per milliliter), as well as lipoproteins and apolipoprotein A-I. The predominant less polar lipids were myristic, palmitic, palmitoleic, stearic, oleic, and linoleic acid, cholesterol, and cholesteryl palmitate, cholesteryl linoleate, and cholesteryl arachidonate. Normal human bronchioepithelial cell secretions exhibited a similar lipid composition. Removal of less-polar lipids significantly decreased the inherent antibacterial activity of nasal fluid against Pseudomonas aeruginosa, which was in part restored after replenishing the lipids. Furthermore, lipids extracted from nasal fluid exerted direct antibacterial activity in synergism with the antimicrobial human neutrophil peptide HNP-2 and liposomal formulations of cholesteryl linoleate and cholesteryl arachidonate were active against P. aeruginosa at physiological concentrations as found in nasal fluid and exerted inhibitory activity against other Gram-negative and Gram-positive bacteria. These data suggest that host-derived lipids contribute to mucosal defense. The emerging concept of host-derived antimicrobial lipids unveils novel roads to a better understanding of the immunology of infectious diseases.

Neutrophil secondary necrosis is induced by LL-37 derived from cathelicidin

Neutrophils represent the most common granulocyte subtype present in blood. The short half-life of circulating neutrophils is regulated by spontaneous apoptosis, and tissue infiltrating neutrophils die by apoptosis and secondary necrosis. The mechanism of neutrophil apoptosis has been the subject of many studies; however, the mechanism of neutrophil secondary necrosis is less clear. Human cathelicidin cationic peptide 18, proteolytically processed to its active form, LL-37, is secreted by neutrophils and epithelial cells and shown to have effects in addition to bacterial lysis. We demonstrate here that LL-37 affects neutrophil lifespan by the pathway of secondary necrosis, rapidly converting annexin V-positive (AV(+)), propidium iodide-negative (PI(-); apoptotic) cells into PI(+) (necrotic) cells with the release of IL-8, IL-1R antagonist, ATP, and intact granules. The effects of LL-37 on apoptotic neutrophils are neither energy-dependent nor affected by pretreatment with G-CSF, GM-CSF, TNF-alpha, and LPS and are partially inhibited by human serum. Moreover, LL-37 decreases CXCR2 expression of AV(-)PI(-) (live) neutrophils, suggesting an effect on the neutrophil response to its chemotactic factors, including IL-8. Thus, the lifespan and inflammatory functions of neutrophils are directly affected by LL-37.

Binding of LL-37 to model biomembranes: insight into target vs host cell recognition

Pursuing the molecular mechanisms of the concentration dependent cytotoxic and hemolytic effects of the human antimicrobial peptide LL-37 on cells, we investigated the interactions of this peptide with lipids using different model membranes, together with fluorescence spectroscopy for the Trp-containing mutant LL-37(F27W). Minimum concentrations inhibiting bacterial growth and lipid interactions assessed by dynamic light scattering and monolayer penetration revealed the mutant to retain the characteristics of native LL-37. Although both LL-37 and the mutant intercalated effectively into zwitterionic phosphatidylcholine membranes the presence of acidic phospholipids caused augmented membrane binding. Interestingly, strongly attenuated intercalation of LL-37 into membranes containing both cholesterol and sphingomyelin (both at X=0.3) was observed. Accordingly, the distinction between target and host cells by LL-37 is likely to derive from i) acidic phospholipids causing enhanced association with the former cells as well as ii) from attenuated interactions with the outer surface of the plasma membrane of the peptide secreting host, imposed by its high content of cholesterol and sphingomyelin. Our results further suggest that LL-37 may exert its antimicrobial effects by compromising the membrane barrier properties of the target microbes by a mechanism involving cytotoxic oligomers, similarly to other peptides forming amyloid-like fibers in the presence of acidic phospholipids.

Complex regulation of human cathelicidin gene expression: novel splice variants and 5'UTR negative regulatory element

Cationic antimicrobial peptides play important roles in host defense, linking innate and adaptive immunity. hCAP18, the only human antimicrobial cathelicidin, consists of a conserved N-terminal cathelin-like domain and a C-terminal peptide, LL-37. Expression is regulated during myeloid differentiation, and tightly controlled during infection and inflammation, suggesting active regulation. Using 5' RACE (rapid amplification of cDNA ends), multiple transcription initiation sites were identified, as well as new splice variants leading to novel augmentations of hCAP18 amino acid composition in bone marrow but not peripheral blood neutrophils. Having expressed hCAP18 promoter constructs in cell lines, we found that full-length (-1739) and truncated (-978) promoter constructs had lower luciferase activities than 5'UTR deletion constructs. Transient transfection of progressively deleted constructs in the non-permissive K562 cell line led us to identify a negative regulatory element within the 53 bp immediately upstream of the ATG of hCAP18. Additionally, transient transfection of 5' deletion constructs identified a positive regulatory element within the 101 bases 5' of promoter sequence containing two GT-boxes. Negative and positive regulatory elements within the hCAP18 gene promoter provide new insights into the possible molecular basis of myeloid gene expression.

IFN-γ- and TNF-Independent Vitamin D-Inducible Human Suppression of Mycobacteria: The Role of Cathelicidin LL-37

Vitamin D deficiency is associated with susceptibility to tuberculosis, and its biologically active metabolite, 1alpha,25 dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)), has pleiotropic immune effects. The mechanisms by which 1alpha,25(OH)(2)D(3) protects against tuberculosis are incompletely understood. 1alpha,25(OH)(2)D(3) reduced the growth of mycobacteria in infected human PBMC cultures in a dose-dependent fashion. Coculture with agonists or antagonists of the membrane or nuclear vitamin D receptors indicated that these effects were primarily mediated by the nuclear vitamin D receptors. 1alpha,25(OH)(2)D(3) reduced transcription and secretion of protective IFN-gamma, IL-12p40, and TNF in infected PBMC and macrophages, indicating that 1alpha,25(OH)(2)D(3) does not mediate protection via these cytokines. Although NOS2A was up-regulated by 1alpha,25(OH)(2)D(3), inhibition of NO formation marginally affected the suppressive effect of 1alpha,25(OH)(2)D(3) on bacillus Calmette Guérin in infected cells. By contrast, 1alpha,25(OH)(2)D(3) strongly up-regulated the cathelicidin hCAP-18 gene, and some hCAP-18 polypeptide colocalized with CD14 in 1alpha,25(OH)(2)D(3) stimulated PBMC, although no detectable LL-37 peptide was found in supernatants from similar 1alpha,25(OH)(2)D(3)-stimulated PBMC cultures. A total of 200 mug/ml of the active peptide LL-37, in turn, reduced the growth of Mycobacterium tuberculosis in culture by 75.7%. These findings suggest that vitamin D contributes to protection against TB by "nonclassical" mechanisms that include the induction of antimicrobial peptides.

Antimicrobial peptides: an overview of a promising class of therapeutics

Antibiotic resistance is increasing at a rate that far exceeds the pace of new development of drugs. Antimicrobial peptides, both synthetic and from natural sources, have raised interest as pathogens become resistant against conventional antibiotics. Indeed, one of the major strengths of this class of molecules is their ability to kill multidrug-resistant bacteria. Antimicrobial peptides are relatively small (6 to 100 aminoacids), amphipathic molecules of variable length, sequence and structure with activity against a wide range of microorganisms including bacteria, protozoa, yeast, fungi, viruses and even tumor cells. They usually act through relatively non-specific mechanisms resulting in membranolytic activity but they can also stimulate the innate immune response. Several peptides have already entered pre-clinical and clinical trials for the treatment of catheter site infections, cystic fibrosis, acne, wound healing and patients undergoing stem cell transplantation. We review the advantages of these molecules in clinical applications, their disadvantages including their low in vivo stability, high costs of production and the strategies for their discovery and optimization.

Protection of mice from lethal Escherichia coli infection by chimeric human bactericidal/permeability-increasing protein and immunoglobulin G1 Fc gene delivery

To evaluate the potentiality of applying gene therapy to bacterial infections, especially for preventing infection in high-risk patients, we investigated protection of mice from challenge with lethal Escherichia coli infection by adeno-associated virus serotype 2 (AAV2)-mediated gene transfer of a chimeric BPI23-Fcgamma1 gene, which consisted of human bactericidal/permeability-increasing protein (BPI) gene encoding the functional N terminus (amino acid residues 1 to 199) of human BPI and an Fcgamma1 gene encoding the Fc segment of human immunoglobulin G1. Here we show that the target protein that was expressed and secreted into the serum of the gene-transferred mice demonstrated the activity of a neutralizing endotoxin, killing E. coli and mediating opsonization. After lethal E. coli infection, the count of bacteria and the levels of endotoxin and proinflammatory cytokines in the gene-transferred mice were decreased. The survival rate of BPI23-Fcgamma1 gene-transferred mice markedly increased, especially in conjunction with antibiotics. Our data suggest that AAV2-mediated chimeric BPI23-Fcgamma1 gene delivery could potentially be used clinically for the protection and treatment of infection with gram-negative bacteria in high-risk individuals.

The trypanolytic factor of human serum

African trypanosomes (the prototype of which is Trypanosoma brucei brucei) are protozoan parasites that infect a wide range of mammals. Human blood, unlike the blood of other mammals, has efficient trypanolytic activity, and this needs to be counteracted by these parasites. Resistance to this activity has arisen in two subspecies of Trypanosoma brucei - Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense - allowing these parasites to infect humans, and this results in sleeping sickness in East Africa and West Africa, respectively. Study of the mechanism by which T. b. rhodesiense escapes lysis by human serum led to the identification of an ionic-pore-forming apolipoprotein - known as apolipoprotein L1 - that is associated with high-density-lipoprotein particles in human blood. In this Opinion article, we argue that apolipoprotein L1 is the factor that is responsible for the trypanolytic activity of human serum.