β-1,3-glucan-lacking <i>Aspergillus fumigatus</i> mediates an efficient antifungal immune response by activating complement and dendritic cells

Complement system and dendritic cells (DCs) form – beside neutrophils and macrophages – the first line of defense to combat fungal infections. Therefore, we here studied interactions of these first immune elements with <i>Aspergillus fumigatus</i> lacking ß-1,3-glucans (<i>fks1_tetOn^rep</i> under repressed conditions) to mechanistically explain the mode of action of echinocandins in more detail. Echinocandins are cell wall active agents blocking β-glucan synthase, making the <i>A. fumigatus fks1_tetOn</i> mutant a good model to study immune-modulatory actions of these drugs. We now demonstrate herein, that complement was activated to significantly higher levels by the <i>fks1-</i>deficient strain compared to its respective wild type. This enhanced covalent linking of complement fragments to the <i>A. fumigatus fks1_tetOn^rep</i> mutant further resulted in enhanced DC binding and internalization of the fungus. Additionally, we found that <i>fks1_tetOn^rep</i> induced a Th1-/Th17-polarizing cytokine profile program in DCs. The effect was essentially dependent on massive galactomannan shedding, since blocking of DC-SIGN significantly reduced the <i>fks1_tetOn^rep-</i>mediated induction of an inflammatory cytokine profile. Our data demonstrate that lack of ß-1,3-glucan, also found under echinocandin therapy, results in improved recognition of <i>Aspergillus fumigatus</i> by complement and DCs and therefore not only directly affects the fungus by its fungistatic actions, but also is likely to exert indirect antifungal mechanisms by strengthening innate host immune mechanisms. <b>Abbreviations</b>: C: complement; CR:complement receptor; DC: dendritic cell; iDC: immature dendritic cell; DC-SIGN: Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin; ERK: extracellular signal–regulated kinases; JNK : c-Jun N-terminal kinases; MAPK: mitogen-activated protein kinase; NHS: normal human serum; PRR: pattern recognition receptor; Th :T helper; TLR :Toll-like receptor; WT: wild type.补体系统与树突状细胞（dendritic cell, DC）与中性粒细胞、巨噬细胞一同，构成了对抗真菌感染的第一道免疫防线。因此，本研究针对这类先天免疫核心组分与缺失β-1,3-葡聚糖的烟曲霉（<i>Aspergillus fumigatus</i>，即抑制条件下的<i>fks1_tetOn^rep</i>突变株）的相互作用展开探究，以期更深入地从机制层面阐释棘白菌素类药物的作用模式。 棘白菌素类药物为作用于真菌细胞壁的制剂，可阻断β-葡聚糖合酶，因此烟曲霉<i>fks1_tetOn</i>突变株成为研究这类药物免疫调节作用的理想模型。本研究证实，相较于其对应的野生型菌株，β-1,3-葡聚糖缺失的<i>fks1_tetOn^rep</i>突变株可显著提升补体系统的激活水平。补体片段与烟曲霉<i>fks1_tetOn^rep</i>突变株的共价结合效率提升，进一步增强了树突状细胞对该真菌的结合与内化能力。 此外，本研究发现<i>fks1_tetOn^rep</i>突变株可诱导树突状细胞形成Th1/Th17极化的细胞因子表达程序。该效应主要依赖于大量半乳甘露聚糖的脱落：阻断DC-SIGN（树突状细胞特异性细胞间黏附分子-3结合非整合素）可显著降低<i>fks1_tetOn^rep</i>突变株介导的炎性细胞因子谱诱导效应。 本研究数据表明，在棘白菌素类药物治疗过程中出现的β-1,3-葡聚糖缺失，可提升补体系统与树突状细胞对烟曲霉的识别能力；因此这类药物不仅可通过抑菌活性直接抑制真菌，还可能通过强化宿主先天免疫机制发挥间接抗真菌作用。 **缩写说明**：C：补体；CR：补体受体；DC：树突状细胞；iDC：未成熟树突状细胞；DC-SIGN：树突状细胞特异性细胞间黏附分子-3结合非整合素（Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin）；ERK：细胞外信号调节激酶（extracellular signal–regulated kinases）；JNK：c-Jun氨基末端激酶（c-Jun N-terminal kinases）；MAPK：丝裂原活化蛋白激酶（mitogen-activated protein kinase）；NHS：正常人血清；PRR：模式识别受体（pattern recognition receptor）；Th：T辅助细胞；TLR：Toll样受体（Toll-like receptor）；WT：野生型（wild type）。