why choose us

300×250 Ad Slot

Research Article: Impaired NLRP3 inflammasome activation by chitin underlies refractory chromoblastomycosis caused by Fonsecaea pedrosoi muriform cells

Date Published: 2026-07-14

Abstract:
Macrophage NLRP3 activation is crucial for antifungal immunity, yet its role in chromoblastomycosis—a chronic subcutaneous mycosis typically caused by Fonsecaea pedrosoi —remains unclear. Unlike prior self-resolving models using conidia and hyphae, clinical disease features muriform cells, a parasitic form resistant to macrophages and linked to chronicity. Notably, chitin, a weak NLRP3 agonist, accumulates on the surface of muriform cells. This study investigates whether chitin accumulation modulates NLRP3 activation and promotes fungal persistence. Human chromoblastomycosis lesions were analyzed by IHC (MPO, CD86, NLRP3) and RT-PCR for cytokine transcripts. WT and NLRP3–/– mice were footpad-inoculated with F. pedrosoi muriform cells for in vivo assessment. Flow cytometric bead array quantified IL-1?, IL-6, IL-10, TNF-?, and IL-17A in footpad homogenates, and the same panel (excluding IL-17A) in stimulated BMDM supernatants. NLRP3 pathway activation in BMDMs was confirmed by western blotting and immunofluorescence. In human lesions, marked MPO+ neutrophil recruitment encapsulated muriform cells, yet multinucleated giant cells sequestered some fungal elements from neutrophils. Despite robust NLRP3 expression and elevated IL-1?, IL-6, TNF-?, and IL-10 versus normal skin (all p < 0.01), muriform cells persisted in tissue. In WT mice, lesions transitioned from purulent (day 7) to granulomatous (day 90), concurrent with declining IL-1?, IL-17A, IL-6, and TNF-?. MPO+ neutrophils abundantly surrounded muriform cells at day 7; at day 90, F4/80+ macrophages enveloped most fungi without elimination, forming multinucleated giant cells—recapitulating human pathology. In NLRP3–/– mice, IL-1? and IL-17A were produced in an NLRP3-independent manner and showed no decline over time. Muriform cells progressively budded and transitioned to hyphae both inside and outside giant cells; MPO+ neutrophils preferentially localized to hyphal areas, while macrophages remained around muriform cells, suggesting compartmentalized inflammation. In vitro , chitinase-treated muriform cells induced higher NLRP3-dependent IL-1?, IL-6, TNF-?, and IL-10 in WT BMDMs versus intact cells (all p < 0.01). Mechanistically, chitin accumulation partially suppressed NF-?B phosphorylation, reducing NLRP3 expression, caspase-1 cleavage, and ASC speck formation. NLRP3 mediates host defense against muriform cells yet fails to resolve chronic infection. Chitin accumulation on muriform cells attenuates NLRP3 activation, thereby promoting chromoblastomycosis chronicity.

Introduction:
Macrophage NLRP3 activation is crucial for antifungal immunity, yet its role in chromoblastomycosis—a chronic subcutaneous mycosis typically caused by Fonsecaea pedrosoi —remains unclear. Unlike prior self-resolving models using conidia and hyphae, clinical disease features muriform cells, a parasitic form resistant to macrophages and linked to chronicity. Notably, chitin, a weak NLRP3 agonist, accumulates on the surface of muriform cells. This study investigates whether chitin accumulation modulates NLRP3…

Read more

300×250 Ad Slot