Sallusto F, Cella M, Danieli C, Lanzavecchia A
Basel Institute for Immunology, Switzerland.
J Exp Med. 1995 Aug 1;182(2):389-400. doi: 10.1084/jem.182.2.389.
We have previously demonstrated that human peripheral blood low density mononuclear cells cultured in granulocyte/macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4 develop into dendritic cells (DCs) that are extremely efficient in presenting soluble antigens to T cells. To identify the mechanisms responsible for efficient antigen capture, we studied the endocytic capacity of DCs using fluorescein isothiocyanate-dextran, horseradish peroxidase, and lucifer yellow. We found that DCs use two distinct mechanisms for antigen capture. The first is a high level of fluid phase uptake via macropinocytosis. In contrast to what has been found with other cell types, macropinocytosis in DCs is constitutive and allows continuous internalization of large volumes of fluid. The second mechanism of capture is mediated via the mannose receptor (MR), which is expressed at high levels on DCs. At low ligand concentrations, the MR can deliver a large number of ligands to the cell in successive rounds. Thus, while macropinocytosis endows DCs with a high capacity, nonsaturable mechanism for capture of any soluble antigen, the MR gives an extra capacity for antigen capture with some degree of selectivity for non-self molecules. In addition to their high endocytic capacity, DCs from GM-CSF + IL-4-dependent cultures are characterized by the presence of a large intracellular compartment that contains high levels of class II molecules, cathepsin D, and lysosomal-associated membrane protein-1, and is rapidly accessible to endocytic markers. We investigated whether the capacity of DCs to capture and process antigen could be modulated by exogenous stimuli. We found that DCs respond to tumor necrosis factor alpha, CD40 ligand, IL-1, and lipopolysaccharide with a coordinate series of changes that include downregulation of macropinocytosis and Fc receptors, disappearance of the class II compartment, and upregulation of adhesion and costimulatory molecules. These changes occur within 1-2 d and are irreversible, since neither pinocytosis nor the class II compartment are recovered when the maturation-inducing stimulus is removed. The specificity of the MR and the capacity to respond to inflammatory stimuli maximize the capacity of DCs to present infectious non-self antigens to T cells.
我们之前已经证明，在粒细胞/巨噬细胞集落刺激因子（GM-CSF）和白细胞介素（IL）-4中培养的人外周血低密度单核细胞可发育为树突状细胞（DC），这些树突状细胞在将可溶性抗原呈递给T细胞方面极为高效。为了确定有效抗原捕获的机制，我们使用异硫氰酸荧光素-葡聚糖、辣根过氧化物酶和路西法黄研究了DC的内吞能力。我们发现DC使用两种不同的机制进行抗原捕获。第一种是通过巨胞饮作用进行高水平的液相摄取。与其他细胞类型不同，DC中的巨胞饮作用是组成性的，可使大量液体持续内化。第二种捕获机制是通过甘露糖受体（MR）介导的，该受体在DC上高水平表达。在低配体浓度下，MR可以在连续几轮中将大量配体递送至细胞。因此，虽然巨胞饮作用赋予DC高容量、不可饱和的捕获任何可溶性抗原的机制，但MR赋予了DC额外的抗原捕获能力，对非自身分子具有一定程度的选择性。除了具有高内吞能力外，来自GM-CSF + IL-4依赖性培养物的DC的特征还在于存在一个大的细胞内区室，该区域含有高水平的II类分子、组织蛋白酶D和溶酶体相关膜蛋白-1，并且内吞标记物可快速进入。我们研究了外源性刺激是否可以调节DC捕获和处理抗原的能力。我们发现DC对肿瘤坏死因子α、CD40配体、IL-1和脂多糖有一系列协同变化的反应，包括巨胞饮作用和Fc受体的下调、II类区室的消失以及黏附分子和共刺激分子的上调。这些变化在1-2天内发生且不可逆，因为当去除成熟诱导刺激时，胞饮作用和II类区室都不会恢复。MR的特异性和对炎症刺激的反应能力使DC将感染性非自身抗原呈递给T细胞的能力最大化。
