Immunohistochemistry (IHC) and immunofluorescence (IF) both use antibodies to detect proteins in tissues, but they differ in detection chemistry, multiplexing capacity, and how the result is read.
How each method works
IHC: Antibodies are detected with a chromogenic substrate — typically an HRP reaction with diaminobenzidine (DAB) producing a brown precipitate. Sections are counterstained with hematoxylin (blue) for context. Read on a brightfield microscope.
IF: Antibodies are detected with fluorophore-conjugated secondaries (or directly conjugated primaries). Each marker uses a different excitation/emission spectrum, allowing multiple proteins to be visualized simultaneously. Read on a fluorescence or confocal microscope.
Comparison
| Property | IHC (chromogenic) | IF |
|---|---|---|
| Multiplexing | Limited (1–3) | 4–7 standard, 30+ with multiplex methods |
| Quantification | Difficult (DAB is non-linear) | Fluorescence intensity is linear |
| Archival stability | Excellent (years) | Limited (fades over time) |
| Co-localization | Hard | Easy |
| Tissue context | Excellent (H&E-like) | Good with DAPI |
| Pathologist familiarity | High | Lower |
| Equipment | Brightfield microscope | Fluorescence/confocal |
When IHC is the right choice
- Clinical pathology — diagnostic standard for most tissue biomarkers (HER2, ER/PR, p53, Ki-67)
- Long-term archival of slides for case review
- Brightfield microscopy access only
- Single-marker visualization with anatomical context
When IF is the right choice
- Multi-marker studies — co-staining 3+ proteins simultaneously
- Quantitative analysis of expression intensity
- Co-localization studies between proteins or with subcellular markers
- Research-grade tumor microenvironment studies
Hybrid and emerging methods
- Multiplex IHC (mIHC) — sequential IHC with chromogen stripping, allowing 4–8 markers per slide
- Tyramide signal amplification (TSA) — covalent fluorophore deposition, enabling 6–8+ marker IF panels
- Imaging mass cytometry (IMC) and CODEX — 30–60 markers per tissue section using metal-tagged or DNA-barcoded antibodies
Practical considerations
- Antigen retrieval. Most FFPE tissues require heat-induced epitope retrieval (HIER) in citrate or EDTA buffer.
- Autofluorescence. FFPE tissues — especially red blood cells, elastin, lipofuscin — autofluoresce strongly. Use Sudan Black B treatment, spectral unmixing, or far-red fluorophores.
- Negative and isotype controls. Always run them.
- Counterstains. Hematoxylin for IHC; DAPI or Hoechst for IF.
IHC and IF aren’t substitutes — they’re tools for different jobs. IHC remains the standard for diagnostic pathology and long-term archives. IF is the foundation for quantitative, multi-marker research.
