Mast cells: multitalented facilitators of protection against bacterial pathogens

Bioinformatics-led discovery of ferroptosis-associated diagnostic biomarkers and molecule subtypes for tuberculosis patients

BACKGROUND

Ferroptosis is closely associated with the pathophysiological processes of many diseases, such as infection, and is characterized by the accumulation of excess lipid peroxides on the cell membranes. However, studies on the ferroptosis-related diagnostic markers in tuberculosis (TB) is still lacking. Our study aimed to explore the role of ferroptosis-related biomarkers and molecular subtypes in TB.

METHODS

GSE83456 dataset was applied to identify ferroptosis-related genes (FRGs) associated with TB, and GSE42826, GSE28623, and GSE34608 datasets for external validation of core biomarkers. Core FRGs were identified using weighted gene co-expression network analysis (WGCNA). Subsequently, two ferroptosis-related subtypes were constructed based on ferroptosis score, and differently expressed analysis, GSEA, GSEA, immune cell infiltration analysis between the two subtypes were performed.Affiliations: Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary.correctly RESULTS: A total of 22 FRGs were identified, of which three genes (CHMP5, SAT1, ZFP36) were identified as diagnostic biomarkers that were enriched in pathways related to immune-inflammatory response. In addition, TB patients were divided into high- and low-ferroptosis subtypes (HF and LF) based on ferroptosis score. HF patients had activated immune- and inflammation-related pathways and higher immune cell infiltration levels than LF patients.

CONCLUSION

Three potential diagnostic biomarkers and two ferroptosis-related subtypes were identified in TB patients, which would help to understand the pathogenesis of TB.Author names: Kindly check and confirm the process of the author names [2,4]correctly.

Uncovering the Mast Cell Response to Mycobacterium tuberculosis

The immunologic mechanisms that contribute to the response to Mycobacterium tuberculosis infection still represent a challenge in the clinical management and scientific understanding of tuberculosis disease. In this scenario, the role of the different cells involved in the host response, either in terms of innate or adaptive immunity, remains key for defeating this disease. Among this coordinated cell response, mast cells remain key for defeating tuberculosis infection and disease. Together with its effector’s molecules, membrane receptors as well as its anatomical locations, mast cells play a crucial role in the establishment and perpetuation of the inflammatory response that leads to the generation of the granuloma during tuberculosis. This review highlights the current evidences that support the notion of mast cells as key link to reinforce the advancements in tuberculosis diagnosis, disease progression, and novel therapeutic strategies. Special focus on mast cells capacity for the modulation of the inflammatory response among patients suffering multidrug resistant tuberculosis or in co-infections such as current COVID-19 pandemic.

Mannan activates tissue native and IgE-sensitized mast cells to proinflammatory response and chemotaxis in TLR4-dependent manner

Mast cells take part in host defense against microorganisms as they are numerous at the portal of infection, exert several essential mechanisms of pathogen destruction, and they express pattern recognition receptors. Accumulating evidence indicates that these cells are involved in the control and clearance of bacterial, viral, or parasitic infections, but much less is known about their contribution in defense against fungi. The study was aimed to establish whether mannan, which comprises an outermost layer and major structural constituent of the fungal cell wall, may directly stimulate tissue mast cells to the antifungal response. Our findings indicate that mannan activates mast cells isolated from the rat peritoneal cavity to initiate the proinflammatory response. We found that mannan stimulates mast cells to release histamine and to generate cysteinyl leukotrienes, cytokines (IFN-γ, GM-CSF, TNF), and chemokines (CCL2, CCL3). It also increased the mRNA expression of various cytokines/chemokines. We also documented that mannan strongly activates mast cells to generate reactive oxygen species and serves as a potent chemoattractant for these cells. Furthermore, we established that mannan-induced activity of mast cells is mediated via TLR4 with the involvement of the spleen tyrosine kinase molecule. Taking together, our results clearly support the idea that mast cells act as sentinel cells and crucially determine the course of the immune response during fungal infection. Additionally, presented data on IgE-coated mast cells suggest that exposure to fungal mannan could influence the severity of IgE-dependent diseases, including allergic ones.

Native and IgE-primed rat peritoneal mast cells exert pro-inflammatory activity and migrate in response to yeast zymosan upon Dectin-1 engagement

Mast cells (MCs) play an essential role in host defense, primarily because of their location, their ability to pathogen destruction via several mechanisms, and the pattern recognition receptors they express. Even though most data is available regarding MC activation by various bacteria- or virus-derived molecules, those cells' activity in response to constituents associated with fungi is not recognized enough. Our research aimed to address whether Saccharomyces cerevisiae-derived zymosan, i.e., β-(1,3)-glucan containing mannan particles, impacts MC activity aspects. Overall, the obtained results indicate that zymosan has the potential to elicit a pro-inflammatory response of rat peritoneal MCs. For the first time ever, we provided evidence that zymosan induces fully mature MC migration, even in the absence of extracellular matrix (ECM) proteins. Moreover, the zymosan-induced migratory response of MCs is almost entirely a result of directional migration, i.e., chemotaxis. We found that zymosan stimulates MCs to degranulate and generate lipid mediators (cysLTs), cytokines (IFN-α, IFN-β, IFN-γ, GM-CSF, TNF), and chemokine (CCL2). Zymosan also upregulated mRNA transcripts for several cytokines/chemokines with pro-inflammatory/immunoregulatory activity. Moreover, we documented that zymosan activates MCs to produce reactive oxygen species (ROS). Lastly, we established that the zymosan-induced MC response is mediated through activation of the Dectin-1 receptor. In general, our results strongly support the notion that MCs contribute to innate antifungal immunity and bring us closer to elucidate their role in host-pathogenic fungi interactions. Besides, provided findings on IgE-sensitized MCs appear to indicate that exposure to fungal zymosan could affect the severity of IgE-dependent disorders, including allergic ones.

Harnessing the Power of Mast Cells in unconventional Immunotherapy Strategies and Vaccine Adjuvants

Mast cells are long-lived, granular, myeloid-derived leukocytes that have significant protective and repair functions in tissues. Mast cells sense disruptions in the local microenvironment and are first responders to physical, chemical and biological insults. When activated, mast cells release growth factors, proteases, chemotactic proteins and cytokines thereby mobilizing and amplifying the reactions of the innate and adaptive immune system. Mast cells are therefore significant regulators of homeostatic functions and may be essential in microenvironmental changes during pathogen invasion and disease. During infection by helminths, bacteria and viruses, mast cells release antimicrobial factors to facilitate pathogen expulsion and eradication. Mast cell-derived proteases and growth factors protect tissues from insect/snake bites and exposure to ultraviolet radiation. Finally, mast cells release mediators that promote wound healing in the inflammatory, proliferative and remodelling stages. Since mast cells have such a powerful repertoire of functions, targeting mast cells may be an effective new strategy for immunotherapy of disease and design of novel vaccine adjuvants. In this review, we will examine how certain strategies that specifically target and activate mast cells can be used to treat and resolve infections, augment vaccines and heal wounds. Although these strategies may be protective in certain circumstances, mast cells activation may be deleterious if not carefully controlled and any therapeutic strategy using mast cell activators must be carefully explored.

Dermal Extracellular Matrix-Derived Hydrogels as an In Vitro Substrate to Study Mast Cell Maturation

Mast cells (MCs) are pro-inflammatory tissue-resident immune cells that play a key role in inflammation. MCs circulate in peripheral blood as progenitors and undergo terminal differentiation in the tissue microenvironment where they can remain for many years. This in situ maturation results in tissue- and species-specific MC phenotypes, culminating in significant variability in response to environmental stimuli. There are many challenges associated with studying mature tissue-derived MCs, particularly in humans. In cases where cultured MCs are able to differentiate in two-dimensional in vitro cultures, there remains an inability for full maturation. Extracellular matrix (ECM) scaffolds provide for a more physiologically relevant environment for cells in vitro and have been shown to modulate the response of other immune cells such as T cells, monocytes, and macrophages. To improve current in vitro testing platforms of MCs and to assess future use of ECM scaffolds for MC regulation, we studied the in vitro response of human MCs cultured on decellularized porcine dermis hydrogels (dermis extracellular matrix hydrogel [dECM-H]). This study investigated the effect of dECM-H on cellular metabolic activity, cell viability, and receptor expression compared to collagen type I hydrogel (Collagen-H). Human MCs showed different metabolic activity when cultured in the dECM-H and also upregulated immunoglobulin E (IgE) receptors associated with MC maturation/activation compared to collagen type I. These results suggest an overall benefit in the long-term culture of human MCs in the dECM-H compared to Collagen-H providing important steps toward a model that is more representative of in vivo conditions. Graphical abstract [Formula: see text] Impact statement Mast cells (MCs) are difficult to culture in vitro as current culture conditions and substrates fail to promote similar phenotypic features observed in vivo. Extracellular matrix (ECM)-based biomaterials offer three-dimensional, tissue-specific environments that more closely resemble in vivo conditions. Our study explores the use of dermal ECM hydrogels for MC culture and shows significant upregulation of metabolic activity, cell viability, and gene expression of markers associated with MC maturation or activation compared to collagen type I-hydrogel and tissue culture plastic controls at 7 days. These results are among the first to describe MC behavior in response to ECM hydrogels.

An implanted device enables in vivo monitoring of extracellular vesicle-mediated spread of pro-inflammatory mast cell response in mice

Mast cells have been shown to release extracellular vesicles (EVs) in vitro. However, EV-mediated mast cell communication in vivo remains unexplored. Primary mast cells from GFP-transgenic and wild type mice, were grown in the presence or absence of lipopolysaccharide (LPS), and the secreted EVs were separated from the conditioned media. Mast cell-derived EVs were next cultured with LPS-naïve mast cells, and the induction of TNF-α expression was monitored. In addition, primary mast cells were seeded in diffusion chambers that were implanted into the peritoneal cavities of mice. Diffusion chambers enabled the release of GFP+ mast cell-derived EVs in vivo into the peritoneal cavity. Peritoneal lavage cells were assessed for the uptake of GFP+ EVs and for TNF-α production. In vitro, LPS-stimulated mast cell-derived EVs were efficiently taken up by non-stimulated mast cells, and induced TNF-α expression in a TLR4, JNK and P38 MAPK dependent manner. In vivo, using implanted diffusion chambers, we confirmed the release and transmission of mast cell-derived EVs to other mast cells with subsequent induction of TNF-α expression. These data show an EV-mediated spreading of pro-inflammatory response between mast cells, and provide the first in vivo evidence for the biological role of mast cell-derived EVs.

Roles of a Mast Cell-Specific Receptor MRGPRX2 in Host Defense and Inflammation

Mast cells are multifunctional immune cells that are found most abundantly at host-environment interfaces, such as the skin, respiratory tract, and oral/gastrointestinal mucosa. Not surprisingly, mast cells act as sentinel cells that sense microbial attacks and initiate a protective immune response and promote healing. Although mast cells share many features with other innate immune effector cells, such as neutrophils and macrophages, they uniquely interact closely with blood vessels and release an extensive set of mediators for the recruitment of innate and adaptive immune cells. A novel human G protein-coupled receptor (GPCR), known as Mas-related GPCR-X2 (MRGPRX2, mouse ortholog, MrgprB2), has recently been identified, which is expressed on mast cells but not neutrophils and macrophages. Interestingly, activation of MrgprB2 by bacteria-derived quorum-sensing peptides inhibits bacterial growth, prevents biofilm formation, and leads to the recruitment of neutrophils to effectively clear bacteria. Furthermore, host defense antimicrobial peptides and small-molecule peptide mimetics also activate mast cells via MRGPRX2/B2. MrgprB2-mediated activation of local mast cells also clears cutaneous bacterial infection, promotes healing, and protects against reinfection. In addition to their role in host defense, mast cells contribute to a number of chronic inflammatory diseases such as periodontitis, neurogenic inflammation, and inflammatory pain likely via the activation of MRGPRX2. In this review, we discuss the roles of MRGPRX2/B2 in the clearance of bacterial infection, wound healing, periodontal disease, neurogenic inflammation, and inflammatory pain. We propose that harnessing mast cells' host defense and immunomodulatory properties via the activation of MRGPRX2 may lead to novel approaches for the treatment of drug-resistant bacterial infections. On the other hand, increased MRGPRX2 expression on mast cells and their inappropriate activation may contribute to periodontitis, neurogenic inflammation, and inflammatory pain. Thus, targeting MRGPRX2 could provide novel approaches to modulate these conditions.

Mast cells are critical for controlling the bacterial burden and the healing of infected wounds

Skin wound infections are a significant health problem, and antibiotic resistance is on the rise. Mast cells (MCs) have been shown to contribute to host-defense responses in certain bacterial infections, but their role in skin wound superinfection is unknown. We subjected 2 MC-deficient mouse strains to Pseudomonas aeruginosa skin wound infection and found significantly delayed wound closure in infected skin wounds. This delay was associated with impaired bacterial clearance in the absence of MCs. Engraftment of MCs restored both bacterial clearance and wound closure. Bacterial killing was dependent on IL-6 released from MCs, and engraftment with IL-6-deficient MCs failed to control wound infection. Treatment with recombinant IL-6 enhanced bacterial killing and resulted in the control of wound infection and normal wound healing in vivo. Taken together, our results demonstrate a defense mechanism for boosting host innate immune responses, namely effects of MC-derived IL-6 on antimicrobial functions of keratinocytes.

Mast cell activators as novel immune regulators

Mast cells are an important cell type of the innate immune system that when activated, play a crucial role in generating protective innate host responses after bacterial and viral infection. Additionally, activated mast cells influence lymph node composition to regulate the induction of adaptive immune responses. The recognition that mast cells play a beneficial role in host responses to microbial infection and induction of adaptive immunity has provided the rationale to evaluate mast cell activators for use as antimicrobials or vaccine adjuvants. This review summarizes the role of mast cell activators in antimicrobial responses while also discussing the use of different classes of mast cell activators as potent vaccine adjuvants that enhance the induction of protective immune responses.

Mast Cells Are Activated by Streptococcus pneumoniae In Vitro but Dispensable for the Host Defense Against Pneumococcal Central Nervous System Infection In Vivo

Mast cells reside on and near the cerebral vasculature, the predominant site of pneumococcal entry into the central nervous system (CNS). Although mast cells have been reported to be crucial in protecting from systemic bacterial infections, their role in bacterial infections of the CNS remained elusive. Here, we assessed the role of mast cells in pneumococcal infection in vitro and in vivo. In introductory experiments using mouse bone marrow-derived mast cells (BMMC), we found that (i) BMMC degranulate and release selected cytokines upon exposure to Streptococcus pneumoniae, (ii) the response of BMMC varies between different pneumococcal serotypes and (iii) is dependent on pneumolysin. Intriguingly though, apart from a slight enhancement of cerebrospinal fluid (CSF) pleocytosis, neither two different mast cell-deficient Kit mutant mouse strains (WBB6F1-Kit^W/Wv and C57BL/6 Kit^W-sh/W-sh mice) nor pharmacologic mast cell stabilization with cromoglycate had any significant impact on the disease phenotype of experimental pneumococcal meningitis. The incomplete reversal of the enhanced CSF pleocytosis by local mast cell engraftment suggests that this phenomenon is caused by other c-Kit mutation-related mechanisms than mast cell deficiency. In conclusion, our study suggests that mast cells can be activated by S. pneumoniae in vitro. However, mast cells do not play a significant role as sentinels of pneumococcal CSF invasion and initiators of innate immunity in vivo.

The Role of Mast Cells in Tuberculosis: Orchestrating Innate Immune Crosstalk?

Tuberculosis causes more annual deaths globally than any other infectious disease. However, progress in developing novel vaccines, diagnostics, and therapies has been hampered by an incomplete understanding of the immune response to Mycobacterium tuberculosis (Mtb). While the role of many immune cells has been extensively explored, mast cells (MCs) have been relatively ignored. MCs are tissue resident cells involved in defense against bacterial infections playing an important role mediating immune cell crosstalk. This review discusses specific interactions between MCs and Mtb, their contribution to both immunity and disease pathogenesis, and explores their role in orchestrating other immune cells against infections.

Stimulation of nAchRα7 Receptor Inhibits TNF Synthesis and Secretion in Response to LPS Treatment of Mast Cells by Targeting ERK1/2 and TACE Activation

The cholinergic anti-inflammatory pathway is recognized as one of the main mechanisms of neuromodulation of the immune system. Activation of the α7 nicotinic acetylcholine receptor (nAchRα7) suppresses cytokine synthesis in distinct immune cells but the molecular mechanisms behind this effect remain to be fully described. Mast cells (MCs) are essential players of allergic reactions and innate immunity responses related to chronic inflammation. Activation of TLR4 receptor in MCs leads to the rapid secretion of pre-synthesized TNF from intracellular pools and to the activation of NFκB, necessary for de novo synthesis of TNF and other cytokines. Here we report that the nAchRα7 receptor specific agonist GTS-21 inhibits TLR4-induced secretion of preformed TNF from MCs in vivo and in vitro. Utilizing bone marrow-derived mast cells (BMMCs) it was found that GTS-21 also diminished secretion of de novo synthesized TNF, TNF mRNA accumulation and IKK-dependent p65-NFκB phosphorylation in response to LPS. nAchRα7 triggering prevented TLR4-induced ERK1/2 phosphorylation, which resulted an essential step for TNF secretion due to the phosphorylation of the metallopeptidase responsible for TNF maturation (TACE). Main inhibitory actions of GTS-21 were prevented by AG490, an inhibitor of JAK-2 kinase. Our results show for the first time, that besides the prevention of NFκB-dependent transcription, inhibitory actions of nAchRα7 triggering include the blockade of pathways leading to exocytosis of granule-stored cytokines in MCs.

Leukotriene receptor expression in mast cells is affected by their agonists

The effects of LTs are mediated by GPCRs: cysLTs interact with CYSLTR1, CYSLTR2, or GPR17, and LTB₄ acts via BLT1R or BLT2R. Data relating to the presence of these receptors in mature tissue mast cells are not entirely known. By confocal microscopy with image analyses and flow cytometry, we established that native rat mast cells isolated from peritoneal cavity constitutively express all studied receptors. Moreover, we clearly documented that LTs by themselves can influence their own receptor expression. Low concentrations of LTs induce translocation of LT receptors from cell interior to plasma membrane, which can lead to increased mast cell responsiveness to LT stimulation. High concentrations of LTs cause internalization and, in consequence, reduction in the number of receptors on the cell surface, and it may result in desensitization of mast cells to subsequent LT stimulation. These observations may imply a physiological feedback mechanism regulating mast cell sensitivity to LT activation within tissues.

Expression of surface and intracellular Toll-like receptors by mature mast cells

Nowadays, more and more data indicate that mast cells play an important role in host defense against pathogens. That is why it is essential to understand the expression of Toll-like receptors (TLRs) by mast cells, because these molecules play particularly significant role in initiation host defense against microorganisms as they recognize both wide range of microbial pathogen-associated molecular patterns (PAMPs) and various endogenous damage-associated molecular patterns (DAMPs) released in response to infection. Therefore, we examined the constitutive expression of both surface and endosomal TLRs in rat native fully mature tissue mast cells. By the use of qRT-PCR we found that these cells express mRNAs for TLR2, TLR3, TLR4, TLR5, TLR7, and TLR9. The expression of TLR3, TLR4, TLR5, TLR7, and TLR9 transcripts were low and comparable and only the expression of TLR2 transcript was significant. By the use of flow cytometry technique, we clearly documented that mast cells express TLR2, TLR4, and TLR5 on cell surface, while TLR3, TLR7, and TLR9 proteins are located both on the cell membrane and intracellularly. The highest expression was observed for TLR5 and the lowest for surface TLR7. These observations undoubtedly indicate that mature tissue mast cells have a broad set of TLR molecules, thus can recognize and bind bacterial, viral, and fungal PAMPs as well as various endogenous molecules generated in response to infection.

IL-37 a New IL-1 Family Member Emerges as a Key Suppressor of Asthma Mediated by Mast Cells

In 1986, we reported a multiple biological effect of IL-1 including immunological, inflammatory, and tumor killing activity. Since then other IL-1 family cytokines have been discovered, some with inflammatory and other with anti-inflammatory activity. In this review article, we speculate on the possible inhibitory effect of IL-37 in the light of new findings. IL-37, formerly termed IL-1 family member 7 (IL-1F7), binding IL-18 receptor α chain, acts as a cytokine with intracellular as well as extracellular functionality and as a natural inhibitor of immune responses and inflammation. IL-37 inhibits many pro-inflammatory cytokine and increases anti-inflammatory cytokines such as IL-10. Asthma pathogenesis involves multiple cell types including mast cells, which are important cellular constituents of the human innate and adaptive immunity. IL-37 has an impact on inflammatory cytokines generated by mast cells and is beneficial for and protective in asthma. However, the precise mechanism(s), safety, and tolerability of IL-37 are unclear and still remain a mystery.

ABBREVIATIONS

GBP (Guanylate Binding Proteins); HMGB1 (High Mobility Group Box protein 1); NLRP (Nucleotide-like Receptor Pyrin domain 1); ASC (Apoptosis-associated Speck-like protein containing CARD, Caspase Recruitment Domain); FGF2 (Fibroblast Growth Factor 2).

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Contribution of FcɛRI-associated vesicles to mast cell-macrophage communication following Francisella tularensis infection

Understanding innate immune intercellular communication following microbial infection remains a key biological issue. Using live cell imaging, we demonstrate that mast cells actively extend cellular projections to sample the macrophage periphery during Francisella tularensis LVS infection. Mast cell MHCII(hi) expression was elevated from less than 1% to 13% during LVS infection. Direct contact during co-culture with macrophages further increased mast cell MHCII(hi) expression to approximately 87%. Confocal analyses of the cellular perimeter revealed mast cell caspase-1 was localized in close proximity with FcɛRI in uninfected mast cells, and repositioned to clustered regions upon LVS infection. Importantly, mast cell FcɛRI-encompassed vesicles are transferred to macrophages by trogocytosis, and macrophage caspase-1 expression is further up-regulated upon direct contact with mast cells. Our study reveals direct cellular interactions between innate cells that may impact the function of caspase-1, a known sensor of microbial danger and requirement for innate defense against many pathogenic microbes including F. tularensis.

α-Hemolysin enhances Staphylococcus aureus internalization and survival within mast cells by modulating the expression of β1 integrin

Mast cells (MCs) are important sentinels of the host defence against invading pathogens. We previously reported that Staphylococcus aureus evaded the extracellular antimicrobial activities of MCs by promoting its internalization within these cells via β1 integrins. Here, we investigated the molecular mechanisms governing this process. We found that S. aureus responded to the antimicrobial mediators released by MCs by up-regulating the expression of α-hemolysin (Hla), fibronectin-binding protein A and several regulatory systems. We also found that S. aureus induced the up-regulation of β1 integrin expression on MCs and that this effect was mediated by Hla-ADAM10 (a disintegrin and metalloproteinase 10) interaction. Thus, deletion of Hla or inhibition of Hla-ADAM10 interaction significantly impaired S. aureus internalization within MCs. Furthermore, purified Hla but not the inactive HlaH35L induced up-regulation of β1 integrin expression in MCs in a dose-dependent manner. Our data support a model in which S. aureus counter-reacts the extracellular microbicidal mechanisms of MCs by increasing expression of fibronectin-binding proteins and by inducing Hla-ADAM10-mediated up-regulation of β1 integrin in MCs. The up-regulation of bacterial fibronectin-binding proteins, concomitantly with the increased expression of its receptor β1 integrin on the MCs, resulted in enhanced S. aureus internalization through the binding of fibronectin-binding proteins to integrin β1 via fibronectin.

Cathelicidin impact on inflammatory cells

Cathelicidins, like other antimicrobial peptides, exhibit direct antimicrobial activities against a broad spectrum of microbes, including both Gram-positive and Gram-negative bacteria, enveloped viruses, and fungi. These host-derived peptides kill the invaded pathogens by perturbing their cell membranes and can neutralize biological activities of endotoxin. Nowadays, more and more data indicate that these peptides, in addition to their antimicrobial properties, possess various immunomodulatory activities. Cathelicidins have the potential to influence and modulate, both directly and indirectly, the activity of various cell populations involved in inflammatory processes and in host defense against invading pathogens. They induce migration of neutrophils, monocytes/macrophages, eosinophils, and mast cells and prolong the lifespan of neutrophils. These peptides directly activate inflammatory cells to production and release of different pro-inflammatory and immunoregulatory mediators, cytokines, and chemokines, however cathelicidins might mediate the generation of anti-inflammatory cytokines as well. Cathelicidins also modulate epithelial cell/keratinocyte responses to infecting pathogens. What is more, they affect activity of monocytes, dendritic cells, keratinocytes, or epithelial cells acting in synergy with cytokines or β-defensins. In addition, these peptides indirectly balance TLR-mediated responses of monocytes, macrophages, dendritic cells, epithelial cells, and keratinocytes. This review discusses the role and significance of cathelicidins in inflammation and innate immunity against pathogens.

Human-derived cathelicidin LL-37 directly activates mast cells to proinflammatory mediator synthesis and migratory response

Cathelicidins, a family of antimicrobial peptides, are well known for their role in host defense, particularly against bacteria. Apart from direct killing of microbes through the membrane disruption, cathelicidins can also exert immunomodulatory effects on cells involved in inflammatory processes. Considering the important role of mast cells in inflammation, the aim of this study was to determine whether LL-37, human-derived cathelicidin, can induce mast cell activation. We have observed that LL-37 directly stimulates mast cell to degranulation and production of some proinflammatory cytokines, but fails to induce cysteinyl leukotriene generation and release. We have also documented that LL-37 acts as a strong mast cell chemoattractant. In intracellular signaling in mast cells activated by LL-37 participates PLC/A2 and, in part, MAPKs, and PI3K. In conclusion, our results indicate that cathelicidins may enhance antibacterial inflammatory response via attracting mast cell to pathogen entry site and via induction of mast cell-derived mediator release.

Clinical view on the importance of dendritic cells in asthma

Allergic asthma is characterized by airway hyperresponsiveness and inflammation and may lead to airway remodeling in uncontrolled cases. Genetic predisposition to an atopic phenotype plays a major component in the pathophysiology of asthma. However, with tremendous role of epigenetic factors and environmental stimuli in precipitating an immune response, the underlying pathophysiological mechanisms are complicated. Dendritic cells are principal antigen-presenting cells and initiators of the immune response in allergic asthma. Their phenotype, guided by multiple factors may dictate the immune reaction to an allergic or tolerogenic response. Involvement of the local cytokine milieu, microbiome and interplay between immune cells add dimension to the fate of immune response. In addition to allergen exposure, these factors modulate DC phenotype and function. In this article, integration of many factors and pathways associated with the recruitment and activation of DCs in the pathophysiology of allergic asthma is presented in a clinical and translational manner.

Epistemology of the origin of cancer: a new paradigm

Background

Carcinogenesis is widely thought to originate from somatic mutations and an inhibition of growth suppressors, followed by cell proliferation, tissue invasion, and risk of metastasis. Fewer than 10% of all cancers are hereditary; the ratio in gastric (1%), colorectal (3-5%) and breast (8%) cancers is even less. Cancers caused by infection are thought to constitute some 15% of the non-hereditary cancers. Those remaining, 70 to 80%, are called “sporadic,” because they are essentially of unknown etiology. We propose a new paradigm for the origin of the majority of cancers.

Presentation of hypothesis

Our paradigm postulates that cancer originates following a sequence of events that include (1) a pathogenic stimulus (biological or chemical) followed by (2) chronic inflammation, from which develops (3) fibrosis with associated changes in the cellular microenvironment. From these changes a (4) pre-cancerous niche develops, which triggers the deployment of (5) a chronic stress escape strategy, and when this fails to resolve, (6) a transition of a normal cell to a cancer cell occurs. If we are correct, this paradigm would suggest that the majority of the findings in cancer genetics so far reported are either late events or are epiphenomena that occur after the appearance of the pre-cancerous niche.

Testing the hypothesis

If, based on experimental and clinical findings presented here, this hypothesis is plausible, then the majority of findings in the genetics of cancer so far reported in the literature are late events or epiphenomena that could have occurred after the development of a PCN. Our model would make clear the need to establish preventive measures long before a cancer becomes clinically apparent. Future research should focus on the intermediate steps of our proposed sequence of events, which will enhance our understanding of the nature of carcinogenesis. Findings on inflammation and fibrosis would be given their warranted importance, with research in anticancer therapies focusing on suppressing the PCN state with very early intervention to detect and quantify any subclinical inflammatory change and to treat all levels of chronic inflammation and prevent fibrotic changes, and so avoid the transition from a normal cell to a cancer cell.

Implication of the hypothesis

The paradigm proposed here, if proven, spells out a sequence of steps, one or more of which could be interdicted or modulated early in carcinogenesis to prevent or, at a minimum, slow down the progression of many cancers.