凋亡細胞受到巨噬細胞的清除是人體重要的恆定機制，如果巨噬細胞無法有效的將凋亡細胞清除就有可能會造成自體免疫疾病。實驗室先前的研究發現SARS病人的血清中有自體抗體的存在並且這種抗體可以與人類的肺上皮細胞發生交互作用。競爭結合的實驗分析指出SARS冠狀病毒棘蛋白區域2 (S2) 確實有交互作用的抗原決定位存在，進一步的實驗鑑定出數個自體抗原。在這些自體抗原之中，annexin II 在早先的研究中就被證實與巨噬細胞吞噬凋亡細胞有重要的相關。我們假設anti-S2抗體可能會與巨噬細胞表面的annexin II結合並且會去抑制巨噬細胞對凋亡細胞的清除能力。人類的單核球細胞株THP-1與U937利用 phorbol 12-myristate 13-acetate (PMA) 活化24到96小時可以促進這些細胞株annexin II蛋白質的表現增加。伴隨著annexin II的表現量上升，活化的細胞株吞噬凋亡細胞的能力也隨之增強。我們利用PMA活化的U937吞噬凋亡細胞後，偵測caspase-3的活性，及利用曠時攝影術研究老鼠腹腔巨噬細胞對凋亡細胞的吞噬作用，來了解anti-S2及anti-annexin II抗體對巨噬細胞所產生的抗吞噬現象。更進一步的發現anti-S2及anti-annexin II的抗體可以抑制小鼠腹腔巨噬細胞的移動，並且凋亡細胞與活化U937細胞株的黏附也會受到anti-S2及anti-annexin II抗體所抑制。因此我們認為巨噬細胞的移動與和凋亡細胞的黏附受到干擾，為anti-S2抗體產生抑制巨噬細胞吞噬能力的主要原因。然而這個抗吞噬的機制與anti-S2抗體傳遞訊號到細胞內都是有待研究的方向。是否對抗S2抗體在SARS免疫致病機轉上扮演重要的角色，是有待我們去釐清的。

Apoptotic cell clearance by phagocytes is a homeostasis mechanism in human. Failure of phagocytes to uptake apoptotic cells may cause autoimmune disease. Pervious study in our laboratory showed that in SARS patient sera, there were autoantibodies that reacted with human lung epithelial cells. Preabsorption and binding assays indicated the existence of cross-reactive epitopes on SARS-CoV spike protein domain 2 (S2). Several candidate autoantigens have been identified. Among them, annexin II has been shown to play an important role in phagocytosis of apoptotic cells by macrophage. We hypothesize that anti-S2 antibody might bind to annexin II on macrophages and inhibit their phagocytic activity to apoptotic cells. Human monocytic cell lines THP-1 and U937 were activated by phorbol 12-myristate 13-acetate (PMA) for 24 to 96 h, which caused an increase in the annexin II expression. An increase in the ability of activated monocytic cells to phagocytose apoptotic cells was also observed. We showed anti-phagocytic effect of anti-S2 antibodies in PMA-activated U937 cells by caspase-3 activity detection and in mouse peritoneal macrophages by time-lapse microscopy. Furthermore, anti-S2 and anti-annexin II antibodies inhibited the migration of peritoneal macrophage. Anti-S2 and anti-annexin II antibodies inhibited the binding of apoptotic cells to PMA-activated U937 cells. We propose that the inhibition of migration and binding to apoptotic cells of macrophage is involved in the anti-phagocytic effect of anti-S2 antibody. The mechanism and signaling of anti-S2-mediated inhibitory effect on phagocytes need to be investigated. Moreover, whether the anti-phagocytic activity of anti-S2 antibodies plays a role in SARS immunopathologic mechanism remains unresolved.

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