Falasca L, Bergamini A, Serafino A, Balabaud C, Dini L
Department of Biology, University of Rome Tor Vergata, Italy.
Exp Cell Res. 1996 Apr 10;224(1):152-62. doi: 10.1006/excr.1996.0123.
Cells undergoing apoptosis are recognized and rapidly phagocytosed by macrophages before their degradation, thus preventing the inflammatory reaction and protecting tissues from the damaging effects of released potentially harmful intracellular contents. In spite of growing interest in the mechanisms leading to the engulfment of apoptotic cells, the molecular bases by which an apoptotic cell is recognized are not entirely understood. Among the several potential mechanisms by which a macrophage can identify a cell as apoptotic, the data reported in the present paper support the idea that Kupffer cells phagocytose apoptotic cells by means of lectin-like receptors. Human Kupffer cells, which possess galactose-specific binding sites, can recognize and phagocytose peripheral blood lymphocytes undergoing apoptosis after heat shock (43 degrees C) or cycloheximide treatment, but not normal living peripheral blood lymphocytes. The putative structure by which apoptotic peripheral blood lymphocytes are targeted as "edible" could be the molecular changes in the plasma membrane, In fact, our experiments indicate that the membranes of apoptotic peripheral blood lymphocytes express increased amounts of N-acetylgalactosamine, D-galactose, and mannose residues when compared with membranes of normal PBL. Phagocytosis was inhibited by adding to the culture medium sugar cocktail solution (glucose, N-acetylgalactosamine, methyl mannopyranoside, fucose, 80 mM final concentration) or to a lower extent by desialylated glycoproteins (lactosylated bovine serum albumin, asialofetuin, 2 mg/ml final concentration), but not by nondesialylated glycoproteins (fetuin, 2 mg/ml final concentration, bovine serum albumin, 20% final concentration). In addition, phagocytosis of apoptotic peripheral blood lymphocytes by human Kupffer cells was a very rapid process, being almost entirely completed within 15 min of incubation.
正在经历凋亡的细胞在降解之前会被巨噬细胞识别并迅速吞噬，从而防止炎症反应，并保护组织免受释放的潜在有害细胞内物质的破坏作用。尽管人们对导致凋亡细胞被吞噬的机制越来越感兴趣，但凋亡细胞被识别的分子基础尚未完全了解。在巨噬细胞识别细胞为凋亡细胞的几种潜在机制中，本文报道的数据支持库普弗细胞通过凝集素样受体吞噬凋亡细胞的观点。具有半乳糖特异性结合位点的人库普弗细胞能够识别并吞噬经热休克（43℃）或环己酰亚胺处理后正在经历凋亡的外周血淋巴细胞，但不能识别正常存活的外周血淋巴细胞。凋亡外周血淋巴细胞被靶向为“可食用”的推定结构可能是质膜中的分子变化。事实上，我们的实验表明，与正常外周血淋巴细胞的膜相比，凋亡外周血淋巴细胞的膜表达了更多的N-乙酰半乳糖胺、D-半乳糖和甘露糖残基。通过向培养基中添加糖混合溶液（葡萄糖、N-乙酰半乳糖胺、甲基甘露糖苷、岩藻糖，终浓度80 mM）可抑制吞噬作用，或者在较低程度上通过去唾液酸化糖蛋白（乳糖基化牛血清白蛋白、去唾液酸胎球蛋白，终浓度2 mg/ml）抑制，但非去唾液酸化糖蛋白（胎球蛋白，终浓度2 mg/ml，牛血清白蛋白，终浓度20%）则不能抑制。此外，人库普弗细胞对凋亡外周血淋巴细胞的吞噬是一个非常快速的过程，在孵育15分钟内几乎完全完成。
