Host defense mechanism and modulation of lipid metabolism by pulmonary surfactant proteins

1.肺表面活性物质蛋白A和D(SP-A和SP-D)和甘露糖结合蛋白A(MBP-A)是C型凝集素超家族中的集合素。这些集合素表现出独特的脂质结合特性。用SP-ASP-D嵌合体研究了结构与功能的关系，发现SP-A区的Glu^&lt；195&gt；-Phe^&lt；228&gt；228&gt；是脂质和II型细胞相互作用所必需的，Cys^&lt；261&gt；-Phe^&lt；355&gt；355&gt；的SP-D区是脂质和肺泡II型细胞相互作用所必需的。识别人SP-A的单抗(mAbPelo和PC6)抑制了SP-A与脂质和肺泡II型细胞的作用。我们利用噬菌体展示多肽文库绘制了抗人SP-A单抗的表位图。用单抗筛选的噬菌体展示了与人SP-A的一致多肽序列，这些序列与人SP-A的同源性很高。用…替换了大鼠SP-A区的嵌合蛋白。更多。大鼠ama4与甘露糖-琼脂糖凝胶上的亲和基质结合，但失去了除糖结合和钙非依赖性GalCer结合外的所有SP-A功能。值得注意的是，大鼠AMA4嵌合体获得了MBP-A所表现出的PI结合特性。本研究表明，SP-A的174-194位氨基酸残基和相应的MBP-A区域对于SP-A与II型细胞的相互作用和依赖于钙离子的集合素的脂质结合是至关重要的。肺表面活性物质蛋白A(SP-A)在肺的抗体非依赖性宿主防御机制中起重要作用。当U937细胞和大鼠肺泡巨噬细胞与SP-A预先孵育时，光滑脂多糖不能诱导细胞分泌肿瘤坏死因子α，而粗制脂多糖诱导的细胞分泌肿瘤坏死因子α略有增加。Western印迹分析表明，CD14是从溶解的U937细胞中分离到的SP-A结合蛋白之一。此外，SP-A还与重组可溶性CD14(RsCD14)直接结合。当rsCD14与SP-A预先孵育时，rsCD14与光滑内毒素的结合显著降低，而rsCD14与粗大内毒素的结合增强。这些结果说明了SP-A对不同的内毒素血清型的不同作用，并提示SP-A与CD14的直接相互作用可能是SP-A调节内毒素诱导的细胞反应的一个可能机制。较少

1. Pulmonary surfactant proteins A and D (SP-A and SP-D) and mannose-binding protein A(MBP-A) are collectins in the C-type lectin superfamily. These collectins exhibit unique lipid binding properties. The structure-function relationship was investigated by using SP-ASP-D chimeras, It was found that the SP-A region of Glu^<195>- Phe^<228> is required for lipid and type II cell interactions and that the SP-D region of Cys^<261>-Phe^<355> is required for optimal lipid interactions.Monoclonal antibodies (mAbs PElO and PC6) that recognize human SP-A inhibit the interactions of SP-A with lipids and alveolar type II cells. We mapped the epitopes for antihuman SP-A mAbs by a phage display peptide library. Phage selected by mAbs displayed the consensus peptide sequences that are nearly identical to ^<184>TPVNYTNWYRG^<194> of human SP-A.Chimeric proteins were generated in which the rat SP-A region Thr^<174>-Gly^<194> was replaced with the MBP-A region Thr^<164>-Asp^<184> (rat ama4, respectively) … More . Rat ama4 bound to an affinity matrix on mannose-sepharose but lost all of the SP-A functions except carbohydrate binding and Ca^<2+> independent GalCer binding. Strikingly, the rat ama4 chimera acquired the PI binding property that MBP-A exhibits. This study demonstrates that the amino acid residues 174-194 of SP-A and the corresponding region of MBP-A are critical for SP-A-type II cell interaction and Ca^<2+>-dependent lipid binding of collectins.2. Pulmonary surfactant protein A (SP-A) plays an important part in antibody independent host defense mechanisms of the lung. SP-A bound to rough forms but not to smooth forms of LPS.When U937 cells and rat alveolar macrophages were preincubated with SP-A ; smooth LPS failed to induce TNFalpha secretion while rough LPS-induced TNFalpha secretion was modestly increased. Western blot analysis revealed that CD14 was one of the SP-A-binding proteins isolated from solubilized U937 cells. In addition, SP-A directly bound to recombinant soluble CD14 (rsCDl4). When rsCDl4 was preincubated with SP-A, the binding of rsCDl4 to smooth LPS was significantly reduced but the association of rsCDl4 with rough LPS was augmented. These results demonstrate the different actions of SP-A upon distinct serotypes of LPS, and indicate that the direct interaction of SP-A with CD14 constitutes a likely mechanism by which SP-A modulates LPS-elicited cellular responses. Less