Factors Influencing Marker Expressions of Cultured Human Cord Blood-Derived Mast Cells

Mast cells (MCs) are tissue-resident immune cells of a hematopoietic origin that play vital roles in innate and adaptive immunity. Human MCs can be isolated and differentiated from various tissue sources, including cord blood, when supplemented with cytokines such as stem cell factor, interleukin 3, and interleukin 6. Our current research study has shown significant differences in the marker expressions of human cord blood-derived mast cells (hCBMCs) based on donor dependency and the type of medium used for culturing and differentiation. These findings are particularly relevant given the challenges of obtaining specialty media influencing MC phenotypic marker expressions. We found that hCBMCs cultured in StemSpanTM-XF medium had a moderate expression of mast/stem cell growth factor receptor Kit (c-KIT) (mRNA and protein), low expressions of FcεRI (mRNA) and TLR2 (mRNA and protein) but had high levels of MRGPRX2 (mRNA and protein) expressions. In contrast, hCBMCs cultured in Stem Line II medium expressed FcεRI and TLR2 (mRNA and protein) with higher c-KIT but had lower MRGPRX2 expressions compared to the hCBMCs cultured in the StemSpanTM-XF medium. These results suggest that it is crucial to consider both donor dependency and the medium when investigating MC functions and that further research is needed to fully understand the impact of these factors on the hCBMC marker expressions.

The Role of Sphingolipids and Sphingosine-1-phosphate-Sphingosine-1-phosphate-receptor Signaling in Psoriasis

Psoriasis is a long-lasting skin condition characterized by redness and thick silver scales on the skin's surface. It involves various skin cells, including keratinocytes, dendritic cells, T lymphocytes, and neutrophils. The treatments for psoriasis range from topical to systemic therapies, but they only alleviate the symptoms and do not provide a fundamental cure. Moreover, systemic treatments have the disadvantage of suppressing the entire body's immune system. Therefore, a new treatment strategy with minimal impact on the immune system is required. Recent studies have shown that sphingolipid metabolites, particularly ceramide and sphingosine-1-phosphate (S1P), play a significant role in psoriasis. Specific S1P-S1P-receptor (S1PR) signaling pathways have been identified as crucial to psoriasis inflammation. Based on these findings, S1PR modulators have been investigated and have been found to improve psoriasis inflammation. This review will discuss the metabolic pathways of sphingolipids, the individual functions of these metabolites, and their potential as a new therapeutic approach to psoriasis.

S. epidermidis Rescues Allergic Contact Dermatitis in Sphingosine 1-Phosphate Receptor 2-Deficient Skin

Recent studies have identified a subtype of the S1P-receptor family called sphingosine-1-phosphate receptor 2 (S1PR2), which plays a crucial role in maintaining the skin barrier. It has been observed that S1PR2 and Staphylococcus epidermidis (S. epidermidis) work together to regulate the skin barrier. However, the interaction between these two factors is still unclear. To investigate this, a study was conducted on healthy skin and allergic contact dermatitis (ACD) using 3,4-Dibutoxy-3-cyclobutene-1,2-dione (SADBE) on the ears of S1pr2fl/fl and S1pr2fl/flK14-Cre mice and using 1 × 106 CFU of S. epidermidis to examine its effects on the skin. The results showed that in S. epidermidis-conditioned ACD, the ear thickness of S1pr2fl/flK14-Cre mice was lower than that of S1pr2fl/fl mice, and mRNA expressions of Il-1β and Cxcl2 of S1pr2fl/flK14-Cre mice were lower than that of S1pr2fl/fl mice in ACD with S. epidermidis. Furthermore, the gene expression of Claudin-1 and Occludin in S1pr2fl/flK14-Cre mice was higher than that of S1pr2fl/fl mice in ACD with S. epidermidis. The study concludes that S. epidermidis colonization improves the skin barrier and prevents ACD even when S1P signaling malfunctions.

Mast cell tolerance in the skin microenvironment to commensal bacteria is controlled by fibroblasts

Activation and degranulation of mast cells (MCs) is an essential aspect of innate and adaptive immunity. Skin MCs, the most exposed to the external environment, are at risk of quickly degranulating with potentially severe consequences. Here, we define how MCs assume a tolerant phenotype via crosstalk with dermal fibroblasts (dFBs) and how this phenotype reduces unnecessary inflammation when in contact with beneficial commensal bacteria. We explore the interaction of human MCs (HMCs) and dFBs in the human skin microenvironment and test how this interaction controls MC inflammatory response by inhibiting the nuclear factor κB (NF-κB) pathway. We show that the extracellular matrix hyaluronic acid, as the activator of the regulatory zinc finger (de)ubiquitinating enzyme A20/tumor necrosis factor α-induced protein 3 (TNFAIP3), is responsible for the reduced HMC response to commensal bacteria. The role of hyaluronic acid as an anti-inflammatory ligand on MCs opens new avenues for the potential treatment of inflammatory and allergic disorders.

Sphingosine 1-Phosphate Signaling at the Skin Barrier Interface

Sphingosine 1-phosphate (S1P) is a product of membrane sphingolipid metabolism. S1P is secreted and acts via G-protein-coupled receptors, S1PR1-5, and is involved in diverse cellular functions, including cell proliferation, immune suppression, and cardiovascular functions. Recent studies have shown that the effects of S1P signaling are extended further by coupling the different S1P receptors and their respective downstream signaling pathways. Our group has recently reported that S1P inhibits cell proliferation and induces differentiation in human keratinocytes. There is a growing understanding of the connection between S1P signaling, skin barrier function, and skin diseases. For example, the activation of S1PR1 and S1PR2 during bacterial invasion regulates the synthesis of inflammatory cytokines in human keratinocytes. Moreover, S1P-S1PR2 signaling is involved in the production of inflammatory cytokines and can be triggered by epidermal mechanical stress and bacterial invasion. This review highlights how S1P affects human keratinocyte proliferation, differentiation, immunoreaction, and mast cell immune response, in addition to its effects on the skin barrier interface. Finally, studies targeting S1P-S1PR signaling involved in inflammatory skin diseases are also presented.

Multiplex genome editing of mammalian cells for producing recombinant heparin

Heparin is an essential anticoagulant used for treating and preventing thrombosis. However, the complexity of heparin has hindered the development of a recombinant source, making its supply dependent on a vulnerable animal population. In nature, heparin is produced exclusively in mast cells, which are not suitable for commercial production, but mastocytoma cells are readily grown in culture and make heparan sulfate, a closely related glycosaminoglycan that lacks anticoagulant activity. Using gene expression profiling of mast cells as a guide, a multiplex genome engineering strategy was devised to produce heparan sulfate with high anticoagulant potency and to eliminate contaminating chondroitin sulfate from mastocytoma cells. The heparan sulfate purified from engineered cells grown in chemically defined medium has anticoagulant potency that exceeds porcine-derived heparin and confers anticoagulant activity to the blood of healthy mice. This work demonstrates the feasibility of producing recombinant heparin from mammalian cell culture as an alternative to animal sources.

Sphingosine 1-Phosphate Receptor 2 Is Central to Maintaining Epidermal Barrier Homeostasis

The outer layer of the epidermis composes the skin barrier, a sophisticated filter constituted by layers of corneocytes in a lipid matrix. The matrix lipids, especially the ceramide-generated sphingosine 1-phosphate, are the messengers that the skin barrier uses to communicate with the basal layer of the epidermis where replicating keratinocytes are located. Sphingosine 1-phosphate is a bioactive sphingolipid mediator involved in various cellular functions through S1PR1‒5, expressed by keratinocytes. We discovered that the S1pr2 absence is linked to an impairment in the skin barrier function. Although S1pr2^-/- mouse skin has no difference in its phenotype and barrier function compared with that of wild-type mouse, after tape stripping, S1pr2^-/- mouse showed significantly higher transepidermal water loss and required another 24 hours to normalize their transepidermal water loss levels. Moreover, after epicutaneous Staphylococcus aureus application, impaired S1pr2^-/- mouse epidermal barrier function allowed deeper bacterial penetration and denser neutrophil infiltration in the dermis. Microarray and RNA sequence of S1pr2^-/- mouse epidermis linked the barrier dysfunction with a decrease in FLG2 and tight junction components. In conclusion, S1pr2^-/- mice have compromised skin barrier function and increased bacteria permeability, making them a suitable model for diseases that present similar characteristics, such as atopic dermatitis.

Boundary Disputes: In Inflamed Skin, Mast Cells Expand and Disorganize Stable Clonal Territories

Skin mast cells (MCs) are distinct from other MCs, and for years, we have tried to understand their origin and peculiarities. A recent study demonstrated that during development, MCs enter the skin from the yolk sac and embryonic liver and are later mixed with cells originating from the bone marrow. A report from Weitzmann et al. (2020) shows that MCs or their precursors occupy distinct areas in the fetal period and that they and their progeny maintain these geographic distributions throughout life. These stable clonal territories are altered only by the arrival of bone marrow‒derived MCs during inflammation.

Detection of GPCR mRNA Expression in Primary Cells Via qPCR, Microarrays, and RNA-Sequencing

A workflow is described for assaying the expression of G protein-coupled receptors (GPCRs) in cultured cells, using a combination of methods that assess GPCR mRNAs. Beginning from the isolation of cDNA and preparation of mRNA, we provide protocols for designing and testing qPCR primers, assaying mRNA expression using qPCR and high-throughput analysis of GPCR mRNA expression via TaqMan qPCR-based, GPCR-selective arrays. We also provide a workflow for analysis of expression from RNA-sequencing (RNA-seq) assays, which can be queried to yield expression of GPCRs and related genes in samples of interest, as well as to test changes in expression between groups, such as in cells treated with drugs or from healthy and diseased subjects. We place priority on optimized protocols that distinguish signal from noise, as GPCR mRNAs are typically present in low abundance, necessitating techniques that maximize sensitivity while minimizing noise. These methods may also be applicable for assessing the expression of members of families of other low abundance genes via high-throughput analyses of mRNAs, followed by independent confirmation and validation of results via qPCR.

Skin wound closure delay in metabolic syndrome correlates with SCF deficiency in keratinocytes

Poor wound closure due to diabetes, aging, stress, obesity, alcoholism, and chronic disease affects millions of people worldwide. Reasons wounds will not close are still unclear, and current therapies are limited. Although stem cell factor (SCF), a cytokine, is known to be important for wound repair, the cellular and molecular mechanisms of SCF in wound closure remain poorly understood. Here, we found that SCF expression in the epidermis is decreased in mouse models of delayed wound closure intended to mimic old age, obesity, and alcoholism. By using SCF conditionally knocked out mice, we demonstrated that keratinocytes' autocrine production of SCF activates a transient c-kit receptor in keratinocytes. Transient activation of the c-kit receptor induces the expression of growth factors and chemokines to promote wound re-epithelialization by increasing migration of skin cells (keratinocytes and fibroblasts) and immune cells (neutrophils) to the wound bed 24-48 h post-wounding. Our results demonstrate that keratinocyte-produced SCF is essential to wound closure due to the increased recruitment of a unique combination of skin cells and immune cells in the early phase after wounding. This discovery is imperative for developing clinical strategies that might improve the body's natural repair mechanisms for treating patients with wound-closure pathologies.

Human Keratinocytes Use Sphingosine 1-Phosphate and its Receptors to Communicate Staphylococcus aureus Invasion and Activate Host Defense

Sphingosine 1-phosphate (S1P) is a bioactive lipid mediator generated when a cell membrane or its components are damaged by various factors. S1P regulates diverse cell activities via S1P receptors (S1PRs). Keratinocytes express S1PR1-5. Although it is known that S1PRs control keratinocyte differentiation, apoptosis, and wound healing, S1PR functions in keratinocyte infections have not been fully elucidated. We propose that the S1P-S1PR axis in keratinocytes works as a biosensor for bacterial invasion. Indeed, in human impetigo infection, we found high epidermal expression of S1PR1 and S1PR2 in the skin. Furthermore, in normal human epidermal keratinocytes in vitro, treatment with Staphylococcus aureus bacterial supernatant not only induced S1P production but also increased the transcription of S1PR2, confirming our in vivo observation, as well as increased the levels of TNFA, IL36G, IL6, and IL8 mRNAs. However, direct treatment of normal human epidermal keratinocytes with S1P increased the expressions of IL36G, TNFA, and IL8, but not IL6. In both S1P- and S. aureus bacterial supernatant-treated normal human epidermal keratinocytes, S1PR1 knockdown reduced IL36G, TNFA, and IL8 transcription, and the S1PR2 antagonist JTE013 blocked the secretion of these cytokines. Overall, we have proven that during infections, keratinocytes communicate damage by using S1P release and tight control of S1PR1 and 2.

Dermal Fibroblasts Control Mast Cell reactivity to commensal bacteria

Background

Our data suggests, and current literature supports, that when mast cells (MCs) leave the blood and interact with dermal fibroblasts (DFs), they assume a bacterial tolerant phenotype in order to prevent unnecessary inflammation during the encounter with the beneficial commensal microbiome. We hypothesize that the mechanisms that induce the MC tolerant phenotype in human skin is due to dermal fibroblasts interactions.

Methods

We mimicked the “in vivo” setting by conditioning human cord blood MC (hMC) with human dermal fibroblast (hDF) and, then exposed them to commensal bacteria supernatant. Human MC transcriptome data from the RNA-seq FANTOM5 data collection on MCs freshly isolated from human skin (FANTOM5 study Motakis_et_al_2013) was used to investigate the innate immune phenotype of MCs in the skin. We determined the genes that make hDFs unique by comparing their gene expression profiles with lung and cardiac fibroblasts using RNA-seq analysis and challenged hMCs with the products of these genes.

Results

We have discovered that hDF conditioned with hMCs, show a decreased expression of interleukins upon commensal stimulation; specifically, multiple cytokines/chemokine such as pro-inflammatory cytokine GM-SCF, IL-8, MCP-1 and anti-inflammatory cytokines IL-10, IL-13 are down-regulated by at least 95% and these cytokines can be controlled by the product of hDF unique genes.

Conclusion

The human dermal MC reactivity is controlled by hDF’s unique genes that play an important role in regulating the hMC NF-Kb pathway.

Skin microbiome regulates SCF level in Keratinocytes and defines mast cell maturation

Background

Mast cell (MC) progenitors enter the skin and become mature in the surrounding microenvironment during embryogenesis and they fully mature 8 to 15 days after birth (in mouse). We published that skin commensal bacteria work together with skin resident cells (especially keratinocytes), in order to retain and differentiate mast cells into the skin. In the present study, we aim to demonstrate that this effect is due to TLR2 sensing of microbiome.

Methods

we used germ free mice (GF), hairless (hr/hr) mice and hr/hr/Tlr2−/− mice. Analyses were performed by immunohistochemistry, qPCR and FACS. IgE cross-linking and 48/80 have been used to test in vivo MCs degranulation.

Results

we found that GF mice present with less mature skin MCs than pathogen free mice (PFM). MCs immaturity correlated with a low level of stem cell factor (SCF) in keratinocytes, a critical MC differentiation and growth factor. Furthermore, compound 48/80, a known degranulation agent, induced less edema in the paws of GF mice than in those of conventional mice. A smaller population of c-Kit positive MCs in the GF mice normalized after being co-housed with PFM mice for 5 weeks to reconstitute their microbiome. On the other hand, hr/hr mice, have a skin increased number of mature and proliferating MCs that correlates with a more gram positive microbiome than their littermates. When hr/hr were backcrossed into Tlr2−/− (so they cannot sense the gram positive commensals) the number of MCs in skin dramatically decreased.

Conclusions

While baseline keratinocyte SCF expression is essential to recruit MCs into the skin, TLR2 stimulation by gram positive skin microbiome, promotes SCF keratinocyte production, which then enhances the maturation and proliferation of skin MCs.

Sphingosine 1-phosphate is a harbinger of S. aureus invasion and activates host defense in epithelial barriers

Background

Sphingosine 1-phosphate (S1P) is a bioactive lipid mediator generated in the skin when cell membrane or barrier components are damaged. S1P regulates diverse cell activities via S1P receptors (S1PR). Keratinocytes express S1PR1–5. Although it is known that S1PRs control keratinocyte differentiation, apoptosis and wound healing, S1PR functions in keratinocyte infections are not fully elucidated. We hypothesized that S1P and S1PR-axis in keratinocytes works as a biosensor for bacterial invasion.

Methods

The expression of S1PRs were studied by immunofluorescence and qPCR. Cytokine transcription and secretion were detected by qPCR and ELISA, respectively. siRNA and S1PR2 antagonist, JTE013, were used to test the different S1PR functions. The S1P synthesis was tested by ATP depletion assay and ELISA.

Results

We found a high epidermal S1PR1 and 2 expressions in human impetigo skin. In vitro, in normal human epidermal keratinocytes (NHEK), S. aureus bacterial supernatant not only induced S1P production but also increased S1PR2 transcription and TNFα, IL36γ, 6 and 8 transcriptions, confirming our in vivo observation. S1P directly increased NHEK IL36γ, TNFα and IL8 expression, but not IL6. In both, S1P and S. aureus bacterial supernatant treated NHEK, S1PR1 knock down reduced IL36γ, TNFα and IL8 transcription, while S1PR2 antagonist, JTE013, blocked their protein secretion.

Conclusions

We proved that, during infections, keratinocytes communicate the infection by sensing S1P release and respond to it using receptors S1PR1 and 2, releasing pro-inflammatory cytokines.

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.

Skin commensal bacteria Staphylococcus epidermidis promote survival of melanocytes bearing UVB-induced DNA damage, while bacteria Propionibacterium acnes inhibit survival of melanocytes by increasing apoptosis

BACKGROUND/PURPOSE

Skin commensal bacteria have been described to help orchestrate skin homeostasis, signaling through innate immunity pathways. This study for the first time aimed at studying the relationship between skin commensals and melanocytes after UVB exposure.

METHODS

An in vitro UVB radiation model with normal human epidermal melanocytes (NHMs) and skin commensal bacteria supernatant from Staphylococcus epidermidis and Propionibacterium acnes was established. Melanocytes DNA damage, cyclobutane pyrimidine dimers (CPD), and cellular proliferation marker Ki-67 were measured by ELISA and immunofluorescence staining. Cell apoptosis was assessed by flow cytometry and PCR array and RT-qPCR.

RESULTS

Normal human epidermal melanocytes are able to survive and proliferate while bearing DNA damage after UVB radiation. Skin commensal bacteria S. epidermidis and its by-product LTA promote melanocytes survival by inducing upregulation of TRAF1, CASP14, CASP5, and TP73. On the other hand, P. acnes can inhibit UVB-irradiated melanocytes survival by increasing apoptosis.

CONCLUSION

Our studies show different aspects of commensal activity on melanocytes during irradiation. The possible balance achieved by the different skin commensal can influence NHM potential to become cancer cells.

Skin neurogenic inflammation

The epidermis closely interacts with nerve endings, and both epidermis and nerves produce substances for mutual sustenance. Neuropeptides, like substance P (SP) and calcitonin gene-related protein (CGRP), are produced by sensory nerves in the dermis; they induce mast cells to release vasoactive amines that facilitate infiltration of neutrophils and T cells. Some receptors are more important than others in the generation of itch. The Mas-related G protein-coupled receptors (Mrgpr) family as well as transient receptor potential ankyrin 1 (TRPA1) and protease activated receptor 2(Par2) have important roles in itch and inflammation. The activation of MrgprX1 degranulates mast cells to communicate with sensory nerve and cutaneous cells for developing neurogenic inflammation. Mrgprs and transient receptor potential vanilloid 4 (TRPV4) are crucial for the generation of skin diseases like rosacea, while SP, CGRP, somatostatin, β-endorphin, vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase-activating polypeptide (PACAP) can modulate the immune system during psoriasis development. The increased level of SP, in atopic dermatitis, induces the release of interferon (IFN)-γ, interleukin (IL)-4, tumor necrosis factor (TNF)-α, and IL-10 from the peripheral blood mononuclear leukocytes. We are finally starting to understand the intricate connections between the skin neurons and resident skin cells and how their interaction can be key to controlling inflammation and from there the pathogenesis of diseases like atopic dermatitis, psoriasis, and rosacea.

Effects of opioid and nonopioid analgesics on canine wheal formation and cultured human mast cell degranulation

Mast cell (MC) degranulation has been implicated in the side effect profile of a variety of clinically useful agents. Thus, after intrathecal delivery, formation of space-occupying, meningeally-derived masses may be related to local MC degranulation. We systematically characterized degranulating effects of opioid and nonopioid analgesics on cutaneous flares in the dog and in primary human MC (hMC) cultures.

METHODS

Dogs were anesthetized with IV propofol and received intradermal (ID) injections (50μL). Flare diameters were measured at 30min. Drugs showing flare responses were tested after intramuscular (IM) cromolyn (10mg/kg), a MC stabilizer. Human primary MCs (human cord blood CD34⁺/CD45⁺ cells) were employed and β-hexosaminidase in cell-free supernatants were measured to assess degranulation.

RESULTS

A significant skin flare for several classes of agents was observed including opioids, ziconotide, ketamine, ST-91, neostigmine, adenosine, bupivacaine, lidocaine, MK-801 and 48/80. Tizanidine, fentanyl, alfentanil, gabapentin and baclofen produced no flare. Flare produced by all ID agents, except adenosine, bupivacaine and lidocaine, was reduced by cromolyn. Naloxone had no effect upon opiate or 48/80 evoked flares. In hMC studies, 48/80 resulted in a concentration-dependent release of β-hexosaminidase. The rank order of drug-induced hMC β-hexosaminidase release was similar to that for flares.

CONCLUSIONS

A variety of therapeutically useful drugs degranulate MCs. This action may account for side effects such as the intrathecal granuloma resulting from spinally-delivered opioids. This degranulating effect may be useful in predicting potential intrathecal toxicity in the development of novel agents.

Interaction of primary mast cells with Borrelia burgdorferi (sensu stricto): role in transmission and dissemination in C57BL/6 mice

Background

Borrelia burgdorferi (sensulato), the causative agent of Lyme borreliosis is a bacterium transmitted by hard ticks, Ixodes spp. Bacteria are injected into the host skin during the tick blood meal with tick saliva. There, Borrelia and saliva interact together with skin cells such as keratinocytes, fibroblasts, mast cells and other specific immune cells before disseminating to target organs.

Methods

To study the role of mast cells in the transmission of Lyme borreliosis, we isolated mouse primary mast cells from bone marrow and incubated them in the presence of Borrelia burgdorferi (sensu stricto) and tick salivary gland extract. We further analyzed their potential role in vivo, in a mouse model of deficient in mast cells (Kit^wsh−/− mice).

Results

To our knowledge, we report here for the first time the bacteria ability to induce the inflammatory response of mouse primary mast cells. We show that OspC, a major surface lipoprotein involved in the early transmission of Borrelia, induces the degranulation of primary mast cells but has a limited effect on the overall inflammatory response of these cells. In contrast, whole bacteria have an opposite effect. We also show that mast cell activation is significantly inhibited by tick salivary gland extract. Finally, we demonstrate that mast cells are likely not the only host cells involved in the early transmission and dissemination of Borrelia since the use of mast cell deficient Kit^wsh−/− mice shows a limited impact on these two processes in the context of this mouse genetic background.

Conclusions

The absence of mast cells did not change the replication rate of Borrelia in the skin. However, in the absence of mast cells, Borrelia dissemination to the joints was faster. Mast cells do not control skin bacterial proliferation during primary infection and the establishment of the primary infection, as shown in the C57BL/6 mouse model studied. Nevertheless, the Borrelia induced cytotokine modulation on mast cells might be involved in long term and/or repeated infections and protect from Lyme borreliosis due to the development of a hypersensitivity to tick saliva.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2243-0) contains supplementary material, which is available to authorized users.

Skin microbiome and mast cells

Microbiotas in the skin have high levels of diversity at the species level, but low phylum-level diversity. The human skin microbiota is composed predominantly of Gram-positive bacteria especially Actinobacteria, which are the dominant bacterial phylum on the skin. Lipoteichoic acid (LTA) is a major constituent of the cell wall of Gram-positive bacteria and is therefore abundant in the skin microbiome. Recent studies have shown that LTA, and other bacterial products, permeates the whole skin and comes into contact with epidermal and dermal cells, including mast cells (MCs), with the potential of stimulating MC toll-like receptors (TLRs). MCs express a variety of pattern recognition receptors, including TLRs, on their cell surface in order to detect bacteria. Recent publications suggest that the skin microbiome has influence on MC migration, localization and maturation in the skin. Germ free (no microbiome) animals possess an underdeveloped immune system and immature MCs. Despite much research done on skin microbiota and many papers describing skin interaction with "the good microbiota", there is still controversy regarding how mast cells, communicate with surface bacteria. The present review intends to quell the controversy by illuminating the communication mechanism between bacteria and MCs.

Skin microbiome promotes mast cell maturation by triggering stem cell factor production in keratinocytes

BACKGROUND

Mast cell (MC) progenitors leave the bone marrow, enter the circulation, and settle in the skin and other tissues. Their maturation in tissues is influenced by the surrounding microenvironment.

OBJECTIVE

We tested the hypothesis that environmental factors play a role in MC maturation in the skin.

METHODS

MCs were numerically, phenotypically, and functionally compared between germ-free (GF), specific pathogen-free, and GF mice reconstituted with microbiota. The maturity of MCs was then correlated with skin levels of stem cell factor (SCF), a critical MC differentiation factor, and lipoteichoic acid (LTA), a Toll-like receptor 2 ligand. MCs were also evaluated in mice with keratinocyte-specific deletion of Scf.

RESULTS

We found that GF mice express abnormally low amounts of SCF, a critical MC differentiation factor, and contain MCs that are largely undifferentiated. Reconstituting the GF microbiota reverted this MC phenotype to normal, indicating that the phenotype is related to ongoing interactions of the microbiota and skin. Consistent with the immaturity of GF MCs, degranulation-provoking compound 48/80 induced less edema in the skin of GF mice than in conventional mice. Our results show that the skin microbiome drives SCF production in keratinocytes, which triggers the differentiation of dermal MCs. Because the skin microbiome is a rich source of LTA, a Toll-like receptor 2 ligand, we mimicked the GF microbiome's effect on MCs by applying LTA to the skin of GF mice. We also demonstrated that MC migration within the skin depends exclusively on keratinocyte-produced SCF.

CONCLUSION

This study has revealed a novel mechanism by which the skin microbiota signals the recruitment and maturation of MCs within the dermis through SCF production by LTA-stimulated keratinocytes.

Melanocytes and melanin represent a first line of innate immunity against Candida albicans

Melanocytes are dendritic cells located in the skin and mucosae that synthesize melanin. Some infections induce hypo- or hyperpigmentation, which is associated with the activation of Toll-like receptors (TLRs), especially TLR4. Candida albicans is an opportunist pathogen that can switch between blastoconidia and hyphae forms; the latter is associated with invasion. Our objectives in this study were to ascertain whether C. albicans induces pigmentation in melanocytes and whether this process is dependent on TLR activation, as well as relating this with the antifungal activity of melanin as a first line of innate immunity against fungal infections. Normal human melanocytes were stimulated with C. albicans supernatants or with crude extracts of the blastoconidia or hyphae forms, and pigmentation and TLR2/TLR4 expression were measured. Expression of the melanosomal antigens Melan-A and gp100 was examined for any correlation with increased melanin levels or antifungal activity in melanocyte lysates. Melanosomal antigens were induced earlier than cell pigmentation, and hyphae induced stronger melanization than blastoconidia. Notably, when melanocytes were stimulated with crude extracts of C. albicans, the cell surface expression of TLR2/TLR4 began at 48 h post-stimulation and peaked at 72 h. At this time, blastoconidia induced both TLR2 and TLR4 expression, whereas hyphae only induced TLR4 expression. Taken together, these results suggest that melanocytes play a key role in innate immune responses against C. albicans infections by recognizing pathogenic forms of C. albicans via TLR4, resulting in increased melanin content and inhibition of infection.

Mast cells are key mediators of cathelicidin-initiated skin inflammation in rosacea

Rosacea is a chronic inflammatory skin disease whose pathophysiological mechanism is still unclear. However, it is known that mast cell (MC) numbers are increased in the dermis of rosacea patients. MC proteases not only recruit other immune cells, which amplify the inflammatory response, but also cause vasodilation and angiogenesis. MCs are also one of the primary sources of cathelicidin LL-37 (Cath LL-37), an antimicrobial peptide that has been shown to be an enabler of rosacea pathogenesis. Here, we demonstrate that MCs are key mediators of cathelicidin-initiated skin inflammation. After Cath LL-37 injection into the dermis, MC-deficient B6.Cg-Kit(W-sh)/HNihrJaeBsmJ (KitW-sh) mice did not develop rosacea-like features. Conversely, chymase (P<0.001), tryptase, and Mmp9 (P<0.01) mRNA levels were significantly higher in C57BL/6 wild-type (WT) mice. Treating WT mice with an MC stabilizer significantly decreased the expressions of Mmp9 and Cxcl2 (P<0.01). Our data were confirmed on erythematotelangiectatic rosacea subjects who showed a decrease in matrix metalloproteinase activity (P<0.05), after 8 weeks of topical cromolyn treatment. We conclude that MCs have a central role in the development of inflammation subsequent to Cath LL-37 activation and that downregulation of activated MCs may be a therapy for rosacea treatment.

Innate immunity and the role of the antimicrobial peptide cathelicidin in inflammatory skin disease

Cathelicidin antimicrobial peptide is an important mediator of the innate immune response. In addition to its potent antimicrobial activity, cathelicidin has been shown to have chemoattractant and angiogenic properties. Recent research has demonstrated that, in addition to its aforementioned functions, cathelicidin plays an important role in the complex pathogenesis of several chronic inflammatory skin diseases. This review will present a concise overview of the role of cathelicidin in infection and in the development of atopic dermatitis, psoriasis, and rosacea. This understanding will direct future research efforts to identify therapeutic approaches that use cathelicidin as a novel drug itself, or aim to modify its expression and regulation.

Commensal bacteria lipoteichoic acid increases skin mast cell antimicrobial activity against vaccinia viruses

Mast cells (MCs) are considered sentinels in the skin and mucosa. Their ability to release antimicrobial peptides, such as cathelicidin, protects against bacterial infections when the epithelial barrier is breached. We recently described that MCs defend against bacterial and viral infections through the release of cathelicidin during degranulation. In this study, we hypothesize that cathelicidin expression is induced in MCs by the activation of TLR2 from bacterial products (lipoteichoic acid) produced by commensal bacteria at the epithelial surface. Our research shows that signaling through TLR2 increases the production and expression of cathelicidin in mast cells, thereby enhancing their capacity to fight vaccinia virus. MCs deficient in cathelicidin were less efficient in killing vaccinia virus after lipoteichoic acid stimulation than wild-type cells. Moreover, the activation of TLR2 increases the MC recruitment at the skin barrier interface. Taken together, our findings reveal that the expression and control of antimicrobial peptides and TLR signaling on MCs are key in fighting viral infection. Our findings also provide new insights into the pathogenesis of skin infections and suggest potential roles for MCs and TLR2 ligands in antiviral therapy.

Skin mast cells protect mice against vaccinia virus by triggering mast cell receptor S1PR2 and releasing antimicrobial peptides

Mast cells (MCs) are well-known effectors of allergic reactions and are considered sentinels in the skin and mucosa. In addition, through their production of cathelicidin, MCs have the capacity to oppose invading pathogens. We therefore hypothesized that MCs could act as sentinels in the skin against viral infections using antimicrobial peptides. In this study, we demonstrate that MCs react to vaccinia virus (VV) and degranulate using a membrane-activated pathway that leads to antimicrobial peptide discharge and virus inactivation. This finding was supported using a mouse model of viral infection. MC-deficient (Kit(wsh-/-)) mice were more susceptible to skin VV infection than the wild type animals, whereas Kit(wsh-/-) mice reconstituted with MCs in the skin showed a normal response to VV. Using MCs derived from mice deficient in cathelicidin antimicrobial peptide, we showed that antimicrobial peptides are one important antiviral granule component in in vivo skin infections. In conclusion, we demonstrate that MC presence protects mice from VV skin infection, MC degranulation is required for protecting mice from VV, neutralizing Ab to the L1 fusion entry protein of VV inhibits degranulation apparently by preventing S1PR2 activation by viral membrane lipids, and antimicrobial peptide release from MC granules is necessary to inactivate VV infectivity.

Plasmacytoid dendritic cells sense skin injury and promote wound healing through type I interferons

Cutaneous injury in mice drives transient TLR7- and TLR9-mediated production of type I interferon by plasmacytoid dendritic cells, which is required for re-epithelialization of the skin.

Plasmacytoid dendritic cells (pDCs) are specialized type I interferon (IFN-α/β)–producing cells that express intracellular toll-like receptor (TLR) 7 and TLR9 and recognize viral nucleic acids in the context of infections. We show that pDCs also have the ability to sense host-derived nucleic acids released in common skin wounds. pDCs were found to rapidly infiltrate both murine and human skin wounds and to transiently produce type I IFNs via TLR7- and TLR9-dependent recognition of nucleic acids. This process was critical for the induction of early inflammatory responses and reepithelization of injured skin. Cathelicidin peptides, which facilitate immune recognition of released nucleic acids by promoting their access to intracellular TLR compartments, were rapidly induced in skin wounds and were sufficient but not necessary to stimulate pDC activation and type I IFN production. These data uncover a new role of pDCs in sensing tissue damage and promoting wound repair at skin surfaces.

Immunotherapy for melanoma: current status and perspectives

Immunotherapy is an important modality in the therapy of patients with malignant melanoma. As our knowledge about this disease continues to expand, so does the immunotherapeutic armamentarium. Nevertheless, successful preclinical models do not always translate into clinically meaningful results. The authors give a comprehensive analysis of most recent advances in the immune anti-melanoma therapy, including interleukins, interferons, other cytokines, adoptive immunotherapy, biochemotherapy, as well as the use of different vaccines. We also present the fundamental concepts behind various immune enhancement strategies, passive immunotherapy, as well as the use of immune adjuvants. This review brings into discussion the results of newer and older clinical trials, as well as potential limitations and drawbacks seen with the utilization of various immune therapies in malignant melanoma. Development of novel therapeutic approaches, along with optimization of existing therapies, continues to hold a great promise in the field of melanoma therapy research. Use of anti-CTLA4 and anti-PD1 antibodies, realization of the importance of co-stimulatory signals, which translated into the use of agonist CD40 monoclonal antibodies, as well as activation of innate immunity through enhanced expression of co-stimulatory molecules on the surface of dendritic cells by TLR agonists are only a few items on the list of recent advances in the treatment of melanoma. The need to engineer better immune interactions and to boost positive feedback loops appear crucial for the future of melanoma therapy, which ultimately resides in our understanding of the complexity of immune responses in this disease.

Activation of TLR2 by a small molecule produced by Staphylococcus epidermidis increases antimicrobial defense against bacterial skin infections

Production of antimicrobial peptides by epithelia is an essential defense against infectious pathogens. In this study we evaluated whether the commensal microorganism Staphylococcus epidermidis may enhance production of antimicrobial peptides by keratinocytes and thus augment skin defense against infection. Exposure of cultured undifferentiated human keratinocytes to a sterile nontoxic small molecule of <10 kDa from S. epidermidis conditioned culture medium (SECM), but not similar preparations from other bacteria, enhanced human beta-defensin 2 (hBD2) and hBD3 mRNA expression and increased the capacity of cell lysates to inhibit the growth of group A Streptococcus (GAS) and S. aureus. Partial gene silencing of hBD3 inhibited this antimicrobial action. This effect was relevant in vivo as administration of SECM to mice decreased susceptibility to infection by GAS. Toll-like receptor 2 (TLR2) was important to this process as a TLR2-neutralizing antibody blocked induction of hBDs 2 and 3, and Tlr2-deficient mice did not show induction of mBD4. Taken together, these findings reveal a potential use for normal commensal bacterium S. epidermidis to activate TLR2 signaling and induce antimicrobial peptide expression, thus enabling the skin to mount an enhanced response to pathogens.

Commensal bacteria regulate Toll-like receptor 3-dependent inflammation after skin injury

The normal microflora of the skin includes staphylococcal species that will induce inflammation when present below the dermis but are tolerated on the epidermal surface without initiating inflammation. Here we reveal a previously unknown mechanism by which a product of staphylococci inhibits skin inflammation. This inhibition is mediated by staphylococcal lipoteichoic acid (LTA), and acts selectively on keratinocytes triggered through Toll-like receptor (TLR) 3. The significance of this is seen by observations that TLR3 activation is required for normal inflammation after injury, and that keratinocytes require TLR3 to respond to RNA from damaged cells with the release of inflammatory cytokines. Staphylococcal LTA inhibits both inflammatory cytokine release from keratinocytes and inflammation triggered by injury through a TLR2-dependent mechanism. These findings show for the first time that the skin epithelium requires TLR3 for normal inflammation after wounding and that the microflora can modulate specific cutaneous inflammatory responses.

Collagen synthesis is suppressed in dermal fibroblasts by the human antimicrobial peptide LL-37

LL-37 is a human cathelicidin antimicrobial peptide that is released in the skin after injury and acts to defend against infection and modulate the local cellular immune response. We observed in human dermal keloids that fibrosis was inversely related to the expression of cathelicidin and sought to determine how LL-37 influenced expression of types I and III collagen genes in dermal fibroblasts. At nano-molar concentrations, LL-37 inhibited baseline and transforming growth factor-beta-induced collagen expression. At these concentrations, LL-37 also induced phosphorylation of extracellular signal-regulated kinase (ERK) within 30 minutes. Activation of ERK, and the activation of a G-protein-dependent pathway, was essential for inhibition of collagen expression as pertussis toxin or an inhibitor of ERK blocked the inhibitory effects of LL-37. c-Jun N-terminal kinase and p38 mitogen-activated protein kinase inhibitors did not alter the effects of cathelicidin. Silencing of the Ets-1 reversed inhibitory effects of LL-37. Taken together, these findings show that LL-37 can directly act on dermal fibroblasts and may have antifibrotic action during the wound repair process.

Mast cell cathelicidin antimicrobial peptide prevents invasive group A Streptococcus infection of the skin

Mast cells (MC) express cathelicidin antimicrobial peptides that act as broad-spectrum antibiotics and influence the immune defense of multiple epithelial surfaces. We hypothesized that MC help protect against skin infection through the expression of cathelicidin. The susceptibility of MC-deficient mice (Kit Wsh(-/-)) to invasive group A streptococcus (GAS) was compared with control mice. Following s.c. injection of GAS, MC-deficient mice had 30% larger skin lesions, 80% more lesional bacteria, and 30% more spleens positive for bacteria. In contrast to results obtained when GAS was injected into skin, no significant differences were noted between MC-deficient mice and control mice after GAS was applied topically, indicating that MC activity is most important after barrier penetration. To determine whether these differences were due to MC expression of cathelicidin, MC-deficient mice were reconstituted with MC derived from either wild-type or cathelicidin-deficient (Camp(-/-)) mice and challenged with GAS. Forty-eight hours after bacterial injection, mice that did not receive MC had an average lesion size of 200 mm(2), mice reconstituted with wild-type MC showed lesions comparable to control mice (25 mm(2)), while mice reconstituted with Camp(-/-) MC showed an average lesion size of 120 mm(2). Surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) analysis of cathelicidin peptide purified from mast cells defined this as a unique 28-aa peptide. Combined, these results show that MC confer defense against Gram-positive bacterial infection in the skin, a function mediated in part by the expression of a unique cathelicidin peptide.

Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea

Acne rosacea is an inflammatory skin disease that affects 3% of the US population over 30 years of age and is characterized by erythema, papulopustules and telangiectasia. The etiology of this disorder is unknown, although symptoms are exacerbated by factors that trigger innate immune responses, such as the release of cathelicidin antimicrobial peptides. Here we show that individuals with rosacea express abnormally high levels of cathelicidin in their facial skin and that the proteolytically processed forms of cathelicidin peptides found in rosacea are different from those present in normal individuals. These cathelicidin peptides are a result of a post-translational processing abnormality associated with an increase in stratum corneum tryptic enzyme (SCTE) in the epidermis. In mice, injection of the cathelicidin peptides found in rosacea, addition of SCTE, and increasing protease activity by targeted deletion of the serine protease inhibitor gene Spink5 each increases inflammation in mouse skin. The role of cathelicidin in enabling SCTE-mediated inflammation is verified in mice with a targeted deletion of Camp, the gene encoding cathelicidin. These findings confirm the role of cathelicidin in skin inflammatory responses and suggest an explanation for the pathogenesis of rosacea by demonstrating that an exacerbated innate immune response can reproduce elements of this disease.

Recognition of hyaluronan released in sterile injury involves a unique receptor complex dependent on Toll-like receptor 4, CD44, and MD-2

Inflammation under sterile conditions is not well understood despite its importance in trauma and autoimmune disease. To investigate this process we established mouse models of sterile injury and explored the role of hyaluronan in mediating inflammation following injury. The response of cultured monocytes to hyaluronan was different than the response to lipopolysaccharide (LPS) despite both being dependent on Toll-like receptor 4 (TLR4). Cultured cells exposed to hyaluronan showed a pattern of gene induction that mimics the response seen in mouse skin after sterile injury with an increase in molecules such as transforming growth factor-beta2 and matrix metalloproteinase-13. These factors were not induced by LPS despite the mutual dependence of both hyaluronan and LPS on TLR4. Explanation for the unique response to hyaluronan was provided by observations that a lack of TLR4 or CD44 in mice diminished the response to sterile injury, and together with MD-2, was required for responsiveness to hyaluronan in vitro. Thus, a unique complex of TLR4, MD-2, and CD44 recognizes hyaluronan. Immunoprecipitation experiments confirmed the physical association of TLR4 and CD44. Taken together, our results define a previously unknown mechanism for initiation of sterile inflammation that involves recognition of released hyaluronan fragments as an endogenous signal of tissue injury.

Cathelicidin Antimicrobial Peptides Block Dendritic Cell TLR4 Activation and Allergic Contact Sensitization

Cathelicidins are antimicrobial peptides of the innate immune system that establish an antimicrobial barrier at epithelial interfaces and have been proposed to have a proinflammatory function. We studied the role of cathelicidin in allergic contact dermatitis, a model requiring dendritic cells of the innate immune response and T cells of the adaptive immune response. Deletion of the murine cathelicidin gene Cnlp enhanced an allergic contact response, whereas local administration of cathelicidin before sensitization inhibited the allergic response. Cathelicidins inhibited TLR4 but not TLR2 mediated induction of dendritic cell maturation and cytokine release, and this inhibition was associated with an alteration of cell membrane function and structure. Further analysis in vivo connected these observations because inhibition of sensitization by exogenous cathelicidin was dependent on the presence of functional TLR4. These observations provide evidence that cathelicidin antimicrobial peptides mediate an anti-inflammatory response in part by their activity at the membrane.

Augmentation of cutaneous immune responses by ATP gamma S: purinergic agonists define a novel class of immunologic adjuvants

Extracellular nucleotides activate ligand-gated P2XR ion channels and G protein-coupled P2YRs. In this study we report that intradermal administration of ATPgammaS, a hydrolysis-resistant P2 agonist, results in an enhanced contact hypersensitivity response in mice. Furthermore, ATPgammaS enhanced the induction of delayed-type hypersensitivity to a model tumor vaccine in mice and enhanced the Ag-presenting function of Langerhans cells (LCs) in vitro. Exposure of a LC-like cell line to ATPgammaS in the presence of LPS and GM-CSF augmented the induction of I-A, CD80, CD86, IL-1beta, and IL-12 p40 while inhibiting the expression of IL-10, suggesting that the immunostimulatory activities of purinergic agonists in the skin are mediated at least in part by P2Rs on APCs. In this regard, an LC-like cell line was found to express mRNA for P2X(1), P2X(7), P2Y(1), P2Y(2), P2Y(4), P2Y(9), and P2Y(11) receptors. We suggest that ATP, when released after trauma or infection, may act as an endogenous adjuvant to enhance the immune response, and that P2 agonists may augment the efficacy of vaccines.

Structure-function relationships among human cathelicidin peptides: dissociation of antimicrobial properties from host immunostimulatory activities

Cathelicidins and other antimicrobial peptides are deployed at epithelial surfaces to defend against infection. These molecules have broad-spectrum killing activity against microbes and can have effects on specific mammalian cell types, potentially stimulating additional immune defense through direct chemotactic activity or induction of cytokine release. In humans, the cathelicidin hCAP18/LL-37 is processed to LL-37 in neutrophils, but on skin it can be further proteolytically processed to shorter forms. The influence of these cathelicidin peptides on keratinocyte function is not known. In the current study, DNA microarray analysis and confirmatory protein analysis showed that LL-37 affects the expression of several chemokines and cytokines by keratinocytes. Analysis of a synthetic peptide library derived from LL-37 showed that antimicrobial activity against bacterial, fungal, and viral skin pathogens resides within specific domains of the parent peptide, but antimicrobial activity does not directly correlate with the ability to stimulate IL-8 production in keratinocytes. IL-8 release was induced by d- and l-amino acid forms of cathelicidin and correlated with membrane permeability, suggesting that highly structure-specific binding to a cell surface receptor is not likely. However, this effect was inhibited by either pertussis toxin or AG1478, an epidermal growth factor receptor tyrosine kinase inhibitor, suggesting that cathelicidin may indirectly stimulate multiple signaling pathways associated with cell surface receptors. Taken together, these observations suggest that proteolytic processing may alter the balance between cathelicidin antimicrobial and host immunostimulatory functions.

Keratinocytes store the antimicrobial peptide cathelicidin in lamellar bodies

Innate immune defense against microbial pathogens occurs by physical barriers, by recruitment of cells such as neutrophils, NK cells, and macrophages, and by secretion of molecules with antimicrobial activity. Such molecules are produced by various epithelia including skin. The importance of antimicrobial peptides has been shown in cathelicidin-deficient mice, which have increased susceptibility to skin infection by Streptococcus. Although keratinocytes increase cathelicidin expression upon injury, their role relative to neutrophil cathelicidin and their sites of peptide storage and activation have not been elucidated. Herein, it is reported that cathelicidin predominantly resides in granules of the superficial epidermis and partially localizes in lamellar bodies as determined by immunogold electron microscopy and immunoblot of lamellar bodies isolated from mice. In cultured keratinocytes, cathelicidin displays a granular distribution and partially localizes within the Golgi apparatus. Cathelicidin processing can be observed by western blot analysis in keratinocyte extracts but not in conditioned media. Further, fluorescent bacteria colocalize with cathelicidin in granules both intracellularly and at the cell surface. These observations illustrate the immune defense potential of keratinocytes acting directly through storage and processing of antimicrobial peptides.

Is JPEG compression of videomicroscopic images compatible with telediagnosis? Comparison between diagnostic performance and pattern recognition on uncompressed TIFF images and JPEG compressed ones

Early melanoma diagnosis is an important goal for dermatologists. Polarized light systems are increasingly employed for dermatoscopic diagnosis of melanocytic lesions. For the purpose of teledermoscopy, whose importance is increasingly growing for consultation and teaching purposes, it is of utmost importance to establish whether, after compression, polarized light images maintain their informativeness. The aim of our study was to check the effects of compression on melanocytic lesion images acquired by means of a digital videomicroscope on the identification of morphological details of the image and on diagnostic accuracy. A total of 170 50-fold-magnified pigmented skin lesion images, acquired in Tagged Image File Format (TIFF) by a digital videomicroscope, were compressed using Joint Photographic Experts Group (JPEG) algorithms (compression factor 30). Two experts in videomicroscopy evaluated both original and compressed images twice by describing single lesion features and expressing a diagnosis. Reproducibility in the assessment of dermoscopic parameters and observer performance were studied by kappa statistics and Receiver Operating Characteristic (ROC) analysis. Both intra- and interobserver reproducibility in the assessment of morphological details were higher when TIFF images were considered, indicating a better image quality. Nonetheless, there was no significant difference in the diagnostic accuracy between uncompressed images and compressed ones, although the intraobserver reproducibility in the diagnostic judgement was higher for uncompressed images. Despite loss in image details, factor 30 compressed videomicroscopic images enable a good diagnostic accuracy.

De novo ceramide synthesis participates in the ultraviolet B irradiation-induced apoptosis in undifferentiated cultured human keratinocytes

Ultraviolet irradiation is a major environmental cause of skin cancers, whereas ultraviolet-induced DNA repair and apoptosis are defense mechanisms that rescue and/or protect keratinocytes from this risk. Multiple pathways are involved in ultraviolet-induced keratinocyte apoptosis, including activation of p38-mitogen-activated protein kinase, protein kinase C, and CD95, each of which are associated with caspase activation. Alternatively, ceramides could serve as ultraviolet-induced, second messenger lipids, because they induce cell cycle arrest and apoptosis in a variety of cell types, including keratinocytes. We investigated the role of ceramide versus caspase, and the responsible pathway for ceramide generation in ultraviolet B-induced apoptosis of cultured normal human keratinocytes maintained in low calcium (0.07 mm) medium. Ultraviolet B (40 mJ per cm2) significantly inhibited cultured normal human keratinocyte proliferation, assessed as [3H-methyl]thymidine-thymidine incorporation into DNA, 2 h after irradiation. Terminal nick deoxynucleotide end-labeling-positive apoptotic cells (14.8% at 24 h and 34.4% at 48 h) and trypan blue-positive apoptotic cells (8.4% at 24 h and 28.6% at 48 h) became evident in a time-dependent manner after ultraviolet B irradiation, in parallel with activation of caspase-3. The ceramide content of irradiated cultured normal human keratinocytes increased significantly by 8 h, whereas glucosylceramide only modestly increased, and sphingomyelin content remained unaltered. Metabolic studies with radiolabeled serine, palmitic acid, and phosphorylcholine revealed that the ultraviolet B-induced increase in ceramide results primarily from increased de novo synthesis rather than accelerated sphingomyelin hydrolysis. Increased ceramide synthesis, in turn, could be attributed to increased activity of ceramide synthase (i.e., 1.7-fold increase 8 h after ultraviolet B irradiation), whereas serine palmitoyltransferase activity did not change. Both fumonisin B1, an inhibitor of ceramide synthase, and ISP-1, myriocin an inhibitor of serine palmitoyltransferase, significantly attenuated the ultraviolet B-induced apoptosis in a caspase-3-independent fashion, whereas co-incubation with a caspase-3 inhibitor (Ac-DEVD-chloromethyl-ketone) further attenuated the ultraviolet B-induced apoptosis. Thus, increased de novo ceramide synthesis signals ultraviolet B-induced apoptosis, by a pathway independent of, but in concert with, caspase-3 activation.

Cutting edge: mast cell antimicrobial activity is mediated by expression of cathelicidin antimicrobial peptide

Cathelicidins (caths) are peptides that are expressed at high levels in neutrophils and some epithelia and can act as natural antibiotics by directly killing a wide range of microorganisms. We hypothesized that caths are expressed in mast cells (MCs), because these cells have been previously associated with inherent antimicrobial activity. Cultured murine MCs contained abundant amounts of cathelin-related antimicrobial peptide (AMP), the murine cath, and this expression was inducible by LPS or lipoteichoic acid. Human skin MCs also expressed cath as detected by immunohistochemical analysis for the human cath LL-37. The functional significance of this expression was shown by comparing MCs cultured from normal mice to MCs from littermates deficient in the cathelin-related AMP gene (Cnlp(-)). MCs derived from Cnlp(-/-) animals had a 50% reduction in their ability to kill group A STREPTOCOCCUS: These MCs expressed equivalent amounts of mRNA for murine beta-defensin-4, a beta-defensin AMP. Thus, different antimicrobials can be identified in MCs, and the presence of cath is necessary for efficient bacterial killing. These observations suggest that the presence of cath is vital to the ability of mammalian MCs to participate in antimicrobial defense.