Lesma E, Moss J, Brewer H B, Bortell R, Greiner D, Mordes J, Rossini A A
Pulmonary-Critical Care Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
J Immunol. 1998 Aug 1;161(3):1212-9.
RT6 is a rat lymphocyte glycosylphosphatidylinositol (GPI)-anchored alloantigen with nicotinamide adenine dinucleotide (NAD) glycohydrolase (NADase) and auto-ADP-ribosyltransferase activities. RT6 may have immunoregulatory properties based in part on the observation that injection of diabetes-resistant (DR)-BB rats with depleting doses of anti-RT6.1 mAb induced autoimmune diabetes and thyroiditis. We now report that injection of DR-BB rats with anti-RT6.1 mAb increased plasma NADase activity, which localized, by fluid phase liquid chromatography fractionation, to the high density lipoprotein (HDL) fraction. Following ultracentrifugation in high salt, however, RT6 was found in the nonlipoprotein fraction, where it existed, under nondenaturing conditions, as a 200-kDa complex and, by SDS-PAGE, as a 30- to 36-kDa species. Thy-1, another GPI-linked protein, and proteins that reacted with anti-GPI-oligosaccharide Abs also translocated from HDL to the nonlipoprotein fraction under similar conditions. Injection of anti-RT6.1 mAb into thymectomized DR and diabetes-prone-BB rats increased soluble RT6 to levels comparable to those observed in euthymic DR-BB rats, suggesting that HDL-bound RT6 is not derived from peripheral lymphocytes. In agreement, NADase activity in the plasma of eviscerated DR-BB rats did not increase following injection of anti-RT6 mAb. These data suggest that HDL is a carrier of plasma RT6 and other GPI-linked proteins, with equilibrium between the lipoprotein and nonlipoprotein fractions being salt dependent. Since GPI-linked proteins in HDL can transfer to cells in a functionally active form, the presence of RT6 in HDL is consistent with it having a role in signaling in nonlymphoid cells.
RT6是一种大鼠淋巴细胞糖基磷脂酰肌醇（GPI）锚定的同种异体抗原，具有烟酰胺腺嘌呤二核苷酸（NAD）糖水解酶（NADase）和自身ADP-核糖基转移酶活性。RT6可能具有免疫调节特性，部分基于以下观察结果：给抗糖尿病（DR）-BB大鼠注射消耗剂量的抗RT6.1单克隆抗体可诱发自身免疫性糖尿病和甲状腺炎。我们现在报告，给DR-BB大鼠注射抗RT6.1单克隆抗体可增加血浆NADase活性，通过液相液相色谱分级分离，该活性定位于高密度脂蛋白（HDL）部分。然而，在高盐条件下超速离心后，RT6存在于非脂蛋白部分，在非变性条件下，它以200 kDa的复合物形式存在，通过SDS-PAGE分析，以30至36 kDa的条带形式存在。Thy-1，另一种GPI连接蛋白，以及与抗GPI-寡糖抗体反应的蛋白质在类似条件下也从HDL转移到非脂蛋白部分。给胸腺切除的DR和糖尿病易感BB大鼠注射抗RT6.1单克隆抗体可使可溶性RT6增加到与正常胸腺DR-BB大鼠中观察到的水平相当，这表明与HDL结合的RT6并非来源于外周淋巴细胞。同样，摘除内脏的DR-BB大鼠注射抗RT6单克隆抗体后，血浆中的NADase活性并未增加。这些数据表明，HDL是血浆RT6和其他GPI连接蛋白的载体，脂蛋白和非脂蛋白部分之间的平衡取决于盐浓度。由于HDL中的GPI连接蛋白可以以功能活性形式转移到细胞中，HDL中存在RT6与其在非淋巴细胞信号传导中的作用一致。
