Antibody Epitope Alteration by Fixation (Flow Cytometry (Sample Considerations))

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Surface marker staining intensity decreases or disappears when antibodies are applied after cell fixation, or intracellular targets remain undetectable despite using fixation/permeabilization buffers, indicating epitope conformational changes or masking. Common causes: 1) Fixation (paraformaldehyde, methanol, acetone) alters protein conformation, making epitopes inaccessible to certain antibody clones 2) Surface staining performed after fixation fails because fixatives cross-link proteins and mask epitopes 3) Intracellular targets (cytokines, transcription factors, phospho-proteins) require specialized fixation/permeabilization buffers matched to subcellular localization 4) Antibody clone compatibility with fixation not verified; some clones tolerate fixation while others require live-cell staining Solutions: 1) Perform surface staining before fixation whenever possible to preserve native epitope conformation 2) Check vendor fixation compatibility pages (BioLegend Fixation page) to identify antibody clones validated for post-fixation surface staining 3) Select appropriate fixation/permeabilization buffers based on subcellular localization: nuclear (transcription factors), cytoplasmic (cytokines), or membrane-associated (phospho-proteins); consult Guide to Flow Cytometry Buffers 4) If clone compatibility information unavailable, empirically test surface staining before vs. after fixation using parallel samples