Role of reactive oxygen species (ROS) in Mycobacterium bovis bacillus Calmette Guérin-mediated up-regulation of the human cathelicidin LL-37 in A549 cells

Bacillus Calmette-Guérin (BCG)-Induced Protection in Brain Disorders

The Bacille Calmette-Guerin (BCG) vaccine is one of the most widely used vaccines in the world for the prevention of tuberculosis. Its immunological capacity also includes epigenetic reprogramming, activation of T cells and inflammatory responses. Although the main usage of the vaccine is the prevention of tuberculosis, different works have shown that the effect of BCG can go beyond the peripheral immune response and be linked to the central nervous system by modulating the immune system at the level of the brain. This review therefore aims to describe the BCG vaccine, its origin, its relationship with the immune system, and its involvement at the brain level.

Estradiol inhibits autophagy of Mycobacterium tuberculosis‑infected 16HBE cells and controls the proliferation of intracellular Mycobacterium tuberculosis

Tracheobronchial tuberculosis (TBTB) is most common in young, middle-aged females. Despite adequate anti-tuberculosis therapy, >90% of patients develop tracheobronchial stenosis, which has a high rate of resulting in disability. The present study aimed to explore the effect of estradiol on the development of TBTB. Estrogen receptor (ER) expression in granulomatous tissue was assessed via immunofluorescence. In order to determine whether estrogen affected the proliferation of intracellular Mycobacterium tuberculosis (Mtb), 16HBE cells were infected with Mtb in vitro, followed by estradiol treatment. Intracellular Mtb was quantified via colony counting. The effect of estradiol on autophagy of infected 16HBE cells was determined via western blotting and transmission electron microscopy. Necrosis assays of infected 16HBE cells were analyzed using propidium iodide staining and assessing lactate dehydrogenase (LDH) release. To determine how estradiol affects autophagy, infected 16HBE cells were treated with ER-specific and non-specific modulators. Reactive oxygen species (ROS) levels were analyzed via flow cytometry. Additionally, the protein expression levels of autophagy-associated proteins were determined via western blotting. Mtb could enter human lobar bronchial goblet cells and ciliated cells in patients with TBTB. The results also demonstrated that ERα was expressed in granulomatous tissue from patients with TBTB. Administration of 10⁻⁶ M estradiol reduced the number of intracellular Mtb colony-forming units in vitro in the 16HBE human bronchial epithelial cell line at day 3 after infection. Furthermore, cells treated with estradiol and infected with Mtb released less LDH at 72 h and exhibited reduced necrosis levels at 24 h compared with the untreated cells. In addition, autophagy of infected 16HBE cells was inhibited by estradiol. Estradiol and the specific ERα agonist had similar effects on autophagy in infected 16HBE cells. Additionally, treatment with the ERα antagonist abolished the inhibition of autophagy by estradiol in infected 16BHE cells. Compared with the untreated infected 16HBE cells, the ROS levels in the infected 16HBE cells treated with estradiol and the ERα agonist significantly decreased. The levels of phosphorylated (p)-mTOR and p-AKT notably increased in estradiol- and ERα agonist-treated infected 16HBE cells. In summary, estradiol may serve a key role in the development of TBTB through binding to ERα.

Comparative Study of the Susceptibility to Oxidative Stress between Two Types of Mycobacterium bovis BCG Tokyo 172

Genomic analysis revealed that the vaccine seed lot of Mycobacterium bovis bacillus Calmette-Guérin (BCG) Tokyo 172 contains two subclones (types I and II), but their phenotypic differences have not been elucidated. In this study, we compared the susceptibility of bacilli types I and II to oxidative stress in vitro and within host cells. Notably, the subclones displayed similar superoxide dismutase activity; however, foam height in the catalase test and lysate catalase/peroxidase activity were higher for type I bacilli than for type II bacilli. Additionally, type I bacilli were less susceptible to hydrogen peroxide (H₂O₂) than type II bacilli. After exposure to H₂O₂, antioxidative stress response genes katG, ahpC, sodA, and trxA were more strongly induced in type I bacilli than in type II bacilli. Further, we investigated cell survival in macrophages. Fewer type II bacilli were recovered than type I bacilli. However, in the presence of apocynin, a specific inhibitor of NADPH oxidase, type II recovery was greater than that of type I. The production of interleukin 1β (IL-1β), IL-12 p40, and tumor necrosis factor alpha (TNF-α) was higher in type I bacillus-infected macrophages than in type II bacillus-infected macrophages. The proportions of type I and type II bacilli in vaccine lots over 3 years (100 lots) were 97.6% ± 1.5% and 2.4% ± 1.5%, respectively. The study results illustrated that type I bacilli are more resistant to oxidative stress than type II bacilli. Overall, these findings provide important information in terms of the quality control and safety of BCG Tokyo 172 vaccine.

IMPORTANCE This study revealed the difference of in vivo and in vitro antioxidative stress properties of BCG Tokyo 172 types I and II as one of the bacteriological characteristics. In particular, the bacilli exhibited differences in catalase/peroxidase activity, which could explain their different protective effects against infection. The differences correlated with survival in the host cell and the production of proinflammatory cytokines to protect against infection by Mycobacterium tuberculosis. The proportion of bacilli types I and II in all commercial lots of BCG Tokyo 172 over 3 years (100 lots) was constant. The findings also highlighted the importance of analyzing their content for quality control during vaccine production.

Poly-dispersed Acid-Functionalized Single-Walled Carbon Nanotubes (AF-SWCNTs) Are Potent Inhibitor of BCG Induced Inflammatory Response in Macrophages

The present study is focused on the modulation of Mycobacterium bovis BCG-induced inflammatory response by poly-dispersed acid-functionalized single-walled carbon nanotubes (AF-SWCNTs) in macrophages. Flow cytometric and confocal microscopy studies indicated that both BCG and AF-SWCNTs were efficiently internalized by RAW 264.7 and MH-S macrophage cell lines and were essentially localized in the cytoplasmic area. BCG-induced production of reactive oxygen species (ROS) and nitric oxide by the two cell lines was significantly inhibited by AF-SWCNTs. Using RT-PCR technique, a marked decline was observed in the expression of BCG-induced pro-inflammatory genes COX-2, iNOS, TNF-α, IL-6, and IL-1β upon treatment with AF-SWCNTs. Results of gelatin zymography indicated that the AF-SWCNTs treatment also induced a marked decline in BCG-induced release of matrix metalloproteinases MMP-2 and MMP-9 by the two macrophage cell lines. The anti-inflammatory effect of AF-SWCNTs in downregulating BCG-induced inflammatory response was further validated in murine peritoneal macrophages. Treatment with AF-SWCNTs led to a steep decline in BCG-induced NO production in murine peritoneal macrophages in vitro as well as in vivo. Peritoneal macrophages isolated from mice treated with BCG and AF-SWCNTs had a significantly lower intracellular expression of COX-2 as compared to the peritoneal macrophages derived from mice treated with BCG alone. Taken together, our results demonstrate a potent anti-inflammatory effect of AF-SWCNTs in alleviating BCG-induced inflammatory responses in macrophages in vitro and in vivo.

Newborn BCG vaccination complemented by boosting correlates better with reduced juvenile diabetes in females, than vaccination alone

Type 1 diabetes (T1D), like other autoimmune diseases, is on the rise since the second half of the 20th century. Hypothetically this has been ascribed to restricted exposure to microbial diversity due to advanced hygienic practices accompanying modernization, and increasing prosperity in urban versus rural habitats. The autoimmune animal model of T1D, inhibited by Bacillus Calmette Guerine (BCG), motivated testing the impact of BCG on T1D incidence in humans. Several epidemiological analyses, short of one, failed to demonstrate a protective effect of BCG against T1D. The present retrospective analysis of two data sets reevaluates the hypothetic inhibitory effect of BCG on human T1D. Reassessment of data from a Swedish study reveals that a single BCG vaccination provided a small but significant protection against T1D. A second data set of T1D prevalence/1000 Israeli military conscripts, from a doctoral thesis presenting 17 birth cohorts at age 17 is evaluated against the national schedule of vaccination related to years of birth. To correct for the annual increasing T1D trend the mean urbanization (census) rate was set as an annual moving average and factored into the prevalence (T1D/1000) of respective birth cohorts. Three groups of cohorts corresponding to BCG vaccination are presently identified; Group A corresponds to the years in which newborns were vaccinated and boosted if necessary, at age 12. Group B corresponds to the period when boosting was discontinued. Group C corresponds to years when newborn BCG vaccination was discontinued. T1D (only in females) was slightly but significantly lower in group B (n = 5 cohorts) versus C (n = 8 cohorts, p = 0.0475, by Mann Whitney U test). T1D in group A (n = 4 cohorts) was lower than in group B (p = 0.02). This analysis supports the hypothesis that in human females postnatal BCG vaccination, reinforced by boosting, has a protective impact on T1D being superior to omitted boosting, which in its turn is still better than stopping vaccination altogether. This analysis further suggests that upon advanced modernization the BCG vaccine compensates for reduced exposure to microbial diversity early in life.

Characterization of a fungal competition factor: Production of a conidial cell-wall associated antifungal peptide

Competition is one of the fundamental driving forces of natural selection. Beauveria bassiana is a soil and plant phylloplane/root fungus capable of parasitizing insect hosts. Soil and plant environments are often enriched with other fungi against which B. bassiana competes for survival. Here, we report an antifungal peptide (BbAFP1), specifically expressed and localized to the conidial cell wall and is released into the surrounding microenvironment inhibiting growth of competing fungi. B. bassiana strains expressing BbAFP1, including overexpression strains, inhibited growth of Alternaria brassicae in co-cultured experiments, whereas targeted gene deletion of BbAFP1 significantly decreased (25%) this inhibitory effect. Recombinant BbAFP1 showed chitin and glucan binding abilities, and growth inhibition of a wide range of phytopathogenic fungi by disrupting membrane integrity and eliciting reactive oxygen species (ROS) production. A phenylalanine residue (F⁵⁰) contributes to chitin binding and antifungal activity, but was not required for the latter. Expression of BbAFP1 in tomato resulted in transgenic plants with enhanced resistance to plant fungal pathogens. These results highlight the importance of fungal competition in shaping primitive competition strategies, with antimicrobial compounds that can be embedded in the spore cell wall to be released into the environment during the critical initial phases of germination for successful growth in its environmental niche. Furthermore, these peptides can be exploited to increase plant resistance to fungal pathogens.

Microbial competition exerts powerful selective pressures for the development of defensive and offensive methods of suppressing potential competitors. One of the most vulnerable stages for any fungi is the initial germination of resting spores in potentially hostile environments. Currently, we know little about how fungi defend other microbial competitors during the beginning stage of conidial germination. Here, we report on an antifungal peptide from B. bassiana (BbAFP1) that is specifically expressed in mature aerial conidia, with the protein localized exclusively to the conidial cell wall. The “pre-loaded” BbAFP1 is released into the surrounding microenvironment where it can act to inhibit the growth of competing fungi during the initial stages of fungal germination, i.e. largely before actual germ tubes are apparent, thus conferring an advantage to B. bassiana in out-competing susceptible competitors in the microenvironment surrounding the spore. The effects of BbAFP1 on membrane integrity were characterized and a key amino acid (F⁵⁰) was shown to function in chitin binding and antifungal activity. Transgenic tomato overexpressing BbAFP1 were shown to exhibit enhanced resistance to plant fungal pathogens. Our study provides new insights into the microbial competition and genes involved in this process that can be exploited to increase plant disease resistance.

Bacillus Calmette-Guérin induces rapid gene expression changes in human bladder cancer cell lines that may modulate its survival

Bacillus Calmette-Guérin (BCG) immunotherapy is the standard therapy for non-muscle invasive bladder cancer. The aim of the present study was to identify genes that are induced in response to BCG immunotherapy, as these may be potential biomarkers for the response to clinical therapy. To model clinical therapy, human bladder cancer cell lines were incubated with BCG (live or lyophilized BCG Connaught) for 2 h. RNA was extracted and evaluated by Representational Differential Analysis (RDA) and oligo arrays. Gene expression was confirmed by reverse transcription polymerase chain reaction on fresh cell lines with differential abilities to internalize BCG. The effect of 2 major BCG soluble proteins, antigen 85B (Ag85B) and Mycobacterium protein tyrosine phosphatase A (MptpA) and BCG Tice^® on gene expression was also determined. GAPDH and β-actin, which are normally used as control genes, were upregulated by BCG. Therefore, the ribosomal RNA gene ribosomal protein S27a was used to normalize gene expression. The genes likely to be induced by BCG internalization and soluble factors were: GSTT2, MGST2, CCL20, TNFα, CCNE1 and IL10RB. Those induced by BCG membrane interactions and/or soluble factors were: MGST1, CXCL6, IL12A, CSF2, IL1β and TOLLIP. MptpA decreased GSTT2 expression, and Ag85B increased TNFα expression. The two BCG strains significantly increased GSTT2, TNFα and TOLLIP levels in MGH cells. However, in J82 cells there was a BCG strain-dependent difference in TNFα expression. An important outcome of the present study was the determination that neither GAPDH nor β-actin were suitable control genes for the analysis of BCG-induced gene expression. BCG Connaught and Tice^® induced similar expression levels of genes in bladder cancer cell lines. BCG soluble proteins modulated gene expression and therefore may affect therapeutic outcomes. The genes identified may be novel biomarkers of the response to BCG therapy.

New Players in Immunity to Tuberculosis: The Host Microbiome, Lung Epithelium, and Innate Immune Cells

Tuberculosis (TB) is a highly contagious infection and devastating chronic disease, causing 10.4 million new infections and 1.8 million deaths every year globally. Efforts to control and eradicate TB are hampered by the rapid emergence of drug resistance and limited efficacy of the only available vaccine, BCG. Immunological events in the airways and lungs are of major importance in determining whether exposure to Mycobacterium tuberculosis (Mtb) results in successful infection or protective immunity. Several studies have demonstrated that the host microbiota is in constant contact with the immune system, and thus continually directs the nature of immune responses occurring during new infections. However, little is known about its role in the eventual outcome of the mycobacterial infection. In this review, we highlight the changes in microbial composition in the respiratory tract and gut that have been linked to the alteration of immune responses, and to the risk, prevention, and treatment of TB. In addition, we summarize our current understanding of alveolar epithelial cells and the innate immune system, and their interaction with Mtb during early infection. Extensive studies are warranted to fully understand the all-inclusive role of the lung microbiota, its interaction with epithelium and innate immune responses and resulting adaptive immune responses, and in the pathogenesis and/or protection from Mtb infection. Novel interventions aimed at influencing the microbiota, the alveolar immune system and innate immunity will shape future strategies of prevention and treatment for TB.

Antioxidant Defenses of Francisella tularensis Modulate Macrophage Function and Production of Proinflammatory Cytokines

Francisella tularensis, the causative agent of a fatal human disease known as tularemia, has been used in the bioweapon programs of several countries in the past, and now it is considered a potential bioterror agent. Extreme infectivity and virulence of F. tularensis is due to its ability to evade immune detection and to suppress the host's innate immune responses. However, Francisella-encoded factors and mechanisms responsible for causing immune suppression are not completely understood. Macrophages and neutrophils generate reactive oxygen species (ROS)/reactive nitrogen species as a defense mechanism for the clearance of phagocytosed microorganisms. ROS serve a dual role; at high concentrations they act as microbicidal effector molecules that destroy intracellular pathogens, and at low concentrations they serve as secondary signaling messengers that regulate the expression of various inflammatory mediators. We hypothesized that the antioxidant defenses of F. tularensis maintain redox homeostasis in infected macrophages to prevent activation of redox-sensitive signaling components that ultimately result in suppression of pro-inflammatory cytokine production and macrophage microbicidal activity. We demonstrate that antioxidant enzymes of F. tularensis prevent the activation of redox-sensitive MAPK signaling components, NF-κB signaling, and the production of pro-inflammatory cytokines by inhibiting the accumulation of ROS in infected macrophages. We also report that F. tularensis inhibits ROS-dependent autophagy to promote its intramacrophage survival. Collectively, this study reveals novel pathogenic mechanisms adopted by F. tularensis to modulate macrophage innate immune functions to create an environment permissive for its intracellular survival and growth.

Wnt/β-catenin signaling reduces Bacillus Calmette-Guerin-induced macrophage necrosis through a ROS -mediated PARP/AIF-dependent pathway

Background

Necrosis of alveolar macrophages following Mycobacterium tuberculosis infection has been demonstrated to play a vital role in the pathogenesis of tuberculosis. Our previous study demonstrated that Wnt/β-catenin signaling was able to promote mycobacteria-infected cell apoptosis by a caspase-dependent pathway. However, the functionality of this signaling in the necrosis of macrophage following mycobacterial infection remains largely unknown.

Methods

Murine macrophage RAW264.7 cells were infected with Bacillus Calmette-Guerin (BCG) in the presence of Wnt/β-catenin signaling. The necrotic cell death was determined by cytometric assay and electronic microscopy; the productions of reactive oxygen species (ROS) and reduced glutathione (GSH) were measured by a cytometric analysis and an enzyme-linked immunosorbent assay, respectively; and the activity of poly (ADP-ribose) polymerase 1 (PARP-1)/apoptosis inhibition factor (AIF) signaling was examined by an immunoblotting assay.

Results

The BCG can induce RAW264.7 macrophage cells necrosis in a dose- and time-dependent manner along with an accumulation of reactive oxygen species (ROS). Intriguingly, an enhancement of Wnt/β-catenin signaling shows an ability to reduce the mycobacteria-induced macrophage necrosis. Mechanistically, the activation of Wnt/β-catenin signaling is capable of inhibiting the necrotic cell death in BCG-infected RAW264.7 cells through a mechanism by which the Wnt signaling scavenges intracellular ROS accumulation and increases cellular GSH concentration. In addition, immunoblotting analysis further reveals that Wnt/β-catenin signaling is capable of inhibiting the ROS-mediated cell necrosis in part through a PARP-1/AIF- dependent pathway.

Conclusions

An activation of Wnt/β-catenin signaling can inhibit BCG-induced macrophage necrosis by increasing the production of GSH and scavenging ROS in part through a mechanism of repression of PARP-1/AIF signaling pathway. This finding may thus provide an insight into the underlying mechanism of alveolar macrophage cell death in response to mycobacterial infection.

H2O2 generation by bacillus Calmette-Guérin induces the cellular oxidative stress response required for bacillus Calmette-Guérin direct effects on urothelial carcinoma biology

PURPOSE

Exposure of urothelial carcinoma cells to bacillus Calmette-Guérin affects cellular redox status and tumor cell biology but the mechanism(s) remain unclear. We examined free radical production by bacillus Calmette-Guérin in tumor cells in response to the bacillus using global profiling of reactive oxygen species/reactive nitrogen species. The relationship between free radical generation and downstream cellular events was evaluated.

MATERIALS AND METHODS

Using fluorescent probes we performed global profiling of reactive oxygen species/reactive nitrogen species in heat killed and viable bacillus Calmette-Guérin, and in the 253J and T24 urothelial carcinoma cell lines after exposure to the bacillus. Inhibition of bacillus Calmette-Guérin internalization and H2O2 pharmacological scavenging were studied for their effect on cellular reactive oxygen species/reactive nitrogen species generation and various physiological end points.

RESULTS

Viable bacillus Calmette-Guérin produced H2O2 and O2(-) but nitric oxide was not generated. Loss of viability decreased H2O2 production by 50% compared to viable bacillus. Bacillus Calmette-Guérin internalization was necessary for the bacillus to induce reactive oxygen species/reactive nitrogen species generation in urothelial carcinoma cells. Pharmacological H2O2 scavenging reversed reactive oxygen species/reactive nitrogen species mediated signaling in urothelial carcinoma cells. Bacillus Calmette-Guérin dependent alterations in tumor biology, including intracellular signaling, gene expression and cytotoxicity, depended on free radical generation.

CONCLUSIONS

This study demonstrates the importance of free radical generation by bacillus Calmette-Guérin and intracellular generation of cellular oxidative stress on the urothelial carcinoma cell response to the bacillus. Manipulating the cellular oxidative stress induced by bacillus Calmette-Guérin represents a potential target to increase the efficacy of the bacillus.

Responses of macrophages against Salmonella infection compared with phagocytosis

To explore the responses of host cell after infection with live Salmonella compared with phagocytosis to dead bacteria, the responses of mouse macrophage after infection with Salmonella enteritidis C50041 and the fixed C50041 (C50041-d) were analyzed. Results indicated that the cytotoxicity induced by C50041 was stronger than C50041-d. Similar changing trends of mitochondrial membrane potential, intracellular concentration of calcium ions, reactive oxygen species and nitric oxide were found between C50041 and C50041-d infection. But the cell responses against C50041 were earlier and stronger than C50041-d. LC3 expression of macrophage induced by C50041 was lower than C50041-d. C50041 significantly inhibited the production of tumor necrosis factor and interleukin (IL)-6. Whereas intracellular caspase-1 activation and IL-1β release induced by C50041 were stronger than C50041-d, caspase-1 activation and IL-1β release are the innate defense responses of macrophage. Therefore, it will be beneficial to explore the use of this pathway in the control of Salmonella infection.

Epithelial G protein-coupled receptor kinases regulate the initial inflammatory response during mycobacterial infection

The interaction between mycobacteria and epithelium is unexplored, but may determine the outcome of the infection. We have analyzed the role of two G protein-coupled receptors, CXCR1 and CXCR2 that are important regulators of many pulmonary diseases. We found that mycobacteria significantly increased the expression of both CXCR1 and CXCR2 on alveolar epithelial cells and both receptors were found to be important for neutrophil diapedesis across primary endothelial cells towards infected mucosa. Mycobacteria, lipoarabinomannan or 19-kDa glycolipoprotein up-regulated the inhibitory G protein-coupled receptor kinase (GRK)2, while GRK3 was less affected. Mycobacteria-induced GRK2 up-regulation decreased chemokine transcription and secretion thereby affecting the neutrophil recruitment to infected mucosa. These events were completely abolished by blocking these receptors prior to infection as the blocking increased epithelial immune responses. We have identified novel interactions occurring in the initial phase of mycobacterial infections by which mycobacterial manipulate epithelial inflammatory responses.

The role of airway epithelial cells in response to mycobacteria infection

Airway epithelial cells (AECs) are part of the frontline defense against infection of pathogens by providing both a physical barrier and immunological function. The role of AECs in the innate and adaptive immune responses, through the production of antimicrobial molecules and proinflammatory factors against a variety of pathogens, has been well established. Tuberculosis (TB), a contagious disease primarily affecting the lungs, is caused by the infection of various strains of mycobacteria. In response to mycobacteria infection, epithelial expression of Toll-like receptors and surfactant proteins plays the most prominent roles in the recognition and binding of the pathogen, as well as the initiation of the immune response. Moreover, the antimicrobial substances, proinflammatory factors secreted by AECs, composed a major part of the innate immune response and mediation of adaptive immunity against the pathogen. Thus, a better understanding of the role and mechanism of AECs in response to mycobacteria will provide insight into the relationship of epithelial cells and lung immunocytes against TB, which may facilitate our understanding of the pathogenesis and immunological mechanism of pulmonary tuberculosis disease.

Bacillus Calmette-Guérin induces cellular reactive oxygen species and lipid peroxidation in cancer cells

OBJECTIVE

To determine whether Bacillus Calmette-Guérin (BCG) and/or BCG-soluble factors could modulate cellular reactive oxygen species (ROS) in human bladder cancer cells and the impact this could have on response to therapy.

METHODS

The expression of α5β1 integrins on human bladder cancer cell lines and their ability to internalize BCG were determined. The effect of live and lyophilized BCG on cellular ROS, lipid peroxidation, and DNA damage was determined using H(2)DCF-DA, TBARS, and comet assays. The cytotoxic effects of live and lyophilized BCG on cancer cells were determined after 24 hours. ROS modulation by Antigen 85B and mycobacterial protein tyrosine phosphatases was monitored.

RESULTS

Live and lyophilized BCG were internalized to a similar extent, but live BCG increased cellular ROS, whereas lyophilized BCG reduced ROS. High ROS levels correlated with increased lipid peroxidation. The cytotoxic effect of BCG was independent of cellular ROS but dependent on internalization. Lyophilized BCG was more cytotoxic to bladder cancer cells than live BCG. BCG soluble factors such as Antigen85B could increase cellular ROS. Internalization of lyophilized BCG abrogated the ROS, and lipid peroxidation increase induced by BCG soluble factors. Both live and lyophilized BCG induced DNA damage but to different extents.

CONCLUSION

The end products of ROS, such as lipid peroxides and superoxide, could induce DNA damage, which could lead to mutations in cancer cells that select for their survival. Reducing BCG instillations may reduce the risk of mutational changes occurring in remnant cancer cells.

Antimicrobial Peptides in Innate Immunity against Mycobacteria

Antimicrobial peptides/proteins are ancient and naturallyoccurring antibiotics in innate immune responses in a variety of organisms. Additionally, these peptides have been recognized as important signaling molecules in regulation of both innate and adaptive immunity. During mycobacterial infection, antimicrobial peptides including cathelicidin, defensin, and hepcidin have antimicrobial activities against mycobacteria, making them promising candidates for future drug development. Additionally, antimicrobial peptides act as immunomodulators in infectious and inflammatory conditions. Multiple crucial functions of cathelicidins in antimycobacterial immune defense have been characterized not only in terms of direct killing of mycobacteria but also as innate immune regulators, i.e., in secretion of cytokines and chemokines, and mediating autophagy activation. Defensin families are also important during mycobacterial infection and contribute to antimycobacterial defense and inhibition of mycobacterial growth both in vitro and in vivo. Hepcidin, although its role in mycobacterial infection has not yet been characterized, exerts antimycobacterial effects in activated macrophages. The present review focuses on recent efforts to elucidate the roles of host defense peptides in innate immunity to mycobacteria.

Potentiation of epithelial innate host responses by intercellular communication

The epithelium efficiently attracts immune cells upon infection despite the low number of pathogenic microbes and moderate levels of secreted chemokines per cell. Here we examined whether horizontal intercellular communication between cells may contribute to a coordinated response of the epithelium. Listeria monocytogenes infection, transfection, and microinjection of individual cells within a polarized intestinal epithelial cell layer were performed and activation was determined at the single cell level by fluorescence microscopy and flow cytometry. Surprisingly, chemokine production after L. monocytogenes infection was primarily observed in non-infected epithelial cells despite invasion-dependent cell activation. Whereas horizontal communication was independent of gap junction formation, cytokine secretion, ion fluxes, or nitric oxide synthesis, NADPH oxidase (Nox) 4-dependent oxygen radical formation was required and sufficient to induce indirect epithelial cell activation. This is the first report to describe epithelial cell-cell communication in response to innate immune activation. Epithelial communication facilitates a coordinated infectious host defence at the very early stage of microbial infection.

All body surfaces are covered by a single layer of epithelial cells. Epithelial cells form a physical barrier to separate the underlying sterile tissue from the environment. In addition, epithelial cells actively sense bacterial and viral infection. The recognition of pathogenic microorganisms results in cell stimulation and the secretion of soluble mediators that attract professional immune cells to the site of infection. This first line host defence works very efficiently despite the often low number of pathogens and the limited amount of mediators secreted per epithelial cell. We therefore investigated whether infection of one individual epithelial cell would result in activation of other, non-infected cells within a confluent epithelial monolayer resulting in a more substantial host response. Indeed, using the model of the gut pathogen Listeria monocytogenes and monitoring infection and epithelial activation at a single cell level, we can clearly show that the epithelial response is mainly mediated by non-infected cells. Also, we identify oxygen radicals as potential mediators to facilitate horizontal epithelial communication upon immune stimulation. Our results thus provide a novel concept of a coordinated epithelial host response upon microbial infection facilitated by horizontal epithelial communication.

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.