Failed Intracellular Antigen Detection After Fixation

Symptom

Intracellular markers such as cytokines, transcription factors, or phosphoproteins show no signal despite proper antibody validation. Surface markers stain normally, but internal targets remain undetected indicating permeabilization issues.

1. 1 Fixation-only protocol applied without subsequent permeabilization step for intracellular access
2. 2 Inappropriate fixative choice that prevents effective permeabilization (excessive cross-linking)
3. 3 Insufficient permeabilization reagent concentration or incubation time in Fix & Perm protocols
4. 4 Alcohol-based fixation used where paraformaldehyde-based Fix & Perm kit would be more appropriate

1. 1 Use dedicated Fix & Perm / Cell Fixation & Permeabilization Kit (e.g., ab185917) for intracellular staining workflows
2. 2 Ensure permeabilization step follows fixation with appropriate detergent-based reagents (saponin, Triton X-100)
3. 3 Select paraformaldehyde-based fixation for intracellular protocols as it permits controlled permeabilization
4. 4 Optimize permeabilization time and reagent concentration for each target; nuclear proteins may require stronger conditions
5. 5 Validate intracellular staining with positive control cells known to express target antigens

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