Pyz Elwira, Marshall Andrew S J, Gordon Siamon, Brown Gordon D
The Institute of Infectious Disease and Molecular Medicine, University of Cape Town, South Africa.
Ann Med. 2006;38(4):242-51. doi: 10.1080/07853890600608985.
Host defence against pathogens requires the recognition of conserved microbial molecules, or 'pathogen-associated molecular patterns' (PAMPs), by their receptors termed 'pattern recognition receptors' (PRRs), represented most notably by toll-like receptors (TLRs) and C-type lectins. The 'non-classical' C-type lectins (these that lack the residues involved in calcium binding, required for carbohydrate binding) are traditionally thought of as being restricted to natural killer (NK) or T cells, playing important roles in immune surveillance. In recent years, however, a growing number of these receptors have been identified on myeloid cells, both of human and mouse origin. In contrast to their NK counterparts that primarily control cellular activation through recognition of major histocompatibility antigen (MHC) class I and related molecules, the myeloid-expressed receptors appear to have a far more diverse range of functions and ligands, including those of exogenous origin. Some of C-type lectin-like molecules possess activating/inhibitory signalling motifs that trigger downstream signalling events, suggesting the role for these receptors as positive/negative regulators of granulocyte and monocyte functions. With the exception of a few myeloid NK-like lectins, the natural ligands for most of these receptors remain unidentified, making it difficult to define their functions in normal physiological, inflammatory or pathological conditions. Importantly, in some cases, these novel C-type lectin-like lectins, encoded by genes from the same gene cluster, can act as receptor/ligand pairs, additionally contributing to the regulation of myeloid cell functions or their interaction with other (like NK) cell types. However, the relevance and importance of such interactions still needs to be assessed. Although few of the myeloid-expressed C-type lectins have been characterized in detail, we review here each of these receptors and highlight their prospective roles in innate and adaptive immunity.
宿主抵御病原体需要通过被称为“模式识别受体”（PRR）的受体来识别保守的微生物分子，即“病原体相关分子模式”（PAMP），其中最典型的代表是Toll样受体（TLR）和C型凝集素。传统上认为“非经典”C型凝集素（即那些缺乏碳水化合物结合所需的钙结合残基的凝集素）仅限于自然杀伤（NK）细胞或T细胞，在免疫监视中发挥重要作用。然而，近年来，在人和小鼠来源的髓系细胞上发现了越来越多这类受体。与主要通过识别主要组织相容性抗原（MHC）I类及相关分子来控制细胞活化的NK细胞不同，髓系表达的受体似乎具有更为多样的功能和配体，包括外源性配体。一些C型凝集素样分子具有激活/抑制信号基序，可触发下游信号事件，这表明这些受体可作为粒细胞和单核细胞功能的正/负调节因子。除了少数髓系NK样凝集素外，这些受体的大多数天然配体仍未明确，这使得难以确定它们在正常生理、炎症或病理条件下的功能。重要的是，在某些情况下，这些由同一基因簇中的基因编码的新型C型凝集素样凝集素可作为受体/配体对，进一步参与调节髓系细胞功能或其与其他（如NK）细胞类型的相互作用。然而，这种相互作用的相关性和重要性仍需评估。尽管很少有髓系表达的C型凝集素得到详细表征，但我们在此综述这些受体，并强调它们在固有免疫和适应性免疫中的潜在作用。
