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

1.肺表面活性蛋白A和D（SP-A和SP-D）以及甘露糖结合蛋白A（MBP-A）是C型凝集素超家族中的凝集素。这些聚集素表现出独特的脂质结合特性。发现Glu^<195>- Phe^的<228>SP-A区是脂质和肺泡II型细胞相互作用所必需的，Cys^ -Phe ^的SP-D区是<261><355>最佳脂质相互作用所必需的，识别人SP-A的单克隆抗体PE 10和PC 6抑制SP-A与脂质和肺泡II型细胞的相互作用。利用噬菌体肽库技术对抗人SP-A单克隆抗体的表位进行了定位。通过单克隆抗体选择的噬菌体展示了与人SP-A的TPVNYTNWYRG^几乎相同的共有肽序列<184><194>。产生了嵌合蛋白，其中大鼠SP-A区域Thr^<174>-Gly^<194>被MBP-A区域Thr^<164>-Asp^<184>（分别为大鼠ama 4）取代。 关于我们 .大鼠ama 4与甘露糖-琼脂糖凝胶上的亲和基质结合，但失去了除了碳水化合物结合和Ca^2+非依赖性GalCer结合之外的所有SP-A功能。引人注目的是，大鼠ama 4嵌合体获得了MBP-A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MBP-A的相应区域对于SP-A-II型细胞相互作用和胶原凝集素的Ca^&lt;2+&gt;依赖性脂质结合是至关重要的.肺表面活性物质蛋白A（SP-A）在非抗体依赖性宿主肺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预孵育时，光滑LPS不能诱导TNF α分泌，而粗糙LPS诱导的TNF α分泌略有增加。Western blot分析表明，CD 14是从溶解的U937细胞中分离的SP-A结合蛋白之一。此外，SP-A直接结合重组可溶性CD 14（rsCD 14）。当rsCD 14与SP-A预孵育时，rsCD 14与光滑LPS的结合显著减少，但rsCD 14与粗糙LPS的结合增强。这些结果证明了SP-A对不同血清型LPS的不同作用，并表明SP-A与CD 14的直接相互作用构成了SP-A调节LPS引起的细胞应答的可能机制。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