Intracellular Targets Not Detected Without Permeabilization (Flow Cytometry (Sample Considerations))

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Cytokines, transcription factors, or phospho-proteins show negative staining despite expected expression. Standard surface staining protocol fails for intracellular markers. Common causes: 1) Intact cell membrane prevents antibody access to cytoplasmic and nuclear compartments 2) Cytokines, transcription factors, and phospho-proteins localize in cytoplasm, nucleus, or organelles 3) Standard staining buffer lacks permeabilization agents (detergents, alcohols) 4) Subcellular localization (cytoplasm vs. nucleus) requires matched buffer formulation Solutions: 1) Use fixation and permeabilization buffers specialized for intracellular targets before antibody staining 2) Consult BioLegend 「Guide to Flow Cytometry Buffers」 to select appropriate buffers based on subcellular localization 3) For cytoplasmic targets (cytokines): use saponin-based permeabilization buffers 4) For nuclear targets (transcription factors): use stronger permeabilization (e.g., methanol, Foxp3 fixation/perm buffer) 5) For phospho-proteins: use specialized phospho-flow buffers preserving phosphorylation states 6) Optimize fixation (typically 1-4% paraformaldehyde, 10-20 minutes) before permeabilization step