凋亡是在胚胎发育过程中发生的正常生理过程以及组织稳态的维持。凋亡程序的特征是某些形态学特征，包括质膜不对称和附着，细胞质和细胞核的缩合以及DNA的核小体间裂解。质膜的损失是zui早的特征之一。在凋亡细胞中，膜磷脂磷脂酰丝氨酸（PS）从质膜的内部和外部叶片转位，从而将PS暴露于外部细胞环境。膜联蛋白V是一种35-36 kDa的Ca2 +依赖性磷脂结合蛋白，对PS具有高亲和力，并与暴露的PS结合细胞。膜联蛋白V可以与包括FITC的荧光染料缀合。该格式保留了对PS的高亲和力，因此用作对正在进行细胞凋亡的细胞的流式细胞分析的敏感探针。由于PS的外化发生在凋亡的早期阶段，FITC膜联蛋白V染色可以比基于核变化如DNA片段化的测定在早期鉴定凋亡。
FITC膜联蛋白V染色先于膜完整性的丧失，伴随着由凋亡或坏死过程引起的zui新细胞死亡阶段。因此，FITC膜联蛋白V的染色通常与重要染料（如碘化丙啶（PI）或7-氨基放线菌素（7-AAD））结合使用，以使研究人员能够鉴定早期凋亡细胞（PI阴性，FITC膜联蛋白V正）。具有完整膜的活细胞排除PI，使死亡和受损细胞的膜可透过PI。例如，认为可行的细胞是FITC膜联蛋白V和PI阴性; 早期凋亡细胞是FITC Annexin V阳性和PI阴性; 细胞凋亡或已经死亡的细胞都是FITC膜联蛋白V和PI阳性。该测定不区分已经经历凋亡死亡的细胞与由于坏死性途径死亡的细胞，因为在任一情况下，死细胞都会用FITC Annexin V和PI染色。然而，随着时间的推移，当细胞凋亡被测量时，细胞可以经常从FITC膜联蛋白V和PI阴性（可行或无可测量的凋亡）追溯到FITC膜联蛋白V阳性和PI阴性（早期凋亡，膜完整性存在），zui后到FITC膜联蛋白V和PI阳性（末期凋亡和死亡）。细胞通过这三个阶段的运动表明细胞凋亡。相比之下，一个单一的观察结果表明，细胞都是FITC膜联蛋白V和PI阳性，本身就显示出关于细胞进行死亡的过程的信息较少。
Apoptosis is a normal physiologic process which occurs during embryonic development as well as in maintenence of tissue homeostasis. The apoptotic program is characterized by certain morphologic features, including loss of plasma membrane asymmetry and attachment, condensation of the cytoplasm and nucleus, and internucleosomal cleavage of DNA. Loss of plasma membrane is one of the earliest features. In apoptotic cells, the membrane phospholipid phosphatidylserine (PS) is translocated from the inner to the outer leaflet of the plasma membrane, thereby exposing PS to the external cellular environment. Annexin V is a 35-36 kDa Ca2+ dependent phospholipid-binding protein that has a high affinity for PS, and binds to cells with exposed PS. Annexin V may be conjugated to fluorochromes including FITC. This format retains its high affinity for PS and thus serves as a sensitive probe for flow cytometric analysis of cells that are undergoing apoptosis. Since externalization of PS occurs in the earlier stages of apoptosis, FITC Annexin V staining can identify apoptosis at an earlier stage than assays based on nuclear changes such as DNA fragmentation.
FITC Annexin V staining precedes the loss of membrane integrity which accompanies the latest stages of cell death resulting from either apoptotic or necrotic processes. Therefore, staining with FITC Annexin V is typically used in conjunction with a vital dye such as propidium iodide (PI) or 7-Amino-Actinomycin (7-AAD) to allow the investigator to identify early apoptotic cells (PI negative, FITC Annexin V positive). Viable cells with intact membranes exclude PI, wheras the membranes of dead and damaged cells are permeable to PI. For example, cells that are considered viable are FITC Annexin V and PI negative; cells that are in early apoptosis are FITC Annexin V positive and PI negative; and cells that are in late apoptosis or already dead are are both FITC Annexin V and PI positive. This assay does not distinguish between cells that have undergone apoptotic death versus those that have died as a result of a necrotic pathway because in either case, the dead cells will stain with both FITC Annexin V and PI. However, when apoptosis is measured over time, cells can be often tracked from FITC Annexin V and PI negative (viable, or no measurable apoptosis), to FITC Annexin V positive and PI negative (early apoptosis, membrane integrity is present) and finally to FITC Annexin V and PI positive (end stage apoptosis and death). The movement of cells through these three stages suggests apoptosis. In contrast, a single observation indicating that cells are both FITC Annexin V and PI positive, in of itself, reveals less information about the process by which the cells underwent their demise.
FITC膜联蛋白V细胞凋亡检测试剂盒（BD Pharmingen）PREPARATION AND STORAGE
Store undiluted at 4°C and protected from prolonged exposure to light. Do not freeze.
FITC膜联蛋白V细胞凋亡检测试剂盒（BD Pharmingen）PRODUCT NOTICES
Since applications vary, each investigator should titrate the reagent to obtain optimal results.
Source of all serum proteins is from USDA inspected abattoirs located in the United States.
Caution: Sodium azide yields highly toxic hydrazoic acid under acidic conditions. Dilute azide compounds in running water before discarding to avoid accumulation of potentially explosive deposits in plumbing.