What is the significance of Annexin (Annexin protein) as a marker?

From the Guidelines

Annexin V is the most commonly used annexin marker for detecting apoptotic cells, and it should be used in conjunction with a vital dye like propidium iodide or 7-AAD to distinguish between early apoptotic and late apoptotic or necrotic cells. The use of Annexin V is widely employed in flow cytometry and microscopy to detect cells undergoing apoptosis, and it is typically conjugated to fluorophores like FITC, PE, or APC, allowing visualization of cells undergoing apoptosis 1. For standard flow cytometry applications, Annexin V is used at concentrations of 1-5 μl per 100,000 cells in calcium-containing binding buffer, as calcium is essential for Annexin V binding to phosphatidylserine 1.

Some key points to consider when using Annexin V include:

• The importance of using a calcium-containing binding buffer, as calcium is essential for Annexin V binding to phosphatidylserine 1
• The need to use Annexin V in conjunction with a vital dye like propidium iodide or 7-AAD to distinguish between early apoptotic and late apoptotic or necrotic cells 1
• The potential for Annexin V binding alone to not differentiate between apoptosis and necrosis, as membrane permeabilization in necrosis also allows Annexin V to bind to internal phosphatidylserine 1
• The use of additional markers, such as P-selectin (CD62p), to differentiate procoagulant from apoptotic platelets 1

Overall, the use of Annexin V is a valuable tool for detecting apoptotic cells, but it should be used in conjunction with other markers and techniques to ensure accurate results. The most recent and highest quality study recommends using Annexin V in conjunction with other markers, such as P-selectin (CD62p), to detect procoagulant platelets 1.

From the Research

Annexin Marker

• Annexin A5 is a 35 kD plasma protein that has strong affinity for phosphatidylserine (PS) in the nano-molar range, making it a useful marker for detecting apoptotic cell death 2.
• The externalisation of PS is a prominent characteristic of apoptosis, and Annexin A5 can bind to this phospholipid, allowing for the visualization of apoptotic cells 2, 3.
• Annexin V-affinity assay is a technique used to detect apoptosis by targeting the loss of phospholipid asymmetry of the plasma membrane, which results in the exposure of PS residues at the outer plasma membrane leaflet 3.
• Annexin A5 imaging has been used to evaluate cell death modifying compounds and plaque stabilizing strategies, and has proven to be a suitable imaging biomarker for cardiovascular disease 2.
• The role of Annexin A5 in the modulation of the immune response against dying and dead cells has been studied, and it has been found to be an important modulator of the immune response against PS-exposing particles like apoptotic cells, necrotic cells, and certain viruses 4.
• Flow cytometry using Annexin-V/propidium iodide and a modified in situ end labeling technique has been used to analyze the dynamic process of apoptosis, and has shown that PS translocation is followed rapidly by oligo-nucleosomal DNA fragmentation, after which cell membrane leakage occurs 5.
• Annexin A5 has been found to interfere with the immunosuppressive effects of apoptotic cells, and may have a role in restoring the immunogenicity of apoptotic cells by blocking their PS-dependent clearance 4.