Colacicco G, Ray A K, Hendrickson H R, Buckelew A R, Scarpelli E M
Prep Biochem. 1976;6(6):443-77. doi: 10.1080/00327487608069129.
Although dipalmitoyl lecithin, is the essential component of the pulmonary surfactant system that is invoked for alveolar stability, there is no explanation as yet for the origin and role of certain proteins that are found with the phospholipid in pulmonary washings. Aqueous lavages obtained from rabbit lung contain three major proteins, two of which are serum proteins (albumin 60%, gamma-globulin 10%), and the third, protein "T" (20%), is described here as pulmonary secretory immunoglobulin A (sIgA1. The protein is first recovered quantitatively in the surface active lipid-protein fraction from filtration of pulmonary lavage on Sephadex G-200. The protein is then isolated from the lipid either by filtration on SDS-Sephadex G-200 or by ethanol-ether precipitation. After reductive cleavage with either mercaptoethanol or dithiothreitol and alkylation with iodoacetamide, three protein peaks are obtained from SDS-sephadex G-200 separation. The products of reductive cleavage are analogous to the secretory component (MW approximately 60,000), H-chain (MW approximately 50,000), L-chain (MW approximately 25,000), and J-piece (MW approximately 28,000) of secretory IgA from colostrum. In immunodiffusion the lung protein and colostrum sIgA show striking identity lines, as do antibodies to rabbit colostrum and to the lung protein. Amino acid and carbohydrate analyses reveal some differences between the two secretory immunoglobulins. Although this protein has been found together with the phospholipid surfactant of the lung in vitro, the present structural study concludes that the protein is sIgA. Although concurrent immunofluorescence studies showed that this protein is in the alveolar lining layer, we cannot as yet conclude that it belongs to the surfactant system of the lung.
尽管二棕榈酰卵磷脂是维持肺泡稳定性的肺表面活性物质系统的重要组成部分，但对于在肺灌洗液中与磷脂一起发现的某些蛋白质的来源和作用，目前尚无解释。从兔肺获得的水洗液含有三种主要蛋白质，其中两种是血清蛋白（白蛋白60%，γ-球蛋白10%），第三种蛋白质“T”（20%），在这里被描述为肺分泌型免疫球蛋白A（sIgA）。该蛋白质首先通过在Sephadex G - 200上过滤肺灌洗液从表面活性脂质 - 蛋白质组分中定量回收。然后通过在SDS - Sephadex G - 200上过滤或乙醇 - 乙醚沉淀从脂质中分离该蛋白质。在用巯基乙醇或二硫苏糖醇进行还原裂解并用碘乙酰胺进行烷基化后，从SDS - sephadex G - 200分离中获得三个蛋白质峰。还原裂解产物类似于初乳中分泌型IgA的分泌成分（分子量约60,000）、重链（分子量约50,000）、轻链（分子量约25,000）和连接片段（分子量约28,000）。在免疫扩散中，肺蛋白和初乳sIgA显示出明显的同一线，兔初乳抗体和肺蛋白抗体也是如此。氨基酸和碳水化合物分析揭示了两种分泌型免疫球蛋白之间的一些差异。尽管在体外已发现该蛋白质与肺的磷脂表面活性剂一起存在，但目前的结构研究得出结论，该蛋白质是sIgA。尽管同时进行的免疫荧光研究表明该蛋白质存在于肺泡内衬层中，但我们目前还不能得出它属于肺表面活性物质系统的结论。
