Department of Microbiology and Immunology, University of Maryland School of Medicine, UMB, Baltimore, USA.
Institute of Marine and Environmental Technology, Columbus Center, University of Maryland, 701 East Pratt Street, Baltimore, MD, 21202, USA.
Adv Exp Med Biol. 2020;1204:169-196. doi: 10.1007/978-981-15-1580-4_7.
Galectins are a family of ß-galactoside-binding lectins characterized by a unique sequence motif in the carbohydrate recognition domain, and evolutionary and structural conservation from fungi to invertebrates and vertebrates, including mammals. Their biological roles, initially understood as limited to recognition of endogenous ("self") carbohydrate ligands in embryogenesis and early development, dramatically expanded in later years by the discovery of their roles in tissue repair, cancer, adipogenesis, and regulation of immune homeostasis. In recent years, however, evidence has also accumulated to support the notion that galectins can bind ("non-self") glycans on the surface of potentially pathogenic microbes, and function as recognition and effector factors in innate immunity. Thus, this evidence has established a new paradigm by which galectins can function not only as pattern recognition receptors but also as effector factors, by binding to the microbial surface and inhibiting adhesion and/or entry into the host cell, directly killing the potential pathogen by disrupting its surface structures, or by promoting phagocytosis, encapsulation, autophagy, and pathogen clearance from circulation. Strikingly, some viruses, bacteria, and protistan parasites take advantage of the aforementioned recognition roles of the vector/host galectins, for successful attachment and invasion. These recent findings suggest that galectin-mediated innate immune recognition and effector mechanisms, which throughout evolution have remained effective for preventing or fighting viral, bacterial, and parasitic infection, have been "subverted" by certain pathogens by unique evolutionary adaptations of their surface glycome to gain host entry, and the acquisition of effective mechanisms to evade the host's immune responses.
半乳糖凝集素是一类β-半乳糖苷结合凝集素，其特征在于糖识别结构域中具有独特的序列基序，并且在真菌、无脊椎动物和脊椎动物（包括哺乳动物）中具有进化和结构上的保守性。它们的生物学功能最初被理解为仅限于识别胚胎发生和早期发育中的内源性（“自身”）碳水化合物配体，后来通过发现它们在组织修复、癌症、脂肪生成和免疫稳态调节中的作用而得到了极大的扩展。然而，近年来的证据也表明，半乳糖凝集素可以结合潜在病原体微生物表面的（“非自身”）聚糖，并作为先天免疫中的识别和效应因子发挥作用。因此，这一证据建立了一个新的范例，即半乳糖凝集素不仅可以作为模式识别受体，还可以作为效应因子，通过与微生物表面结合来抑制黏附和/或进入宿主细胞，通过破坏其表面结构直接杀死潜在的病原体，或者通过促进吞噬作用、包封作用、自噬作用和从循环中清除病原体。引人注目的是，一些病毒、细菌和原生动物寄生虫利用上述载体/宿主半乳糖凝集素的识别作用，成功地附着和入侵。这些新发现表明，半乳糖凝集素介导的先天免疫识别和效应机制，在整个进化过程中一直有效地预防或对抗病毒、细菌和寄生虫感染，但某些病原体通过其表面糖组的独特进化适应，获得了宿主进入的能力，并获得了逃避宿主免疫反应的有效机制，从而被“颠覆”。
