Mast Cell Activation Protects Cornea by Promoting Neutrophil Infiltration via Stimulating ICAM-1 and Vascular Dilation in Fungal Keratitis

Mast cells and ocular surface: An update review

Mast cells (MCs), traditionally viewed as key players in IgE-mediated allergic responses, are increasingly recognized for their versatile roles. Situated at critical barrier sites such as the ocular surface, these sentinel cells participate in a broad array of physiological and pathological processes. This review presents a comprehensive update on the immune pathophysiology of MCs, with a particular focus on the mechanisms underlying innate immunity. It highlights their roles at the ocular surface, emphasizing their participation in allergic reactions, maintenance of corneal homeostasis, neovascularization, wound healing, and immune responses in corneal grafts. The review also explores the potential of MCs as therapeutic targets, given their significant contributions to disease pathogenesis and their capacity to modulate immunity. Through a thorough examination of current literature, we aim to elucidate the immune pathophysiology and multifaceted roles of MCs in ocular surface health and disease, suggesting directions for future research and therapeutic innovation.

Unveiling the Web: Exploring the Multifaceted Role of Neutrophil Extracellular Traps in Ocular Health and Disease

Neutrophil extracellular traps (NETs) play an essential role in antimicrobial defense. However, NETs have also been shown to promote and mediate a wide spectrum of diseases, including cancer, diabetes mellitus, cardiovascular diseases, and ocular diseases. Data regarding NETs in ocular diseases remain limited. In physiological conditions, NETs protect the eye from debris and cleave proinflammatory cytokines, including several interleukins. On the other hand, NETs play a role in corneal diseases, such as dry eye disease and ocular graft-versus-host disease, where they promote acinar atrophy and delayed wound healing. Additionally, NET levels positively correlate with increased severity of uveitis. NETs have also been described in the context of diabetic retinopathy. Although increased NET biomarkers are associated with an increased risk of the disease, NETs also assist in the elimination of pathological blood vessels and the regeneration of normal vessels. Targeting NET pathways for the treatment of ocular diseases has shown promising outcomes; however, more studies are still needed in this regard. In this article, we summarize the literature on the protective roles of NETs in the eye. Then, we describe their pathogenetic effects in ocular diseases, including those of the cornea, uvea, and retinal blood vessels. Finally, we describe the therapeutic implications of targeting NETs in such conditions.

Wessely corneal ring phenomenon: An unsolved pathophysiological dilemma

The cornea is a densely innervated, avascular tissue showing exceptional inflammatory and immune responses. The cornea is a site of lymphangiogenic and angiogenic privilege devoid of blood and lymphatic vessels that limits the entry of inflammatory cells from the adjacent and highly immunoreactive conjunctiva. Immunological and anatomical differences between the central and peripheral cornea are also necessary to sustain passive immune privilege. The lower density of antigen-presenting cells in the central cornea and the 5:1 peripheral-to-central corneal ratio of C1 are 2 main features conferring passive immune privilege. C1 activates the complement system by antigen-antibody complexes more effectively in the peripheral cornea and, thus, protects the central corneas' transparency from immune-driven and inflammatory reactions. Wessely rings, also known as corneal immune rings, are non-infectious ring-shaped stromal infiltrates usually formed in the peripheral cornea. They result from a hypersensitivity reaction to foreign antigens, including those of microorganism origin. Thus, they are thought to be composed of inflammatory cells and antigen-antibody complexes. Corneal immune rings have been associated with various infectious and non-infectious causes, including foreign bodies, contact lens wear, refractive procedures, and drugs. We describe the anatomical and immunologic basis underlying Wessely ring formation, its causes, clinical presentation, and management.

Identification of hub genes and pathways of ferroptosis in Fusarium keratitis by bioinformatics methods

Background

Fungal keratitis is a common blinding eye disease, and Fusarium is one of the main species that cause fungal keratitis. As is well known, oxidative stress plays an important role in Fusarium keratitis and it is also a significant initiating factor of ferroptosis. But the relationship between Fusarium keratitis and ferroptosis is currently unclear. This study aimed to speculate and validate potential ferroptosis-related genes in Fusarium keratitis using bioinformatics analysis, which provided ideas for further research on its specific mechanism and new targets for its treatment.

Methods

The microarray expression profiling dataset (GSE58291) came from Gene Expression Omnibus (GEO). The differentially expressed genes (DEGs) were obtained by the limma package of the R software. The DEGs were performed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. Then, the DEGs were intersected with the genes in the ferroptosis database. The top 5 hub genes were obtained by the protein-protein interaction (PPI) network analysis and the cytoHubba plug-in of Cytoscape software. The hub genes were subjected to GSEA analysis. Then we analyzed the immune infiltration of the samples by CIBERSORT and ssGSEA algorithm. Finally, we validated the mRNA of hub genes by qPCR.

Results

A total of 1,368 DEGs were identified and 26 ferroptosis-related DEGs were obtained. At the same time, ferroptosis-related pathways were enriched by GO and KEGG using DEGs. HMOX1, CYBB, GPX2, ALOX5 and SRC were obtained by the PPI network analysis and the cytoHubba plug-in of Cytoscape software. The iron metabolism and immune response related pathways were enriched using GSEA. They included hematopoietic cell lineage, lysosome and FC gamma R mediated phagocytosis. T cells follicular helper, monocytes, macrophages and mast cells might play an important role in Fusarium keratitis using analysis of immune infiltration. Finally, qPCR confirmed that the expression of HMOX1, CYBB, ALOX5 mRNA in the DON group was significantly elevated, while the expression of GPX2 were significantly decreased.

Conclusions

Ferroptosis may play an important role in Fusarium keratitis. HMOX1, CYBB, ALOX5 and GPX2 may be key ferroptosis-related genes in the pathogenesis of Fusarium keratitis.

Macromolecules in polysorbate 80 for injection: an important cause of anaphylactoid reactions

Polysorbate 80 for injection (TW80) is a common excipient used for injection whose macromolecular impurities, including those that cause anaphylactoid reactions, are frequently ignored. The main aim of this study was to prove that the macromolecular impurities in the excipient are an important cause of anaphylactoid reactions. Component A (containing macromolecules > 100 kDa), Component B (containing macromolecules from 10 to 100 kDa), and Component C (containing substances < 10 kDa) were prepaired from the original TW80 using ultrafilters. The original TW80 contained numerous substances with molecular weights > 10kD. The original TW80 and Components A and B caused strong anaphylactoid reactions in both guinea pigs and rabbits by intravenous administration. Moreover, the original TW80 and Components A and B even caused strong passive cutaneous anaphylactoid (PCA) reactions and pulmonary capillary permeability. The PCA reaction and increased permeability were partly prevented by cromolyn sodium. Additionally, the original TW80 and Components A and B caused vasodilation and severe hemolysis in vitro. The anaphylactoid reactions were associated with histamine release but not with mast cell degranulation. Nevertheless, Component C almost caused no anaphylactoid reactions or hemolysis and was weaker in the few reactions that ocurred. Taken together, these results suggest that macromolecular substances are one of the main risk factors responsible for anaphylactoid reactions and hemolysis caused by TW80.

Candidalysin, a Virulence Factor of Candida albicans, Stimulates Mast Cells by Mediating Cross-Talk Between Signaling Pathways Activated by the Dectin-1 Receptor and MAPKs

PURPOSE

Although mast cells (MCs) modulate the activity of effector cells during Candida albicans infection, their role in the pathogenesis of candidiasis remains unclear. Candidalysin, a C. albicans-derived peptide toxin, is a crucial factor in fungal infections. We aimed to investigate the effect of candidalysin on MC activation and the underlying molecular mechanism.

METHODS

Serum from candidalysin-immunized mice was used to measure candidalysin expression in patients infected with C. albicans. MC degranulation and migration were evaluated by β-hexosaminidase release assay and chemotaxis assay, respectively. EIA and ELISA were used to evaluate the production of eicosanoids and cytokines/chemokines, respectively. The production of nitric oxide (NO) was measured with a DAF-FM diacetate kit, while reactive oxygen species (ROS) production was analyzed by flow cytometry. MAPK activation was evaluated by Western blotting.

RESULTS

We detected high candidalysin expression in the lesions of patients infected with C. albicans, and the MC number was increased in these lesions. LL-37 colocalized with MCs in the lesions of candidiasis patients. Candidalysin-enhanced MC accumulation in mice and treating LAD2 and HMC-1 cells with candidalysin induced their degranulation, migration, and production of pro- and anti-inflammatory cytokines/chemokines, eicosanoids, ROS, NO, and LL-37. Interestingly, C. albicans strains lacking candidalysin failed to induce MC activation. Moreover, candidalysin increased dectin-1 expression, and the inhibition of dectin-1 decreased MC activation. Downstream dectin-1 signaling involved the MAPK pathways.

CONCLUSION

The finding that candidalysin causes cutaneous MC activation may improve our understanding of the role of MCs in the pathology of cutaneous C. albicans infection.

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.

Immunologic mechanism of fungal keratitis

Fungal keratitis (FK) is a refractory disease that poses a serious threat to vision, with common risk factors like eye trauma, contact lens wearing, topical corticosteroids and antibiotic abuse. Nowadays, topical and systemic anti-fungal drugs and ocular surgeries are still the main therapeutic modalities. However, the pathogenesis of FK, especially the immunologic mechanism within it, has not yet been deeply clarified. A better understanding of the pathogenesis of FK is imperative for more effective therapies and prognosis. Meanwhile, the immune protection strategies are also urgently required to manage FK. This review highlights recent advances in the immunologic mechanism in the pathogenesis of FK, in hope of providing valuable reference information for more effective anti-fungal treatment.

Resident Innate Immune Cells in the Cornea

The cornea is a special interface between the internal ocular tissue and the external environment that provides a powerful chemical, physical, and biological barrier against the invasion of harmful substances and pathogenic microbes. This protective effect is determined by the unique anatomical structure and cellular composition of the cornea, especially its locally resident innate immune cells, such as Langerhans cells (LCs), mast cells (MCs), macrophages, γδ T lymphocytes, and innate lymphoid cells. Recent studies have demonstrated the importance of these immune cells in terms of producing different cytokines and other growth factors in corneal homeostasis and its pathologic conditions. This review paper briefly describes the latest information on these resident immune cells by specifically analyzing research from our laboratory.

Mast Cells Populate the Corneoscleral Limbus: New Insights for Our Understanding of Limbal Microenvironment

Purpose

Although stem cell activity represents a crucial feature in corneal and ocular surface homeostasis, other cells populating this region and the neighboring zones might participate and influence local microenvironment. Mast cells, the long-lived and tissue-sited immune cells, have been previously reported in corneoscleral specimens. Herein, mast cells were investigated in corneoscleral tissues and related to microenvironment protein expression.

Methods

Twenty-six (14 male/12 female; older than 60 years) human corneoscleral specimens were sectioned for light and fluorescent immunostaining (CD45, p63, Ck-3/7/12/19, tryptase/AA1, and chymase/CC1). Corneal, limbal, and conjunctival squares were produced for molecular and biochemical analysis. Statistical comparisons were carried out by ANOVA.

Results

Toluidine blue staining identified metachromatic intact or degranulated mast cells in the area below the palisades' Vogt (Ck-3/12-positive epithelium and underneath p63 immunoreactivity). Tryptase immunoreactivity was observed close to palisades' Vogt, whereas no specific signal was detected for chymase. Tryptase/AA1 transcripts were quantified in limbal and conjunctival RNA extracts, whereas no specific amplification was detected in corneal ones. Few mediators were overexpressed in limbal extracts with respect to corneal (Neural cell adhesion molecule (NCAM), Intercellular adhesion molecule 3 (ICAM3), Brain-derived Neurotrophic factor (BDNF), and neurotrophin 3 (NT3); P < 0.00083) and conjunctival (NCAM, ICAM3, and NT3; P < 0.05) protein extracts. A trend to an increase was observed for Nerve Growth Factor (NGF) in limbal extracts (P > 0.05).

Conclusions

The specific observation of tryptase phenotype and the interesting protein signature of microenvironment (adhesion molecules, growth factors, and neurotrophins), known to partake mast cell behavior, at least in other areas, would provide additional information to better understand this crucial zone in the framework of ocular surface healthiness.

NR4A1 regulates cerebral ischemia-induced brain injury by regulating neuroinflammation through interaction with NF-κB/p65

Stroke is reported as a leading cause of mortality and disability in the world. Neuroinflammation is significantly induced responding to ischemic stroke, and this process is accompanied with microglial activation. However, the pathogenesis contributing to ischemic stroke remains unclear. NR4A1 (Nur77) is a nuclear receptor that is expressed in macrophages, playing a significant role in regulating inflammatory response. In the present study, we attempted to explore the effects of NR4A1 on ischemic stroke using in vivo and in vitro studies. Results suggested that NR4A1 expression in microglia was markedly increased after cerebral ischemic damage. Then, we found that NR4A1 knockout attenuated ischemia-triggered infarction volume and neuron injury. Also, cognitive impairments were improved in ischemic mice with NR4A1 deficiency, resulting in functional improvements. Moreover, M1 polarization in microglia and neutrophil recruitment was significantly alleviated by NR4A1 deletion, as evidenced by the reduced expression of M1 markers, chemokines, as well as intracellular adhesion molecule-1 (ICAM-1) and myeloperoxidase (MPO) levels. Importantly, we found that NR4A1 could interact with nuclear factor-κB (NF-κB)/p65 based on in vivo and in vitro results. Suppressing p65 activation by the use of its inhibitor clearly reduced the NR4A1 expression, M1 polarization and neutrophil recruitments, while rescued the expression of anti-inflammatory factors in microglia treated with oxygen-glucose deprivation (OGD). Therefore, NR4A1 suppression in microglia restrained neuroinflammation through interacting with NF-κB/p65 to attenuate ischemic stroke.

Small-Molecule Host-Defense Peptide Mimetic Antibacterial and Antifungal Agents Activate Human and Mouse Mast Cells via Mas-Related GPCRs

Host-defense peptides (HDPs) have an important therapeutic potential against microbial infections but their metabolic instability and cellular cytotoxicity have limited their utility. To overcome these limitations, we utilized five small-molecule, nonpeptide HDP mimetics (smHDPMs) and tested their effects on cytotoxicity, antimicrobial activity, and mast cell (MC) degranulation. None of the smHDPMs displayed cytotoxicity against mouse 3T3 fibroblasts or human transformed liver HepG2 cells. However, one compound had both antifungal and antibacterial activity. Surprisingly, all five compounds induced degranulation in a human MC line, LAD2, and this response was substantially reduced in Mas-related G protein-coupled receptor (GPCR)-X2 (MRGPRX2)-silenced cells. Furthermore, all five compounds induced degranulation in RBL-2H3 cells expressing MRGPRX2 but this response was abolished in cells expressing naturally occurring loss-of-function missense variants G165E (rs141744602) and D184H (rs372988289). Mrgprb2 is the likely mouse ortholog of human MRGPRX2, which is expressed in connective tissue MCs (CTMCs) such as cutaneous and peritoneal MCs (PMCs). All five smHDPMs induced degranulation in wild-type PMCs but not in cells derived from Mrgprb2⁻/⁻ mice. These findings suggest that smHDPMs could serve as novel targets for the treatment of drug-resistant fungal and bacterial infections because of their ability to harness CTMCs’ host defense functions.