Abstract

Aspergillus fumigatus is an opportunistic fungal pathogen with small airborne spores (conidia) that may escape clearance by upper airways and directly impact the alveolar epithelium. Consequently, innate alveolar defense mechanisms are being activated, including professional phagocytosis by alveolar macrophages, recruitment of circulating neutrophils and probably enhanced secretion of pulmonary surfactant by the alveolar type II (AT II) cells. However, no data are available in support of the latter hypothesis. We therefore used a coculture model of GFP-Aspergillus conidia with primary rat AT II cells and studied fungal growth, cellular Ca²⁺ homeostasis, and pulmonary surfactant exocytosis by live cell video microscopy. We observed all stages of fungal development, including reversible attachment, binding and internalization of conidia as well as conidial swelling, formation of germ tubes and outgrowth of hyphae. In contrast to resting conidia, which did not provoke immediate cellular effects, metabolically active conidia, fungal cellular extracts (CE) and fungal culture filtrates (CF) prepared from swollen conidia caused a Ca²⁺-independent exocytosis. Ca²⁺ signals of greatly varying delays, durations and amplitudes were observed by applying CE or CF obtained from hyphae of A. fumigatus, suggesting compounds secreted by filamentous A. fumigatus that severely interfere with AT II cell Ca²⁺ homeostasis. The mechanisms underlying the stimulatory effects, with respect to exocytosis and Ca²⁺ signaling, are unclear and need to be identified.

中文翻译：

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烟曲霉对原代肺泡 II 型细胞表面活性物质胞吐作用的刺激

摘要

烟曲霉是一种机会性真菌病原体，带有小的空气传播孢子（分生孢子），可以通过上呼吸道清除并直接影响肺泡上皮。因此，先天性肺泡防御机制被激活，包括肺泡巨噬细胞的专业吞噬作用、循环中性粒细胞的募集以及肺泡 II 型 (AT II) 细胞可能增强肺表面活性剂的分泌。然而，没有数据支持后一种假设。因此，我们使用了 GFP-曲霉分生孢子与原代大鼠 AT II 细胞的共培养模型，并研究了真菌生长、细胞 Ca ²⁺通过活细胞视频显微镜观察体内平衡和肺表面活性物质胞吐作用。我们观察了真菌发育的所有阶段，包括分生孢子的可逆附着、结合和内化，以及分生孢子肿胀、胚管形成和菌丝生长。与静息分生孢子不会立即引起细胞效应相反，代谢活跃的分生孢子、真菌细胞提取物 (CE) 和从肿胀分生孢子制备的真菌培养滤液 (CF) 引起 Ca ²⁺独立的胞吐作用。通过应用从烟曲霉菌丝获得的 CE 或 CF 观察到Ca ²⁺信号的延迟、持续时间和幅度变化很大，表明由丝状烟曲霉分泌的化合物严重干扰 AT II 细胞 Ca ²⁺稳态。在胞吐作用和 Ca ²⁺信号传导方面，刺激作用的潜在机制尚不清楚，需要确定。