IRF9 / Interferon regulatory factor 9 · IHC design guide

Design Immunohistochemistry for IRF9

Plan chromogenic IRF9 IHC in paraffin sections with the IHC-validated antibody at 2–5 μg/mL (datasheet A04485). Expect nuclear staining in most tissues, with high staining in bronchial respiratory epithelium and endometrial glands (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 Predominantly nuclear in tissue (HPA tissue IHC), antibody A04485, validated IHC image, and IHC protocol steps — Printable **IRF9** IHC protocol sheet — expected localisation Predominantly nuclear in tissue (HPA tissue IHC), antibody A04485, controls and protocol steps. Open the full IRF9 IHC guide →

Navigate to: Protocols Staining pattern Controls Antibodies

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	Predominantly nuclear in tissue (HPA tissue IHC)
	Staining pattern	Nuclear staining in cells across most tissues (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 paraffin sections. (standard IHC practice; not target-specific)
	Caveat	Disregard cell membrane staining as off target (HPA tissue IHC)
	Regulation	Type I IFN promotes nuclear entry (UniProt)
	Isoform / epitope	No isoforms annotated; one 1–393 chain (UniProt)

Section 1

Recommended IRF9 IHC & IF Protocols

The catalog antibody protocol uses EDTA retrieval (datasheet: A04485); the published IRF9 IHC protocols below provide additional approaches for tumor sections (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 for the catalog antibody (datasheet: A04485); citrate retrieval is reported for lung tumor sections (PMC7827113).

Section 2

What Is the Expected IRF9 Staining Pattern?

In paraffin-section IHC, expect IRF9 mainly in nuclei across many tissues, including strong staining in bronchial respiratory epithelial cells and endometrial glandular cells (HPA: nuclear expression in most tissues; High in these cells). Cytoplasmic IRF9 is also biologically plausible, with nuclear translocation after type I interferon activation (UniProt Q00978: localization and function). IRF9 has no transmembrane segment (UniProt Q00978: topology). HPA rates its tissue IHC Approved but reports low consistency with RNA expression (HPA: reliability).

What am I looking at on my slide?
Distinct nuclear staining in respiratory epithelium of bronchus or nasopharynx.	This matches cells scored High and the predominantly nuclear tissue pattern (HPA: tissue IHC). Score the epithelial nuclei against nearby background; an HPA High designation does not require every cell in a section to stain equally (general IHC interpretation).
Nuclear staining with some cytoplasmic signal in a plausible positive cell type.	Both compartments are reported for IRF9, and type I interferon activation can move IRF9 into nuclei (UniProt Q00978: localization and function). The distribution alone cannot establish whether a particular section was interferon stimulated (UniProt Q00978: activation-dependent translocation).
Sharp cell-surface outlines dominate while nuclei are faint or absent.	Treat the membrane pattern as suspect: HPA explicitly disregards cell membrane staining as off target, and IRF9 has no transmembrane segment (HPA: tissue IHC reliability; UniProt Q00978: topology). Reassess the nuclear signal before calling the section positive.
Strong staining appears primarily in a cell population HPA lists as Not detected, such as adipocytes.	That pattern conflicts with the reported adipocyte result (HPA: adipose tissue, Not detected). Cross-reactivity or endogenous chromogen-generating activity are possibilities (general IHC interpretation); compare cell identity and a control lacking primary antibody before assigning IRF9.
A broad haze covers nuclei, cytoplasm, and spaces between cells.	Diffuse background has little localization value (general IHC interpretation). Because HPA's supported tissue pattern is mainly nuclear, haze should not be scored as IRF9-positive cells without a distinguishable cellular pattern (HPA: tissue IHC profile).

💡Expected IRF9 appearanceCall a section positive when identifiable bronchial or nasopharyngeal respiratory epithelial cells, or endometrial glandular cells, show clear predominantly nuclear staining consistent with their HPA High scores; dominant membrane outlining is suspect (HPA: tissue IHC profile, High cells, and off-target membrane note).

How each factor affects the staining
Tissue and cell selection	Bronchus and nasopharynx respiratory epithelium, endometrial, epididymal and fallopian-tube glandular cells, and bladder urothelium are scored High (HPA: tissue IHC). Adipocytes, cardiomyocytes and skeletal-muscle myocytes are Not detected (HPA: tissue IHC). Compare named cell populations rather than whole-section averages (general IHC interpretation).
Activation and compartment	IRF9 associates with STAT2 in the cytoplasm; after type I interferon signaling, the STAT1:STAT2:IRF9 complex enters the nucleus (UniProt Q00978: subunit, function, localization). A cytoplasmic component can therefore be plausible, but staining location alone does not measure pathway activation (UniProt Q00978: localization and function).
Antibody evidence	HPA labels antibody HPA001862 Approved for IHC, while warning of low agreement between antibody staining and RNA expression and disregarding membrane staining as off target (HPA: antibody validation and tissue IHC reliability). Interpret unexpected cell types and compartments cautiously.
IF/ICC Q: Why might its pattern differ from tissue IHC?	A: HPA reports supported cytosolic localization in ICC-IF, whereas its tissue IHC profile is nuclear in most tissues (HPA: subcellular and tissue IHC). UniProt lists both cytoplasm and nucleus and describes activation-linked nuclear entry (UniProt Q00978: localization). The assays' reported patterns should be read in their own context.
Antigen retrieval and fixation sensitivity	The supplied HPA and UniProt records give no IRF9-specific retrieval condition or fixation-sensitivity result (HPA: supplied tissue and subcellular records; UniProt Q00978: supplied record). Follow the IHC-validated antibody's documented paraffin-section procedure when available (general IHC practice); do not infer an IRF9-specific effect from staining intensity.

Why is my staining missing, weak or wrong?
Situation	Likely cause	Next action
No signal in bronchial respiratory epithelium or endometrial glands.	These cells are scored High, so a blank result warrants a technical check; the HPA score does not diagnose which step failed (HPA: tissue IHC).	Confirm the expected cell type is present, then review primary-antibody use, antigen retrieval, detection reagents, and counterstain against the documented IHC procedure (general IHC practice). Repeat with a known staining-positive section.
Nuclei stain, but cell borders show stronger chromogen.	HPA regards cell membrane staining as off target; IRF9 lacks a transmembrane segment (HPA: tissue IHC reliability; UniProt Q00978: topology).	Score the nuclear component separately from border staining, and compare with a control lacking primary antibody (general IHC practice). Do not count membrane outlines as evidence of IRF9.
Adipocytes or skeletal-muscle myocytes appear strongly positive.	HPA reports IRF9 Not detected in those cell populations (HPA: adipose tissue and skeletal muscle IHC). Cell-type misidentification, cross-reactivity, or endogenous detection activity can mimic a positive result (general IHC interpretation).	Verify cell morphology and compare a control lacking primary antibody; repeat staining with appropriate detection controls before assigning the signal to IRF9 (general IHC practice).
Diffuse brown haze obscures nuclear boundaries.	Nonspecific antibody binding or background from the detection system can reduce contrast (general chromogenic IHC practice). HPA's expected tissue profile is chiefly nuclear (HPA: tissue IHC).	Check blocking, washes, reagent concentration, and detection controls using the documented IHC workflow; judge signal only where cell boundaries and nuclei remain readable (general IHC practice).
A weakly stained section is called negative despite visible epithelial nuclei.	HPA reports Low in some cell populations and High in others; intensity depends on the cell population examined (HPA: tissue IHC). Low contrast can also complicate scoring (general IHC interpretation).	Identify the specific cell type, compare its HPA category, and score nuclear staining against local background and a control lacking primary antibody (HPA: tissue IHC; general IHC practice).
Predominantly cytoplasmic signal seems at odds with an IHC image.	HPA reports cytosol in ICC-IF but mainly nuclear expression in tissue IHC; UniProt supports both locations and activation-linked nuclear entry (HPA: subcellular and tissue IHC; UniProt Q00978: localization).	Record assay and compartment separately, inspect the nuclear signal in the paraffin section, and avoid inferring interferon activation from localization alone (UniProt Q00978: localization and function; general IHC interpretation).

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.

← swipe / scroll for more images →

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

Sample controls for IRF9 IHC & IF

🧪Run bronchus first: respiratory epithelial cells should stain for IRF9 (HPA: High in bronchus respiratory epithelial cells). Use adipose tissue as the negative comparator (HPA: Not detected in adipocytes); any unstained neighboring cells on the bronchus slide should show counterstain without specific DAB signal, but their IRF9-negative status is unverified (standard IHC practice).

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 no-primary (secondary-only) and isotype controls matched to the primary antibody’s rabbit host and clonality, plus an IRF9-knockout biological negative if available (caption: rabbit anti-IRF9; standard IHC practice). Block endogenous peroxidase and check for background in the bronchus section before interpreting DAB staining (caption: peroxidase detection with DAB; standard IHC practice).

⚠️Feasibility: A target-specific fixation window or fixation effect is unreported, and the selected A04485 paraffin-section caption does not state a fixative (caption: fixative not stated). The caption uses heat-mediated EDTA retrieval at pH 8.0, but does not establish whether retrieval is required; it also gives no basis to judge frozen sections or IF/ICC easier (caption: paraffin-section IHC with EDTA retrieval). Bronchial inflammatory cells can contribute endogenous peroxidase background, so interpret their DAB signal cautiously (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 in paraffin sections by checking retrieval, nuclear localisation, controls, and scoring before interpreting differences between specimens.

How should I optimise retrieval when IRF9 nuclear staining is weak?

Start with heat-mediated EDTA, pH 8.0, antigen retrieval for IRF9 paraffin-section IHC (datasheet A04485). The selected tissue image used this retrieval before 2 μg/ml primary antibody overnight at 4°C; hold those conditions constant while comparing retrieval times on adjacent sections (caption A04485). If nuclear signal remains weak, adjust heating in documented steps and inspect tissue morphology alongside a matched staining control; consider another buffer only as a fallback (standard IHC practice; HPA tissue IHC: nuclear expression in most tissues). Compare central viable regions after matched DAB development, since edge staining and damaged nuclei can falsely suggest improved retrieval (standard IHC practice).

Could fixation explain variable IRF9 staining between paraffin blocks?

The selected paraffin-section caption does not state its fixative, so IRF9-specific fixation sensitivity is unknown (caption A04485). Compare specimens with recorded fixative and exposure times while holding EDTA pH 8.0 retrieval and the 2 μg/ml primary concentration constant (datasheet A04485; caption A04485; standard IHC practice). Match section thickness, processing, and DAB development, then compare staining in viable nuclei; variation in these steps can resemble antigen loss (standard IHC practice; HPA tissue IHC: nuclear expression in most tissues). Include a staining control in each run and report fixation conditions with the score, since the available tissue patterns do not establish fixation tolerance (standard IHC practice).

Should I score cytoplasmic IRF9 staining in chromogenic IHC?

Score nuclear and cytoplasmic staining separately: IRF9 is annotated in both compartments and can move into nuclei after type I interferon activation (UniProt Q00978 subcellular localisation and function). Tissue IHC shows predominantly nuclear expression, whereas cell-based IF supports cytosolic localisation, so specimen context matters (HPA tissue IHC: nuclear expression in most tissues; HPA subcellular: cytosol supported). Record the percentage and intensity of nuclear-positive viable cells before considering cytoplasmic DAB signal, using the same counterstain and development conditions across sections (standard IHC practice). Do not score membrane staining as IRF9 without independent validation; that pattern was disregarded as off-target in the tissue survey (HPA tissue IHC: reliability description).

What can epitope information tell me about discordant IRF9 staining?

The supplied record describes a 393-amino-acid chain and annotates 0 isoforms, but gives no antibody epitope position (UniProt Q00978 processing and isoforms; caption A04485). IRF9 has no annotated transmembrane segment, signal peptide, or glycosylation sites, so a membrane pattern requires particular scrutiny rather than an assumed surface epitope (UniProt Q00978 topology, processing, and glycosylation; HPA tissue IHC: membrane staining disregarded). Phosphoserine at residue 139 is annotated, but its effect on this antibody's staining cannot be inferred without epitope information (UniProt Q00978 modified residues; caption A04485). When results disagree, compare retrieval and controls on adjacent sections and seek independent antibody or orthogonal evidence before assigning an isoform or modification-specific explanation (standard IHC practice).

How can IF help assess an ambiguous IRF9 IHC pattern?

Use IF/ICC as a separate localisation check, multiplexing IRF9 with an epithelial marker when examining the respiratory or glandular cell populations reported as positive in tissue IHC (HPA tissue IHC: bronchus respiratory epithelium and endometrial glandular cells; standard IF practice). Select a fluorophore channel that separates signal from the specimen's autofluorescence and include single-stain and no-primary controls to assess bleed-through and background (standard IF practice). Because IRF9 is annotated in the cytoplasm and nucleus and has no transmembrane segment, permeabilise cells sufficiently to access intracellular epitopes while preserving nuclear boundaries (UniProt Q00978 subcellular localisation and topology; standard IF practice). Compare nuclear and cytosolic signals separately; supported cytosolic IF staining and predominantly nuclear tissue IHC provide different reference contexts (HPA subcellular: cytosol supported; HPA tissue IHC: nuclear expression in most tissues).

How do I reduce diffuse DAB background without losing IRF9 signal?

First compare a no-primary section with the test section to locate signal from the secondary reagent, endogenous peroxidase, or chromogen deposition (standard IHC practice). The selected image used 10% goat serum blocking, 2 μg/ml rabbit primary overnight at 4°C, and a peroxidase-conjugated secondary for 30 minutes at 37°C (caption A04485). Apply a peroxidase block and consistent washes and DAB development, then titrate the primary if diffuse staining persists; these are general workflow adjustments (standard IHC practice). Inspect viable central tissue separately from folds, section edges, and necrosis before calling weak nuclear staining positive (standard IHC practice; HPA tissue IHC: nuclear expression in most tissues).

What is a defensible way to quantify IRF9 in paraffin sections? ⚠ ANSWER MARKED FOR VERIFICATION

Define the scored cell population and viable region before reviewing staining intensity, then report nuclear IRF9 separately from cytoplasmic signal (standard IHC practice; UniProt Q00978 subcellular localisation). An H-score sums the percentage of cells at intensity 0–3 multiplied by intensity, giving a 0–300 nuclear score; also report percentage positive when thresholds matter (standard IHC practice). Normalise counts to the number of viable cells of the specified type, or report positive-cell density per mm² of viable tissue when architecture prevents cell-based scoring (standard IHC practice). Keep retrieval, antibody concentration, DAB development, and scoring thresholds matched across groups, and document the predominantly nuclear tissue reference pattern (datasheet A04485; caption A04485; HPA tissue IHC: nuclear expression in most tissues).

How can I distinguish genuine IRF9 staining from tissue artefact?

Prioritise reproducible staining in viable nuclei within a defined cell population: tissue IHC reports nuclear expression in most tissues, with high staining in bronchial respiratory epithelial cells (HPA tissue IHC: profile and bronchus). Interpret cytoplasmic staining in context because IRF9 is annotated in both compartments and moves into nuclei following type I interferon signalling (UniProt Q00978 subcellular localisation and function). Treat membrane-only signal cautiously; the tissue survey disregarded membrane staining as off-target and reported low consistency between staining and RNA expression (HPA tissue IHC: reliability description). Check section edges, necrosis, and no-primary controls for artefact or endogenous enzyme signal, and confirm a disputed pattern with independent evidence before making a biological claim (standard IHC practice).

Boster reagents

Best IRF9 / Interferon regulatory factor 9 IHC Antibodies

A04485 has IHC and IF image data; M04485 lists ICC/IF without an image. Both list Human reactivity (catalog: image captions, applications, reactivity).

Real IHC data

Anti-Interferon regulatory factor 9/IRF9 Antibody ®

Cat # A04485

View product →

A04485 is human-reactive, with IHC shown in a paraffin-embedded human breast cancer section and IF shown in U2OS cells (catalog: reactivity; A04485 IHC/IF captions). M04485 lists Human reactivity and ICC/IF applications, but has no IHC or IF image caption (catalog: M04485 reactivity, applications, image alts).

Which to pick: Choose A04485 for tissue IHC: its own caption shows a paraffin-embedded section with EDTA pH 8 retrieval and DAB detection; the fixative is unreported (A04485 IHC caption). For IF/ICC, A04485 has a U2OS IF image, while rabbit monoclonal M04485, clone 21I34, lists ICC/IF without an image (A04485 IF caption; catalog: M04485 title, applications, image alts). Neither SKU establishes cross-species use because both list Human reactivity only (catalog: 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.