Structure and function of a lectin-like protein of macrophage cell membrane that recognizes oxidized cells

我们从以下几个方面对巨噬细胞识别氧化细胞的分子机制进行了研究。1)阐明了我们先前分离的作为巨噬细胞表面受体分子候选的50 kDa凝集素样蛋白的结构和功能；2)阐明了碳水化合物配体在氧化细胞上识别的机制。此外，在上述研究过程中，我们发现这种识别机制不仅适用于氧化细胞的识别，也适用于死亡细胞的识别。研究结果如下：1.研究结果如下。根据分离株p50的部分氨基酸序列，用聚合酶链式反应从人细胞cDNA文库中克隆了该受体分子的候选蛋白。结论：1.对克隆的基因编码的氧化细胞识别蛋白的鉴定正在进行中。免疫荧光染色证实巨噬细胞表面存在p50，免疫荧光标记p50部分氨基酸序列。此外，该抗体还抑制了氧化细胞对巨噬细胞的识别，证实了p50是氧化细胞的受体。研究发现，处于早期凋亡阶段的T细胞被巨噬细胞识别的机制与氧化细胞的识别机制相同，该机制涉及细胞表面的唾液酸聚乳糖氨基链。有趣的是，这种碳水化合物依赖的识别机制比磷脂酰丝氨酸识别机制更早起作用。识别出的糖链为细胞膜上CD43糖蛋白的糖链。此外，氧化细胞或早期凋亡细胞的CD43呈簇状分布。这一发现证实了我们的假设，即氧化或凋亡细胞的膜糖蛋白聚集将产生细胞识别所需的碳水化合物配体。

We have carried out studies on the molecular mechanism of macrophage recognition of oxidized cells in the following aspects. 1) Elucidation of structure and function of 50 kDa lectin-like protein which we had isolated previously as a candidate for a receptor molecule of macrophage surface, and 2) elucidation of the mechanism of appearance of the carbohydrate ligands for the recognition on the oxidized cells. Furthermore, in the course of the above studies, we have found that this recognition mechanism works not only in the recognition of oxidized cells but also of the cells dying by apotosis. The findings are as follows.1. A candidate protein for the receptor molecule was cloned from human cell cDNA library by PCR, based on the partial amino acid sequence of isolated p50. Identification of the protein coded by the cloned cDNA as the oxidized-cell recognizing protein is now in progress.2. Presence of p50 on macrophage surface was confirmed microscopically by immunofluorescence usig the antibody against the partial amino acid sequence of p50. In addition, macrophage recognition of oxidized cells was inhibited by the antibody, comfirming p50 as a receptor for the oxidized cells.3. It was found that T cells at an early apoptotic stage were recognized by macrophages through the same mechanism, involving sialyl polylactosaminyl chains on the cell surface, as the recognition of oxidized cells. Interestingly, this carbohydrate-dependent recognition mechanism worked earlier than phosphatidylserine-recognizing mechanism.4. The carbohydrate chains recognized were found to be those of CD43 glycoprotein of the cell membrane. Moreover, CD43 of oxidized cells or early apoptotic cells were found to undergo clustering. This finding substantiated our hypothesis that clustering of membrane glycoproteins of oxidized or apoptotic cells would generate carbohydrate ligands for the cell recognition.