Physiological roles of apoptotic cell clearance

由活化的巨噬细胞和未成熟树突状细胞分泌的乳脂球EGF因子8（MFG-E8）连接凋亡细胞和吞噬细胞，并促进凋亡细胞的吞噬作用。我们发现MFG-E8突变体，命名为D89 E，携带一个点突变的RGD基序，抑制各种吞噬细胞的吞噬凋亡细胞。当静脉注射到小鼠体内时，D89 E蛋白诱导自身抗体的产生，包括抗磷脂抗体和抗核抗体。通过共注射同基因凋亡胸腺细胞，自身抗体的产生得到增强。在通过D89 E诱导自身抗体产生后，治疗的小鼠显示出自身抗体滴度的长期升高，并在腹股沟中形成IgG沉积。这些结果表明，凋亡细胞吞噬功能的损害导致自身抗体的production.We产生的转基因小鼠中，II型肺上皮细胞以及巨噬细胞被瞬时消融。人白喉毒素受体在溶菌酶M基因启动子的调控下在小鼠体内表达。小鼠经白喉毒素染毒后，出现急性肺损伤，并在4天内死亡。在用白喉毒素处理的小鼠中，II型细胞以及肺泡巨噬细胞被删除。白喉毒素处理的转基因小鼠支气管肺泡灌洗液中表面活性蛋白A和B的量大大减少。当将野生型小鼠的骨髓移植到受辐射的转基因小鼠中时，肺泡巨噬细胞对白喉毒素产生了抵抗力，但小鼠仍然遭受急性肺损伤。这些结果表明，II型细胞的消融引起致命的急性呼吸窘迫与表面活性蛋白的量减少。

Milk fat globule-EGF-factor 8 (MFG-E8), secreted by activated macrophages and immature dendritic cells, links apoptotic cells and phagocytes, and promotes phagocytosis of apoptotic cells. We found that an MFG-E8 mutant, designated as D89E, carrying a point mutation in an RGD motif, inhibited the phagocytosis of apoptotic cells by a wide variety of phagocytes. When intravenously injected into mice, the D89E protein induced the production of auto-antibodies including anti-phospholipids antibodies and anti-nuclear antibodies. The production of auto-antibodies was enhanced by the co-injection of syngeneic apoptotic thymocytes. Following the induction of auto-antibody production by D89E, the treated mice showed a long-term elevation of the titer for auto-antibodies, and developed IgG deposition in the gromeruli. These results indicated that the impairment of apoptotic cell phagocytosis led to auto-antibody production.We generated transgenic mice in which type II lung epithelial cells as well as macrophages were transiently ablated. Human diphtheria toxin receptor was expressed under the control of the lysozyme M gene promoter in the mice. When diphtheria toxin was administrated to the mice, they suffered from acute lung injury, and died within 4 days. Type II cells as well as alveolar macrophages were deleted in the mice treated with diphtheria toxin. The amount of surfactant proteins A and B in bronchoalveolar lavage fluid was greatly reduced in the diphtheria toxin-treated transgenic mice. When the bone marrow from wild-type mice was transplanted into the irradiated transgenic mice, the alveolar macrophages became resistant to diphtheria toxin, but the mice still suffered from acute lung injury. These results indicated that ablation of type II cells caused lethal acute respiratory distress in association with the reduced amount of surfactant proteins.