Human cathelicidin CAP18/LL-37 changes mast cell function toward innate immunity

Vitamin D Influences the Activity of Mast Cells in Allergic Manifestations and Potentiates Their Effector Functions against Pathogens

Mast cells (MCs) are abundant at sites exposed to the external environment and pathogens. Local activation of these cells, either directly via pathogen recognition or indirectly via interaction with other activated immune cells and results in the release of pre-stored mediators in MC granules. The release of these pre-stored mediators helps to enhance pathogen clearance. While MCs are well known for their protective role against parasites, there is also significant evidence in the literature demonstrating their ability to respond to viral, bacterial, and fungal infections. Vitamin D is a fat-soluble vitamin and hormone that plays a vital role in regulating calcium and phosphorus metabolism to maintain skeletal homeostasis. Emerging evidence suggests that vitamin D also has immunomodulatory properties on both the innate and adaptive immune systems, making it a critical regulator of immune homeostasis. Vitamin D binds to its receptor, called the vitamin D receptor (VDR), which is present in almost all immune system cells. The literature suggests that a vitamin D deficiency can activate MCs, and vitamin D is necessary for MC stabilization. This manuscript explores the potential of vitamin D to regulate MC activity and combat pathogens, with a focus on its ability to fight viruses.

The Contribution of Antimicrobial Peptides to Immune Cell Function: A Review of Recent Advances

The development of novel antimicrobial agents to replace antibiotics has become urgent due to the emergence of multidrug-resistant microorganisms. Antimicrobial peptides (AMPs), widely distributed in all kingdoms of life, present strong antimicrobial activity against a variety of bacteria, fungi, parasites, and viruses. The potential of AMPs as new alternatives to antibiotics has gradually attracted considerable interest. In addition, AMPs exhibit strong anticancer potential as well as anti-inflammatory and immunomodulatory activity. Many studies have provided evidence that AMPs can recruit and activate immune cells, controlling inflammation. This review highlights the scientific literature focusing on evidence for the anti-inflammatory mechanisms of different AMPs in immune cells, including macrophages, monocytes, lymphocytes, mast cells, dendritic cells, neutrophils, and eosinophils. A variety of immunomodulatory characteristics, including the abilities to activate and differentiate immune cells, change the content and expression of inflammatory mediators, and regulate specific cellular functions and inflammation-related signaling pathways, are summarized and discussed in detail. This comprehensive review contributes to a better understanding of the role of AMPs in the regulation of the immune system and provides a reference for the use of AMPs as novel anti-inflammatory drugs for the treatment of various inflammatory diseases.

Antimicrobial peptides´ immune modulation role in intracellular bacterial infection

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

Differential effects of PEGylated Cd-free CuInS2/ZnS quantum dot (QDs) on substance P and LL-37 induced human mast cell activation

CuInS₂/ZnS-PEG quantum dots (QDs) are among the most widely used near infrared non-cadmium QDs and are favored because of their non-cadmium content and strong tissue penetration. However, with their increasing use, there is great concern about whether exposure to QDs is potentially risky to the environment and humans. Furthermore, toxicological data related to CuInS₂/ZnS-PEG QDs are scarce. In the study, we found that CuInS₂/ZnS-PEG QDs (0-100 μg/mL) could internalize into human LAD2 mast cells without affecting their survival rate, nor did it cause degranulation or release of IL-8 and TNF-α. However, CuInS₂/ZnS-PEG QDs significantly inhibited Substance P (SP) and LL-37-induced degranulation and chemotaxis of LAD2 cells by inhibiting calcium mobilization. Lower concentrations of CuInS₂/ZnS-PEG QDs promoted the release of TNF-α and IL-8 stimulated by SP, but higher concentrations of CuInS₂/ZnS-PEG QDs significantly inhibited the release of TNF-α and IL-8. On the other hand, CuInS₂/ZnS-PEG QDs promoted LL-37-mediated TNF-α release from LAD2 cells in a dose-dependent manner from 6.25 to 100 μg/mL, while release of IL-8 triggered by LL-37 was dose-dependently inhibited within a dose concentration of 12.5-100 μg/mL. Collectively, our data demonstrated that CuInS₂/ZnS-PEG QDs differentially mediated human mast cell activation induced by SP and LL-37.

Immunomodulatory and Allergenic Properties of Antimicrobial Peptides

With the growing problem of the emergence of antibiotic-resistant bacteria, the search for alternative ways to combat bacterial infections is extremely urgent. While analyzing the effect of antimicrobial peptides (AMPs) on immunocompetent cells, their effect on all parts of the immune system, and on humoral and cellular immunity, is revealed. AMPs have direct effects on neutrophils, monocytes, dendritic cells, T-lymphocytes, and mast cells, participating in innate immunity. They act on B-lymphocytes indirectly, enhancing the induction of antigen-specific immunity, which ultimately leads to the activation of adaptive immunity. The adjuvant activity of AMPs in relation to bacterial and viral antigens was the reason for their inclusion in vaccines and made it possible to formulate the concept of a “defensin vaccine” as an innovative basis for constructing vaccines. The immunomodulatory function of AMPs involves their influence on cells in the nearest microenvironment, recruitment and activation of other cells, supporting the response to pathogenic microorganisms and completing the inflammatory process, thus exhibiting a systemic effect. For the successful use of AMPs in medical practice, it is necessary to study their immunomodulatory activity in detail, taking into account their pleiotropy. The degree of maturity of the immune system and microenvironment can contribute to the prevention of complications and increase the effectiveness of therapy, since AMPs can suppress inflammation in some circumstances, but aggravate the response and damage of organism in others. It should also be taken into account that the real functions of one or another AMP depend on the types of total regulatory effects on the target cell, and not only on properties of an individual peptide. A wide spectrum of biological activity, including direct effects on pathogens, inactivation of bacterial toxins and influence on immunocompetent cells, has attracted the attention of researchers, however, the cytostatic activity of AMPs against normal cells, as well as their allergenic properties and low stability to host proteases, are serious limitations for the medical use of AMPs. In this connection, the tasks of searching for compounds that selectively affect the target and development of an appropriate method of application become critically important. The scope of this review is to summarize the current concepts and newest advances in research of the immunomodulatory activity of natural and synthetic AMPs, and to examine the prospects and limitations of their medical use.

Antimicrobial peptides and the gut microbiome in inflammatory bowel disease

Antimicrobial peptides (AMP) are highly diverse and dynamic molecules that are expressed by specific intestinal epithelial cells, Paneth cells, as well as immune cells in the gastrointestinal (GI) tract. They play critical roles in maintaining tolerance to gut microbiota and protecting against enteric infections. Given that disruptions in tolerance to commensal microbiota and loss of barrier function play major roles in the pathogenesis of inflammatory bowel disease (IBD) and converge on the function of AMP, the significance of AMP as potential biomarkers and novel therapeutic targets in IBD have been increasingly recognized in recent years. In this frontier article, we discuss the function and mechanisms of AMP in the GI tract, examine the interaction of AMP with the gut microbiome, explore the role of AMP in the pathogenesis of IBD, and review translational applications of AMP in patients with IBD.

Do Mast Cells Contribute to the Antifungal Host Defense?

The fungal kingdom includes a group of microorganisms that are widely distributed in the environment, and therefore the exposure to them is almost constant. Furthermore, fungal components of the microbiome, i.e., mycobiome, could serve as a reservoir of potentially opportunistic pathogens. Despite close encounters with fungi, defense mechanisms that develop during fungal infections remain unexplored. The strategic location of mast cells (MCs) close to the external environment places them among the first cells to encounter pathogens along with the other innate immune cells. MCs are directly involved in the host defense through the ability to destroy pathogens or indirectly by activating other immune cells. Most available data present MCs’ involvement in antibacterial, antiviral, or antiparasitic defense mechanisms. However, less is known about their contribution in defense mechanisms against fungi. MCs may support immune responses to fungi or their specific molecules through initiated degranulation, synthesis and release of cytokines, chemokines, mediators, and generation of reactive oxygen species (ROS), as well as immune cells’ recruitment, phagocytosis, or provision of extracellular DNA traps. This review summarizes current knowledge on host defense mechanisms against fungi and MCs’ involvement in those processes. It also describes the effects of fungi or fungus-derived constituents on MCs’ activity.

Unlocking the Non-IgE-Mediated Pseudo-Allergic Reaction Puzzle with Mas-Related G-Protein Coupled Receptor Member X2 (MRGPRX2)

Mas-related G-protein coupled receptor member X2 (MRGPRX2) is a class A GPCR expressed on mast cells. Mast cells are granulated tissue-resident cells known for host cell response, allergic response, and vascular homeostasis. Immunoglobulin E receptor (FcεRI)-mediated mast cell activation is a well-studied and recognized mechanism of allergy and hypersensitivity reactions. However, non-IgE-mediated mast cell activation is less explored and is not well recognized. After decades of uncertainty, MRGPRX2 was discovered as the receptor responsible for non-IgE-mediated mast cells activation. The puzzle of non-IgE-mediated pseudo-allergic reaction is unlocked by MRGPRX2, evidenced by a plethora of reported endogenous and exogenous MRGPRX2 agonists. MRGPRX2 is exclusively expressed on mast cells and exhibits varying affinity for many molecules such as antimicrobial host defense peptides, neuropeptides, and even US Food and Drug Administration-approved drugs. The discovery of MRGPRX2 has changed our understanding of mast cell biology and filled the missing link of the underlying mechanism of drug-induced MC degranulation and pseudo-allergic reactions. These non-canonical characteristics render MRGPRX2 an intriguing player in allergic diseases. In the present article, we reviewed the emerging role of MRGPRX2 as a non-IgE-mediated mechanism of mast cell activation in pseudo-allergic reactions. We have presented an overview of mast cells, their receptors, structural insight into MRGPRX2, MRGPRX2 agonists and antagonists, the crucial role of MRGPRX2 in pseudo-allergic reactions, current challenges, and the future research direction.

Serum IL-17 levels in patients with rosacea

BACKGROUND

Rosacea is a chronic inflammatory skin disease characterized with increased serum and tissue inflammatory mediators. IL-17 is a well-known inflammatory mediator that plays important roles in pathogenesis of inflammatory skin diseases. Previous studies reported that Th17 pathway is activated in rosacea and IL-17, one of Th17 signature cytokines, is elevated in tissue samples of rosacea patients.

OBJECTIVES

The aim of this study was to investigate serum IL-17 levels in rosacea patients and to study its relationship with disease characteristics.

METHODS

Sixty patients diagnosed with rosacea and 60 healthy controls were included in the study. Serum IL-17 concentrations were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The mean serum IL-17 level was 8.03 pg/mL (SD = 1.47) in rosacea patients and 7.37 pg/mL (Sd = 1.19) in controls. Serum IL-17 levels were significantly higher in rosacea (p = 0.002). Serum IL-17 levels were similar among patients with erythematotelangiectatic (ET) and papulopustular (PP) rosacea (8.02 vs 8.06, p = 0.83). Serum IL-17 levels did not correlate with rosacea severity (p = 0.59, r = 0.07 in ET rosacea; p = 0.88, r = 0.02 in PP rosacea), age of onset (p = 0.58, r = -0.07), and disease duration (p = 0.37, r = -0.11). Primary features and global assessments did not correlate with serum IL-17 levels (all p > 0.05). Among secondary features, edema showed a significant negative correlation with serum IL-17 concentrations (p = 0.037, r = -0.26).

CONCLUSIONS

Our study showed increased serum IL-17 levels in rosacea patients and a significant correlation between IL-17 concentrations and secondary features of the disease suggesting IL-17 may contribute to pathogenesis of rosacea and may be a new target for rosacea treatment.

5-Bromo-3,4-dihydroxybenzaldehyde from Polysiphonia morrowii attenuate IgE/BSA-stimulated mast cell activation and passive cutaneous anaphylaxis in mice

The present study investigates the anti-allergic activity of the marine algal bromophenol, 3-bromo-4,5-dihydroxybenzaldehyde (BDB), isolated from Polysiphonia morrowii Harvey in immunoglobulin (Ig)E/bovine serum albumin (BSA)-stimulated mouse bone marrow-derived cultured mast cells (BMCMCs) and a passive cutaneous anaphylaxis (PCA) mice ear model. BDB effectively inhibited β-hexosaminidase release (IC₅₀ = 80.12 µM), in IgE/BSA-stimulated BMCMCs without a cytotoxic response. Also, BDB down-regulated the expression or secretion of cytokines, interleukin (IL)-1β, IL-4, IL-5, IL-6, IL-10, IL-13, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α and the chemokine (thymus and activation-regulated chemokine (TARC). The above effects could be attributed to the dose-dependent decrease of FcεRI expression on the surface of BMCMCs and its stable IgE binding. Moreover, BDB suppressed the nuclear factor (NF)-κB and spleen tyrosine kinase (SYK)-linker for T-cell activation (LAT)-GRB2 associated binding protein 2 (Gab2) signaling axis activated by IgE/BSA stimulation. Furthermore, oral administration of BDB to IgE-sensitized mice effectively attenuated IgE-triggered PCA reaction. Collectively, the anti-allergic effects of BDB suggest its potential applicability as a candidate for in-depth test trials.

Significance of LL-37 on Immunomodulation and Disease Outcome

LL-37, also called cathelicidin, is an important part of the human immune system, which can resist various pathogens. A plethora of experiments have demonstrated that it has the multifunctional effects of immune regulation, in addition to antimicrobial activity. Recently, there have been increasing interest in its immune function. It was found that LL-37 can have two distinct functions in different tissues and different microenvironments. Thus, it is necessary to investigate LL-37 immune functions from the two sides of the same coin. On the one side, LL-37 promotes inflammation and immune response and exerts its anti-infective and antitumor effects; on the other side, it has the ability to inhibit inflammation and promote carcinogenesis. This review presents a brief summary of its expression, structure, and immunomodulatory effects as well as brief discussions on the role of this small peptide as a key factor in the development and treatment of various inflammation-related diseases and cancers.

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.

β-Defensin Strengthens Antimicrobial Peritoneal Mast Cell Response

Mast cells (MCs) are engaged in the processes of host defense, primarily via the presence of receptors responsible for the detection of pathogen-associated molecular patterns (PAMPs). Since BDs are exclusively host defense molecules, and MCs can elicit the antimicrobial response, this study is aimed at determining whether BDs might be involved in MC pathogen defense. We found that defensin BD-2 significantly augments the mRNA and protein expression of Toll-like receptors (TLRs) and retinoic acid-inducible gene-I-like receptor (RLR) essential for the detection of viral molecules, i.e., TLR3, TLR7, TLR9, and RIG-I in mature tissue rat peritoneal MCs (PMCs). We established that BD-2 might stimulate PMCs to release proinflammatory and immunoregulatory mediators and to induce a migratory response. Presented data on IgE-coated PMC upon BD-2 treatment suggest that in the case of allergies, there is an enhanced MC immune response and cell influx to the site of the ongoing infection. In conclusion, our data highlight that BD-2 might strongly influence MC features and activity, mainly by strengthening their role in the inflammatory mechanisms and controlling the activity of cells participating in antimicrobial processes.

Host Cathelicidin Exacerbates Group B Streptococcus Urinary Tract Infection

Group B Streptococcus (GBS) causes frequent urinary tract infection (UTI) in susceptible populations, including individuals with type 2 diabetes and pregnant women; however, specific host factors responsible for increased GBS susceptibility in these populations are not well characterized. Here, we investigate cathelicidin, a cationic antimicrobial peptide, known to be critical for defense during UTI with uropathogenic Escherichia coli (UPEC). We observed a loss of antimicrobial activity of human and mouse cathelicidins against GBS and UPEC in synthetic urine and no evidence for increased cathelicidin resistance in GBS urinary isolates. Furthermore, we found that GBS degrades cathelicidin in a protease-dependent manner. Surprisingly, in a UTI model, cathelicidin-deficient (Camp-/-) mice showed decreased GBS burdens and mast cell recruitment in the bladder compared to levels in wild-type (WT) mice. Pharmacologic inhibition of mast cells reduced GBS burdens and histamine release in WT but not Camp-/- mice. Streptozotocin-induced diabetic mice had increased bladder cathelicidin production and mast cell recruitment at 24 h postinfection with GBS compared to levels in nondiabetic controls. We propose that cathelicidin is an important immune regulator but ineffective antimicrobial peptide against GBS in urine. Combined, our findings may in part explain the increased frequency of GBS UTI in diabetic and pregnant individuals.IMPORTANCE Certain populations such as diabetic individuals are at increased risk for developing urinary tract infections (UTI), although the underlying reasons for this susceptibility are not fully known. Additionally, diabetics are more likely to become infected with certain types of bacteria, such as group B Streptococcus (GBS). In this study, we find that an antimicrobial peptide called cathelicidin, which is thought to protect the bladder from infection, is ineffective in controlling GBS and alters the type of immune cells that migrate to the bladder during infection. Using a mouse model of diabetes, we observe that diabetic mice are more susceptible to GBS infection even though they also have more infiltrating immune cells and increased production of cathelicidin. Taken together, our findings identify this antimicrobial peptide as a potential contributor to increased susceptibility of diabetic individuals to GBS UTI.

Botulinum toxin blocks mast cells and prevents rosacea like inflammation

BACKGROUND

Rosacea is a chronic inflammatory skin condition whose etiology has been linked to mast cells and the antimicrobial peptide cathelicidin LL-37. Individuals with refractory disease have demonstrated clinical benefit with periodic injections of onabotulinum toxin, but the mechanism of action is unknown.

OBJECTIVES

To investigate the molecular mechanism by which botulinum toxin improves rosacea lesions.

METHODS

Primary human and murine mast cells were pretreated with onabotulinum toxin A or B or control. Mast cell degranulation was evaluated by β-hexosaminidase activity. Expression of botulinum toxin receptor Sv2 was measured by qPCR. The presence of SNAP-25 and VAMP2 was established by immunofluorescence. In vivo rosacea model was established by intradermally injecting LL-37 with or without onabotulinum toxin A pretreatment. Mast cell degranulation was assessed in vivo by histologic counts. Rosacea biomarkers were analyzed by qPCR of mouse skin sections.

RESULTS

Onabotulinum toxin A and B inhibited compound 48/80-induced degranulation of both human and murine mast cells. Expression of Sv2 was established in mouse mast cells. Onabotulinum toxin A and B increased cleaved SNAP-25 and decreased VAMP2 staining in mast cells respectively. In mice, injection of onabotulinum toxin A significantly reduced LL-37-induced skin erythema, mast cell degranulation, and mRNA expression of rosacea biomarkers.

CONCLUSIONS

These findings suggest that onabotulinum toxin reduces rosacea-associated skin inflammation by directly inhibiting mast cell degranulation. Periodic applications of onabotulinum toxin may be an effective therapy for refractory rosacea and deserves further study.

The RLR/NLR expression and pro-inflammatory activity of tissue mast cells are regulated by cathelicidin LL-37 and defensin hBD-2

Considering the significance of mast cells (MCs) in the course of various physiological and pathological processes, and the pivotal role of endogenous molecules, i.e., cathelicidins and defensins as multifunctional modulators, the study examines the constitutive and cathelicidin LL-37/defensin hBD-2-induced expression of certain NLRs and RLRs, i.e., NOD1, NOD2, and RIG-I, in fully-mature tissue MCs, and the impact of LL-37 and hBD-2 on MC pro-inflammatory activity. All experiments were carried out in vitro on freshly-isolated peritoneal (P)MCs. qRT-PCR, western blotting, flow cytometry, and confocal microscopy were used to evaluate both constitutive and LL-37/hBD-2-induced expression of NOD1, NOD2, and RIG-I receptors. ROS was determined using H2DCFDA, and Boyden microchamber assay was used to define the migratory response. Standard techniques assessed histamine, cysLT, and chemokine generation. PMCs express NOD1, NOD2, and RIG-I constitutively. LL-37 and hBD-2 enhance the expression and induce translocation of the studied receptors and directly activate the pro-inflammatory and migratory responses of PMCs. Observations demonstrate that LL-37 and hBD-2 might augment MC capability and sensitivity to NLR and RLR ligands and strengthen the role of MCs in inflammation.

Cathelicidin LL-37 Affects Surface and Intracellular Toll-Like Receptor Expression in Tissue Mast Cells

Undoubtedly, mast cells take part in host defense against microorganisms as they are numerous at the portal of infection, they release many proinflammatory and antimicrobial mediators, and they express pattern recognition receptors, such as TLRs. These receptors play a key role in recognition and binding molecules associated with microorganisms and molecules associated with damage. Cathelicidins exhibit direct antimicrobial activities against a broad spectrum of microbes by perturbing their cell membranes. Accumulating evidence suggests a role for these molecules in supporting cell activation. We examined the impact of human cathelicidin LL-37 on tissue mast cell TLR expression and distribution. Depending on context, we show that LL-37 stimulation resulted in minor to major effects on TLR2, TLR3, TLR4, TLR5, TLR7, and TLR9 expression. Confocal microscopy analysis showed that, upon stimulation, TLRs may translocate from the cell interior to the surface and conversely. FPR2 and EGFR inhibitors reduced the increase in expression of selected receptors. We also established that LL-37 acts as a powerful inducer of CCL3 and ROS generation. These results showed that in response to LL-37, mast cells enhance the capability to detect invading pathogens by modulation of TLR expression in what may be involved FPR2 or EGFR molecules.

Mouse Bone Marrow Sca-1+ CD44+ Mesenchymal Stem Cells Kill Avirulent Mycobacteria but Not Mycobacterium tuberculosis through Modulation of Cathelicidin Expression via the p38 Mitogen-Activated Protein Kinase-Dependent Pathway

Mycobacterium tuberculosis primarily infects lung macrophages. However, a recent study showed that M. tuberculosis also infects and persists in a dormant form inside bone marrow mesenchymal stem cells (BM-MSCs) even after successful antibiotic therapy. However, the mechanism(s) by which M. tuberculosis survives in BM-MSCs is still not known. Like macrophages, BM-MSCs do not contain a well-defined endocytic pathway, which is known to play a central role in the clearance of internalized mycobacteria. Here, we studied the fate of virulent and avirulent mycobacteria in Sca-1⁺ CD44⁺ BM-MSCs. We found that BM-MSCs were able to kill avirulent Mycobacterium smegmatis and Mycobacterium bovis BCG but not the pathogenic species M. tuberculosis Further mechanistic studies revealed that pathogenic M. tuberculosis dampens the antibacterial response of BM-MSCs by downregulating the expression of the cationic antimicrobial peptide cathelicidin. In contrast, avirulent mycobacteria were effectively killed by inducing the Toll-like receptor 2/4 (TLR2/4) pathway-dependent expression of cathelicidin, while small interfering RNA (siRNA)-mediated cathelicidin silencing increased the survival of M. bovis BCG in BM-MSCs. We also showed that M. bovis BCG infection caused increased expression levels of MyD88, phospho-interleukin-1 receptor-associated kinase 4 (pIRAK-4), and the p38 mitogen-activated protein kinase (MAPK) signaling pathway. Further downstream investigations demonstrated that IRAK-4-p38 activation increased the nuclear translocation of NF-κB, which subsequently induced the expression of cathelicidin and the cytokine interleukin-1β (IL-1β), resulting in the decreased survival of M. bovis BCG. On the other hand, inhibition of TLR2/4, pIRAK-4, p38, and NF-κB nuclear translocation decreased cathelicidin and IL-1β expression levels and therefore increased the survival of avirulent mycobacteria. This is the first report that demonstrates that virulent mycobacteria manipulate the TLR2/4-MyD88-IRAK-4-p38-NF-κB-Camp-IL-1β pathway to survive inside bone marrow stem cells.

Preventive effects of the novel antimicrobial peptide Nal-P-113 in a rat Periodontitis model by limiting the growth of Porphyromonas gingivalis and modulating IL-1β and TNF-α production

Background

P-113 (AKRHHGYKRKFH-NH2) is a 12-amino-acid histidine-rich peptide derived from histatin 5 that is highly degradable in high salt concentrations and biological fluids such as serum, plasma and saliva. Nal-P-113, a novel antimicrobial peptide whose histidine residues are replaced by the bulky amino acids β-naphthylalanine, causes the antimicrobial peptide to retain its bactericidal activity even in physiological environments. This study evaluated the effect of the novel antimicrobial peptide Nal-P-113 in a rat periodontitis model and the mechanisms of action of Nal-P-113 for suppressing periodontitis.

Methods

Periodontitis was induced in mandibular first molars in rats receiving a ligature and infected with Porphyromonas gingivalis. Animals were randomly divided into six groups: a, P. gingivalis W83 alone; b, P. gingivalis W83 with 6.25 μg/mL of Nal-P-113; c, P. gingivalis W83 with 25 μg/mL of Nal-P-113; d, P. gingivalis W83 with 100 μg/mL of Nal-P-113; e, P. gingivalis W83 with 400 μg/mL of Nal-P-113; and f, control without P. gingivalis W83 or Nal-P-113. Morphometric analysis was used to evaluate alveolar bone loss. Microbiological assessment of the presence of Porphyromonas gingivalis and total bacteria was performed using absolute quantitative real-time PCR and scanning electron microscopy. Gingival tissue was collected for western blot and immunohistochemical assays of IL-1β and TNF-α levels.

Results

Alveolar bone loss was inhibited by 100 μg/mL or 400 μg/mL of Nal-P-113 compared to the control group (P < 0.05). Lower amounts of P. gingivalis and total bacteria were found in groups d and e compared with group a (P < 0.05). A decrease in the levels of IL-1β and TNF-α was detected in group d and group e compared to the control group (P < 0.05). The amount of P. gingivalis was positively correlated with IL-1β and TNF-α expression in periodontal tissue (P < 0.05).

Conclusions

Nal-P-113 exhibited protective effects on Porphyromonas gingivalis-induced periodontitis in rats by limiting the amount of bacteria and modulating IL-1β and TNF-α production. The use of Nal-P-113 in vivo might serve as a beneficial preventive or therapeutic approach for periodontitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-017-1931-9) contains supplementary material, which is available to authorized users.

Emerging Roles for MAS-Related G Protein-Coupled Receptor-X2 in Host Defense Peptide, Opioid, and Neuropeptide-Mediated Inflammatory Reactions

Mast cells (MCs) are tissue-resident immune cells that contribute to host defense but are best known for their roles in allergic and inflammatory diseases. In humans, MCs are divided into two subtypes based on the protease content of their secretory granules. Thus, human lung MCs contain only tryptase and are known as MC_T, whereas skin MCs contain both tryptase and chymase and are known as MC_TC. Patients with severe asthma display elevated MCs in the lung, which undergo phenotypic change from MC_T to MC_TC. Although the human genome contains four Mas related G protein coupled receptor X (MRGPRX) genes, an important feature of MC_TC is that they selectively express MRGPRX2. It is activated by antimicrobial host defense peptides such as human β-defensins and the cathelicidin LL-37 and likely contributes to host defense. MRGPRX2 is also a receptor for the neuropeptide substance P, major basic protein, eosinophil peroxidase, opioids, and many FDA-approved cationic drugs. Increased expression of MRGPRX2 or enhanced downstream signaling likely contributes to chronic inflammatory diseases such as rosacea, atopic dermatitis, chronic urticaria, and severe asthma. In this chapter, I will discuss the expression profile and function of MRGPRX1-4 and review the emerging roles of MRGPRX2 on host defense, chronic inflammatory diseases, and drug-induced pseudoallergic reactions. I will also examine the novel aspects of MRGPRX2 signaling in MCs as it related to degranulation and review the mechanisms of its regulation.

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.

New topical treatment of vulvodynia based on the pathogenetic role of cross talk between nociceptors, immunocompetent cells, and epithelial cells

Topical treatments of localized neuropathic pain syndromes in general are mostly neglected, mainly due to the fact that most pain physicians expect that a topical formulation needs to result in a transdermal delivery of the active compounds. On the basis of the practical experience, this study brings forth a new, somewhat neglected element of the vulvodynia pathogenesis: the cross talk between the nerve endings of nociceptors, the adjacent immunocompetent cells, and vaginal epithelial cells. Insight into this cross talk during a pathogenic condition supports the treatment of vulvodynia with topical (compounded) creams. Vulvodynia was successfully treated with an analgesic cream consisting of baclofen 5% together with the autacoid palmitoylethanolamide 1%, an endogenous anti-inflammatory compound. In this review, data is presented to substantiate the rationale behind developing and prescribing topical products for localized pain states such as vulvodynia. Most chronic inflammatory disorders are based on a network pathogenesis, and monotherapeutic inroads into the treatment of such disorders are obsolete.

Roles of Mas-related G protein-coupled receptor X2 on mast cell-mediated host defense, pseudoallergic drug reactions, and chronic inflammatory diseases

Mast cells (MCs), which are granulated tissue-resident cells of hematopoietic lineage, contribute to vascular homeostasis, innate/adaptive immunity, and wound healing. However, MCs are best known for their roles in allergic and inflammatory diseases, such as anaphylaxis, food allergy, rhinitis, itch, urticaria, atopic dermatitis, and asthma. In addition to the high-affinity IgE receptor (FcεRI), MCs express numerous G protein-coupled receptors (GPCRs), which are the largest group of membrane receptor proteins and the most common targets of drug therapy. Antimicrobial host defense peptides, neuropeptides, major basic protein, eosinophil peroxidase, and many US Food and Drug Administration-approved peptidergic drugs activate human MCs through a novel GPCR known as Mas-related G protein-coupled receptor X2 (MRGPRX2; formerly known as MrgX2). Unique features of MRGPRX2 that distinguish it from other GPCRs include their presence both on the plasma membrane and intracellular sites and their selective expression in MCs. In this article we review the possible roles of MRGPRX2 on host defense, drug-induced anaphylactoid reactions, neurogenic inflammation, pain, itch, and chronic inflammatory diseases, such as urticaria and asthma. We propose that host defense peptides that kill microbes directly and activate MCs through MRGPRX2 could serve as novel GPCR targets to modulate host defense against microbial infection. Furthermore, mAbs or small-molecule inhibitors of MRGPRX2 could be developed for the treatment of MC-dependent allergic and inflammatory disorders.

Non-coding Double-stranded RNA and Antimicrobial Peptide LL-37 Induce Growth Factor Expression from Keratinocytes and Endothelial Cells

A critical function for skin is that when damaged it must simultaneously identify the nature of the injury, repair barrier function, and limit the intrusion of pathogenic organisms. These needs are carried out through the detection of damage-associated molecular patterns (DAMPs) and a response that includes secretion of cytokines, chemokines, growth factors, and antimicrobial peptides (AMPs). In this study, we analyzed how non-coding double-stranded RNA (dsRNAs) act as a DAMP in the skin and how the human cathelicidin AMP LL-37 might influence growth factor production in response to this DAMP. dsRNA alone significantly increased the expression of multiple growth factors in keratinocytes, endothelial cells, and fibroblasts. Furthermore, RNA sequencing transcriptome analysis found that multiple growth factors increase when cells are exposed to both LL-37 and dsRNA, a condition that mimics normal wounding. Quantitative PCR and/or ELISA validated that growth factors expressed by keratinocytes in these conditions included, but were not limited to, basic fibroblast growth factor (FGF2), heparin-binding EGF-like growth factor (HBEGF), vascular endothelial growth factor C (VEGFC), betacellulin (BTC), EGF, epiregulin (EREG), and other members of the transforming growth factor β superfamily. These results identify a novel role for DAMPs and AMPs in the stimulation of repair and highlight the complex interactions involved in the wound environment.

Mechanism study on a new antimicrobial peptide Sphistin derived from the N-terminus of crab histone H2A identified in haemolymphs of Scylla paramamosain

Histone H2A is known to participate in host immune defense through generating special antimicrobial peptides (AMPs), for which it has been an interesting research focus to characterize this kind of peptides in vertebrates and invertebrates. Although thousands of AMPs have been reported in variety of life species, only several AMPs are known in crabs and in particular no H2A-derived AMP has yet been reported. In the present study, a 38-amino acid peptide with antimicrobial activity was determined based on the sequence analysis of a histone H2A identified from the mud crab Scylla paramamosain. The histone H2A derived peptide was an AMP-like molecule and designated as Sphistin. Sphistin showed typical features of AMPs such as amphiphilic α-helical second structrue and positive charge net. The synthetic Sphistin exerted high antimicrobial activity against Gram-positive, Gram-negative bacteria and yeast, among which Aeromonas hydrophila, Pseudomonas fluorescens and Pseudomonas stutzeri are important aquatic pathogens. Leakage of the cell content and disruption of the cell surface were observed in bacterial cells treated with Sphistin using scanning electron microscopy. It was proved that the increasing cytoplasmic membrane permeability of Escherichia coli was caused by Sphistin. Further observation under confocal microscopy showed that Sphistin could combine onto the membrane of Staphylococcus aureus, E. coli MC1061 and Pichia pastoris but not translocate into the cytoplasm. Moreover, the affinity of Sphistin with either LPS or LTA was also testified that there was an interaction between Sphistin and cell membrane. Thus, the antimicrobial mechanism of this peptide likely exerted via adsorption and subsequently permeabilization of the bacterial cell membranes other than penetrating cell membrane. In addition, synthetic Sphistin exhibited no cytotoxicity to primary cultured crab haemolymphs and mammalian cells even at a high concentration of 100 μg/mL for 24 h. This is the first report of a histone-derived Sphistin identified from S. paramamosain with a specific antimicrobial activity and mechanism, which could be a new candidate for future application in aquaculture and veterinary medicine.

Modulation of host defense peptide-mediated human mast cell activation by LPS

Human β-defensin3 (hBD3) and the cathelicidin LL-37 are host defense peptides (HDPs) that directly kill microbes and display immunomodulatory/wound-healing properties via the activation of chemokine, formylpeptide and epidermal growth factor receptors on leukocytes and epithelial cells. A C-terminal 14 amino acid hBD3 peptide with all Cys residues replaced with Ser (CHRG01) and an LL-37 peptide consisting of residues 17-29 (FK-13) display antimicrobial activity but lack immunomodulatory property. Surprisingly, we found that CHRG01 and FK-13 caused Ca(2+) mobilization and degranulation in human mast cells via a novel G protein-coupled receptor known as Mas-related gene-X2 (MrgX2). At local sites of bacterial infection, the negatively charged LPS likely interacts with cationic HDPs to inhibit their activity and thus providing a mechanism for pathogens to escape host defense mechanisms. We found that LPS caused almost complete inhibition of hBD3 and LL-37-induced Ca(2+) mobilization and mast cell degranulation. In contrast, it had no effect on CHRG01 and FK-13-induced mast cell responses. These findings suggest that HDP derivatives that kill microbes, harness mast cell's host defense and wound-healing properties via the activation of MrgX2 but are resistant to inhibition by LPS could be utilized for the treatment of antibiotic-resistant microbial infections.

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.

Cathelicidin rCRAMP stimulates rat mast cells to generate cysteinyl leukotrienes, synthesize TNF and migrate: involvement of PLC/A2, PI3K and MAPK signaling pathways

Cathelicidins represent a family of cationic peptides involved in host defense systems. Apart from exerting direct anti-microbial effects, cathelicidins can regulate immune responses by affecting the activity of cells playing a role in antibacterial defense. Taking into account that mast cells are critical components of host defense, the aim of this study was to determine whether rat cathelicidin-related anti-microbial peptide (rCRAMP) can influence mast cell activity. We have demonstrated that activation of fully mature rat mast cells with rCRAMP resulted in generation and release of cysteinyl leukotrienes (cysLTs). However, rCRAMP failed to induce mast cell degranulation and histamine release. We also found that rCRAMP stimulated rat mast cells to synthesize TNF, but not CXCL8. What is more, this peptide induced GM-CSF, IL-1β, CCL2 and CCL3 but not IL-33 mRNA expression in mast cells. Finally, we showed that this cathelicidin serves as potent chemoattractant for rat mast cells. rCRAMP-mediated cysLT synthesis and mast cell migration were strongly inhibited by IL-10 pre-treatment. With the use of specific inhibitors, we established that activation of PLC/A2 and ERK1/2, but not p38, was required for rCRAMP-induced mast cell stimulation, while PI3K-dependent pathway is involved in both TNF synthesis and mast cell migration. Our results suggest that cathelicidins can amplify inflammatory responses by causing mast cells accumulation and by stimulating these cells to release potent pro-inflammatory mediators.

Mast cells as targets for immunotherapy of solid tumors

Mast cells have historically been studied mainly in the context of allergic disease. In recent years, we have come to understand the critical importance of mast cells in tissue remodeling events and their role as sentinel cells in the induction and development of effective immune responses to infection. Studies of the role of mast cells in tumor immunity are more limited. The pro-tumorigenic role of mast cells has been widely reported. However, mast cell infiltration predicts improved prognosis in some cancers, suggesting that their prognostic value may be dependent on other variables. Such factors may include the nature of local mast cell subsets and the various activation stimuli present within the tumor microenvironment. Experimental models have highlighted the importance of mast cells in orchestrating the anti-tumor events that follow immunotherapies that target innate immunity. Mast cells are long-lived tissue resident cells that are abundant around many solid tumors and are radiation resistant making them unique candidates for combined treatment modalities. This review will examine some of the key roles of mast cells in tumor immunity, with a focus on potential immunotherapeutic interventions that harness the sentinel role of mast cells.

Antimicrobial peptide LL-37 promotes bacterial phagocytosis by human macrophages

LL-37/hCAP-18 is the only human member of the cathelicidin family and plays an important role in killing various pathogens, as well as in immune modulation. In this study, we investigated the effect of LL-37 on bacterial phagocytosis by macrophages and demonstrate that LL-37 enhances phagocytosis of IgG-opsonized Gram-negative and Gram-positive bacteria in a dose- and time-dependent manner by dTHP-1 cells. In addition, LL-37 enhanced phagocytosis of nonopsonized Escherichia coli by human macrophages. Consistently, LL-37 elevated the expression of FcγRs on macrophages but not the complement receptors CD11b and -c. Further studies revealed that the expression of TLR4 and CD14 is also increased on LL-37-treated macrophages. Several lines of evidence indicated that the FPR2/ALX receptor mediated LL-37-induced phagocytosis. However, TLR4 signaling was also coupled to the phagocytic response, as a specific TLR4 antibody significantly suppressed phagocytosis of IgG-opsonized E. coli and nonopsonized E. coli by dTHP-1 cells. Finally, macrophages from Cnlp(-/-) mice exhibited diminished bacterial phagocytosis compared with macrophages from their WT littermates. In conclusion, we demonstrate a novel, immune-modulatory mechanism of LL-37, which may contribute to bacterial clearance.

The Human Cathelicidin Antimicrobial Peptide LL-37 as a Potential Treatment for Polymicrobial Infected Wounds

Diabetic patients often have ulcers on their lower-limbs that are infected by multiple biofilm-forming genera of bacteria, and the elimination of the biofilm has proven highly successful in resolving such wounds in patients. To that end, antimicrobial peptides have shown potential as a new anti-biofilm approach. The single human cathelicidin peptide LL-37 has been shown to have antimicrobial and anti-biofilm activity against multiple Gram-positive and Gram-negative human pathogens, and have wound-healing effects on the host. The combination of the anti-biofilm effect and wound-healing properties of LL-37 may make it highly effective in resolving polymicrobially infected wounds when topically applied. Such a peptide or its derivatives could be a platform from which to develop new therapeutic strategies to treat biofilm-mediated infections of wounds. This review summarizes known mechanisms that regulate the endogenous levels of LL-37 and discusses the anti-biofilm, antibacterial, and immunological effects of deficient vs. excessive concentrations of LL-37 within the wound environment. Here, we review recent advances in understanding the therapeutic potential of this peptide and other clinically advanced peptides as a potential topical treatment for polymicrobial infected wounds.

Reciprocal effects of Guizhi decoction to the Guizhi decoction syndrome by toll-like receptor mRNA expression and cytokines secretion

OBJECTIVE

To explore the pathological mechanisms of Guizhi Decoction () syndrome and the therapeutic molecular mechanisms of the Guizhi Decoction, Mahuang Decoction (), Sangju Decoction ( ) and Yinqiao Powder (), as well as the potentially biological basis that Guizhi Decoction is most effective only for the patients with Guizhi Decoction syndrome in clinical practice.

METHODS

We first got serum samples from the patients suffering from both upper respiratory tract infection and Guizhi Decoction syndrome identified by the doctors of Chinese medicine (CM) in the clinic. Four formulas with therapeutic actions of pungent warmth or pungent coolness for superficial syndromes were chosen and four kinds of rat serum samples each containing one of the above-mentioned herbal formulas were collected, then the effects of Guizhi Decoction syndromes' patient serum as well as the effects of sera containing the formulas after being stimulated by the patient serum samples on both the mRNA expression of certain toll-like receptor (TLR) subtypes and the release of some inflammatory cytokines in RAW264.7 cells were tested and analyzed in vitro.

RESULTS

The expression of TLR-3, TLR-4 and TLR-9 mRNA among the 9 tested TLR subforms were up-regulated in the macrophages stimulated by the sera from untreated upper respiratory infection patients with the Guizhi Decoction syndrome (symptomcomplex). The products such as interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α and interferon (IFN)-β from stimulated macrophages through TLR signaling pathways were also increased correspondingly. Interestingly, the changes induced by the Guizhi Decoction syndrome patients' sera were masked significantly after the macrophages were incubated with the sera from donors treated with Guizhi Decoction. Similarly, the three other exterior-releasing formulas were all effective in reversing the up-regulated changes of certain TLR subforms to different degrees, but both the number of targeted TLRs and efficacy of them seemed to be inferior to that of Guizhi Decoction.

CONCLUSION

Evidence from these experiments might contribute to the scientific explanation of both the pharmacological mechanisms of Guizhi Decoction and also the CM theory that Guizhi Decoction is specifically prescribed for the treatment of Guizhi Decoction syndrome (The gearing formula to the symptom-complex).

Host defense peptides: an alternative as antiinfective and immunomodulatory therapeutics

Host defense peptides are conserved components of innate immune response present among all classes of life. These peptides are potent, broad spectrum antimicrobial agents with potential as novel therapeutic compounds. Also, the ability of host defense peptides to modulate immunity is an emerging therapeutic concept since its selective modulation is a novel antiinfective strategy. Their mechanisms of action and the fundamental differences between pathogens and host cells surfaces mostly lead to a not widely extended microbial resistance and to a lower toxicity toward host cells. Biological libraries and rational design are novel tools for developing such molecules with promising applications as therapeutic drugs.

Mas-related gene X2 (MrgX2) is a novel G protein-coupled receptor for the antimicrobial peptide LL-37 in human mast cells: resistance to receptor phosphorylation, desensitization, and internalization

Human LL-37 is a multifunctional antimicrobial peptide that promotes inflammation, angiogenesis, wound healing, and tumor metastasis. Most effects of LL-37 are mediated via the activation of the cell surface G protein-coupled receptor FPR2 on leukocytes and endothelial cells. Although LL-37 induces chemotaxis, degranulation, and chemokine production in mast cells, the receptor involved and the mechanism of its regulation remain unknown. MrgX2 is a member of Mas-related genes that is primarily expressed in human dorsal root ganglia and mast cells. We found that a human mast cell line LAD2 and CD34(+) cell-derived primary mast cells, which natively express MrgX2, responded to LL-37 for sustained Ca(2+) mobilization and substantial degranulation. However, an immature human mast cell line, HMC-1, that lacks functional MrgX2 did not respond to LL-37. shRNA-mediated knockdown of MrgX2 in LAD2 mast cell line and primary CD34(+) cell-derived mast cells caused a substantial reduction in LL-37-induced degranulation. Furthermore, mast cell lines stably expressing MrgX2 responded to LL-37 for chemotaxis, degranulation, and CCL4 production. Surprisingly, MrgX2 was resistant to LL-37-induced phosphorylation, desensitization, and internalization. In addition, shRNA-mediated knockdown of the G protein-coupled receptor kinases (GRK2 and GRK3) had no effect on LL-37-induced mast cell degranulation. This study identified MrgX2 as a novel G protein-coupled receptor for the antibacterial peptide LL-37 and demonstrated that unlike most G protein-coupled receptors it is resistant to agonist-induced receptor phosphorylation, desensitization, and internalization.

Surface TLR2 and TLR4 expression on mature rat mast cells can be affected by some bacterial components and proinflammatory cytokines

The aim of our study was to determine whether some bacterial components as well as some proinflammatory cytokines can affect surface mast cell levels. By the use of flow cytometry technique, we documented that freshly isolated mature rat peritoneal mast cells do express surface TLR2 and TLR4 protein, but not CD14 molecules, and respond to stimulation with TLR2 and TLR4 ligands by cysteinyl leukotriene generation. The level of TLR2 protein is modulated by PGN and CCL5 treatment, but not by LPS, LAM, TNF, or IL-6. Surface mast cell TLR4 expression is affected by LPS, LAM, IL-6, and CCL5. Considering that TLR-mediated activation conditions not only engaged these cells in antibacterial defense and development of inflammation but also might influence allergic processes, our observations that surface TLR2 and TLR4 expression can be regulated both bacterial components and proinflammatory cytokines seem to be very intriguing and importance.

Regulation of mast cell responses in health and disease

Mast cells are multifunctional cells that initiate not only IgE-dependent allergic diseases but also play a fundamental role in innate and adaptive immune responses to microbial infection. They are also thought to play a role in angiogenesis, tissue remodeling, wound healing, and tumor repression or growth. The broad scope of these physiologic and pathologic roles illustrates the flexible nature of mast cells, which is enabled in part by their phenotypic adaptability to different tissue microenvironments and their ability to generate and release a diverse array of bioactive mediators in response to multiple types of cell-surface and cytosolic receptors. There is increasing evidence from studies in cell cultures that release of these mediators can be selectively modulated depending on the types or groups of receptors activated. The intent of this review is to foster interest in the interplay among mast cell receptors to help understand the underlying mechanisms for each of the immunological and non-immunological functions attributed to mast cells. The second intent of this review is to assess the pathophysiologic roles of mast cells and their products in health and disease. Although mast cells have a sufficient repertoire of bioactive mediators to mount effective innate and adaptive defense mechanisms against invading microorganisms, these same mediators can adversely affect surrounding tissues in the host, resulting in autoimmune disease as well as allergic disorders.

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

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

Does allergy impair innate immunity? Leads and lessons from atopic dermatitis

Host defence responses against invading pathogens are well-balanced, inflammatory processes of the innate and adaptive immune system. Impaired development or abnormal function of either system can result in failure to control pathogens and to clear infections. Infections have been claimed to modulate the onset and course of allergic diseases. This so-called hygiene hypothesis is still an active area of research. In contrast, the effects of allergies on infections and pathogen-directed immune responses are less well understood. Here, we have reviewed the existing evidence that allergies result in impaired innate immunity and we discuss recent observations that may explain why and how innate immunity is dysfunctional in allergic patients. With a focus on atopic dermatitis as a model of allergic disease, we speculate that one of the key features of allergic conditions, namely Th2 polarization, leads to several independent inhibitory effects on host defence and consequently to a higher risk of infections in allergic patients. A better understanding of impaired host defence and its mechanisms in allergic subjects will help to improve the management of these diseases.

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.

Cathelicidin LL-37: a multitask antimicrobial peptide

The antimicrobial peptide LL-37 is the only known member of the cathelicidin family of peptides expressed in humans. LL-37 is a multifunctional host defense molecule essential for normal immune responses to infection and tissue injury. LL-37 peptide is a potent killer of different microorganisms with the ability to prevent immunostimulatory effects of bacterial wall molecules such as lipopolysaccharide and can therefore protect against lethal endotoxemia. Additional reported activities of LL-37 include chemoattractant function, inhibition of neutrophil apoptosis, and stimulation of angiogenesis, tissue regeneration, and cytokine release (e.g. IL-8). Cellular production of LL-37 is affected by multiple factors, including bacterial products, host cytokines, availability of oxygen, and sun exposure through the activation of CAP-18 gene expression by vitamin D(3). At infection sites, the function of LL-37 can be inhibited by charge-driven interactions with DNA and F-actin released from dead neutrophils and other cells lysed as the result of inflammation. A better understanding of LL-37's biological properties is necessary for its possible therapeutic application for immunomodulatory purposes as well as in treating bacterial infection.

Phenylbutyrate induces antimicrobial peptide expression

Antimicrobial peptides (AMPs) are important components of our first line of defense. Induction of AMPs such as LL-37 of the cathelicidin family might provide a novel approach in treating bacterial infections. In this study we identified 4-phenylbutyrate (PBA) as a novel inducer of AMP expression and investigated affected regulatory pathways. We treated various cell lines with PBA and assessed mRNA expression by real-time reverse transcriptase PCR (RT-PCR). Cathelicidin AMP (CAMP) gene expression was found to be upregulated in all four cell lines tested. Additionally, we found that the beta-defensin 1 gene was upregulated in the lung epithelial cell line VA10 while being downregulated in the monocytic cell line U937. Further we found that PBA induced CAMP gene expression synergistically with 1,25-dihydroxyvitamin D(3) at both protein and mRNA levels. The general mechanism of induction of CAMP gene expression by PBA was found to be dependent on protein synthesis. Results from quantitative chromatin immunoprecipitation experiments challenge the common view that histone deacetylase inhibitors directly increase CAMP gene expression. Furthermore, we have demonstrated that inhibition of the mitogen-activated protein kinases MEK1/2 and c-Jun N-terminal kinase attenuate PBA-induced CAMP gene expression. Similarly, alpha-methylhydrocinnamate (ST7), an analogue of PBA, increases CAMP gene expression. Our findings contribute to understanding of the regulation of AMP expression and suggest that PBA and/or ST7 is a promising drug candidate for treatment of microbial infections by strengthening the epithelial antimicrobial barriers.

Novel peptide therapeutics for treatment of infections

As antibiotic resistance increases worldwide, there is an increasing pressure to develop novel classes of antimicrobial compounds to fight infectious disease. Peptide therapeutics represent a novel class of therapeutic agents. Some, such as cationic antimicrobial peptides and peptidoglycan recognition proteins, have been identified from studies of innate immune effector mechanisms, while others are completely novel compounds generated in biological systems. Currently, only selected cationic antimicrobial peptides have been licensed, and only for topical applications. However, research using new approaches to identify novel antimicrobial peptide therapeutics, and new approaches to delivery and improving stability, will result in an increased range of peptide therapeutics available in the clinic for broader applications.

The cathelicidin LL-37 activates human mast cells and is degraded by mast cell tryptase: counter-regulation by CXCL4

The cathelicidin LL-37 represents a potent antimicrobial and cell-stimulating agent, most abundantly expressed in peripheral organs such as lung and skin during inflammation. Because mast cells (MC) overtake prominent immunomodulatory roles in these organs, we wondered whether interactions exist between MC and LL-37. In this study, we show for the first time to our knowledge that physiological concentrations of LL-37 induce degranulation in purified human lung MC. Intriguingly, as a consequence LL-37 rapidly undergoes limited cleavage by a released protease. The enzyme was identified as beta-tryptase by inhibitor studies and by comparison to the recombinant protease. Examining the resulting LL-37 fragments for their functional activity, we found that none of the typical capacities of intact LL-37, i.e., MC degranulation, bactericidal activity, and neutralization of LPS, were retained. Conversely, we found that another inflammatory protein, the platelet-derived chemokine CXCL4, protects LL-37 from cleavage by beta-tryptase. Interestingly, CXCL4 did not act as a direct enzyme inhibitor, but destabilized active tetrameric beta-tryptase by antagonizing the heparin component required for the integrity of the tetramer. Altogether our results suggest that interaction of LL-37 and MC initiates an effective feedback loop to limit cathelicidin activity during inflammation, whereas CXCL4 may represent a physiological counter-regulator of beta-tryptase activity.

Cell specificity, anti-inflammatory activity, and plausible bactericidal mechanism of designed Trp-rich model antimicrobial peptides

To develop novel short Trp-rich antimicrobial peptides (AMPs) with potent cell specificity (targeting bacteria but not eukaryotic cells) and anti-inflammatory activity, a series of 11-meric Trp-rich model peptides with different ratios of Leu and Lys/Arg residues, XXWXXWXXWXX-NH(2) (X indicates Leu or Lys/Arg), was synthesized. K(6)L(2)W(3) displayed an approximately 40-fold increase in cell specificity, compared with the natural Trp-rich AMP indolicidin (IN). Lys-containing peptides (K(8)W(3), K(7)LW(3) and K(6)L(2)W(3)) showed approximately 2- to 4-fold higher cell specificities than did their counterparts, the Arg-containing peptides (R(8)W(3), R(7)LW(3) and R(6)L(2)W(3)), indicating that multiple Lys residues are more important than multiple Arg residues in the design of AMPs with good cell specificity. The excellent resistance of d-enantiomers (K(6)L(2)W(3)-D and R(6)L(2)W(3)-D) and Orn/Nle-containing peptides (O(6)L(2)W(3) and O(6)L(2)W(3)) to trypsin digestion compared with the rapid breakdown of the l-enantiomers (K(6)L(2)W(3) and R(6)L(2)W(3)), highlights the clinical potential of such peptides. K(6)L(2)W(3), R(6)L(2)W(3), K(6)L(2)W(3)-D and R(6)L(2)W(3)-D caused weak dye leakage from bacterial membrane-mimicking negatively charged EYPG/EYPE (7:3, v/v) liposomes. Confocal microscopy showed that these peptides penetrated the cell membrane of Escherichia coli and accumulated in the cytoplasm, as observed for buforin-2. Gel retardation studies revealed that the peptides bound more strongly to DNA than did IN. These results suggested that one possible peptide bactericidal mechanism may relate to the inhibition of intracellular functions via interference with DNA/RNA synthesis. Furthermore, some model peptides, containing K(6)L(2)W(3), K(5)L(3)W(3), R(6)L(2)W(3), O(6)L(2)W(3), O(6)L(2)W(3), and K(6)L(2)W(3)-D inhibited LPS-induced inducible nitric oxide synthase (iNOS) mRNA expression, the release of nitric oxide (NO) following LPS stimulation in RAW264.7 cells and had powerful LPS binding activities at bactericidal concentrations. Collectively, our results indicated that these peptides have potential for future development as novel antimicrobial and anti-inflammatory agents.