Influence of cell wall modifications by chitin deacetylases on the human immune response against Cryptococcus neoformans and other human pathogenic fungi

人类病原真菌可导致严重的全身感染，特别是在免疫功能低下的人中。导致有效防御入侵真菌的分子机制仍然知之甚少。对新生隐球菌感染的研究表明，细胞壁的组成对该真菌的毒力是必不可少的。与其他一些病原真菌一样，它的细胞壁中含有几丁糖，而不是几丁质(聚N-乙酰-氨基葡萄糖)，后者是由几丁质脱乙酰酶(CDAS)部分脱乙酰化新生的几丁质产生的。甲壳素寡聚体是一种微生物相关分子模式(MAMP)，可被人类免疫系统的Toll样受体2(TLR2)、纤维蛋白原C结构域1(FBCD1)或LYSMD3等模式识别受体识别。然而，甲壳素被其四种不同的CDA(CnCDAs 1-4)转化为壳聚糖，可能会使新生葡萄球菌逃避宿主免疫系统的识别。这些酶被认为是病原体的重要毒力因子，阻止几丁质被人几丁质酶降解为免疫刺激寡聚体。在本项目中，我们通过(1)分析真菌CnCDAs以及人类几丁质分解酶(CHT)、酸性哺乳动物几丁质酶(AMCase)和溶菌酶的底物特异性，(2)调查体外培养后或体内感染的不同人类病原真菌的真菌细胞壁中壳聚糖的数量和结构，以及(3)测试壳聚糖及其酶降解产物对表皮和免疫细胞的免疫刺激作用，从而将这一假说视为一个跨学科的联合体。因此，该项目将有助于更好地了解宿主-微生物之间的相互作用，并制定防止真菌感染的抗感染战略。

Human pathogenic fungi can cause severe systemic infections, especially in immunocompromised people. The molecular mechanisms leading to an effective defence against the invading fungi are still poorly understood. Studies on Cryptococcus neoformans infections suggest that the composition of the cell wall is essential for the virulence of the fungus. Like some other pathogenic fungi, it has chitosan in its cell wall instead of chitin (poly-N-acetyl-glucosamine), which is produced by the partial deacetylation of nascent chitin by chitin deacetylases (CDAs). Oligomeric chitin was shown to act as a microbe-associated molecular pattern (MAMP) and is recognised by pattern recognition receptors such as Toll-like receptor 2 (TLR2), fibrinogen C domain containing 1 (FBCD1) or LYSMD3 of the human immune system. However, the conversion of chitin to chitosan by its four different CDAs (CnCDAs 1-4) may allow C. neoformans to evade recognition by the host immune system. The enzymes are considered to be important virulence factors of the pathogen, preventing the degradation of chitin by human chitinases to immunostimulatory oligomers. In the present project, we address this hypothesis as an interdisciplinary consortium by (1) analysing the substrate specificities of the fungal CnCDAs as well as the human chitinolytic enzymes chitotriosidase (ChT), acidic mammalian chitinase (AMCase) and lysozyme, (2) investigating the amount and structure of chitosans in the fungal cell wall of different human pathogenic fungi after in vitro cultivation or in materials from in vivo infections, and (3) test the immunostimulatory effect of chitosans and their enzymatic degradation products on epidermal and immune cells. The project will thus contribute to a better understanding of host-microbe interactions and the development of anti-infective strategies preventing fungal infections.