IRF9 / Interferon regulatory factor 9 · IHC design guide

Design Immunohistochemistry for IRF9

Plan paraffin IHC around nuclear IRF9 staining in most tissues (HPA tissue IHC). Compare high-staining respiratory or glandular cells with reported unstained cells, and disregard membrane staining as off target (HPA tissue IHC).

Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use

Immunohistochemistry protocol sheet for IRF9 (IHC for IRF9): expected localisation Nuclear staining in most tissues (HPA tissue IHC), antibody A04485, validated IHC image, and IHC protocol steps — Printable **IRF9** IHC protocol sheet — expected localisation Nuclear staining in most tissues (HPA tissue IHC), antibody A04485, controls and protocol steps. Open the full IRF9 IHC guide →

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IRF9 Immunohistochemistry Experimental Design Guide

Expected localisation, validated protocols, controls and antibodies — the at-a-glance facts below, then the full design guide.

Must know before staining

	Expected localisation	Nuclear staining in most tissues (HPA tissue IHC)
	Staining pattern	Nuclear signal in respiratory and glandular cells (HPA tissue IHC)
	Antigen retrieval	EDTA pH 8.0 HIER, heat-mediated (datasheet A04485)
	Positive control ⓘ	Bronchus+4 more · see all
	Negative control ⓘ	Adipose tissue+4 more · see all

Important caveats

Reasons your staining may differ from the expected pattern.

	Fixation	Keep fixation consistent across sections (standard IHC practice; not target-specific)
	Caveat	Disregard cell membrane staining as off target (HPA tissue IHC)
	Regulation	Type I IFN promotes nuclear translocation (UniProt)
	Isoform / epitope	One 1–393 chain; no isoforms annotated (UniProt)

Section 1

Recommended IRF9 IHC & IF Protocols

The catalog antibody uses EDTA pH 8.0 retrieval (datasheet: A04485). The published IHC protocols below cover pulmonary artery, lung tumor, prostate, and xenograft sections (PMC8672195; PMC7827113; PMC3753051; PMC13426216).

Recommended immunohistochemistry (IHC-P) protocol parameters
Sample	Paraffin-embedded human breast cancer tissue; fixative not specified (datasheet A04485)
Fixation	Image fixative and duration unreported (datasheet A04485); verify before use.
Sectioning	4–5 µm sections on charged slides (standard)
Deparaffinisation	Xylene, graded ethanol series to water (standard)
Antigen retrieval	Heat retrieval: EDTA pH 8.0 (datasheet A04485); 20 min, 95–100 °C (standard)
Peroxidase block	3% H2O2, 10 min, room temperature (standard)
Blocking	10% goat serum (datasheet A04485)
Primary antibody	Rabbit anti-IRF9, 2-5μg/ml (datasheet A04485)
Primary incubation	Overnight at 4 °C (datasheet A04485)
Detection	HRP-conjugated secondary, DAB chromogen (datasheet A04485)
Counterstain	Hematoxylin, blue, dehydrate and mount (standard)
Expected result	IRF9-positive staining in respiratory epithelial cells of bronchus (HPA tissue IHC: High). HPA tissue profile: Nuclear expression in most tissues. No signal in the no-primary control.

💡Decision noteStart with heat-mediated EDTA pH 8.0 retrieval (datasheet: A04485); EDTA pH 9.0 and citrate are published alternatives (PMC8672195; PMC7827113).

Section 2

What Is the Expected IRF9 Staining Pattern?

For paraffin-section IHC, expect predominantly nuclear IRF9 staining in many tissues, including respiratory, glandular and urothelial cells (HPA: nuclear expression in most tissues; High in the listed cell types). IRF9 can also reside in the cytoplasm and moves into the nucleus after type I interferon activation (UniProt Q00978: subcellular location). It has no transmembrane segment (UniProt Q00978: topology). HPA rates its tissue IHC pattern Approved but reports low agreement with RNA data (HPA: reliability description).

What am I looking at on my slide?
Distinct nuclear staining in bronchial or nasopharyngeal respiratory epithelium, or endometrial glandular cells (HPA: High in these cells).	This fits the reported tissue IHC pattern (HPA: nuclear expression in most tissues). Compare staining with nearby cell types and a negative control; HPA's Approved rating carries a low RNA-agreement caveat (HPA: reliability description).
Strong staining outlines cell borders instead of nuclei.	Treat a membrane pattern as suspect: HPA viewed membrane staining as off target and disregarded it (HPA: reliability description). IRF9 lacks a transmembrane segment (UniProt Q00978: topology). Review morphology and detection controls before scoring these cells as positive.
An apparently strong positive result occurs mainly in adipocytes or cardiomyocytes.	Those cells are reported as not detected in the sampled tissues (HPA: adipocytes in adipose tissue; cardiomyocytes in heart muscle). Check cell identification and controls. Cross-reactivity or endogenous detection activity is possible, but the slide alone cannot establish either cause.
Colour spreads across nuclei, cytoplasm and empty spaces without clear cell boundaries.	Diffuse background prevents reliable compartment scoring. Check the no-primary control and compare with a known-positive section; review blocking, washes and detection conditions as general IHC troubleshooting. HPA's tissue pattern alone cannot identify the source of background.
No convincing signal appears in a bronchial section's respiratory epithelial cells.	This differs from HPA's High staining report for those cells (HPA: bronchus). Confirm that the expected cells are present, then review the antibody and detection workflow with controls. A negative section does not by itself prove that IRF9 is absent.

💡Expected IRF9 appearanceCall a result positive when the relevant epithelial or glandular cells show clear, predominantly nuclear staining at an intensity distinguishable from background; prominent membrane outlines are suspect (HPA: nuclear tissue profile, High examples and membrane-staining caveat).

How each factor affects the staining
Cell context and activation	UniProt places IRF9 in cytoplasm and nucleus and reports nuclear translocation after IFN-alpha/beta activation (UniProt Q00978: subcellular location). Interpret a nuclear IHC result in tissue context; compartment alone does not establish whether a specimen received an interferon stimulus.
Strength of the tissue reference	HPA reports High staining in bronchial respiratory epithelium and endometrial glands, Medium in breast glands, and no detection in adipocytes (HPA: tissue IHC). These are useful comparisons, but its Approved pattern has low agreement with RNA data (HPA: reliability description).
Antibody validation	The listed antibody HPA001862 is Approved for IHC, while its ICC status is Supported (HPA: antibody validation). Do not describe its IHC result as Enhanced: the supplied validation record does not assign that status (HPA: antibody validation).
IF/ICC Q: Should cytosolic staining match paraffin-section IHC?	A: HPA reports supported cytosolic localisation in ICC-IF, while its tissue IHC profile is mainly nuclear (HPA: subcellular and tissue IHC). UniProt lists both compartments and activation-dependent nuclear translocation (UniProt Q00978: subcellular location). Assess each application against its own evidence.

Why is my staining missing, weak or wrong?
Situation	Likely cause	Next action
Expected epithelial nuclei are faint or unstained.	The section may lack the expected cells, or the IHC workflow may have produced insufficient detectable signal; neither cause is established by HPA.	Verify the cells on the counterstained section. Run a reported High tissue alongside it and check primary-antibody and chromogenic-detection steps (HPA: High in bronchial respiratory epithelium).
Cell borders stain more strongly than nuclei.	HPA specifically regarded membrane staining as off target (HPA: reliability description).	Exclude border-only staining from positive nuclear scoring. Compare a no-primary control and inspect the reported nuclear pattern in a positive tissue (HPA: nuclear tissue profile).
A reported negative cell type appears strongly positive.	Cell misidentification, cross-reactivity or endogenous detection activity may explain the result; the cause remains unproven (HPA: no detection in adipocytes and cardiomyocytes).	Recheck morphology and the no-primary control, then compare with a reported High cell type on a separately assessed section (HPA: bronchial respiratory epithelial cells).
Most of the section has diffuse chromogenic colour.	General IHC background can obscure cell boundaries and nuclear localisation; the HPA tissue record does not identify its source.	Check the no-primary control, blocking and washes, then reassess whether nuclei can be distinguished from surrounding tissue before scoring.
Nuclear and cytoplasmic staining coexist.	Both locations are compatible with UniProt's IRF9 annotation; nuclear translocation follows IFN-alpha/beta activation (UniProt Q00978: subcellular location).	Score nuclear and cytoplasmic compartments separately. Compare the nuclear component with HPA tissue IHC, without inferring activation state from staining alone (HPA: nuclear tissue profile).
A change in antigen retrieval seems to alter staining.	The supplied HPA and UniProt records provide no target-specific retrieval or fixation sensitivity.	Record the retrieval conditions and compare controlled sections under the same scoring criteria. Treat any change as an assay observation until independently verified; do not assign it an IRF9-specific mechanism.

Source: UniProt Q00978 Human Protein Atlas tissue Human Protein Atlas subcellular

Experiment evidence

IHC & IF images showing IRF9 staining

IHC analysis of IRF9 using anti-IRF9 antibody (A04485). IRF9 was detected in a paraffin-embedded section of human breast cancer tissue. Heat mediated antigen retrieval was performed in EDTA buffer (pH 8.0, epitope retrieval solution). The tissue section was blocked with 10% goat serum. The tissue section was then incubated with 2 μg/ml rabbit anti-IRF9 Antibody (A04485) overnight at 4°C. Peroxidase Conjugated Goat Anti-rabbit IgG was used as secondary antibody and incubated for 30 minutes at 37°C. The tissue section was developed using HRP Conjugated Rabbit IgG Super Vision Assay Kit (Catalog # SV0002) with DAB as the chromogen.

A04485 · IHCIHC analysis of IRF9 using anti-IRF9 antibody (A04485). IRF9 was detected in a paraffin-embedded section of human breast cancer tissue. Heat

IF analysis of IRF9 using anti-IRF9 antibody (A04485) and anti-Tubulin Alpha antibody (M03989-3). IRF9 was detected in immunocytochemical section of U2OS cell. Enzyme antigen retrieval was performed using IHC enzyme antigen retrieval reagent (AR0022) for 15 mins. The cells were blocked with 10% goat serum. And then incubated with 5 μg/mL rabbit anti-IRF9 Antibody (A04485) and mouse anti-Tubulin Alpha antibody (M03989-3) overnight at 4°C. DyLight®488 Conjugated Goat Anti-Rabbit IgG (BA1127) and Cy3 Conjugated Goat Anti-Mouse IgG (BA1031) were used as secondary antibody at 1:500 dilution and incubated for 30 minutes at 37°C. Visualize using a fluorescence microscope and filter sets appropriate for the label used.

A04485 · IFIF analysis of IRF9 using anti-IRF9 antibody (A04485) and anti-Tubulin Alpha antibody (M03989-3). IRF9 was detected in immunocytochemical se

HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000213928-IRF9/tissue/cerebral+cortex#imid_739784

HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000213928-IRF9/tissue/colon#imid_739710

HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000213928-IRF9/tissue/liver#imid_739711

HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000213928-IRF9/tissue/kidney#imid_739712

HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody HPA001862; green = IRF9, blue = nucleus, red = microtubules.

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Real IHC / IF data behind the staining-pattern expectations in this section.

Sample controls for IRF9 IHC & IF

🧪Run bronchus first and require staining in respiratory epithelial cells (HPA: High in bronchus respiratory epithelial cells); use adipose tissue as the negative comparator and assess adipocytes (HPA: Not detected in adipocytes). On the positive slide, treat cells outside the respiratory epithelium as internal negative comparators only where they visibly lack specific staining; their IRF9 status is not established by the supplied HPA row.

Positive control tissue: Bronchus (Respiratory epithelial cells, HPA High)

Negative control tissue: Adipose tissue (HPA Not detected)

ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show IRF9 in A-431, U-251MG, U2OS, with annotated localisation: Cytosol (supported) (HPA subcellular).

Technical controls: Include a no-primary, secondary-only control; a rabbit IgG isotype control matched to the primary antibody’s clonality where applicable; and IRF9-knockout tissue or a validated peptide-block control (caption: rabbit anti-IRF9 antibody; standard IHC practice). Quench endogenous peroxidase before HRP/DAB detection and check bronchial luminal material for nonspecific deposit when scoring (caption: HRP/DAB detection; standard IHC practice).

⚠️Feasibility: No target-specific fixation window or fixation effect is reported, and the selected A04485 paraffin-section caption does not state a fixative (caption: fixative unreported). The caption reports staining after heat-mediated retrieval in EDTA at pH 8.0, but does not establish that retrieval is required; it provides no comparison showing frozen sections or IF are easier (caption: EDTA retrieval and paraffin-section IHC). No bronchus-specific artefact is documented in the supplied evidence; assess staining within respiratory epithelial cells while excluding luminal debris from scoring (HPA: High in bronchus respiratory epithelial cells; standard IHC practice).

HPA tissue IHC evidence for IRF9

Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Approved — Low consistency between antibody staining and RNA expression data. Cell membrane staining viewed as off target and disregarded.). Rows are taken directly from the HPA tissue chart — click any row's HPA link to view the source.

Positive expression · recommended positive controls

Tissue	Cell type	Level	Evidence	Source
Bronchus	Respiratory epithelial cells	High	Protein (IHC)	HPA →
Endometrium	Glandular cells	High	Protein (IHC)	HPA →
Epididymis	Glandular cells	High	Protein (IHC)	HPA →
Fallopian tube	Glandular cells	High	Protein (IHC)	HPA →
Nasopharynx	Respiratory epithelial cells	High	Protein (IHC)	HPA →

Undetected expression · recommended negative controls

Tissue	Cell type	Level	Evidence	Source
Adipose tissue	Adipocytes	Not detected	Protein (IHC)	HPA →
Adrenal gland	Glandular cells	Not detected	Protein (IHC)	HPA →
Heart muscle	Cardiomyocytes	Not detected	Protein (IHC)	HPA →
Hippocampus	Glial cells	Not detected	Protein (IHC)	HPA →
Parathyroid gland	Glandular cells	Not detected	Protein (IHC)	HPA →

Section 3

Advanced IRF9 IHC Tips

Troubleshoot IRF9 staining by checking retrieval, compartment, controls and scoring against the tested paraffin section workflow and reported tissue patterns.

Which retrieval conditions should I try first for weak IRF9 staining?

Start with heat mediated antigen retrieval in EDTA at pH 8.0 for paraffin sections (datasheet A04485). The selected image used that buffer before an overnight 4°C primary incubation, so retain those conditions while checking whether deparaffinisation and heating were consistent across sections (datasheet A04485; standard IHC practice). Compare a retrieval time series on adjacent sections using the same detection conditions, and judge signal in intact cells against a no primary control (standard IHC practice). If staining remains weak, test another retrieval buffer as a fallback on matched sections, recording changes in both nuclear signal and tissue damage (standard IHC practice).

How should I troubleshoot fixation related loss of IRF9 staining?

The selected paraffin section caption does not state a fixative, so target specific fixation sensitivity is unknown for this antibody (datasheet A04485). Record the specimen’s fixative and fixation duration, then compare adjacent, similarly processed sections before attributing weak staining to fixation (standard IHC practice). Keep retrieval at EDTA pH 8.0 and primary incubation at 2 μg/ml overnight at 4°C while examining whether morphology and staining change together (datasheet A04485). Include a section with established IRF9 staining in the same run to distinguish a processing problem from a detection problem; do not infer fixation tolerance from tissue patterns (HPA: tissue IHC; standard IHC practice).

How should I evaluate cytoplasmic and nuclear IRF9 staining?

Score nuclear and cytoplasmic staining separately: IRF9 is reported in both compartments and translocates to the nucleus after type I interferon activation (UniProt Q00978). The tissue IHC profile describes nuclear expression in most tissues, whereas cell based IF reports supported cytosolic localisation; assay context therefore matters (HPA: tissue IHC; HPA: subcellular). Inspect intact cell boundaries and a nuclear counterstain before assigning compartment, and compare areas processed in the same run (standard IHC practice). If activation status is known, report it beside compartment scores; nuclear staining alone does not establish that interferon signaling occurred (UniProt Q00978 function; standard IHC interpretation).

Can IRF9 isoforms or epitope accessibility explain discordant staining?

No isoforms are annotated in the supplied record, so an isoform specific explanation is unsupported here (UniProt Q00978). IRF9 is a 393 amino acid protein with no annotated transmembrane segment, signal peptide or glycosylation sites; phosphoserine 139 is listed as a modified residue (UniProt Q00978). The selected caption does not identify this antibody’s epitope, so neither epitope masking nor modification dependent binding can be assigned as the cause of a staining pattern (datasheet A04485). Compare matched retrieval conditions and, if available, an independently validated antibody with a documented epitope before proposing an epitope based explanation (standard IHC practice).

How can IF help resolve an ambiguous IRF9 IHC pattern?

Use IF as a separate assay and include a marker for the expected cell population, such as an epithelial marker when examining the respiratory epithelial staining reported in bronchus (HPA: High in bronchus respiratory epithelial cells; standard IF practice). Select fluorophores in channels with low measured tissue autofluorescence and include unstained and single stain controls before interpreting overlap (standard IF practice). Permeabilise sufficiently for antibodies to reach cytosolic and nuclear IRF9, which has no annotated transmembrane segment, while checking that cell boundaries remain interpretable (UniProt Q00978; standard IF practice). Compare the IF compartment pattern with matched IHC sections, recognising that supported cytosolic IF and predominantly nuclear tissue IHC have both been reported (HPA: subcellular; HPA: tissue IHC).

What controls help distinguish IRF9 signal from chromogenic background?

Run a no primary control through the peroxidase and DAB steps to reveal detection background under the same development conditions (standard IHC practice). The selected section used 10% goat serum block, 2 μg/ml primary antibody overnight at 4°C, and a 30 minute secondary incubation at 37°C (datasheet A04485). If staining is widespread, assess endogenous peroxidase blocking, secondary antibody background and DAB development time on adjacent sections before changing the primary concentration (standard IHC practice). Treat isolated membrane staining cautiously because the tissue IHC assessment disregarded membrane staining as off target and reported low agreement with RNA data (HPA: tissue IHC reliability).

How should I quantify IRF9 across paraffin sections? ⚠ ANSWER MARKED FOR VERIFICATION

Define the cell population and compartment before scoring, then record the percentage of positive cells and staining intensity within that population (standard IHC practice; UniProt Q00978 localisation). An H-score can combine the percentages at intensity grades 0–3, reported separately for nuclear and cytoplasmic signal (standard IHC practice). For spatial comparisons, report positive cells per mm² of viable tissue or normalise positive counts to all evaluable cells of the chosen type (standard IHC practice). Keep retrieval, DAB development, counterstain and image thresholds consistent across samples, and report excluded damaged or necrotic regions (standard IHC practice).

Which IRF9 staining patterns warrant further validation?

Interpret staining in intact cells alongside controls and compartment scores: IRF9 can occur in cytoplasm and nucleus, with nuclear entry reported after type I interferon activation (UniProt Q00978). Strong staining confined to membranes warrants scrutiny because membrane staining was disregarded as off target in the tissue IHC assessment (HPA: tissue IHC reliability). Check whether the stained cell population fits the sampled tissue; bronchial respiratory epithelial cells showed high staining, while adipocytes were reported as not detected (HPA: tissue IHC). Discount edge effects, necrotic regions and signal retained in no primary controls, including endogenous enzyme activity, before calling a biological difference (standard IHC practice).

Boster reagents

Best IRF9 / Interferon regulatory factor 9 IHC Antibodies

A04485 has human paraffin-section IHC and U2OS-cell IF images (A04485 IHC/IF captions).

Real IHC data

Anti-Interferon regulatory factor 9/IRF9 Antibody ®

Cat # A04485

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A04485 will render with an IHC image from a human breast cancer paraffin section (A04485 IHC caption). Its IF image shows U2OS cells (A04485 IF caption).

Which to pick: Choose A04485 for human paraffin-section IHC; its own image caption reports EDTA pH 8 retrieval and 2 μg/mL primary antibody, but does not report the fixative (A04485 IHC caption). For IF/ICC, A04485 has an IF image at 5 μg/mL, while M04485 is a rabbit monoclonal, clone 21I34, listed for ICC/IF without a supplied image (A04485 IF caption; catalog: M04485 clone, applications and image fields). Neither SKU has documented reactivity beyond human (catalog: A04485 and M04485 reactivity).

Each figure is that product's own IHC / IF validation image from its datasheet.

References

UniProt Consortium. UniProt entry Q00978 (IRF9_HUMAN, Interferon regulatory factor 9).
Human Protein Atlas. IRF9 tissue IHC expression (reliability: Approved).
Human Protein Atlas. IRF9 subcellular location (ICC-IF): Localized to the cytosol..
Human Protein Atlas. IRF9 antibody validation summary (1 antibodies).
Upregulation of IRF9 Contributes to Pulmonary Artery Smooth Muscle Cell Proliferation During Pulmonary Arterial Hypertension. Frontiers in pharmacology 2021 — PMC8672195.
Interferon Regulatory Factor 9 Promotes Lung Cancer Progression via Regulation of Versican. Cancers 2021 — PMC7827113.
IL6 sensitizes prostate cancer to the antiproliferative effect of IFNα2 through IRF9. Endocrine-related cancer 2013 — PMC3753051.
Apatinib resistance mediated by IRF9 nuclear translocation in head and neck squamous cell carcinoma. iScience 2026 — PMC13426216.
PubMed PMID:1630447 — UniProt-cited evidence.
PubMed PMID:15489334 — UniProt-cited evidence.
PubMed PMID:11846981 — UniProt-cited evidence.