Mincle inhibits neutrophils and macrophages apoptosis in A. fumigatus keratitis

The Role of LC3-Associated Phagocytosis Inhibits the Inflammatory Response in Aspergillus fumigatus Keratitis

Purpose

The purpose of this study was to investigate the role and mechanism of microtubule-associated protein light chain-3 (LC3)-associated phagocytosis (LAP) in the immune response to Aspergillus fumigatus (A. fumigatus) keratitis.

Methods

The formation of single-membrane phagosomes was visualized in the corneas of healthy or A. fumigatus-infected humans and C57BL/6 mice using transmission electron microscopy (TEM). Rubicon siRNA (si-Rubicon) was used to block Rubicon expression. RAW 264.7 cells or mice corneas were infected with A. fumigatus with or without pretreatment of si-Rubicon and scrambled siRNA. RAW 264.7 cells were pretreated with Dectin-1 antibody or Dectin-1 overexpressed plasmid and then stimulated with A. fumigatus. Flow cytometry was used to label macrophages in normal and infected corneas of mice. In mice with A. fumigatus keratitis, the severity of the disease was assessed using clinical scores. We used lentiviral technology to transfer GV348-Ubi-GFP-LC3-II-SV40-Puro Lentivirus into the mouse cornea. The GFP-LC3 fusion protein was visualized in corneal slices using a fluorescence microscope. We detected the mRNA and protein expressions of the inflammatory factors IL-6, IL-1β, and IL-10 using real-time PCR (RT-PCR) and ELISA. We detected the expression of LAP-related proteins Rubicon, ATG-7, Beclin-1, and LC3-II using Western blot or immunofluorescence.

Results

Accumulation of single-membrane phagosomes within macrophages was observed in the corneas of patients and mice with A. fumigatus keratitis using TEM. Flow cytometry (FCM) analysis results show that the number of macrophages in the cornea of mice significantly increases after infection with A. fumigatus. LAP-related proteins were significantly elevated in the corneas of mice and RAW 264.7 cells after infection with A. fumigatus. The si-Rubicon treatment elevated the clinical score of mice. In A. fumigatus keratitis mice, the si-Rubicon treated group showed significantly higher expression of IL-6 and IL-1β and lower expression of IL-10 and LC3-II compared to the control group. In RAW 264.7 cells, treatment with the Dectin-1 overexpressed plasmid upregulated the expression of LAP-related proteins, a process that was significantly inhibited by the Dectin-1 antibody.

Conclusions

LAP participates in the anti-inflammatory immune process of fungal keratitis (FK) and exerts an anti-inflammatory effect. LAP is regulated through the Dectin-1 signaling pathway in A. fumigatus keratitis.

Immune Mechanisms of Filamentous Fungal Keratitis

Filamentous fungal keratitis is a particularly serious eye infection that often results in ulceration, corneal perforation, and blindness. The cornea acts as a natural barrier against harmful agents due to the close connection of its epithelial cells. In addition, on its surface, there is a large number of substances with anti-inflammatory and bactericidal properties, such as secretory IgA and mucin glycoproteins, and antimicrobial peptides (AMPs), such as human β-defensin 2 (HBD-2) and LL-37, which are especially increased in filamentous fungal keratitis. The interaction between pathogenic fungi and the host's immune mechanisms is a complex process: pathogen-associated molecular pattern (PAMP) molecules (chitin, β-glucan, and mannan) found in the fungal cell wall are recognized by pattern recognition receptors (PRRs) (toll-like receptors {TLRs}, C-type lectin receptors {CLRs}, nucleotide-binding oligomerization domain-like receptors {NLRs}, and scavenger receptors {SR}) found in host defense cells, triggering the secretion of various types of cytokines, such as interleukins (IL), tumor necrosis factors (TNFs), and chemokines, which recruit macrophages and neutrophils to migrate to the site of infection and activate inflammatory responses. In addition, the interaction of hyphae and corneal epithelial cells can activate cluster of differentiation (CD) 4+ T cells, CD8+ T cells, and B cells and induce secretion of T-helper (Th)-type cytokines 2 (IL-4 and IL-13) and IgG.

Pseudolaric Acid B Ameliorates Fungal Keratitis Progression by Suppressing Inflammation and Reducing Fungal Load

This study aimed to determine the mechanisms of antifungal and anti-inflammation effects of pseudolaric acid B (PAB) on Aspergillus fumigatus (A. fumigatus) keratitis. In vitro MIC assay and crystal violet staining were conducted to evaluate the efficacy of PAB against A. fumigatus. PAB inhibited A. fumigatus growth and inhibited the formation of fungal biofilms in a dose-dependent manner. Molecular docking analysis revealed that PAB possesses strong binding properties with Rho1 of A. fumigatus, which is devoted to encoding (1,3)-β-d-glucan of A. fumigatus. RT-PCR results also showed that Rho1 was inhibited by PAB. In vivo, PAB treatment reduced clinical scores, fungal load, and macrophage infiltration, which were increased by A. fumigatus in mice corneas. In addition, PAB treatment suppressed the expression of Mincle, p-Syk, and cytokines (TNF-α, MIP2, iNOS, and CCL2) in infected corneas and in RAW264.7 cells, which were tested by RT-PCR, Western blot, and enzyme-linked Immunosorbent Assay. Notably, trehalose-6,6-dibehenate, an agonist of Mincle, pretreatment reversed the regulatory function of PAB in RAW 264.7 cells. Moreover, flow cytometry showed that PAB upregulated the ratio of M2/M1 macrophages in A. fumigatus-infected corneas and RAW264.7 cells. In conclusion, PAB produced antifungal activities against A. fumigatus and decreased the inflammatory response in mouse A. fumigatus keratitis.

The therapeutic role and mechanism of 4-Methoxycinnamic acid in fungal keratitis

Fungal keratitis is an infectious vision-threatening disease that has a poor prognosis, and the clinical therapeutic drugs have multiple limitations, such as epithelial toxicity and low bioavailability. Therefore, new antifungal treatment strategies must be developed. 4-Methoxycinnamic acid (MCA) is a widely occurring natural phenolic acid that has been proven to have multiple effects, such as antibacterial, antifungal, anti-inflammatory, neuroprotective, and inhibiting cancer. In this research, we explored the effects and underlying mechanisms of MCA on A. fumigatus keratitis and the antifungal effects of the combination of MCA and natamycin (NATA) on A. fumigatus. We found that MCA exerts antifungal effects by inhibiting the synthesis of the fungal cell wall, changing the permeability of fungal cell membranes. Moreover, the MCA-NATA combination exhibited synergy for A. fumigatus. In addition, MCA exerted an anti-inflammatory effect by downregulating the inflammatory factors (IL-1β, TNF-α, IL-6, and iNOS) in C57BL/6 mice and RAW264.7 cells. The anti-inflammatory mechanism of MCA was associated with the Mincle signal pathway. In summary, MCA acts as a potential therapeutic drug for fungal keratitis and a potential antifungal sensitizer for natamycin. MCA inhibits fungal cell wall synthesis, destroys the permeability of fungal cell membranes, and mediates the anti-inflammatory, immune response of the host.

Research progress on Mincle as a multifunctional receptor

Macrophage-induced C-type lectin (Mincle), a lipopolysaccharide-induced protein, is widely expressed on antigen-presenting cells. Mincle acts as a pattern recognition receptor that recognizes pathogen-associated molecular patterns of pathogens such as bacteria and fungi, mainly glycolipids, which induces an acquired immune response against microbial infection. Interestingly, Mincle can also identify patterns of lipid damage-associated molecule patterns released by injured cells, such as Sin3-associated protein 130 and β-glucosylceramides, which induces sterile inflammation and ultimately accelerates the progression of stroke, obesity, hepatitis, kidney injury, autoimmune diseases and tumors by promoting tissue inflammation. This article will review the various functions of Mincle, such as mediating sterile inflammation of tissues to accelerate disease progression, initiating immune responses to fight infection and promoting tumor progression.

Benzyl isothiocyanate improves the prognosis of Aspergillus fumigatus keratitis by reducing fungal load and inhibiting Mincle signal pathway

Aspergillus fumigatus keratitis is a potential blinding disease associated with A. fumigatus invasion and excessive inflammatory response. Benzyl isothiocyanate (BITC) is a secondary metabolite with broad antibacterial and anti-inflammatory activity extracted from cruciferous species. However, the role of BITC in A. fumigatus keratitis has not been discovered yet. This study aims to explore the antifungal and anti-inflammatory effects and mechanisms of BITC in A. fumigatus keratitis. Our results provided evidences that BITC exerted antifungal effects against A. fumigatus by damaging cell membranes, mitochondria, adhesion, and biofilms in a concentration-dependent manner. In vivo, fungal load and inflammatory response including inflammatory cell infiltration and pro-inflammatory cytokine expression were reduced in BITC-treated A. fumigatus keratitis. Additionally, BITC significantly decreased Mincle, IL-1β, TNF-α, and IL-6 expression in RAW264.7 cells that stimulated by A. fumigatus or Mincle ligand trehalose-6,6-dibehenate. In summary, BITC possessed fungicidal activities and could improve the prognosis of A. fumigatus keratitis by reducing fungal load and inhibiting the inflammatory response mediated by Mincle.

Roles of pattern recognition receptors in response to fungal keratitis

Fungal keratitis is one of the leading causes of blindness worldwide, which has become an increasingly serious threat to public ocular health, but no effective treatment strategies are available now. Pattern recognition receptors (PRRs) of the innate immune system are the first line of host defense against fungal infections. They could recognize pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) and trigger an array of inflammatory responses. Over the last decades, research has resulted in significant progress regarding the roles of PRRs in fungal keratitis. This review will highlight the importance of several pattern recognition receptors (C-type lectin-like receptors, Toll-like receptors, and NOD-like receptors) in regulating the innate immunity under fungal keratitis and describe the crosstalk and collaboration in PRRs contributing to disease pathology. Meanwhile, some potential therapy-based PRRs against corneal fungal infections are discussed.

Mechanism of antifungal activity and therapeutic action of β-ionone on Aspergillus fumigatus keratitis via suppressing LOX1 and JNK/p38 MAPK activation

PURPOSE

To investigate the anti-inflammatory and antifungal role of β-ionone (BI) in fungal keratitis (FK).

METHODS

In vitro antifungal activity of BI against Aspergillus fumigatus (A. fumigatus) was evaluated by using minimum inhibitory concentration (MIC), crystal violet staining, biofilm biomass measurement, propidium iodide uptake test, and adherence assay. And RT-PCR was carried out to measure the levels of RodA, RodB, Rho, FKs, CshA-D, RlmA, Cyp51A-B and Cdr1B. Network pharmacology analysis was applied to predict the relationship between BI and FK. Cell Count Kit-8 (CCK8) assay was utilized to detect the cytotoxicity of BI to RAW264.7 and immortalized human corneal epithelial cells (HCECs). The underlying mechanism of BI at regulating the level of inflammatory factors in FK was assessed by RT-PCR, ELISA and Western blot in vitro and in vivo. The therapeutic effect of BI has investigated in A. fumigatus keratitis by employing the clinical score, pathological examination, plate count, immunofluorescence and myeloperoxidase (MPO) assay. We also used the slit-lamp microscopy, clinical scores, and HE staining to assess the effect of natamycin compared with BI treatment in vivo.

RESULTS

BI suppressed the growth of A. fumigatus and had a significant effect on A. fumigatus biofilms and membrane permeability. RT-PCR demonstrated that exposure of A. fumigatus to BI inhibited the expression of genes that function in hydrophobin (RodA, RodB), cell wall integrity (Rho, FKs, CshA-D, RlmA), azole susceptibility (Cyp51A-B, Cdr1B). Network pharmacology showed that the effects of BI in FK implicate with C-type lectin receptor signaling pathway. In vivo, after A. fumigatus infection, BI treatment markedly reduced the severity of FK by decreasing clinical score, neutrophil recruitment, and fungal load. And BI treatment also obviously reduced the expression of inflammatory cytokines, Lectin-like oxidized LDL receptor (LOX-1), phosphorylation of p38MAPK and p-JNK versus the DMSO-treated group. BI and natamycin both significantly increased corneal transparency and decreased inflammatory cell recruitment in the FK in the mice model.

CONCLUSION

These results indicated that BI had fungicidal activities against A. fumigatus. It also ameliorated FK in mice by reducing inflammation, which was regulated by LOX-1, p-p38MAPK and p-JNK.

The role of Glabridin in antifungal and anti-inflammation effects in Aspergillus fumigatus keratitis

PURPOSE

To investigate the effect of Glabridin (GLD) in Aspergillus fumigatus keratitis and its associated mechanisms.

METHODS

Aspergillus fumigatus (A. fumigatus) conidia was inoculated in 96-well plate, and minimal inhibitory concentration (MIC) and biofilm formation ability were evaluated after GLD treatment. Spore adhesion ability was evaluated in conidia infected human corneal epithelial cells (HCECs). Keratitis mouse model was created by corneal intrastromal injection with A. fumigatus conidia, and GLD treatment started at the day after infection. The number of fungal colonies was calculated by plate count, and degree of corneal inflammation was assessed by clinical score. Flow cytometry, myeloperoxidase (MPO), and immunofluorescence staining (IFS) experiments were used to assess neutrophil infiltrations. PCR, ELISA and Western blot were conducted to determine levels of TLR4, Dectin-1 as well as downstream inflammatory factors.

RESULTS

GLD treatment suppressed the proliferation, biofilm formation abilities and adhesive capability of A. fumigatus. In mice upon A. fumigatus infection, treatment of GLD showed significantly decreased severity of corneal inflammation, reduced number of A. fumigatus in cornea, and suppressed neutrophil infiltration in cornea. GLD treatment obviously inhibited mRNA and protein levels of Dectin-1, TLR4 and proinflammatory mediators such as IL-1β, HMGB1, and TNF-α in mice corneas compared to the control group.

CONCLUSION

GLD has antifungal and anti-inflammatory effects in fungal keratitis through suppressing A. fumigatus proliferation and alleviating neutrophil infiltration, and repressing the expression of TLR4, Dectin-1 and proinflammatory mediators.

LOX-1 Regulates Neutrophil Apoptosis and Fungal Load in A. Fumigatus Keratitis

PURPOSE

To determine whether LOX-1 regulates neutrophil apoptosis and fungal load in A. fumigatus keratitis.

METHODS

Fas, FasL, CASP3, CASP8, CASP9 and BCL2 were tested in normal and infected corneas of C57BL/6 mice. Mice corneas were infected with A. fumigatus with or without pretreatment of LOX-1 neutralizing antibody or inhibitor (Poly I). Clinical score was recored and HE staining was tested. Fungal load in mice corneas was observed by plate counting. Poly morphonuclear neutrophilic leukocytes (PMNs) were stimulated with 75% ethanol-killed A. fumigatus with or without pretreatment of LOX-1 neutralizing antibody or Poly I. PCR, western blot and immunostaining tested expression of Fas, FasL, CASP3, CASP8, CASP9, BCL2 and cleaved caspase-3. PMNs infiltration and TUNEL-positive cells were assessed by immunofluorescent staining. Flow cytometry assay tested the percentage of apoptosis neutrophils.

RESULTS

Fas, Fas ligand, caspase-8, caspase-9 and caspase-3 mRNA levels were significantly higher in C57BL/6 mice corneas infected with A. fumigatus than normal corneas. Poly I treatment alleviated the severity and decreased clinical score at 3, 5 and 7 days post infecrion (p.i.). HE staining showed less infiltration in corneal tissue after LOX-1 inhibition. Plate counting experiment showed that number of viable fungus in corneas of Poly I treated group was significantly less than control group. LOX-1 neutralizing antibody or Poly I treatment significantly decreased neutrophil infiltration, the quantity of TUNEL-positive cells, the expression of Fas, Fas ligand, caspase-8, caspase-9, caspase-3, cleaved caspase-3 and the percentage of apoptosis neutrophils compared with control corneas. LOX-1 neutralizing antibody treatment significantly decreased Fas, FasL, CASP3, CASP8, CASP9 and cleaved caspase-3 expression in neutrophils.

CONCLUSION

LOX-1 inhibition decrease neutrophil apoptosis and fungal load in A. fumigatus keratitis.

Macrophage-Inducible C-Type Lectin Signaling Exacerbates Acetaminophen-Induced Liver Injury by Promoting Kupffer Cell Activation in Mice

Overdose of acetaminophen (APAP) has become one of the most frequent causes of acute liver failure. Macrophage-inducible C-type lectin (Mincle) acts as a key moderator in immune responses by recognizing spliceosome-associated protein 130 (SAP130), which is an endogenous ligand released by necrotic cells. This study aims to explore the function of Mincle in APAP-induced hepatotoxicity. Wild-type (WT) and Mincle knockout (KO) mice were used to induce acute liver injury by injection of APAP. The hepatic expressions of Mincle, SAP130, and Mincle signaling intermediate (Syk) were markedly upregulated after the APAP challenge. Mincle KO mice showed attenuated injury in the liver, as shown by reduced pathologic lesions, decreased alanine aminotransferase and aspartate aminotransferase levels, downregulated levels of inflammatory cytokines, and decreased neutrophil infiltration. Consistently, inhibition of Syk signaling by GS9973 alleviated APAP hepatotoxicity. Most importantly, Kupffer cells (KCs) were found as the major cellular source of Mincle. The depletion of KCs abolished the detrimental role of Mincle, and the adoptive transfer of WT KC to Mincle KO mice partially reversed the hyporesponsiveness to hepatotoxicity induced by APAP. Furthermore, the expression levels of interleukin (IL)-1β and neutrophil-attractant CXC chemokines were substantially lower in KCs isolated from APAP-treated Mincle KO mice compared with those from WT mice. Similar results were found in primary Mincle KO KCs treated with a ligand of Mincle (trehalose-6,6-dibehenate) or in conditioned media obtained from APAP-treated hepatocytes. Collectively, Mincle can regulate the inflammatory response of KCs, which is necessary for the complete progression of hepatotoxicity induced by APAP. SIGNIFICANCE STATEMENT: Acetaminophen (APAP) overdose is becoming a main cause of drug-induced acute liver damage in the developed world. This study showed that macrophage-inducible C-type lectin (Mincle) deletion or inhibition of Mincle downstream signaling attenuates APAP hepatotoxicity. Furthermore, Mincle as a modulator of Kupffer cell activation contributes to the full process of hepatotoxicity induced by APAP. This mechanism will offer valuable insights to overcome the limitation of APAP hepatotoxicity treatment.

Aspergillus fumigatus-Stimulated Human Corneal Epithelial Cells Induce Pyroptosis of THP-1 Macrophages by Secreting TSLP

Fungal keratitis (FK) is a keratopathy caused by pathogenic fungal infection. The aim of this work is to explore the role of thymic stromal lymphopoietin (TSLP) in FK. Human corneal epithelial cells (HCECs) were treated with Aspergillus fumigatus hyphae, and we found that TSLP was highly expressed and secreted in the hyphae-treated HCECs. Hyphae-treated HCECs or TSLP treatment enhanced the expression of caspase-1 P20, GSDMD-N (p30), IL-1β, and IL-18 in the human THP-1 macrophages. The influence conferred by hyphae-treated HCECs or TSLP treatment was rescued by TSLP neutralizing antibody or VX-765 (caspase-1 inhibitor) treatment. Moreover, TSLP treatment promoted the expression of NLRP3, ASC, caspase-1 P20, GSDMD-N (p30), IL-1β, and IL-18 in the THP-1 macrophages, which was abolished by NLRP3 knockdown. Furthermore, TSLPR silencing suppressed the expression of NLRP3, ASC, caspase-1 P20, GSDMD-N (p30), IL-1β, and IL-18 in the TSLP-treated THP-1 macrophages. In conclusion, our article confirms that Aspergillus fumigatus-stimulated HCECs induce pyroptosis of THP-1 macrophages by secreting TSLP. TSLP/TSLPR induces caspase-1-dependent pyroptosis through activation of NLRP3 inflammasome. Thus, our work suggests that TSLP may be a potential target for FK treatment.

Mammalian Ste20-like kinase 4 inhibits the inflammatory response in Aspergillus fumigatus keratitis

Mammalian Ste20-like kinase 4 (MST4), a new member of the germinal-center kinase STE20 family, was recently demonstrated to be a negative regulator of inflammation. However, whether MST4 participates in the inflammatory response to fungal infection remains unknown. Our study investigated the role and molecular mechanisms of MST4 in mice cornea and corneal epithelial cells exposed to Aspergillus fumigatus (A. fumigatus). Protein level of MST4 was detected in mice corneas and human corneal epithelial cells (HCECs) by Western blot analysis. The MST4 protein level was significantly elevated in mice corneas infected with A. fumigatus and HCECs exposed to A. fumigatus. MST4 expression was also detected in mice corneas by immunofluorescence staining. Furthermore, we found recombinant MST4 inhibited proinflammatory cytokines expressions induced by A. fumigatus at both the mRNA and protein levels in mice corneas and HCECs. To further investigate the mechanism of MST4's anti-inflammatory effect in A. fumigatus keratitis, we verified recombinant MST4 can inhibit curdlan-mediated proinflammatory cytokines production in HCECs. Surprisingly, recombinant MST4 protein downregulated A. fumigatus-induced Dectin-1 expression in both mRNA and protein levels in mice corneas. Recombinant MST4 can inhibit the mRNA expression level of Dectin-1 which was induced by curdlan in HCECs. MST4 can also inhibit the expression of Dectin-1 in mRNA levels increased by Dectin-1 overexpression plasmid in HCECs. Moreover, A. fumigatus or curdlan significantly induced the phosphorylation of Syk, which was consequently suppressed by recombinant MST4. Finally, recombinant MST4 promotes HCECs proliferation, which contribute to cornea wound healing. Taken together, our results provide evidences that MST4 inhibits inflammatory signaling response in A. fumigatus keratitis by downregulating Dectin-1/p-Syk pathway and simultaneously promotes HCECs proliferation.

Regulation of LOX-1 on adhesion molecules and neutrophil infiltration in mouse Aspergillus fumigatus keratitis

AIM

To determine whether lectin-like ox-LDL receptor (LOX-1) regulates adhesion molecules expression and neutrophil infiltration in Aspergillus fumigatus (A. fumigatus) keratitis of C57BL/6 mice.

METHODS

C57BL/6 mice were pretreated with a neutralizing antibody to LOX-1 (5 µg/5 µL) or control nonspecific IgG (5 µg/5 µL), LOX-1 inhibitor Poly-I (2 µg/5 µL) or PBS by subconjunctival injection. Fungal keratitis (FK) mouse models of C57BL/6 mice were established by scraping corneal central epithelium, smearing A. fumigatus on the corneal surface and covering the eye with contact lenses. The corneal response to infection was assessed via clinical score. The mRNA levels of the adhesion molecules intercellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), P-selectin and E-selectin were tested in control and infected corneas by reverse transcription-polymerase chain reaction (RT-PCR). The protein levels of ICAM-1 were evaluated by immunofluorescence (IF) and Western blot. Neutrophils were extracted from the abdominal cavity of C57BL/6 mice followed by pretreatment using antibody to LOX-1 (10 µg/mL) or control nonspecific IgG (10 µg/mL), the Poly-I (4 µg/mL) or PBS. The cells were then stimulated with A. fumigatus and tested mRNA and protein levels of lymphocyte function-associated antigen-1 (LFA-1) using RT-PCR and Western blot. IF and myeloperoxidase (MPO) assays were used to assess neutrophil infiltration in mice corneas.

RESULTS

Pretreatment of LOX-1 antibody or the Poly-I reduced the degree of inflammation of cornea and decreased the clinical FK score compared with pretreatment of IgG or PBS (both P<0.01). And these pretreatment also displayed an obvious decline in the mRNA levels of ICAM-1, VCAM-1, P-selectin, E-selectin and LFA-1 expression compared with control groups (all P<0.01). Furthermore, pretreated with LOX-1 antibody or Poly-I, the protein levels of ICAM-1 and LFA-1 also decreased compared with control groups (all P<0.05). Neutrophil infiltration in the cornea was significantly reduced after pretreatment of LOX-1 antibody or Poly-I compared with control groups by IF and MPO assays (both P<0.01).

CONCLUSION

Inhibition of LOX-1 can decrease the expression of adhesion molecules and reduce neutrophil infiltration in A. fumigatus infected corneas of C57BL/6 mice.

C-type Lectins in Immunity to Lung Pathogens

The respiratory tract is tasked with responding to a constant and vast influx of foreign agents. It acts as an important first line of defense in the innate immune system and as such plays a crucial role in preventing the entry of invading pathogens. While physical barriers like the mucociliary escalator exert their effects through the clearance of these pathogens, diverse and dynamic cellular mechanisms exist for the activation of the innate immune response through the recognition of pathogen-associated molecular patterns (PAMPs). These PAMPs are recognized by pattern recognition receptors (PRRs) that are expressed on a number of myeloid cells such as dendritic cells, macrophages, and neutrophils found in the respiratory tract. C-type lectin receptors (CLRs) are PRRs that play a pivotal role in the innate immune response and its regulation to a variety of respiratory pathogens such as viruses, bacteria, and fungi. This chapter will describe the function of both activating and inhibiting myeloid CLRs in the recognition of a number of important respiratory pathogens as well as the signaling events initiated by these receptors.

Regulation of neutrophil function by selective targeting of glycan epitopes expressed on the integrin CD11b/CD18

Polymorphonuclear neutrophils (PMNs) play a critical role in the innate immune response to invading pathogens. However, dysregulated mucosal trafficking of PMNs and associated epithelial tissue damage is a pathological hallmark of numerous inflammatory conditions including inflammatory bowel disease. The glycoprotein CD11b/CD18 plays a well-described role in regulating PMN transepithelial migration and PMN inflammatory functions. Previous studies have demonstrated that targeting of the N-linked glycan Lewis X on CD11b blocks PMN transepithelial migration (TEpM). Given evidence of glycosylation-dependent regulation of CD11b/CD18 function, we performed MALDI TOF Mass Spectrometry (MS) analyses on CD11b/CD18 purified from human PMNs. Unusual glycan epitopes identified on CD11b/CD18 included high Mannose oligosaccharides recognized by the Galanthus Nivalis lectin and biantennary galactosylated N-glycans recognized by the Phaseolus Vulgaris erythroagglutinin lectin. Importantly, we show that selective targeting of glycans on CD11b with such lectins results in altered intracellular signaling events that inhibit TEpM and differentially affect key PMN inflammatory functions including phagocytosis, superoxide release and apoptosis. Taken together, these data demonstrate that discrete glycan motifs expressed on CD11b/CD18 such as biantennary galactose could represent novel targets for selective manipulation of CD11b function and reduction of PMN-associated tissue damage in chronic inflammatory diseases.

Inhibition of LOX-1 alleviates the proinflammatory effects of high-mobility group box 1 in Aspergillus fumigatus keratitis

AIM

To investigate the inflammatory amplification effect of high-mobility group box 1 (HMGB1) in Aspergillus fumigatus (A. fumigatus) keratitis and the relationship between lectin-like oxidized low-density lipoprotein receptor 1 (LOX-1) and HMGB1 in keratitis immune responses.

METHODS

Phosphate buffer saline (PBS), and Boxb were injected into BALB/c mice subconjunctivally before the corneas were infected with A. fumigatus. RAW264.7 macrophages and neutrophils were pretreated with PBS and Boxb to determine the HMGB1 inflammatory amplification effects. Abdominal cavity extracted macrophages were pretreated with Boxb and Poly (I) (a LOX-1 inhibitor) before A. fumigatus hyphae stimulation to prove the the relationship between the two molecules. LOX-1, interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-2 (MIP-2) and IL-10 were assessed by polymerase chain reaction and Western blot.

RESULTS

Pretreatment with Boxb exacerbated corneal inflammation. In macrophages and neutrophils, A. fumigatus induced LOX-1, IL-1β, TNF-α and MIP-2 expression in Boxb group was higher than those in PBS group. Poly (I) treatments before infection alleviated the proinflammatory effects of Boxb in abdominal cavity extracted macrophages. Pretreatment with Boxb did not influence Dectin-1 mRNA levels in macrophages and neutrophils.

CONCLUSION

In fungal keratitis, HMGB1 is a proinflammatory factor in the first line of immune response. HMGB1 mainly stimulates neutrophils and macrophages to produce inflammatory cytokines and chemokines during the immune response. LOX-1 participates in HMGB1 induced inflammatory exacerbation in A. fumigatus keratitis.

Expression and role of calcitonin gene-related peptide in mouse Aspergillus fumigatus keratitis

AIM

To investigate the expression and role of calcitonin gene-related peptide (CGRP) in the mouse models induced by Aspergillus fumigatus (A. fumigatus).

METHODS

C57BL/6 mice were randomized into a control group and A. fumigatus keratitis group. The cornea photography was assessed under the slit lamp and the clinical score was recorded after infection. Western blot, real-time polymerase chain reaction (PCR) and immunohistofluorescence analysis were applied to detect CGRP expression in cornea of both groups. In vitro, tests were conducted with C57BL/6 mice macrophages to investigate CGRP expression after interaction with A. fumigatus. Cytokines expression induced by exogenous CGRP and the antagonist CGRP8-37 in A. fumigatus-exposed macrophages was evaluated by real-time PCR and ELISA.

RESULTS

The cornea expression of CGRP was significantly elevated in C57BL/6 mice corneas and macrophages after A. fumigatus infection. After treatment with exogenous CGRP, the levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and IL-6 were reduced, and IL-10 level was increased in the A. fumigatus stimulated-macrophages. However, IL-1β, TNF-α and IL-6 levels were upregulated after pretreatment of CGRP8-37. But the mRNA levels of MIP-2, TGF-β and IL-10 were not changed.

CONCLUSION

This study provides evidence that A. fumigatus increased CGRP expression. CGRP may play a protective role against inflammation in A. fumigatus keratitis.

The role of netrin-1 in the mouse cornea during Aspergillus fumigatus infection

PURPOSE

To explore the effects of netrin-1 on inflammation in Aspergillus fumigatus-infected mouse corneas and on proliferation and migration in human corneal epithelial cells (HCECs).

METHODS

Netrin-1 and the receptor A2BAR were detected in normal and infected corneas from C57BL/6 mice and RAW 264.7 cells. The mice were injected subconjunctivally with recombinant netrin-1. The severity of the disease was determined by clinical scores, photography with a slit lamp, RT-PCR, western blotting, myeloperoxidase (MPO) assays and immunofluorescence staining of polymorphonuclear neutrophilic leukocytes (PMNs). The effects of netrin-1 on RAW 264.7 cells in vitro were determined by RT-PCR. The role of A2BAR was demonstrated in vivo by detecting the expression of IL-1β, TNF-α, and IL-10 in corneas pretreated subconjunctivally with an A2BAR antagonist (PSB1115). RAW 264.7 cells were stimulated with Aspergillus fumigatus (A. fumigates) and netrin-1 with or without PSB1115 pretreatment. A cell counting kit-8 (CCK-8) assay was used to evaluate cell proliferation ability, and cell migration ability was determined by cell scratch experiments with HCECs.

RESULTS

Netrin-1 expression decreased slightly after A. fumigatus infection and then increased to its peak. A2BAR expression increased at 1 day post infection (p.i.), with a subsequent decline. Compared to the PBS control, exogenous netrin-1 attenuated the inflammatory response, PMN infiltration, and expression of the proinflammatory factors IL-1β and TNF-α, while IL-10 expression was up-regulated. In RAW 264.7 cells, recombinant netrin-1 obviously inhibited the mRNA expression of IL-1β and TNF-α and promoted the mRNA expression of the anti-inflammatory cytokine IL-10. Pretreatment with PSB1115 resulted in disease aggravation and higher levels of the proinflammatory factors IL-1β and TNF-α both in vivo and in vitro. And the effect of netrin-1 on inflammatory factors was abolished by PSB1115. Moreover, compared to the control treatment, exogenous netrin-1 significantly facilitated the proliferation and migration of HCECs.

CONCLUSIONS

Netrin-1 attenuates inflammation in C57BL/6 mice infected with A. fumigatus, and it may play this role via the receptor A2BAR. Additionally, netrin-1 can promote the proliferation and migration of HCECs.

Pannexin 1 Channels Contribute to IL-1β Expression via NLRP3/Caspase-1 Inflammasome in Aspergillus Fumigatus Keratitis

Purpose: Pannexin 1 channels are deemed to play important roles in inflammation. However, there is limited information regarding their roles in fungal infection diseases, especially fungal keratitis. This study aimed to investigate the role of pannexin 1 channels in Aspergillus fumigatus (A. fumigatus) keratitis. Materials and Methods: Mouse models or immortalized human corneal epithelial cells (HCECs) were infected with or without A. fumigatus for given time. The expression of pannexin 1 channels was tested by qPCR, western blot and immunofluorescence staining. Mice of A. fumigatus keratitis were pretreated with carbenoxolone (CBX) or 2'(3')-O-(4-Benzoylbenzoyl) adenosine-5'-triphosphate (BzATP) to block or activate the opening of pannexin 1 channels respectively. The clinical score was recorded. Cornea tissues were examined for the downstream signals of pannexin 1 channels, including NLRP3, Caspase-1 and IL-1β, and myeloperoxidase (MPO) by PCR and ELISA. Data were analyzed with commercial data analysis software and a P < 0.05 was considered to be statistically significant. Results: Upon A. fumigatus infection, pannexin 1 expression increased at both the mRNA and the protein levels in mice corneas (P< 0.05, n = 3). Immunofluorescence indicated that pannexin 1 channels were mainly located in the corneal epithelial layer, and they were upregulated after A. fumigatus infection. In vitro, the same tendency was found at the mRNA and the protein levels in HCECs (P< 0.05, n = 8). In mouse model, blockage of pannexin 1 channels by CBX caused more severely keratitis. The downstream signals of pannexin 1 channels (NLRP3/Caspase-1/IL-1β) and MPO were down-regulated. Whereas activation the opening of pannexin 1 channels by BzATP reduced corneal infection with increased expression of Caspase-1 and IL-1β. Conclusions: Pannexin 1 channels play important roles in the regulation of progression and leucocytes aggregation during corneal A. fumigatus infection via the NLRP3/Caspase-1/IL-β pathway.

Mincle in the innate immune response of mice fungal keratitis

AIM

To investigate how macrophage inducible C-type lectin (Mincle) influences inflammation in mice fungal keratitis induced by Aspergillus fumigatus (A. fumigatus).

METHODS

C57BL/6 mice were infected with A. fumigatus after pretreated with Mincle agonist TDB or Mincle neutralizing antibody (MincleAb), taking DMSO or IgG as control group respectively. The cornea lesions were monitored with slit-lamp microscope and evaluated by clinical score. Mincle expression was assessed using reverse transcription-ploymerase chain reaction (RT-PCR) and immunostaining. The expression of cytokines (IL-1β, TNF-α and IL-6) chemokines (CXCL-1 and MIP-2) was determined by RT-PCR and ELISA. Neutrophil infiltration was observed by immunostaining. The levels of nitric oxide (NO) generated by corneas were tested by Griess reaction.

RESULTS

Mincle mRNA and protein levels were higher in infected corneas than normal corneas of C57BL/6 mice, saving clinical scores revealed differences. When pretreated with Mincle agonist TDB, the mRNA and protein levels of IL-1β, TNF-α and IL-6 in infected corneas were significantly increased compared with the control group (P<0.01). Results of the counterpart in corneas pretreated with Mincle neutralizing antibody was decreased consistently (P<0.01). Expression of CXCL1 and MIP-2 mRNA levels were up-regulated in TDB group and down-regulated in MincleAb group (P<0.01), coincide with neutrophil aggregation degree in corneas showed by immunostaining. As for the concentration of NO, it was promoted in TDB group compared with DMSO control group, and decreased in MincleAb group compared with IgG control group.

CONCLUSION

Mincle plays a dual role in mice fungal keratitis. It participates in the innate immune system by enhancing inflammation. What's more, Mincle can mediate cytotoxic effects by regulating the formation of NO.