Utilizing EdU to Track Leukocyte Recruitment to the Brain

Detecting the proliferation of cells with copper(I)-catalyzed azide-alkyne cycloaddition (click chemistry) and the thymidine analogue, 5-ethynyl-2'-deoxyuridine (EdU), is a simpler and more versatile method than traditional antibody-based approaches. Instead of the harsh series of steps typically used for 5-bromo-2'-deoxyuridine (BrdU) detection, detecting EdU does not require DNA denaturation and is suitable for use with other applications. This approach was implemented in an animal model of ischemic stroke. The following protocol details how to use EdU to label, track, and visualize leukocyte recruitment for flow cytometry and fluorescence microscopy, including the processes for EdU injection and blood and tissue sample preparation. Considerations for timing, dosing, and cell viability are also outlined to tailor the protocol to experimental needs. This method could be applied to various models that require extended tracking periods, as the signal from EdU can last several cell divisions, depending on cell type and condition. Key features • EdU labeling is simple and compatible with routine laboratory methods. • This method is compatible with genetically encoded fluorophores, such as GFP and tdTomato. • EdU incorporation in circulating leukocytes varies depending on the specific cell subtype. • This technique can be adapted to track leukocyte recruitment, including when cells are recruited from the bloodstream.