Annexin V can be used as one of the most sensitive indicators to detect the early-stage apoptosis. In normal live cells, phosphatidylserine (PS) is located only on the inner face of plasma membrane. However, in the early-stage apoptosis, PS is translocated from the inner to the outer leaflet of the plasma membrane, thus exposing PS to cell surface. Annexin V is a Ca 2+ -dependent phospholipid- binding protein that has a high affinity for PS. Therefore, Annexin V can identify early-stage apoptosis by binding to PS exposed on the outer leaflet. Annexin V can be labeled with green fluorophore (FITC), the labeled Annexin V-FITC is used as a probe to detect the occurrence of apoptosis by flow cytometry or by fluorescence microscopy. Propidium iodide (PI) is a nucleic acid binding dye, and it is impermeant to live cells with intact membrane and early apoptotic cells. However, PI can stain the nucleus through permeating to cell membrane of mid-stage or late-stage apoptotic cells and necrosis cells, which show red fluorescence under certain laser excitation.

Target	Annexin V-EGFP/PI Cell Apoptosis
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Research Articles on Annexin V-EGFP / PI Cell Apoptosis Detection Kit

Isotype Control 同型对照 同型对照（Isotype Control），使用与一抗相同种属来源、相同亚型、相同剂量和相同的免疫球蛋白及亚型的免疫球蛋白，用于消除由于抗体非特异性结合到细胞表面而产生的背景染色。 同型对照 同型对照的主要目的是确定一抗的结合是特异性的，而不是非特异性的Fc受体或与其他蛋白的相互作用。还可以用来竞争性的结合抗体，与功能阻断抗体发挥同样的功能。 同型对照要与一抗的来源，Ig分型和标记完全一致。 如果一抗是多抗，可以用an normal serum（与一抗相同的正常血清） （must be the same species as primary antibody）。This control is easy to achieve and can be used routinely in immunohistochemical staining.这个可以咨询试剂商。同型对照为免疫荧光标记中的阴性对照。由于荧光标记单抗的组来源不同，应选用相同来源的未标记单抗作为同型对照来 调整背景染色。举个例子：比如检测一抗为单抗的mouse anti rat CD11b，clone OX-42 purified IgG，那么它的isotype 是mouse IgG2a， 所以可以用purified（纯化的） mouse IgG2a来做OX-42的同型对照（Isotype Control）。一般的的生物技术公司和国内的代理都有出售。 同型对照：是指与MoAb相同的、未免疫小鼠的免疫球蛋白亚类，若使用直接免疫荧光染色法，同型对照也应标记荧光色素，如IgG1 FITC、IgG2a、PE等。主要考虑了细胞的自发荧光、FC受体介导的抗体结合和非特异性抗体结合等影响因素。此外，同型对照与MoAb所标记的荧光 色素、浓度、F：P比值（标记的荧光色素与免疫球蛋白分子的比值）应该相同为最佳，这对准确设定阴性与阳性细胞的界标有重要意义，切忌使用与MoAb不相 匹配的同型对照，最好为同一实验室、采用相同工艺或方法制备（如同一品牌）的产品。