Calcitermin, a novel antimicrobial peptide isolated from human airway secretions

Capping motifs in antimicrobial peptides and their relevance for improved biological activities

N-capping (N-cap) and C-capping (C-cap) in biologically active peptides, including specific amino acids or unconventional group motifs, have been shown to modulate activity against pharmacological targets by interfering with the peptide's secondary structure, thus generating unusual scaffolds. The insertion of capping motifs in linear peptides has been shown to prevent peptide degradation by reducing its susceptibility to proteolytic cleavage, and the replacement of some functional groups by unusual groups in N- or C-capping regions in linear peptides has led to optimized peptide variants with improved secondary structure and enhanced activity. Furthermore, some essential amino acid residues that, when placed in antimicrobial peptide (AMP) capping regions, are capable of complexing metals such as Cu2+, Ni2+, and Zn2+, give rise to the family known as metallo-AMPs, which are capable of boosting antimicrobial efficacy, as well as other activities. Therefore, this review presents and discusses the different strategies for creating N- and C-cap motifs in AMPs, aiming at fine-tuning this class of antimicrobials.

Impact of C- and N-terminal protection on the stability, metal chelation and antimicrobial properties of calcitermin

The main limitation to the use of antimicrobial peptides (AMPs) as regular drugs, against antibiotic and antifungal resistance, mainly relates to their rapid degradation by proteolytic enzymes. The introduction of suitable structural changes in the peptide chain can make the peptide less susceptible to the action of proteases, thus overcoming this problem. To improve the plasma stability of calcitermin, a metal-chelating AMP present in the human respiratory tract and investigated in the present study, C- and/or N- terminal modifications have been introduced in the native sequence. Evaluation of peptide stability has been performed to determine the half-life times in human plasma of both native calcitermin and its derivatives. However, the protection of the peptide termini can also affect its metal coordination behaviour. Thus, the characterization of Zn2+ and Cu2+ complexes has been performed by means of several techniques, including potentiometry, high-resolution mass spectrometry, UV-Vis, circular dichroism and EPR. On the basis of the obtained results, it was possible to compare the biological activity of the studied systems, taking into account both the metal-binding ability and the peptide stability to search for a link among them. A significant result of this study is that the N-terminal protection increases the calcitermin half-life over seven times and the formation of metal complexes confers resistance towards degradation almost doubling its half-life.

Metal-protein solution interactions investigated using model systems: Thermodynamic and spectroscopic methods

The first-row D-block metal ions are essential for the physiology of living organisms, functioning as cofactors in metalloproteins or structural components for enzymes: almost half of all proteins require metals to perform the biological function. Understanding metal-protein interactions is crucial to unravel the mysteries behind molecular biology, understanding the effects of metal imbalance and toxicity or the diseases due to disorders in metal homeostasis. Metal-protein interactions are dynamic: they are noncovalent and affected by the environment to which the system is exposed. To reach a complete comprehension of the system, different conditions must be considered for the experimental investigation, in order to get information on the species distribution, the ligand coordination modes, complex stoichiometry and geometry. Thinking about the whole environment where a protein acts, investigations are often challenging, and simplifications are required to study in detail the mechanisms of metal interaction. This chapter is intended to help researchers addressing the problem of the complexity of metal-protein interactions, with particular emphasis on the use of peptides as model systems for the metal coordination site. The thermodynamic and spectroscopic methods most widely employed to investigate the interaction between metal ions and peptides in solution are here covered. These include solid-phase peptide synthesis, potentiometric titrations, calorimetry, electrospray ionization mass spectrometry, UV-Vis spectrophotometry, circular dichroism (CD), nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). Additional experimental methods, which can be employed to study metal complexes with peptides, are also briefly mentioned. A case-study is finally reported providing a practical example of the investigation of metal-protein interaction by means of thermodynamic and spectroscopic methods applied to peptide model systems.

The Synergy between Zinc and Antimicrobial Peptides: An Insight into Unique Bioinorganic Interactions

Antimicrobial peptides (AMPs) are essential components of innate immunity across all species. AMPs have become the focus of attention in recent years, as scientists are addressing antibiotic resistance, a public health crisis that has reached epidemic proportions. This family of peptides represents a promising alternative to current antibiotics due to their broad-spectrum antimicrobial activity and tendency to avoid resistance development. A subfamily of AMPs interacts with metal ions to potentiate antimicrobial effectiveness, and, as such, they have been termed metalloAMPs. In this work, we review the scientific literature on metalloAMPs that enhance their antimicrobial efficacy when combined with the essential metal ion zinc(II). Beyond the role played by Zn(II) as a cofactor in different systems, it is well-known that this metal ion plays an important role in innate immunity. Here, we classify the different types of synergistic interactions between AMPs and Zn(II) into three distinct classes. By better understanding how each class of metalloAMPs uses Zn(II) to potentiate its activity, researchers can begin to exploit these interactions in the development of new antimicrobial agents and accelerate their use as therapeutics.

Calcitermin-Loaded Smart Gels Activity against Candida albicans: A Preliminary In Vitro Study

Calcitermin is an antimicrobial peptide of 15 amino acids found in human nasal fluid characterized by antifungal and antibacterial properties. Candida albicans is the most common human fungal pathogen affecting many tissues, such as vaginal mucosa. In this study a formulation suitable for calcitermin administration on vaginal mucosa was developed for the treatment of fungal infections. To favor topical application, mucosal adhesion, and permanence, gels based on poloxamer 407 and xanthan gum were designed and compared with regard to their rheological behavior, erosion, and leakage. The selected gel was loaded with calcitermin, whose release kinetic was evaluated in vitro by Franz cells. An antifungal activity assay was conducted to assess the calcitermin anticandidal potential and the effect of its inclusion in the selected gel. The rheological study revealed the elastic and viscous moduli behavior as a function of poloxamer 407 and xanthan gum concentration. Xanthan gum presence decreased the transition temperature of the gel, while prolonging its erosion and leakage. Particularly, poloxamer 407, 18% and xanthan gum 0.4% were chosen. The calcitermin loading in the selected gel resulted in a transparent and homogeneous formulation and in a 4-fold decrease of the release rate with respect to the calcitermin solution, as evidenced by Franz cell study. The anticandidal activity tests demonstrated that calcitermin-loaded gel was more active against Candida albicans with respect to the peptide solution.

Transcriptional Heterogeneity and the Microbiome of Cutaneous T-Cell Lymphoma

Cutaneous T-Cell Lymphomas (CTCL) presents with substantial clinical variability and transcriptional heterogeneity. In the recent years, several studies paved the way to elucidate aetiology and pathogenesis of CTCL using sequencing methods. Several T-cell subtypes were suggested as the source of disease thereby explaining clinical and transcriptional heterogeneity of CTCL entities. Several differentially expressed pathways could explain disease progression. However, exogenous triggers in the skin microenvironment also seem to affect CTCL status. Especially Staphylococcus aureus was shown to contribute to disease progression. Only little is known about the complex microbiome patterns involved in CTCL and how microbial shifts might impact this malignancy. Nevertheless, first hints indicate that the microbiome might at least in part explain transcriptional heterogeneity and that microbial approaches could serve in diagnosis and prognosis. Shaping the microbiome could be a treatment option to maintain stable disease. Here, we review current knowledge of transcriptional heterogeneity of and microbial influences on CTCL. We discuss potential benefits of microbial applications and microbial directed therapies to aid patients with CTCL burden.

Zn2+ and Cu2+ Binding to the Extramembrane Loop of Zrt2, a Zinc Transporter of Candida albicans

Zrt2 is a zinc transporter of the ZIP family. It is predicted to be located in the plasma membrane and it is essential for Candida albicans zinc uptake and growth at acidic pH. Zrt2 from C. albicans is composed of 370 amino acids and contains eight putative transmembrane domains and an extra-membrane disordered loop, corresponding to the amino acid sequence 126–215. This protein region contains at least three possible metal binding motifs: HxHxHxxD (144–153), HxxHxxEHxD (181–193) and the Glu- and Asp- rich sequence DDEEEDxE (161–168). The corresponding model peptides, protected at their termini (Ac-GPHTHSHFGD-NH₂, Ac-DDEEEDLE-NH₂ and Ac-PSHFAHAQEHQDP-NH₂), have been investigated in order to elucidate the thermodynamic and coordination properties of their Zn²⁺ and Cu²⁺ complexes, with the further aim to identify the most effective metal binding site among the three fragments. Furthermore, we extended the investigation to the peptides Ac-GPHTHAHFGD-NH₂ and Ac-PAHFAHAQEHQDP-NH₂, where serine residues have been substituted by alanines in order to check if the presence of a serine residue may favor the displacement of amidic protons by Cu²⁺. In the native Zrt2 protein, the Ac-GPHTHSHFGD-NH₂ region of the Zrt2 loop has the highest metal binding affinity, showing that three alternated histidines separated by only one residue (-HxHxH-) bind Zn²⁺ and Cu²⁺ more strongly than the region in which three histidines are separated by two and three His residues (-HxxHxxxH- in Ac-PSHFAHAQEHQDP-NH₂). All studied Zrt2 loop fragments have lower affinity towards Zn²⁺ than the zinc(II) binding site on the Zrt1 transporter; also, all three Zrt2 regions bind Zn²⁺ and Cu²⁺ with comparable affinity below pH 5 and, therefore, may equally contribute to the metal acquisition under the most acidic conditions in which the Zrt2 transporter is expressed.

The impact of metal availability on immune function during infection

Nutrient transition metals are required cofactors for many proteins to perform functions necessary for life. As such, the concentration of nutrient metals is carefully maintained to retain critical biological processes while limiting toxicity. During infection, invading bacterial pathogens must acquire essential metals, such as zinc, manganese, iron, and copper, from the host to colonize and cause disease. To combat this, the host exploits the essentiality and toxicity of nutrient metals by producing factors that limit metal availability, thereby starving pathogens or accumulating metals in excess to intoxicate the pathogen in a process termed 'nutritional immunity'. As a result of inflammation, a heterogeneous environment containing both metal-replete and -deplete niches is created, in which nutrient metal availability may have an underappreciated role in regulating immune cell function during infection. How the host manipulates nutrient metal availability during infection, and the downstream effects that nutrient metals and metal-sequestering proteins have on immune cell function, are discussed in this review.

Antifungal activity of dendritic cell lysosomal proteins against Cryptococcus neoformans

Cryptococcal meningitis is a life-threatening disease among immune compromised individuals that is caused by the opportunistic fungal pathogen Cryptococcus neoformans. Previous studies have shown that the fungus is phagocytosed by dendritic cells (DCs) and trafficked to the lysosome where it is killed by both oxidative and non-oxidative mechanisms. While certain molecules from the lysosome are known to kill or inhibit the growth of C. neoformans, the lysosome is an organelle containing many different proteins and enzymes that are designed to degrade phagocytosed material. We hypothesized that multiple lysosomal components, including cysteine proteases and antimicrobial peptides, could inhibit the growth of C. neoformans. Our study identified the contents of the DC lysosome and examined the anti-cryptococcal properties of different proteins found within the lysosome. Results showed several DC lysosomal proteins affected the growth of C. neoformans in vitro. The proteins that killed or inhibited the fungus did so in a dose-dependent manner. Furthermore, the concentration of protein needed for cryptococcal inhibition was found to be non-cytotoxic to mammalian cells. These data show that many DC lysosomal proteins have antifungal activity and have potential as immune-based therapeutics.

Antimicrobial Peptides and Proteins: From Nature's Reservoir to the Laboratory and Beyond

Rapid rise of antimicrobial resistance against conventional antimicrobials, resurgence of multidrug resistant microbes and the slowdown in the development of new classes of antimicrobials, necessitates the urgent development of alternate classes of therapeutic molecules. Antimicrobial peptides (AMPs) are small proteins present in different lifeforms in nature that provide defense against microbial infections. They have been effective components of the host defense system for a very long time. The fact that the development of resistance by the microbes against the AMPs is relatively slower or delayed compared to that against the conventional antibiotics, makes them prospective alternative therapeutics of the future. Several thousands of AMPs have been isolated from various natural sources like microorganisms, plants, insects, crustaceans, animals, humans, etc. to date. However, only a few of them have been translated commercially to the market so far. This is because of some inherent drawbacks of the naturally obtained AMPs like 1) short half-life owing to the susceptibility to protease degradation, 2) inactivity at physiological salt concentrations, 3) cytotoxicity to host cells, 4) lack of appropriate strategies for sustained and targeted delivery of the AMPs. This has led to a surge of interest in the development of synthetic AMPs which would retain or improve the antimicrobial potency along with circumventing the disadvantages of the natural analogs. The development of synthetic AMPs is inspired by natural designs and sequences and strengthened by the fusion with various synthetic elements. Generation of the synthetic designs are based on various strategies like sequence truncation, mutation, cyclization and introduction of unnatural amino acids and synthons. In this review, we have described some of the AMPs isolated from the vast repertoire of natural sources, and subsequently described the various synthetic designs that have been developed based on the templates of natural AMPs or from de novo design to make commercially viable therapeutics of the future. This review entails the journey of the AMPs from their natural sources to the laboratory.

Application of Salivary Biomarkers in the Diagnosis of Fibromyalgia

Fibromyalgia (FM) is a highly prevalent syndrome that impairs the quality of life of the patients; however, its diagnosis is complex and mainly centered on pain symptoms. The study of salivary biomarkers has proven highly useful for the diagnosis and prognosis of numerous diseases. The objective of this review was to gather published data on the utilization of salivary biomarkers to facilitate and complement the diagnosis of FM. Salivary biomarkers used in FM diagnosis include cortisol; calgranulin; and the enzymes α-amylase, transaldolase, and phosphoglycerate mutase. Increased serum levels of C-reactive protein, cytokines interleukin 1-β, interleukin 6, interleukin 8, interleukin 10, interleukin 17, tumor necrosis factor α, and various chemokines may serve as salivary biomarkers, given observations of their increased serum levels in patients with FM. Further research is warranted to study in depth the role and performance of biomarkers currently used in FM diagnosis/prognosis and to identify novel salivary biomarkers for this disease.

The Best Peptidomimetic Strategies to Undercover Antibacterial Peptides

Health-care systems that develop rapidly and efficiently may increase the lifespan of humans. Nevertheless, the older population is more fragile, and is at an increased risk of disease development. A concurrently growing number of surgeries and transplantations have caused antibiotics to be used much more frequently, and for much longer periods of time, which in turn increases microbial resistance. In 1945, Fleming warned against the abuse of antibiotics in his Nobel lecture: "The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant". After 70 years, we are witnessing the fulfilment of Fleming's prophecy, as more than 700,000 people die each year due to drug-resistant diseases. Naturally occurring antimicrobial peptides protect all living matter against bacteria, and now different peptidomimetic strategies to engineer innovative antibiotics are being developed to defend humans against bacterial infections.

Metal Sequestration and Antimicrobial Activity of Human Calprotectin Are pH-Dependent

Human calprotectin (CP, S100A8/S100A9 oligomer) is an abundant innate immune protein that sequesters transition metal ions in the extracellular space to limit nutrient availability and the growth of invading microbial pathogens. Our current understanding of the metal-sequestering ability of CP is based on biochemical and functional studies performed at neutral or near-neutral pH. Nevertheless, CP can be present throughout the human body and is expressed at infection and inflammation sites that tend to be acidic. Here, we evaluate the metal binding and antimicrobial properties of CP in the pH range of 5.0-7.0. We show that Ca(II)-induced tetramerization, an important process for the extracellular functions of CP, is perturbed by acidic conditions. Moreover, a low pH impairs the antimicrobial activity of CP against some bacterial pathogens, including Staphylococcus aureus and Salmonella enterica serovar Typhimurium. At a mildly acidic pH, CP loses the ability to deplete Mn from microbial growth medium, indicating that Mn(II) sequestration is attenuated under acidic conditions. Evaluation of the Mn(II) binding properties of CP at pH 5.0-7.0 indicates that mildly acidic conditions decrease the Mn(II) binding affinity of the His₆ site. Lastly, CP is less effective at preventing capture of Mn(II) by the bacterial solute-binding proteins MntC and PsaA at low pH. These results indicate that acidic conditions compromise the ability of CP to sequester Mn(II) and starve microbial pathogens of this nutrient. This work highlights the importance of considering the local pH of biological sites when describing the interplay between CP and microbes in host-pathogen interactions.

Bioinorganic chemistry of calcitermin - the picklock of its antimicrobial activity

Calcitermin, an antimicrobial peptide from the fluid of the human airways, is a well-conserved, 15 amino acid C-terminal cleavage fragment of calgranulin C (VAIALKAAHYHTHKE), which is active under acidic pH conditions (pH 5.4). In an attempt to understand the impact of the coordination of Zn(ii) and Cu(ii) on the biological activity of calcitermin, we mutated each of the histidines with an alanine and studied the thermodynamics, binding mode and antimicrobial activity of wild type calcitermin and its H9A, H11A and H13A mutants and their Zn(ii) and Cu(ii) complexes. Both metals strongly enhance the antimicrobial activity of calcitermin-like peptides, although the link between the minimal inhibitory concentration (MIC) values and the stability, charge or structure of the complexes is not so obvious. As expected, the increase in the number of histidines makes the coordination of both metals more effective. There is no preferred Cu(ii) binding site in calcitermin: the stabilities of the Cu(ii)-H9A and Cu(ii)-H13A complexes are almost identical, while the Cu(ii)-H11A complex (in which two histidines are separated by three amino acids and only one His residue is involved in binding) is less stable. On the other hand, the higher stability of the Zn(ii)-H13A complex with respect to those formed by H9A and H11A suggests a pivotal role of His9 and His11 in Zn(ii) complexation. Impressive MIC breakpoints were obtained, similar and lower than those for commonly used antimicrobial agents that treat Candida albicans (Zn(ii) and Cu(ii) complexes of WT calcitermin and H9A, as well as H9A alone), Enterococcus faecalis (H11A, H13A and their metal complexes) and Staphylococcus aureus (H13A and its complexes).

Bovine mucous membranes as a source of antimicrobial compounds

Loss of food quality, deterioration of organoleptic properties and accumulation of anti-alimentary compounds are in focus of modern food science. Nowadays, such traditional methods as processing, physical and chemical treatment are used for improving of shelf life. An alternative ways of shelf life increasing are quite a sharp problem. Antimicrobial peptides (AMPs) could be an actual alternative. According to Antimicrobial Peptide Database (http://aps.unmc.edu/AP/main.php), 2884 antimicrobial peptides from six kingdoms were found and identified. Mucous membranes of farm animals due to their border position and intensive contact with different pathogens could be a capacious source of such substances. Objects of the study were bovine oral cavity mucosa, nasal cavity mucosa, tracheal cavity mucosa, rectal mucosa, tongue mucosa, saliva gland and submandibular lymph nodes. Two-dimensional electrophoresis (2DE) was performed according to the method of O'Farrell, 35 protein fractions were identified by MALDI-TOF MS and MS/MS mass spectrometry. A number of qualitative and quantitative differences were revealed. A large number of histones (H2bd-like, H2BC, HIST1H2BD, HIST2H2AC, HIST1H2AH, histone H3.3 and H2bl-like, HIST2H2AC and histone H3.3, mixture HIST1H2AJ, HIST2H2BE and histone H2A type 2-C) were found in all mucous membranes as well as several tissue-specific proteins (proteins S100-A12 and AGR2, isoforms of ribosomal proteins, myelin P2, odorant-binding protein, secretoglobin), which could be a precusors of bioactive peptides

Antimicrobial peptide–metal ion interactions – a potential way of activity enhancement

We discuss the potential correlation between the antimicrobial peptide–metal binding mode, structure, thermodynamics and mode of action.

Discovery of Antimicrobial Peptides in Cervical-Vaginal Fluid from Healthy Nonpregnant Women via an Integrated Proteome and Peptidome Analysis

Cervical-vaginal fluid (CVF) covers the lower part of the female reproductive system and functions in the homeostasis and immunity of the surrounding tissues. In contrast to the CVF proteome of both nonpregnant and pregnant women, the CVF peptidome has not been reported to date. In the current study, we identified 1087 proteins in CVF, of which 801 proteins were not previously identified in CVF proteomes. The presence of the tissue-specific proteins oviductal glycoprotein 1 and tubulin polymerization-promoting protein family member 3 strongly suggests that the tissues of the upper female reproductive tract contribute to the protein composition of CVF. The tremendous catalytic potential of CVF was highlighted by the identification of 85 proteases and the detection of pH-dependent trypsin-like proteolytic activity. Over 1000 endogenous peptides were detected in the CVF peptidome, and 39 peptides are predicted to have antimicrobial activity. The detailed proteomic and peptidomic analysis of CVF will further aid in the delineation of pathways related to reproduction, immunity and host defense, and assist in developing new biomarkers for malignant and other diseases of the female reproductive tract. Data are available via ProteomeXchange with identifiers PXD004450 (CVF peptidome) and PDX004363 (CVF proteome).

Human Antimicrobial Peptides in Bodily Fluids: Current Knowledge and Therapeutic Perspectives in the Postantibiotic Era

Antimicrobial peptides (AMPs) are an integral part of the innate immune defense mechanism of many organisms. Due to the alarming increase of resistance to antimicrobial therapeutics, a growing interest in alternative antimicrobial agents has led to the exploitation of AMPs, both synthetic and isolated from natural sources. Thus, many peptide-based drugs have been the focus of increasing attention by many researchers not only in identifying novel AMPs, but in defining mechanisms of antimicrobial peptide activity as well. Herein, we review the available strategies for the identification of AMPs in human body fluids and their mechanism(s) of action. In addition, an overview of the distribution of AMPs across different human body fluids is provided, as well as its relation with microorganisms and infectious conditions.

Molecular inhibition mechanisms of cell migration and invasion by coix polysaccharides in A549 NSCLC cells via targeting S100A4

S100 calcium binding protein A4 (S100A4) promotes extracellular signal transduction, intercellular adhesion, motility and mobility. Different extracts from Coix lachryma-jobi have been used for the treatment of various types of cancer in Asia. In our previous study, the polysaccharide fraction extact, CP1, induced cell apoptosis of non‑small cell lung cancer cells. In the current study, CP1 inhibited migration and invasion of A549 cells in a scratch wound healing assay and matrigel invasion assay, respectively. Furthermore, reverse transcription‑polymerase chain reaction and western blotting demonstrated that CP1 downregulated the gene and protein expression levels of S100A4. In silico docking analysis demonstrated that polysaccharides may not interfere with dimerization, whereas, the affinity of polysaccharides for an S100A4‑NMIIA pocket was margnially greater than at the dimerization sites. Thus, CP1 inhibited A549 cell migration and invasion potentially via downregulation of S100A4, and may also interact with the binding site of S100A4‑NMIIA, which indicated that CP1 has potential as an alternative cancer chemotherapeutic by targeting S100A4.

The salivary proteome profile in patients affected by SAPHO syndrome characterized by a top-down RP-HPLC-ESI-MS platform

SAPHO syndrome is a rare and often unrecognized disease with prominent inflammatory cutaneous and articular symptoms characterized by musculoskeletal manifestations (synovitis, hyperostosis, osteomyelitis) associated with dermatological conditions (severe acne and pustulosis). The acidic soluble fraction of whole saliva from 10 adult women affected by SAPHO syndrome and from a group of 28 healthy women was analysed by RP-HPLC-ESI-MS with the aim of discovering salivary biomarkers of the disorder. The levels of the oral proteins and peptides were correlated with clinical data. The following proteins showed a significant decreased concentration in saliva of SAPHO subjects with respect to controls: cystatin S1 and SN, histatins, the major acidic PRPs, P-C and P-B peptides. The cystatin SN abundance lowered according to the disease duration and histatins showed positive correlations with the C reactive protein. Statistical analysis performed excluding one patient with a different pattern of salivary proteins/peptides highlighted a positive relationship between cystatin S1, histatins 3, histatin 5, and the neutrophil count. Moreover, histatin 3 correlated positively with the total white cell count and negatively with the erythrocyte sedimentation rate. Levels and frequency of S100A12 protein showed a trend to increase in SAPHO patients. The high expression of this pro-inflammatory protein is probably related to the inflammatory response and to the altered neutrophil responses to functional stimuli that characterize SAPHO syndrome suggesting a possible application as a salivary biomarker.

[Translational research in pediatric rheumatology. Current research approaches to the innate immune system]

Translational research aims at closely linking basic research and clinical observations so that important mechanistic insights identified in one field should trigger progress in the other. Particularly in the field of pediatric rheumatology this approach has significantly improved the understanding and therapy of several diseases in recent years. One focus of our research in this respect is on the structure, release mechanisms and function of damage associated molecular patterns (DAMP), particularly S100 proteins. Due to their huge potential as inflammation biomarkers for more specific diagnostics these proteins are of particular clinical interest. Overactivated cells of the innate immune system play a crucial role in the development of rheumatic diseases. Innate mechanisms, such as the generation of neutrophil extracellular traps (NETosis) were linked to the pathogenesis of inflammatory diseases, such as systemic lupus erythematosus and rheumatoid arthritis. Furthermore, it became increasingly more evident that various excessive sterile inflammatory mechanisms and reactions significantly contribute to an activation of adaptive immune responses and thus to the development of autoimmunity. Studying such potentially DAMP-dependent pathways at the interface between innate and adaptive immunity can provide a better understanding of autoinflammatory conditions in pediatric rheumatology and to identify novel targets for optimization of therapy.

Keratin and S100 calcium-binding proteins are major constituents of the bovine teat canal lining

The bovine teat canal provides the first-line of defence against pathogenic bacteria infecting the mammary gland, yet the protein composition and host-defence functionality of the teat canal lining (TCL) are not well characterised. In this study, TCL collected from six healthy lactating dairy cows was subjected to two-dimensional electrophoresis (2-DE) and mass spectrometry. The abundance and location of selected identified proteins were determined by western blotting and fluorescence immunohistochemistry. The variability of abundance among individual cows was also investigated. Two dominant clusters of proteins were detected in the TCL, comprising members of the keratin and S100 families of proteins. The S100 proteins were localised to the teat canal keratinocytes and were particularly predominant in the cornified outermost layer of the teat canal epithelium. Significant between-animal variation in the abundance of the S100 proteins in the TCL was demonstrated. Four of the six identified S100 proteins have been reported to have antimicrobial activity, suggesting that the TCL has additional functionality beyond being a physical barrier to invading microorganisms. These findings provide new insights into understanding host-defence of the teat canal and resistance of cows to mastitis.

Antimicrobial proteins and peptides in human lung diseases: A friend and foe partnership with host proteases

Lung antimicrobial proteins and peptides (AMPs) are major sentinels of innate immunity by preventing microbial colonization and infection. Nevertheless bactericidal activity of AMPs against Gram-positive and Gram-negative bacteria is compromised in patients with chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF) and asthma. Evidence is accumulating that expression of harmful human serine proteases, matrix metalloproteases and cysteine cathepsins is markedely increased in these chronic lung diseases. The local imbalance between proteases and protease inhibitors compromises lung tissue integrity and function, by not only degrading extracellular matrix components, but also non-matrix proteins. Despite the fact that AMPs are somewhat resistant to proteolytic degradation, some human proteases cleave them efficiently and impair their antimicrobial potency. By contrast, certain AMPs may be effective as antiproteases. Host proteases participate in concert with bacterial proteases in the degradation of key innate immunity peptides/proteins and thus may play immunomodulatory activities during chronic lung diseases. In this context, the present review highlights the current knowledge and recent discoveries on the ability of host enzymes to interact with AMPs, providing a better understanding of the role of human proteases in innate host defense.

Nutritional Immunity: S100 Proteins at the Host-Pathogen Interface

The S100 family of EF-hand calcium (Ca(2+))-binding proteins is essential for a wide range of cellular functions. During infection, certain S100 proteins act as damage-associated molecular patterns (DAMPs) and interact with pattern recognition receptors to modulate inflammatory responses. In addition, these inflammatory S100 proteins have potent antimicrobial properties and are essential components of the immune response to invading pathogens. In this review, we focus on S100 proteins that exhibit antimicrobial properties through the process of metal limitation, termed nutritional immunity, and discuss several recent advances in our understanding of S100 protein-mediated metal sequestration at the site of infection.

The Human Antimicrobial Protein Calgranulin C Participates in Control of Helicobacter pylori Growth and Regulation of Virulence

During infectious processes, antimicrobial proteins are produced by both epithelial cells and innate immune cells. Some of these antimicrobial molecules function by targeting transition metals and sequestering these metals in a process referred to as "nutritional immunity." This chelation strategy ultimately starves invading pathogens, limiting their growth within the vertebrate host. Recent evidence suggests that these metal-binding antimicrobial molecules have the capacity to affect bacterial virulence, including toxin secretion systems. Our previous work showed that the S100A8/S100A9 heterodimer (calprotectin, or calgranulin A/B) binds zinc and represses the elaboration of the H. pylori cag type IV secretion system (T4SS). However, there are several other S100 proteins that are produced in response to infection. We hypothesized that the zinc-binding protein S100A12 (calgranulin C) is induced in response to H. pylori infection and also plays a role in controlling H. pylori growth and virulence. To test this, we analyzed gastric biopsy specimens from H. pylori-positive and -negative patients for S100A12 expression. These assays showed that S100A12 is induced in response to H. pylori infection and inhibits bacterial growth and viability in vitro by binding nutrient zinc. Furthermore, the data establish that the zinc-binding activity of the S100A12 protein represses the activity of the cag T4SS, as evidenced by the gastric cell "hummingbird" phenotype, interleukin 8 (IL-8) secretion, and CagA translocation assays. In addition, high-resolution field emission gun scanning electron microscopy (FEG-SEM) was used to demonstrate that S100A12 represses biogenesis of the cag T4SS. Together with our previous work, these data reveal that multiple S100 proteins can repress the elaboration of an oncogenic bacterial surface organelle.

Cationic antimicrobial peptides as potential new therapeutic agents in neonates and children: a review

PURPOSE OF REVIEW

Antimicrobial resistance towards conventional antibiotics is a serious problem for modern medicine and for our society. Multidrug-resistant bacteria are very difficult to treat and treatment options have begun to run out. Here, we summarize the newest studies of drug development using cationic antimicrobial peptides as lead molecules for novel antimicrobial drugs.

RECENT FINDINGS

A new development is the use of antimicrobial peptides not only as direct antimicrobial lead structures but also using their ability to influence the immune system. Such approaches can be used to develop drugs that influence the immune system in a unique way, supporting specific branches of immune cells in order to clear infection. Applying such an 'immune boost' would also minimize the danger of new resistance emerging in bacteria. In addition, searching for and testing substances that trigger the production of host antimicrobial peptides is still ongoing and opens up a totally new avenue for the use of antimicrobial peptides against infections. Currently, more than 10 clinical trials, phase 2 or 3, using antimicrobial peptides are in progress or have been recently completed.

SUMMARY

Multidrug resistance is an urgent problem for modern medicine and novel antimicrobials are needed. Despite some drawbacks, antimicrobial peptides seem now to appear more numerous in clinical trials, indicating the success in developing peptides into novel therapeutics. This can be critical especially for neonates and children, as treatment options for infections with Gram-negatives in neonatal ICUs are becoming rare.

Elevated gene expression of S100A12 is correlated with the predominant clinical inflammatory factors in patients with bacterial pneumonia

Inflammation is the predominant characteristic of pneumonia. The present study aimed to to identify a faster and more reliable novel inflammatory marker for the diagnosis of pneumonia. The expression of the S100A12 gene was analyzed by reverse transcription quantitative polymerase chain reaction in samples obtained from 46 patients with bacterial pneumonia and other infections, compared with samples from 20 healthy individuals, using the 2‑ΔΔCt method. The expression levels of S100A12 were increased in 12 patients with bacterial pneumonia. Compared with clinical inflammatory data, a positive correlation was observed between the expression of the S100A12 gene and levels of white blood cells, C‑reactive protein (CRP), thrombocytocrit, neutrophils, erythrocyte sedimentation and soterocytes, and an inverse correlation was observed with the width of red blood cell volume distribution and platelet distribution, monocytes and hemoglobin, using Pearson's product‑moment correlation method. The P‑value of CRP and erythrocyte sedimentation were revealed to be statistically significant (P<0.05). A sporadic distribution of S100A12 was observed in a heatmap among the patients with different infections and bacterial pneumonia. Furthermore, the expression of S100A12 occurred in parallel to the number of clumps of inflamed tissue observed in chest computed tomography and X‑ray. The value of gene expression of S100A12 (>1.0) determined using the 2‑ΔΔCt method was associated with more severe respiratory diseases in the patients compromised by bacterial pneumonia, sepsis and pancreatitis. These findings suggested that S100A12 is an effective marker for inflammatory diseases.

Human antimicrobial peptides and proteins

As the key components of innate immunity, human host defense antimicrobial peptides and proteins (AMPs) play a critical role in warding off invading microbial pathogens. In addition, AMPs can possess other biological functions such as apoptosis, wound healing, and immune modulation. This article provides an overview on the identification, activity, 3D structure, and mechanism of action of human AMPs selected from the antimicrobial peptide database. Over 100 such peptides have been identified from a variety of tissues and epithelial surfaces, including skin, eyes, ears, mouths, gut, immune, nervous and urinary systems. These peptides vary from 10 to 150 amino acids with a net charge between -3 and +20 and a hydrophobic content below 60%. The sequence diversity enables human AMPs to adopt various 3D structures and to attack pathogens by different mechanisms. While α-defensin HD-6 can self-assemble on the bacterial surface into nanonets to entangle bacteria, both HNP-1 and β-defensin hBD-3 are able to block cell wall biosynthesis by binding to lipid II. Lysozyme is well-characterized to cleave bacterial cell wall polysaccharides but can also kill bacteria by a non-catalytic mechanism. The two hydrophobic domains in the long amphipathic α-helix of human cathelicidin LL-37 lays the basis for binding and disrupting the curved anionic bacterial membrane surfaces by forming pores or via the carpet model. Furthermore, dermcidin may serve as ion channel by forming a long helix-bundle structure. In addition, the C-type lectin RegIIIα can initially recognize bacterial peptidoglycans followed by pore formation in the membrane. Finally, histatin 5 and GAPDH(2-32) can enter microbial cells to exert their effects. It appears that granulysin enters cells and kills intracellular pathogens with the aid of pore-forming perforin. This arsenal of human defense proteins not only keeps us healthy but also inspires the development of a new generation of personalized medicine to combat drug-resistant superbugs, fungi, viruses, parasites, or cancer. Alternatively, multiple factors (e.g., albumin, arginine, butyrate, calcium, cyclic AMP, isoleucine, short-chain fatty acids, UV B light, vitamin D, and zinc) are able to induce the expression of antimicrobial peptides, opening new avenues to the development of anti-infectious drugs.

S100A12 and soluble receptor for advanced glycation end products levels during human severe sepsis

S100A12 is highly expressed, and serum levels correlate with individual disease activity in patients with inflammatory diseases. We here sought to determine the extent of S100A12 release and its soluble high-affinity receptor for advanced glycation end products (sRAGE) in patients with severe sepsis stratified to the three most common infectious sources (lungs, abdomen, and urinary tract) and to determine S100A12 and sRAGE concentrations at the site of infection during peritonitis. Two patient populations were studied: (a) 51 patients with sepsis due to (i) peritonitis (n = 12), (ii) pneumonia (n = 29), or (iii) urinary tract infection (n = 10); and (b) 17 patients with peritonitis. In addition, eight healthy humans were studied after intravenous injection of lipopolysaccharide (4 ng/kg). Compared with healthy volunteers, patients with severe sepsis displayed increased circulating S100A12 concentrations at day 0 (591.2 ± 101.0 vs. 106.2 ± 15.6 ng/mL [control subjects], P < 0.0001) and at day 3 (637.2 ± 111.2 vs. 106.2 ± 15.6 ng/mL [control subjects], P < 0.0001). All three severe sepsis subgroups had elevated serum S100A12 concentrations at both time points (sepsis due to [i] peritonitis [393.5 ± 89.9 at day 0 and 337.9 ± 97.2 at day 3 vs. 106.2 ± 15.6 ng/mL, control subjects, P < 0.005 and P < 0.05, respectively]; [ii] pneumonia [716.9 ± 167.0 at day 0 and 787.5 ± 164.7 at day 3 vs. 106.2 ± 15.6 ng/mL, control subjects, both P < 0.0001]; and [iii] urinary tract infection [464.2 ± 115.6 at day 0 and 545.6 ± 254.9 at day 3 vs. 106.2 ± 15.6 ng/mL, control subjects, P < 0.0001 and P < 0.05, respectively]). Remarkably, patients with sepsis due to pneumonia had the highest S100A12 levels (716.9 ± 167.0 and 787.5 ± 164.7 ng/mL at days 0 and 3, respectively). S100A12 levels were not correlated to either Acute Physiology and Chronic Health Evaluation II scores (r = -0.185, P = 0.19) or Sepsis-Related Organ Failure Assessment scores (r = -0.194, P = 0.17). Intravenous lipopolysaccharide injection in healthy humans elevated systemic S100A12 levels (peak levels at 3 h of 59.6 ± 22.0 vs. 12.4 ± 3.6 ng/mL; t = 0 h, P < 0.005). In contrast to S100A12, sRAGE concentrations did not change during severe sepsis or human endotoxemia. During peritonitis, S100A12 concentrations in abdominal fluid (12945.8 ± 4142.1 ng/mL) were more than 100-fold higher than in concurrently obtained plasma (121.2 ± 80.4 ng/mL, P < 0.0005), whereas sRAGE levels in abdominal fluid (148.8 ± 36.0 pg/mL) were lower than those in plasma (648.7 ± 145.6 pg/mL, P < 0.005) and did not increase. In conclusion, in severe sepsis, S100A12 is released systemically irrespective of the primary source of infection. During abdominal sepsis, S100A12 release likely predominantly occurs at the site of infection. Concentrations of its high-affinity sRAGE do not change during infection or human endotoxemia.

Transition metal ions at the crossroads of mucosal immunity and microbial pathogenesis

Transition metal ions are essential micronutrients for all living organisms. In mammals, these ions are often protein-bound and sequestered within cells, limiting their availability to microbes. Moreover, in response to infection, mammalian hosts further reduce the availability of metal nutrients by activating epithelial cells and recruiting neutrophils, both of which release metal-binding proteins with antimicrobial function. Microorganisms, in turn, have evolved sophisticated systems to overcome these limitations and acquire the metal ions essential for their growth. Here we review some of the mechanisms employed by the host and by pathogenic microorganisms to compete for transition metal ions, with a discussion of how evading “nutritional immunity” benefits pathogens. Furthermore, we provide new insights on the mechanisms of host-microbe competition for metal ions in the mucosa, particularly in the inflamed gut.

Functions of S100 proteins

The S100 protein family consists of 24 members functionally distributed into three main subgroups: those that only exert intracellular regulatory effects, those with intracellular and extracellular functions and those which mainly exert extracellular regulatory effects. S100 proteins are only expressed in vertebrates and show cell-specific expression patterns. In some instances, a particular S100 protein can be induced in pathological circumstances in a cell type that does not express it in normal physiological conditions. Within cells, S100 proteins are involved in aspects of regulation of proliferation, differentiation, apoptosis, Ca2+ homeostasis, energy metabolism, inflammation and migration/invasion through interactions with a variety of target proteins including enzymes, cytoskeletal subunits, receptors, transcription factors and nucleic acids. Some S100 proteins are secreted or released and regulate cell functions in an autocrine and paracrine manner via activation of surface receptors (e.g. the receptor for advanced glycation end-products and toll-like receptor 4), G-protein-coupled receptors, scavenger receptors, or heparan sulfate proteoglycans and N-glycans. Extracellular S100A4 and S100B also interact with epidermal growth factor and basic fibroblast growth factor, respectively, thereby enhancing the activity of the corresponding receptors. Thus, extracellular S100 proteins exert regulatory activities on monocytes/macrophages/microglia, neutrophils, lymphocytes, mast cells, articular chondrocytes, endothelial and vascular smooth muscle cells, neurons, astrocytes, Schwann cells, epithelial cells, myoblasts and cardiomyocytes, thereby participating in innate and adaptive immune responses, cell migration and chemotaxis, tissue development and repair, and leukocyte and tumor cell invasion.

Association of high levels of α-defensins and S100A proteins with Candida mannan detection in bronchoalveolar lavage fluid of preterm neonates

BACKGROUND

Candida mannan (Mn) detection in bronchoalveolar lavage fluid (BALF) was shown to be useful for earlier identification and preemptive therapy targeting in preterm infants at high risk of invasive Candida infection. We investigated whether early detection of Candida Mn in BALF is associated with the presence of some neutrophilic products, as markers of prenatal infection/inflammation.

METHODS

BALF specimens were collected during the first 48 h of life from mechanically ventilated preterm newborns. Samples were analyzed by high-performance liquid chromatography-electrospray ionization-mass spectrometry. The relative amounts of α-defensins 1-4 and S100A proteins were measured by extracted ion current peak area. Absolute and differential white cell counts in BALF were obtained. Mn antigen concentrations were determined by the Platelia Candida antigen kit.

RESULTS

Twenty-five studied neonates were divided into two groups: Mn-positive group and Mn-negative group. Levels of α-defensins 1-4 and S100A12 were significantly higher in the Mn-positive group than in the Mn-negative group. Moreover, positive significant correlations between the absolute number of neutrophils and the levels of α-defensins 1-4 and S100A8 were observed.

CONCLUSION

The detection of Mn antigen in BALF of preterm infants is consistent with evidence of an innate immune response in their lungs as demonstrated by higher levels of α-defensins and S100A proteins.

Innate immune activation in neonatal tracheal aspirates suggests endotoxin-driven inflammation

BACKGROUND

Tracheal aspirates (TAs) from critically ill neonates accumulate bacterial endotoxin and demonstrate mobilization of endotoxin-binding proteins, but the potential bioactivity of endotoxin in TAs is unknown. We characterized innate immune activation in TAs of mechanically ventilated neonates.

METHODS

Innate immune activation in TAs of mechanically ventilated neonates was characterized using a targeted 84-gene quantitative real-time (qRT) PCR array. Protein expression of cytokines was confirmed by multiplex assay. Expression and localization of the endotoxin-inducible antimicrobial protein Calgranulin C (S100A12) was assessed by flow cytometry. Endotoxin levels were measured in TA supernatants using the Limulus amoebocyte lysate assay.

RESULTS

Analyses by qRT-PCR demonstrated expression of pattern recognition receptors, Toll-like receptor-nuclear factor κB and inflammasome pathways, cytokines/chemokines and their receptors, and anti-infective proteins in TA cells. Endotoxin positivity increased with postnatal age. As compared with endotoxin-negative TAs, endotoxin-positive TAs demonstrated significantly greater tumor necrosis factor (TNF), interleukin (IL)-6, IL-10, and serpin peptidase inhibitor, clade E, member 1 (SERPINE1) mRNA, and IL-10, TNF, and IL-1β protein. Expression of S100A12 protein was localized to TA neutrophils.

CONCLUSION

Correlation of endotoxin with TA inflammatory responses suggests endotoxin bioactivity and the possibility that endotoxin antagonists could mitigate pulmonary inflammation and its sequelae in this vulnerable population.

Exoproteome of Staphylococcus aureus reveals putative determinants of nasal carriage

Due to the increasing prevalence of nosocomial and community-acquired antibiotic resistant Staphylococcus aureus (SA), understanding the determinants of SA nasal carriage has become a major imperative. Previous research has revealed many host and bacterial factors that contribute to SA nasal carriage. To assess bacterial factors that facilitate nasal carriage, we compared the exoproteome of a nasal carrier strain of SA to a genetically similar noncarrier strain. Additionally, the carrier strain biofilm exoproteome was also compared against its planktonic counterpart. Using high throughput proteomics, it was observed that the carrier strain of SA secretes a greater number of proteins that may promote successful colonization of the human nose, including cell attachment and immunoevasive proteins, than the noncarrier strain. Similarly, SA carrier strain biofilm exoproteome contains a greater number of immunoevasive proteins than its planktonic counterpart. Analysis of the most abundant immunoevasive proteins revealed that Staphylococcal protein A was present at significantly higher levels in carrier than in noncarrier strains of SA, suggesting an association with nasal carriage. While further analyses of specific differences between carrier and noncarrier strains of SA are required, many of the differentially expressed proteins identified can be considered to be putative determinants of nasal carriage.

Inflammation-associated S100 proteins: new mechanisms that regulate function

This review focuses on new aspects of extracellular roles of the calgranulins. S100A8, S100A9 and S100A12 are constitutively expressed in neutrophils and induced in several cell types. The S100A8 and S100A9 genes are regulated by pro- and anti-inflammatory mediators and their functions may depend on cell type, mediators within a particular inflammatory milieu, receptors involved in their recognition and their post-translational modification. The S100A8 gene induction in macrophages is dependent on IL-10 and potentiated by immunosuppressive agents. S100A8 and S100A9 are oxidized by peroxide, hypochlorite and nitric oxide (NO). HOCl generates intra-chain sulfinamide bonds; stronger oxidation promotes cross-linked forms that are seen in human atheroma. S100A8 is >200-fold more sensitive to oxidative cross-linking than low-density lipoprotein and may reduce oxidative damage. S100A8 and S100A9 can be S-nitrosylated. S100A8-SNO suppresses mast cell activation and inflammation in the microcirculation and may act as an NO transporter to regulate vessel tone in inflammatory lesions. S100A12 activates mast cells and is a monocyte and mast cell chemoattractant; a G-protein-coupled mechanism may be involved. Structure-function studies are discussed in relation to conservation and divergence of functions in S100A8. S100A12 induces cytokines in mast cells, but not monocytes/macrophages. It forms complexes with Zn(2+) and, by chelating Zn(2+), S100A12 significantly inhibits MMPs. Zn(2+) in S100A12 complexes co-localize with MMP-9 in foam cells in atheroma. In summary, S100A12 has pro-inflammatory properties that are likely to be stable in an oxidative environment, because it lacks Cys and Met residues. Conversely, S100A8 and S100A9 oxidation and S-nitrosylation may have important protective mechanisms in inflammation.

ANTI-INFECTIVE PROTECTIVE PROPERTIES OF S100 CALGRANULINS

The calgranulins are a subgroup of proteins in the S100 family (calgranulin A, S100A8; calgranulin B, S100A9 and calgranulin C, S100A12) that provide protective anti-infective and anti-inflammatory functions for the mammalian host. In this review, we discuss the structure-function relationships whereby S100A8 and S100A9, and for comparison, S100A12, provide intra- and extracellular protection during the complex interplay between infection and inflammation and how the calgranulins are regulated to optimally protect the host. Ideally located to support epithelial barrier function, calprotectin, a complex of S100A8/S100A9, is expressed in squamous mucosal keratinocytes and innate immune cells present at mucosal surfaces. The calgranulins are also abundantly produced in neutrophils and monocytes, whereas expression is induced in epidermal keratinocytes, gastrointestinal epithelial cells and fibroblasts during inflammation. The calgranulins show species-specific expression and function. For example, S100A8 is chemotactic in rodents but not in humans. In humans, S100A12 appears to serve as a functional chemotactic homolog to murine S100A8. Transition metal-binding and oxidation sites within calgranulins are able to create structural changes that may orchestrate new protective functions or binding targets. The calgranulins thus appear to adopt a variety of roles to protect the host. In addition to serving as a leukocyte chemoattractant, protective functions include oxidant scavenging, antimicrobial activity, and chemokine-like activities. Each function may reflect the concentration of the calgranulin, post-transcriptional modifications, oligomeric forms, and the proximal intracellular or extracellular environments. Calprotectin and the calgranulins are remarkable as multifunctional proteins dedicated to protecting the intra- and extracellular environments during infection and inflammation.

The cationic peptide magainin II is antimicrobial for Burkholderia cepacia-complex strains

This study was undertaken to determine the antibacterial activity of eight cationic antimicrobial peptides towards strains of genomovars I-V of the Burkholderia cepacia complex (Bcc) in time-kill assays. All but one of the peptides failed to show activity against the panel of test strains. The exception was magainin II, a 23 aa peptide isolated from the epidermis of the African clawed frog, Xenopus laevis, which exhibited significant bactericidal activity for Bcc genomovars most frequently associated with lung infection of patients with cystic fibrosis. In vitro studies indicated that magainin II protected a human bronchial epithelial cell line (BEAS-2B) from killing by Bcc and suggest that this peptide may have therapeutic potential against these organisms.

Subversion of interleukin-1-mediated host defence by a nasal carrier strain of Staphylococcus aureus

Staphylococcus aureus, a major source of nosocomial and community-acquired infections, has a nasal carriage rate exceeding 25% in the human population. To elucidate host-pathogen interactions pertaining to nasal carriage, we examined the role of interleukin-1 (IL-1) in the colonization of human nasal epithelial cells (NEC) by a nasal carrier strain and a non-carrier strain of S. aureus. Using an organotypic model of the nasal epithelium, we observed that inoculation with a non-carrier strain of S. aureus induced production of IL-1 from NEC, but the expression of this cytokine was significantly reduced when NEC were inoculated with a carrier strain. Moreover, both IL-1alpha and IL-1beta significantly decreased the growth of the nasal carrier strain of S. aureus (P < 0.001, n = 17 to n = 25); however the growth of the non-carrier strain was unaffected. Interestingly, it was found that several nasal carrier strains of S. aureus form quorum-dependent biofilms, which can be partially inhibited when preincubated with IL-1alpha. Taken together these data suggest that, although nasal carrier strains of S. aureus are sensitive to IL-1, they display a significant colonization advantage by both preventing the host from expressing IL-1 and elaborating a protective biofilm.

Human antimicrobial proteins effectors of innate immunity

We live in a world populated by an enormous number of micro-organisms. This necessitates the existence of highly effective mechanisms to control microbial growth. Through many research efforts, a chemical defense system based on the production of antimicrobial proteins (AMPs) has been identified. AMPs are endogenous, small proteins exhibiting antimicrobial activity against a wide variety of micro-organisms. The wide distribution of these molecules in the plant and animal kingdom reflects their biological significance. Various human AMPs show a potent effect on pathogenic micro-organisms including antibiotic-resistant bacteria. Thus, there is great interest in understanding the role of AMPs within innate immunity and evaluating their use and/or specific induction to fend off infections. In this review, we provide an overview of the characteristics of human AMPs and discuss examples where AMPs may be involved in the pathogenesis of infectious and inflammatory diseases.

Identification of immune genes and proteins involved in the response of bovine mammary tissue to Staphylococcus aureus infection

BACKGROUND

Mastitis in dairy cattle results from infection of mammary tissue by a range of micro-organisms but principally coliform bacteria and Gram positive bacteria such as Staphylococcus aureus. The former species are often acquired by environmental contamination while S. aureus is particularly problematic due to its resistance to antibiotic treatments and ability to reside within mammary tissue in a chronic, subclinical state. The transcriptional responses within bovine mammary epithelial tissue subjected to intramammary challenge with S. aureus are poorly characterised, particularly at the earliest stages of infection. Moreover, the effect of infection on the presence of bioactive innate immune proteins in milk is also unclear. The nature of these responses may determine the susceptibility of the tissue and its ability to resolve the infection.

RESULTS

Transcriptional profiling was employed to measure changes in gene expression occurring in bovine mammary tissues sampled from three dairy cows after brief and graded intramammary challenges with S. aureus. These limited challenges had no significant effect on the expression pattern of the gene encoding beta-casein but caused coordinated up-regulation of a number of cytokines and chemokines involved in pro-inflammatory responses. In addition, the enhanced expression of two genes, S100 calcium-binding protein A12 (S100A12) and Pentraxin-3 (PTX3) corresponded with significantly increased levels of their proteins in milk from infected udders. Both genes were shown to be expressed by mammary epithelial cells grown in culture after stimulation with lipopolysaccharide. There was also a strong correlation between somatic cell count, a widely used measure of mastitis, and the level of S100A12 in milk from a herd of dairy cows. Recombinant S100A12 inhibited growth of Escherichia coli in vitro and recombinant PTX3 bound to E. coli as well as C1q, a subunit of the first component of the complement cascade.

CONCLUSION

The transcriptional responses in infected bovine mammary tissue, even at low doses of bacteria and short periods of infection, probably reflect the combined contributions of gene expression changes resulting from the activation of mammary epithelial cells and infiltrating immune cells. The secretion of a number of proinflammatory cytokines and chemokines from mammary epithelial cells stimulated by the bacteria serves to trigger the recruitment and activation of neutrophils in mammary tissue. The presence of S100A12 and PTX3 in milk from infected udder quarters may increase the anti-bacterial properties of milk thereby helping to resolve the mammary tissue infection as well as potentially contributing to the maturation of the newborn calf epithelium and establishment of the newborn gut microbial population.

Psoriasin (S100A7) is a principal antimicrobial peptide of the human tongue

The human tongue is particularly resistant to bacterial infections although the mouth is continuously exposed to a complex and abundant ensemble of microbes, such as the common intestinal bacterium Escherichia coli. We show that lingual epithelia produce and release, as a primary E. coli-killing compound, the S100 protein psoriasin. No significant reduction in psoriasin release could be achieved through repeated rinsing of the epithelial surface of the tongue. Psoriasin is produced in the upper layers of the lingual epithelia but is lacking in the most superficial and basal cells. It displays a gradient pattern of expression with decreasing expression from the anterior one-third to the posterior portion of the tongue. Thus, psoriasin may be the key to the resistance of the human tongue toward E. coli.

Flagellin is the principal inducer of the antimicrobial peptide S100A7c (psoriasin) in human epidermal keratinocytes exposed to Escherichia coli

Epidermal keratinocytes (KCs) express antimicrobial peptides as a part of the innate immune response. It has recently been shown that the culture supernatant of Escherichia coli induces the expression of S100A7c (psoriasin) in KCs and that S100A7c efficiently kills E. coli. Here we have investigated which of the microbial components triggers the up-regulation of S100A7c expression. Exposure of human primary KCs to ligands of the human Toll-like receptors (TLRs) revealed that only the TLR5 ligand flagellin strongly induced the expression of S100A7c mRNA and protein, whereas all other TLR ligands had no significant effect. In contrast to the supernatant from flagellated wild-type (WT) E. coli, the supernatant of a flagellin-deficient E. coli strain (DeltaFliC) did not induce S100A7c expression. Small interfering RNA-mediated knockdown of TLR5 expression suppressed the ability of KCs to up-regulate S100A7c expression in response to both flagellin and WT E. coli supernatant. Taken together, our data demonstrate that bacterial flagellin is essential and sufficient for the induction of S100A7c expression in KCs by E. coli.