Interaction of THP-1 Monocytes with Conidia and Hyphae of Different Curvularia Strains

Host cell-type and pathogen-specific immunomodulatory functions of macrophage migration inhibitory factor (MIF) in infectious keratitis

Therapeutic management of inflammation in infectious keratitis (IK) requires new strategy and targets for selective immunomodulation. Targeting host cell-type specific inflammatory responses might be a viable strategy to curtail unnecessary inflammation and reduce tissue damage without affecting pathogen clearance. This study explores the possibility of pathogen and host cell-type dependent differences in the inflammatory pathways relevant in the pathogenesis of IK. Human corneal epithelial cell line (HCEC) and phorbol 12-myristate-13 acetate (PMA) differentiated THP-1 macrophage line were infected with either Aspergillus flavus conidia or Acanthamoeba castellanii trophozoites and the elicited inflammatory responses were studied in terms of gene expression and secretion of proinflammatory factors interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-α) and an upstream inflammatory regulator and mediator protein-the Macrophage Migration Inhibitory Factor (MIF). Given the pleotropic mode of MIF function in diverse cell types relevant in many human diseases, we tested if MIF driven responses to infection is different in HCECs and THP-1 macrophages by studying its expression, secretion and involvement in inflammation by siRNA mediated knockdown. We also examined IK patient tear samples for MIF levels. Infection with A. flavus or A. castellanii induced IL-8 and TNF-α responses in HCECs and THP-1 macrophages but to different levels. Our preliminary human data showed that the level of secreted MIF protein was elevated in IK patient tear, however, MIF secretion by the two cell types were strikingly different in-vitro, under both normal and infected conditions. We found that HCECs released MIF constitutively, which was significantly inhibited with infection, whereas THP-1 macrophages were stimulated to release MIF during infection. MIF gene expression remained largely unaffected by infection in both the cell lines. Although MIF in HCECs appeared to be intracellularly captured during infection, MIF knockdown in HCECs associated with a partial reduction of the IL-8 and TNF-α expression produced by either of the pathogens, suggesting a pro-inflammatory role for MIF in HCECs, independent of its canonical cytokine like function. In contrast, MIF knockdown in THP-1 macrophages accompanied a dramatic increase in IL-8 and TNF-α expression during A. castellanii infection, while the responses to A. flavus infection remained unchanged. These data imply a host cell-type and pathogen specific distinction in the MIF- related inflammatory signaling and MIF as a potential selective immunomodulatory target in infectious keratitis.

Parietal composition of Lichtheimia corymbifera: Differences between spore and germ tube stages and host-pathogen interactions

The molecular composition and structural organization of the cell wall of filamentous fungi underlie the ability of the host to identify them as pathogens. Although the organization of the fungal cell wall, composed of 90% polysaccharides, is similar from one fungus to another, small variations condition their ability to trigger pattern recognition receptors. Because the incidence of mucormycosis, an emerging life-threatening infection caused by the species of the order Mucorales is increasing worldwide, the precise composition of the cell wall of two strains of Lichtheimia corymbifera was investigated in the early growth stages of germination (spores and germ-tubes) using trimethylsilylation and confocal microscopy. This study also characterizes the response of THP-1 cells to Mucorales. The study identified the presence of uncommon monosaccharides (fucose, galactose, and glucuronic acid) whose respective proportions vary according to the germination stage, revealing early parietal reorganization. Immunofluorescence studies confirmed the exposure of β-glucan on the surface of swollen spores and germ-tubes. Both spores and germ-tubes of L. corymbifera promoted an early and strong pro-inflammatory response, through TLR-2. Our results show the singularity of the cell wall of the order Mucorales, opening perspectives for the development of specific diagnostic biomarkers.

Expression of Cytokine Profiles in Human THP-1 Cells during Phase Transition of Talaromyces marneffei

Talaromyces marneffei, a dimorphic fungus, exhibits temperature-dependent growth, existing in a filamentous form at 25 °C and as a yeast at 37 °C. Several studies have highlighted the important roles of macrophages in defense against T. marneffei infection. However, the immune responses to the interaction of macrophages with T. marneffei cells during phase transition require further investigation. This study reports the expression of cytokine profiles in human THP-1 cells during infection by T. marneffei. THP-1 cells were infected with T. marneffei conidia at different multiplicity of infections (MOIs). Surviving conidia transformed into yeasts after phagocytosis by macrophages, and the number of yeasts gradually increased over 36 h. The transcription and secretion levels of pro- and anti-inflammatory cytokines were examined at different times by qRT-PCR and ELISA. Transcription levels of IL-8, IL-12, IL-1β, and TNF-α increased significantly at 12 or 24 h and then slightly decreased at 36 h. In contrast, the transcription levels of IL-6, IL-10, and TGF-β gradually increased at all MOIs. The levels of IL-6 and IL-10 secretion corresponded to their levels of transcription. These results indicated that as the number of intracellular yeasts increased, the infected macrophages first underwent slight M1 polarization before shifting to M2 polarization. This polarization transition was confirmed by the fungicidal ability and the expression of macrophage surface markers. By inducing the M2-type polarization of macrophages, the intracellular T. marneffei cells can successfully evade the immune response. Our study provides a novel insight into the immune characterization during the transition of T. marneffei infection and could further contribute to possible diagnostic and therapeutic interventions for this infection.

Magnesium impairs Candida albicans immune evasion by reduced hyphal damage, enhanced β-glucan exposure and altered vacuole homeostasis

With a limited arsenal of available antifungal drugs and drug-resistance emergence, strategies that seek to reduce Candida immune evasion and virulence could be a promising alternative option. Harnessing metal homeostasis against C. albicans has gained wide prominence nowadays as a feasible antifungal strategy. Herein, the effect of magnesium (Mg) deprivation on the immune evasion mechanisms of C. albicans is demonstrated. We studied host pathogen interaction by using the THP-1 cell line model and explored the avenue that macrophage-mediated killing was enhanced under Mg deprivation, leading to altered cytokine (TNFα, IL-6 and IL10) production and reduced pyroptosis. Insights into the mechanisms revealed that hyphal damage inside the macrophage was diminished under Mg deprivation. Additionally, Mg deprivation led to cell wall remodelling; leading to enhanced β-1,3-glucan exposure, crucial for immune recognition, along with concomitant alterations in chitin and mannan levels. Furthermore, vacuole homeostasis was disrupted under Mg deprivation, as revealed by abrogated morphology and defective acidification of the vacuole lumen. Together, we demonstrated that Mg deprivation affected immune evasion mechanisms by: reduced hyphal damage, enhanced β-1,3-glucan exposure and altered vacuole functioning. The study establishes that Mg availability is indispensable for successful C. albicans immune evasion and specific Mg dependent pathways could be targeted for therapy.

Evaluation of blood cell viability rate, gene expression, and O-GlcNAcylation profiles as indicative signatures for fungal stimulation of salmonid cell models

Fungal diseases of fish are a significant economic problem in aquaculture. Using high-throughput expression analysis, we identified potential transcript markers in primary head kidney and secondary embryonic cells from salmonid fish after stimulation with the inactivated fungi Mucor hiemalis and Fusarium aveneacium and with purified fungal molecular patterns. The transcript levels of most of the 45 selected genes were altered in head-kidney cells after 24 h of stimulation with fungal antigens. Stimulation with the inactivated fungus M. hiemalis induced the most pronounced transcriptional changes, including the pathogen receptor-encoding genes CLEC18A and TLR22, the cytokine-encoding genes IL6 and TNF, and the gene encoding the antimicrobial peptide LEAP2. In parallel, we analyzed the total GlcNAcylation status of embryonic salmonid cells with or without stimulation with inactivated fungi. O-GlcNAcylation modulates gene expression, intracellular protein, and signal activity, but we detected no significant differences after a 3-h stimulation. A pathway analysis tool identified the "apoptosis of leukocytes" based on the expression profile 24 h after fungal stimulation. Fluorescence microscopy combined with flow cytometry revealed apoptosis in 50 % of head-kidney leukocytes after 3 h stimulation with M. hiemalis, but this level decreased by > 5% after 24 h of stimulation. The number of apoptotic cells significantly increased in all blood cells after a 3-h stimulation with fungal molecular patterns compared to unstimulated controls. This in vitro approach identified transcript-based parameters that were strongly modulated by fungal infections of salmonid fish.

Differential inflammatory response to Aspergillus flavus and Candida albicans infection in human retinal pigment epithelial cells: Role in treatment of endophthalmitis

OBJECTIVE

Fungal endophthalmitis is an emerging vision-threatening complication in tropical countries and the Retinal pigment epithelial cells (RPE) are said to play a major role in the retinal pathology. The aim of this study was to compare the immune response of Retinal pigment epithelial cells (RPE) challenged with A. flavus and C. albicans strains, isolated from patients with fungal endophthalmitis.

MATERIAL AND METHODS

Retinal Pigment epithelial cells (ARPE-19) cells were infected with A. flavus and C. albicans, and gene expression were assessed for TLRs, immune-mediators, and matrix metalloproteinases (MMPs).

RESULTS

We observed a time-dependent gene expression of TLRs (TLR-2,-7 and -9); IL-8 and TNF-α in RPE cells challenged with A. flavus and C. albicans. Additonally, IL-6 (3.3 fold), IL-10 (15.2 fold), and IL-17 (5.6 fold) were significantly up-regulated only in cells infected with A. flavus. Additionally, MMP-9 gene expression was up-regulated in both A.flavus as well as C.albicans infected cells, while MMP- 2 gene expression was induced only in cells infected with C.albicans. A total of 9 upregulated differential expression of genes (DEGs) in A. flavus infected cells and 7 DEGs in C. albicans infected cells were used to construct Protein-protein interaction (PPI) network.

CONCLUSION

RPE cells induced a differential innate immune response depending on fungal species involved (A.flavus and C.albicans) and may provide clues for novel treatment targets and better prognosis.

Cellular and Molecular Response of Macrophages THP-1 during Co-Culture with Inactive Trichophyton rubrum Conidia

Trichophyton rubrum is causing an increasing number of invasive infections, especially in immunocompromised and diabetic patients. The fungal invasive infectious process is complex and has not yet been fully elucidated. Therefore, this study aimed to understand the cellular and molecular mechanisms during the interaction of macrophages and T. rubrum. For this purpose, we used a co-culture of previously germinated and heat-inactivated T. rubrum conidia placed in contact with human macrophages cell line THP-1 for 24 h. This interaction led to a higher level of release of interleukins IL-6, IL-2, nuclear factor kappa beta (NF-κB) and an increase in reactive oxygen species (ROS) production, demonstrating the cellular defense by macrophages against dead fungal elements. Cell viability assays showed that 70% of macrophages remained viable during co-culture. Human microRNA expression is involved in fungal infection and may modulate the immune response. Thus, the macrophage expression profile of microRNAs during co-culture revealed the modulation of 83 microRNAs, with repression of 33 microRNAs and induction of 50 microRNAs. These data were analyzed using bioinformatics analysis programs and the modulation of the expression of some microRNAs was validated by qRT-PCR. In silico analysis showed that the target genes of these microRNAs are related to the inflammatory response, oxidative stress, apoptosis, drug resistance, and cell proliferation.

Response of Human Neutrophil Granulocytes to the Hyphae of the Emerging Fungal Pathogen Curvularia lunata

Curvularia lunata is an ascomycete filamentous fungus causing local and invasive phaeohyphomycoses in both immunocompromised and immunocompetent patients. Neutrophils are crucial participants of the first line host defense against fungal infections. They migrate to the infected site and eliminate the infectious agents by various mechanisms including phagocytoses, oxidative damage, or formation of neutrophil extracellular trap (NET). Neutropenia may be a risk factor for phaeohyphomycoses, and restoration of the neutrophil function can improve the outcome of the infection. In the present study, interaction of primary human neutrophil granulocytes with the hyphae C. lunata was examined and compared to that with the well characterized filamentous fungal pathogen Aspergillus fumigatus. Neutrophils could recognize the serum opsonized hyphae of C. lunata and attach to them. Myeloperoxidase release was also activated by a soluble factor present in the culture supernatant of the fungus. Induction of the oxidative burst was found to depend on serum opsonization of the hyphae. Although extracellular hydrogen peroxide production was induced, the fungus efficiently blocked the oxidative burst by acidifying the reaction environment. This blockage also affected the NET forming ability of the neutrophils.

Anti-CotH3 antibodies protect mice from mucormycosis by prevention of invasion and augmenting opsonophagocytosis

Mucorales are fungal pathogens that cause mucormycosis, a lethal angioinvasive disease. Previously, we demonstrated that Rhizopus, the most common cause of mucormycosis, invades endothelial cells by binding of its CotH proteins to the host receptor GRP78. Loss of CotH3 renders the fungus noninvasive and attenuates Rhizopus virulence in mice. Here, we demonstrate that polyclonal antibodies raised against peptides of CotH3 protected diabetic ketoacidotic (DKA) and neutropenic mice from mucormycosis compared to mice treated with control preimmune serum. Passive immunization with anti-CotH3 antibodies enhanced neutrophil inlfux and triggered Fc receptor-mediated enhanced opsonophagocytosis killing of Rhizopus delemar. Monoclonal antibodies raised against the CotH3 peptide also protected immunosuppressed mice from mucormycosis caused by R. delemar and other Mucorales and acted synergistically with antifungal drugs in protecting DKA mice from R. delemar infection. These data identify anti-CotH3 antibodies as a promising adjunctive immunotherapeutic option against a deadly disease that often poses a therapeutic challenge.

Staphylococcus aureus Phenol-Soluble Modulins α1-α3 Act as Novel Toll-Like Receptor (TLR) 4 Antagonists to Inhibit HMGB1/TLR4/NF-κB Signaling Pathway

Phenol-soluble modulins (PSMs) have recently emerged as key virulence determinants, particularly in highly aggressive Staphylococcus aureus isolates. These peptides contribute to the pathogenesis of S. aureus infections, participating in multiple inflammatory responses. Here, we report a new role for S. aureus PSMs in high mobility group box-1 protein (HMGB1) induced inflammation by modulating toll-like receptor (TLR) 4 pathway. Direct ligation of TLR4 with S. aureus PSMα1–α3 and PSMβ1–β2 was identified by surface plasmon resonance. Remarkably, the binding affinity of TLR4 with HMGB1 was attenuated by PSMα1–α3. Further study revealed that PSMα1–α3 directly inhibited HMGB1-induced NF-κB activation and proinflammatory cytokines production in vitro using HEK-Blue hTLR4 cells and THP-1 cells. To analyze the molecular interactions between PSMs and TLR4, blast similarity search was performed and identified that PSMα1 and PSMβ2 were ideal templates for homology modeling. The three-dimensional structures of PSMα2, PSMα4, PSMβ1, and δ-toxin were successfully generated with MODELLER, and further refined using CHARMm. PSMs docking into TLR4 were done using ZDOCK, indicating that PSMα1–α3 compete with HMGB1 for interacting with the surrounding residues (336–477) of TLR4 domain. Our study reveals that S. aureus PSMα1–α3 can act as novel TLR4 antagonists, which account at least in part for the staphylococcal immune evasion. Modulation of this process will lead to new therapeutic strategies against S. aureus infections.