Henß Isabell, Kleinemeier Christoph, Strobel Lea, Brock Matthias, Löffler Jürgen, Ebel Frank
Institute for Infectious Diseases and Zoonoses, Ludwig-Maximilians-University Munich, Munich, Germany.
Department of Internal Medicine II, University Hospital of Wuerzburg, Wuerzburg, Germany.
Front Microbiol. 2022 Jun 16;13:896145. doi: 10.3389/fmicb.2022.896145. eCollection 2022.
All species form phialidic conidia (PC) when the mycelium is in contact with the air. These small, asexual spores are ideally suited for an airborne dissemination in the environment. and a few closely related species from section can additionally generate accessory conidia (AC) that directly emerge from the hyphal surface. In this study, we have identified galactomannan as a major surface antigen on AC that is largely absent from the surface of PC. Galactomannan is homogeneously distributed over the entire surface of AC and even detectable on nascent AC present on the hyphal surface. In contrast, β-glucans are only accessible in distinct structures that occur after separation of the conidia from the hyphal surface. During germination, AC show a very limited isotropic growth that has no detectable impact on the distribution of galactomannan. The AC of the strain used in this study germinate much faster than the corresponding PC, and they are more sensitive to desiccation than PC. During infection of murine J774 macrophages, AC are readily engulfed and trigger a strong tumor necrosis factor-alpha (TNFα) response. Both processes are not hampered by the presence of laminarin, which indicates that β-glucans only play a minor role in these interactions. In the phagosome, we observed that galactomannan, but not β-glucan, is released from the conidial surface and translocates to the host cell cytoplasm. AC persist in phagolysosomes, and many of them initiate germination within 24 h. In conclusion, we have identified galactomannan as a novel and major antigen on AC that clearly distinguishes them from PC. The role of this fungal-specific carbohydrate in the interactions with the immune system remains an open issue that needs to be addressed in future research.
当菌丝体与空气接触时，所有物种都会形成瓶梗状分生孢子（PC）。这些小型无性孢子非常适合在环境中通过空气传播。并且来自该组的一些密切相关物种还可以产生直接从菌丝表面长出的副分生孢子（AC）。在本研究中，我们已确定半乳甘露聚糖是AC上的主要表面抗原，而PC表面基本不存在这种抗原。半乳甘露聚糖均匀分布在AC的整个表面，甚至在菌丝表面的新生AC上也可检测到。相比之下，β-葡聚糖仅在分生孢子从菌丝表面分离后出现的特定结构中才可触及。在萌发过程中，AC表现出非常有限的各向同性生长，对半乳甘露聚糖的分布没有可检测到的影响。本研究中使用的菌株的AC比相应的PC发芽快得多，并且它们比PC对干燥更敏感。在感染小鼠J774巨噬细胞期间，AC很容易被吞噬并引发强烈的肿瘤坏死因子-α（TNFα）反应。这两个过程都不受海带多糖存在的阻碍，这表明β-葡聚糖在这些相互作用中仅起次要作用。在吞噬体中，我们观察到半乳甘露聚糖而非β-葡聚糖从分生孢子表面释放并转移到宿主细胞细胞质中。AC在吞噬溶酶体中持续存在，并且其中许多在24小时内开始萌发。总之，我们已确定半乳甘露聚糖是AC上一种新的主要抗原，这使其与PC明显区分开来。这种真菌特异性碳水化合物在与免疫系统相互作用中的作用仍然是一个有待未来研究解决的开放性问题。
