Dysregulation of CD36 upon TLR-2 stimulation in monocytes from patients with atopic dermatitis and the TLR2 R753Q polymorphism

Toll-like receptors in atopic dermatitis: pathogenesis and therapeutic implications

Toll-like receptors (TLR), the key players of the innate immune system, contribute to the pathogenesis of atopic dermatitis (AD) through multiple pathways. TLRs play a crucial role in delaying barrier repair, promoting Th2-mediated dermatitis, shifting the response toward Th1 in the chronic phase, and contributing to the establishment of the itch-scratch cycle, as well as mediating the effects of UV radiation. The dysregulation of proinflammatory and immunomodulatory effects of TLRs can be attributed to their ligand structures, receptor heterodimerization, the relative frequency of each TLR, interactions with other receptors/signalling pathways, cytokine milieu, and genetic polymorphisms. Current AD treatments like vitamin-D analogs, tacrolimus, and cyclosporine partially work through TLR modulation. Direct TLR stimulation using different compounds has shown therapeutic benefits in preclinical studies. However, significant challenges exist, including off-target effects due to ubiquitous TLR expression and complex roles in immune responses. Future directions include CRISPR-based gene editing to understand TLR functions, development of specific TLR modulators for targeted therapy, and machine learning applications to predict drug responses and identify novel ligands. Patient heterogeneity, including the presence or absence of polymorphisms, variations in TLR expression levels, and differences in immune responses, underscores the need for personalized therapeutic approaches.

Assessment of changes in genetic transcriptome in nasal epithelial cells exposed to ozone-aged black carbon and pollen allergen by high-throughput transcriptomics

Background

Air pollution may be associated with increased airway responsiveness to allergens in allergic rhinitis (AR). Ozone-aged environmental black carbon (O₃BC) is an important constituent of atmospheric particulate matter (PM), for which the mechanisms underlying its effects have not been fully elucidated in AR. The objective of the present study was to determine the O₃BC and pollen-induced alterations in the transcriptome in human nasal epithelial cells (hNECs) in vitro.

Methods

hNECs from nasal epithelial mucosal samples of healthy individuals undergoing nasal surgery (turbinoplasty or septoplasty) were established as air–liquid interface (ALI) cultures and exposed to O₃BC, pollen, or a combination of O₃BC+ pollen. Changes in cell viability were analyzed by fluorescence and changes in the transcriptome by high-throughput RNA sequencing (RNA-seq). Several differentially expressed genes were verified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Enrichment analysis, based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) database, was performed to determine major biological functions and pathways involved.

Results

Exposure to ≥ 50 μg/ml O₃BC or 25 μg/ml O₃BC+ 200 μg /ml pollen significantly decreased cell viability of the hNECs compared to control (p < 0.05) or 25 μg/ml O₃BC alone (p < 0.05); whereas exposure to pollen alone did not alter cell viability at any concentration investigated. High-throughput RNA sequencing analysis indicated that there was significant difference in gene expression between pollen or O₃BC alone and O₃BC+ pollen exposed cells. Exposure to 200 μg/ml O₃BC was associated with hypoxia stress response GO terms, whereas exposure to 25 μg/ml O₃BC+ 200 μg/ml pollen was associated with inflammatory response GO terms; including regulation of neutrophil migration and chemotaxis, macrophage differentiation and chemotaxis, mast cell activation, and phagocytosis. KEGG pathway analysis indicated the top 10 upstream regulators to be IL1B, CSF1, CCL2, TLR2, LPL, IGF8, SPP1, CXCL8, FCER1G and IL1RN; of which expressions of inflammation-related genes IL1B, CSF1 and FCER1G were significantly increased.

Conclusion

O₃BC and pollen allergen combined exposure may induce innate immune and allergic inflammation in hNECs, and therefore potentially exacerbate the symptoms of AR in affected individuals.

Tet38 of Staphylococcus aureus Binds to Host Cell Receptor Complex CD36-Toll-Like Receptor 2 and Protects from Teichoic Acid Synthesis Inhibitors Tunicamycin and Congo Red

Using an affinity column retention assay, we showed that the purified Tet38 membrane transporter of Staphylococcus aureus bound specifically to host cell CD36 and to the complex CD36-Toll-like receptor 2 (TLR-2), but not to TLR-2 alone or TLR-2 and S. aureus lipoteichoic acid (LTA). We tested the effect of LTA on the internalization of S. aureus tet38 mutant QT7 versus RN6390 by A549 epithelial cells. Addition of anti-LTA antibody to the bacteria prior to adding to A549 cells reduced internalization of QT7 2-fold compared to that with nonspecific antibody treatment. QT7 internalized 4- to 6-fold less than RN6390 with or without anti-LTA antibody. These data suggested that Tet38 and LTA were independently involved in the invasion process. The wall teichoic acid (WTA) inhibitor tunicamycin had an 8-fold decrease in activity with overexpression of tet38 and a 2-fold increase in activity in QT7 (tet38). Reserpine (an inhibitor of efflux pumps) reduced the effect of tet38 overexpression on tunicamycin resistance 4-fold. In addition, tet38 affected growth in the presence of LTA inhibitor Congo red, with overexpression increasing growth and deletion of tet38 reducing growth. In conclusion, Tet38 contributes to S. aureus invasion of A549 via direct binding to CD36 of the complex CD36-TLR-2, and LTA independently bound to TLR-2. The reduction of tunicamycin resistance in the presence of reserpine and the survival ability of the tet38 overexpressor in the presence of Congo red suggest that Tet38 can also protect the synthesis of LTA and WTA in S. aureus against their inhibitors, possibly functioning as an efflux pump.

Immunologic Targets in Atopic Dermatitis and Emerging Therapies: An Update

Atopic dermatitis is one of the most common chronic inflammatory skin diseases. It usually begins in childhood, has a considerable impact on patients' quality of life, and incurs substantial healthcare costs. The standard-of-care treatments for patients with moderate to severe disease are very limited and have variable and typically insufficient efficacy and many side effects, some of which are quite serious. However, over the last decade, considerable advances in our understanding of the pathogenesis of atopic dermatitis have paved the way for a number of new treatments. Most notable are the drugs that target the Th2-polarized immune system, which is thought to play a key role in many of the signs and symptoms characteristic of this disease. In this article, we briefly review the pathophysiology of atopic dermatitis, while noting that each patient's disease phenotype is likely due to a unique interplay of several disease-specific dysregulated pathways. Lastly, we cover emerging therapies for atopic dermatitis, focusing on those that target specific components of the immune system, which are altered in atopic dermatitis. The hope is that these new biologics or small-molecule antagonists, which have high specificity for their target molecules, will decrease the undesirable side effects caused by off-target effects commonly observed with current immunosuppressive agents that are characterized by broad biological actions.

Molecular Mechanisms of Cutaneous Inflammatory Disorder: Atopic Dermatitis

Atopic dermatitis (AD) is a multifactorial inflammatory skin disease resulting from interactions between genetic susceptibility and environmental factors. The pathogenesis of AD is poorly understood, and the treatment of recalcitrant AD is still challenging. There is accumulating evidence for new gene polymorphisms related to the epidermal barrier function and innate and adaptive immunity in patients with AD. Newly-found T cells and dendritic cell subsets, cytokines, chemokines and signaling pathways have extended our understanding of the molecular pathomechanism underlying AD. Genetic changes caused by environmental factors have been shown to contribute to the pathogenesis of AD. We herein present a review of the genetics, epigenetics, barrier dysfunction and immunological abnormalities in AD with a focus on updated molecular biology.

Impaired Toll-like receptor 2-mediated Th1 and Th17/22 cytokines secretion in human peripheral blood mononuclear cells from patients with atopic dermatitis

BACKGROUND

Impaired Toll-like receptor 2 (TLR2) function has been associated with the pathogenesis of atopic dermatitis (AD). However, there are only few studies reporting on the TLR2-induced immunological responses of circulating leucocytes of AD patients. We thus investigated the expression and secretion of Th1, Th2 and Th17/22 cytokines triggered by TLR2 ligands in human peripheral blood mononuclear cells (PBMCs) from AD patients. Expression of TLR2, 1, 6 and high-affinity receptor for IgE (FcεRI) were further investigated to evaluate the outcome of immune response in AD.

METHODS

Expression of TLR2, 1, 6 and FcεRI in PBMCs from AD patients and healthy individuals were measured by qPCR. Subsequent to stimulation with TLR2 ligands PGN and Pam3CSK4, expression and secretion of Th1, Th2 and Th17/22 cytokines were investigated by qPCR and ELISA.

RESULTS

The levels of TLR2, 1, 6 mRNA were not altered in both groups of subjects while that of FcεRI was increased in AD patients. Subsequent to the activation by TLR2 ligands, PBMCs from AD patients significantly released less IFN-γ, IL-17F and IL-22 than those from healthy controls while no detectable level of release was observed with the other cytokines. In contrast, significantly higher levels of mRNA expression for TNF-α, IL5, IL-17A and IL-22 were observed in TLR2 activated PBMCs of AD patients than those of healthy control.

CONCLUSIONS

PBMCs from AD patients are defective in the secretion of Th1 and Th17/22 cytokines in response to TLR2 ligands. The inconsistent increased expression of the mRNA for the corresponding Th1 cytokines and the Th2 cytokines IL-5 suggested that there may be alterations of downstream signaling events in the cytokine release mechanisms of PBMCs that are associated with the development of AD.

Molecular biology of atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with specific genetic and immunological mechanisms. The rapid development of new techniques in molecular biology had ushered in new discoveries on the role of cytokines, chemokines, and immune cells in the pathogenesis of AD. New polymorphisms of AD are continually being reported in different populations. The physical and immunological barrier of normal intact skin is an important part of the innate immune system that protects the host against microbials and allergens that are associated with AD. Defects in the filaggrin gene FLG may play a role in facilitating exposure to allergens and microbial pathogens, which may induce Th2 polarization. Meanwhile, Th22 cells also play roles in skin barrier impairment through IL-22, and AD is often considered to be a Th2/Th22-dominant allergic disease. Mast cells and eosinophils are also involved in the inflammation via Th2 cytokines. Release of pruritogenic substances by mast cells induces scratching that further disrupts the skin barrier. Th1 and Th17 cells are mainly involved in chronic phase of AD. Keratinocytes also produce proinflammatory cytokines such as thymic stromal lymphopoietin (TSLP), which can further affect Th cells balance. The immunological characteristics of AD may differ for various endotypes and phenotypes. Due to the heterogeneity of the disease, and the redundancies of these mechanisms, our knowledge of the pathophysiology of the disease is still incomplete, which is reflected by the absence of a cure for the disease.

Activation of innate immunity by bacterial ligands of toll-like receptors

Tγδ and B1 lymphocytes are essential components of the mucosal immune system, activated directly by different bacterial and viral ligands without additional costimulatory signals and preprocessing of other immune effectors. This ability enables the immune system to provide rapid protection against pathogens and contributes to the decoding mechanism of the sensitizing activity of mucosal antigens. The early interaction of these cells results in the production of antibodies of immunoglobulin M (IgM) and IgA isotypes, but not immunoglobulin E (IgE). We studied the subcutaneous, intranasal, and oral delivery as three major routes of potential entry for antigens of opportunistic microorganisms, using the immunomodulator Immunovac-VP-4, which is able to activate Tγδ and B1 lymphocytes. The subcutaneous and intranasal routes produced a significant increase of these cells in lymph nodes associated with the nasal cavity (NALT) and in those associated with bronchial tissue (BALT). The oral route significantly increased levels of these cells in the spleen, in NALT, BALT, and in nodes associated with the gut (GALT). We found that mucosal application of Immunovac-VP-4, which contains antigens of conditionally pathogenic microorganisms, in conjunction with the activation of Tγδ and B1, induces adaptive immune mechanisms not only in the lymphoid formations associated with the respiratory system and with GALT, but also in the spleen [increased expression of cluster of differentiation 3 (CD3), CD4, CD8, CD19, and CD25]. This indicates that there is migration of lymphoid cells from the regional lymph nodes and mucosal lymphoid tissues via the lymph and blood to distant organs, resulting in lymphoid development, and both local and systemic immunity. Mucosal application of Immunovac-VP-4 in mice potentiates the cytotoxic activity of NK cells in the NALT, BALT, and GALT. The highest cytotoxicity was observed in cells, derived from lymphoid tissue of the intestine after oral immunization. Although we found that cytokine production was increased by all three immunization routes, it was most intensive after subcutaneous injection. Our findings confirm that there is an intensive exchange of lymphocytes not only between lymphoid formations in the mucous membranes of the respiratory tract and of GALT, but also with the spleen, which means that if effective mucosal vaccines are developed, they can induce both local and systemic immunity.

The cutaneous innate immune response in patients with atopic dermatitis

Orchestrating when and how the cutaneous innate immune system should respond to commensal or pathogenic microbes is a critical function of the epithelium. The cutaneous innate immune system is a key determinant of the physical, chemical, microbial, and immunologic barrier functions of the epidermis. A malfunction in this system can lead to an inadequate host response to a pathogen or a persistent inflammatory state. Atopic dermatitis is the most common inflammatory skin disorder and characterized by abnormalities in both skin barrier structures (stratum corneum and tight junctions), a robust T(H)2 response to environmental antigens, defects in innate immunity, and an altered microbiome. Many of these abnormalities may occur as the consequence of epidermal dysfunction. The epidermis directly interfaces with the environment and, not surprisingly, expresses many pattern recognition receptors that make it a key player in cutaneous innate immune responses to skin infections and injury. This review will discuss the role epidermal innate receptors play in regulation of skin barriers and, where possible, discuss the relevance of these findings for patients with atopic dermatitis.

Insight into newly discovered innate immune modulation in atopic dermatitis

Atopic dermatitis (AD) is a highly pruritic, chronic relapsing inflammatory skin disease characterized by innate and adaptive immune reactions. In AD, innate immune mechanisms such as pattern recognition receptors and antimicrobial peptides have been investigated in detail, but recently, epidermis-derived cytokines, namely thymic stromal lymphopoietin (TSLP), IL-25 and IL-33, were shown to participate in innate immune reactions independently of adaptive immunity. In addition to conventional innate cells, such as mast cells, basophils and eosinophils, Th2 cytokine-producing invariant natural killer T (iNKT) cells, innate lymphoid cells (ILCs) and Th17/Th22 cytokine-producing innate cells - iNKT cells and natural killer (NK)-like cells - can participate in innate immune modulation in AD. Accordingly, early control of innate immune responses in AD before activation of adaptive immune responses by conventional T and B cells that perpetuate chronic skin inflammation may adequately alleviate acute exacerbations of AD. Therefore, we hypothesized that select immune modulators targeting the innate immune response could potentially be used for individualized treatment of AD.

Functional consequences of CD36 downregulation by TLR signals

TLR recognition activates the secretion of pro- and anti-inflammatory cytokines and it also modulates the expression of crucial molecules involved in phagocytosis and antimicrobial activity. Scavenger receptors can act as TLR co-receptors or facilitate antigen loading. However, it remains unknown whether TLR can modulate the expression of these scavenger receptors. We stimulated human peripheral blood mononuclear cells (PBMC) with TLR2 (Pam3CSK4 and FSL1) and TLR4 ligand lipopolysaccharide (LPS) and then analyzed CD36 expression on different monocyte subpopulations by flow cytometry. TLR2 and TLR4 ligands can downregulate CD36 on the surface of monocytes, guiding the protein to intracellular compartments. Even though TLR-activation induced TNFα, IL-10 and IL-6 production, only recombinant TNFα was able to downregulate CD36. Neutralizing anti-TNFα antibodies showed that the Pam3CSK4 and FSL1-induced downregulation was partially mediated by TNFα but not by IL-6 or IL-10. However, LPS-induced downregulation could have also been caused by direct TLR4 targeting and signaling, and/or mediated by other unknown factors. CD36 downregulation reduced the capability of monocytes to phagocyte apoptotic neutrophils. In conclusion, modulation of scavenger receptor expression by TLR targeting on monocytes has functional consequences. Characterization this complex regulation may help us to understand this innate response and develop specific therapeutic drugs for each mechanism.

Toll Like Receptors Signaling Pathways as a Target for Therapeutic Interventions

This review summarizes the key role of Toll-Like Receptor (TLRs) molecules for igniting the immune system. Activated by a broad spectrum of pathogens, cytokines or other specific molecules, TLRs trigger innate immune responses. Published data demonstrate that the targeting and suppression of TLRs and TLR-related proteins with particular inhibitors may provide pivotal treatments for patients with cancer, asthma, sepsis, Crohn's disease and thrombosis. Many drugs that target cytokines act in the late phases of the activated pathways, after the final peptides, proteins or glycoproteins are formed in the cell environment. TLR activity occurs in the early activation of cellular pathways; consequently inhibiting them might be most beneficial in the treatment of human diseases.

Combined occurrence of filaggrin mutations and IL-10 or IL-13 polymorphisms predisposes to atopic dermatitis

BACKGROUND

Although filaggrin mutations are presently believed to play a key role in the development of atopic dermatitis (AD), obviously also immunological factors involved in acquired immune response are important for the development of allergic inflammation.

OBJECTIVE

To assess the frequency of FLG mutations and the polymorphisms 590 C/T in the IL-4 gene, -1082A/G in the IL-10 gene and -1055C/T in the IL-13 gene in patients with AD and their correlations between severity of AD and asthma.

METHODS

R501X and 2282del4 FLG mutations and IL-4, IL-10 and IL-13 polymorphisms were assayed in 163 patients with AD of Polish origin.

RESULTS

In the Polish patients with AD, the prevalence of FLG mutations was higher in patients with AD than in the controls and 2282del4 FLG mutation was more frequent than R501X, and it was associated with a 6-fold higher risk for AD development (P < 0.001; OR: 5.76), moderate or severe disease course, early onset of asthma and palmar hyperlinearity. Significant interactions between the 2282del4 FLG mutation and the CT genotype for IL-13 or GG genotype for IL-10 and a higher risk for developing AD were demonstrated.

CONCLUSION

FLG mutation, alone and in combination with certain IL-10 or IL-13 polymorphisms, enhances the risk for the development of AD in the Polish population.