Sporothrix globosa melanin regulates autophagy via the TLR2 signaling pathway in THP-1 macrophages

Low-Density Neutrophil Levels Are Correlated with Sporotrichosis Severity: Insights into Subcutaneous Fungal Infection

Low-density neutrophils (LDNs) constitute a distinct subset of neutrophils among PBMCs. They are key mediators in systemic infections, amplifying inflammatory responses and potentially influencing disease severity and chronicity. However, their roles in subcutaneous fungal infections have not been previously investigated. In this study, we observed increased neutrophil counts in the blood and tissues of patients with sporotrichosis through automated blood analysis, histology, and immunohistochemistry. In addition, we found elevated granulocyte colony-stimulating factor levels by ELISAs. Flow cytometry analysis revealed a significant increase in CD16+CD66b+ LDNs compared with that in healthy controls. In vitro stimulation with Sporothrix globosa induced LDN generation. We observed positive correlations of LDN frequency with levels of CRP and myeloperoxidase. Conversely, granulocyte colony-stimulating factor levels were negatively correlated with LDN frequency. LDNs exhibited a combined mature/immature phenotype. Notably, transcriptomic analysis showed downregulation of pro-inflammatory signaling pathways in LDNs; functional assays also demonstrated reduced phagocytosis, ROS production, and neutrophil extracellular trap formation after stimulation with Sporothrix globosa. Degranulation did not exhibit significant changes, suggesting that LDNs constitute an impaired subpopulation. Our findings in the context of subcutaneous fungal infections indicate that LDN levels are significantly elevated in sporotrichosis and positively correlated with disease severity.

Role of Dectin-1 in immune response of macrophages induced by Fonsecaea monophora wild strain and melanin-deficient mutant strain

Chromoblastomycosis is a chronic granulomatous subcutaneous fungal disease caused mainly by Fonsecaea monophora in southern China. Melanin is an important virulence factor in wild strain (Mel+), and the strains lack of the polyketide synthase gene is a melanin-deficient mutant strain (Mel-). We investigated the effect of melanin in F. monophora on Dectin-1 receptor-mediated immune responses in macrophages. Conidia and tiny hyphae of Mel+ and Mel- were co-cultured with THP-1 macrophages expressing normal or low levels of Dectin-1. Compare the killing rate, phagocytosis rate, and expression levels of the inflammatory cytokines tumour necrosis factor-α, interleukin-1β, interleukin-6, and nitric oxide in each group. The results showed that the killing rate, phagocytosis rate, and pro-inflammatory factor levels of Mel+ infected macrophages with normal expression of Dectin-1 were lower than those of Mel-. And the knockdown of Dectin-1 inhibited the phagocytic rate, killing rate, and proinflammatory factor expression in macrophages infected with Mel+ and Mel-. And there was no significant difference in the above indexes between Mel+ and Mel- groups in Dectin-1 knockdown macrophages. In summary, the study reveals that melanin of F. monophora inhibits the immune response effect of the host by hindering its binding to Dectin-1 on the surface of macrophage, which may lead to persistent fungal infections.

Extracellular vesicles derived from Talaromyces marneffei contain immunogenic compounds and modulate THP-1 macrophage responses

Pathogenic eukaryotes including fungi release extracellular vesicles (EVs) which are composed of a variety of bioactive components, including peptides, nucleic acids, polysaccharides, and membrane lipids. EVs contain virulence-associated molecules suggesting a crucial role of these structures in disease pathogenesis. EVs derived from the pathogenic yeast phase of Talaromyces (Penicillium) marneffei, a causative agent of systemic opportunistic mycoses "talaromycosis," were studied for their immunogenic components and immunomodulatory properties. Some important virulence factors in EVs including fungal melanin and yeast phase specific mannoprotein were determined by immunoblotting. Furthermore, fluorescence microscopy revealed that T. marneffei EVs were internalized by THP-1 human macrophages. Co-incubation of T. marneffei EVs with THP-1 human macrophages resulted in increased levels of supernatant interleukin (IL)-1β, IL-6 and IL-10. The expression of THP-1 macrophage surface CD86 was significantly increased after exposed to T. marneffei EVs. These findings support the hypothesis that fungal EVs play an important role in macrophage "classical" M1 polarization. T. marneffei EVs preparations also increased phagocytosis, suggesting that EV components stimulate THP-1 macrophages to produce effective antimicrobial compounds. In addition, T. marneffei EVs stimulated THP-1 macrophages were more effective at killing T. marneffei conidia. These results indicate that T. marneffei EVs can potently modulate macrophage functions, resulting in the activation of these innate immune cells to enhance their antimicrobial activity.