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HTRA2 / Serine protease HTRA2, mitochondrial · IHC design guide
Design Immunohistochemistry for HTRA2
Plan HTRA2 staining in paraffin sections using its observed cytoplasmic tissue pattern (HPA tissue IHC) and expected mitochondrial location (UniProt). Interpret results with the tissue staining reliability caveat in mind (HPA tissue IHC).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
HTRA2 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 | Cytoplasmic in tissue (HPA tissue IHC); mitochondrial intermembrane space expected (UniProt) | |
| Staining pattern | Cytoplasmic staining in most tissues (HPA tissue IHC) | |
| Antigen retrieval | EDTA pH 8.0 HIER, heat-mediated (datasheet A01941-3) | |
| Positive control | Adrenal gland+4 more · see all | |
| Negative control | Heart muscle+4 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep fixation conditions consistent across sections. (standard IHC practice; not target-specific) | |
| Caveat | Antibody staining has low consistency with RNA expression (HPA tissue IHC) | |
| Regulation | Apoptotic stimuli release HTRA2 into cytosol (UniProt) | |
| Isoform / epitope | Four isoforms; maturation removes residues 32–133, so check epitope position (UniProt) |
Section 1
Recommended HTRA2 IHC & IF Protocols
The catalog antibody protocol uses EDTA retrieval (datasheet A01941-3). Two published HTRA2 IHC protocols provide liver and frontal cortex examples (PMC6829542; PMC6657433).
| Sample | Paraffin-embedded human liver cancer tissue; fixative not specified (datasheet A01941-3) |
| Fixation | Image fixative and duration unreported (datasheet A01941-3); 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 A01941-3); 20 min, 95–100 °C (standard) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% goat serum (datasheet A01941-3) |
| Primary antibody | Rabbit anti-HTRA2, 2-5 μg/ml (datasheet A01941-3) |
| Primary incubation | Overnight at 4 °C (datasheet A01941-3) |
| Detection | HRP-conjugated secondary, DAB chromogen (datasheet A01941-3) |
| Counterstain | Hematoxylin, blue, dehydrate and mount (standard) |
| Expected result | HTRA2-positive staining in glandular cells of adrenal gland (HPA tissue IHC: Medium). HPA tissue profile: Cytoplasmic expression in most tissues. No signal in the no-primary control. |
💡Decision noteStart with EDTA pH 8.0 heat retrieval for the catalog antibody (datasheet A01941-3); the liver protocol used citrate pH 6.0 (PMC6829542).
Section 2
What Is the Expected HTRA2 Staining Pattern?
HTRA2 is predominantly in the mitochondrial intermembrane space, with a membrane segment at residues 105–125; apoptotic stimuli can release it into the cytosol (UniProt O43464 localization and topology). In tissue IHC, expect cytoplasmic staining in many cell types, including glandular, neuronal, respiratory epithelial, endothelial and hematopoietic cells reported at medium intensity (HPA tissue IHC). Interpret this pattern cautiously: HPA rates its tissue IHC reliability Uncertain because antibody staining and RNA expression have low consistency (HPA tissue IHC).
| Cytoplasmic, granular staining in adrenal glandular cells or cerebral cortex neurons. | This fits the mitochondrial location and HPA's Medium staining in those cells (UniProt O43464 localization; HPA tissue IHC). Granularity is an expected visual interpretation, not proof of mitochondrial identity on a chromogenic section (general IHC practice). |
| Predominantly nuclear staining in otherwise intact cells. | A predominantly nuclear pattern lacks support from the reported mitochondrial location and cytoplasmic tissue profile (UniProt O43464 localization; HPA tissue IHC). Treat it as suspect and compare with controls; cytosolic release after apoptosis does not establish nuclear localization (UniProt O43464 localization; general IHC practice). |
| Strong signal in cardiomyocytes or skeletal myocytes. | HPA reports HTRA2 as Not detected in these cells, so strong staining needs scrutiny (HPA tissue IHC). That category is an observation, not proof of biological absence, especially given HPA's Uncertain IHC reliability (HPA tissue IHC). Check for cross-reactivity or endogenous chromogen activity (general IHC practice). |
| Even color across cells, stroma and empty areas. | Diffuse staining without a cellular pattern is more consistent with background than the reported cytoplasmic distribution (HPA tissue IHC; general IHC practice). Compare a no-primary control, then inspect blocking, washes and chromogen development before assigning an HTRA2 score (general IHC practice). |
| No stain in a tissue reported at medium intensity. | Absent signal in adrenal glandular cells or cerebral cortex neurons conflicts with HPA's observations but does not establish HTRA2 absence (HPA tissue IHC). Review section integrity, detection controls and the antibody's IHC validation before interpreting the specimen (general IHC practice; HPA antibody validation). |
💡Expected HTRA2 appearanceCall a result positive when staining is mainly cytoplasmic in HPA-reported cells, with roughly Medium intensity in its listed examples; isolated strong nuclear staining or uniform background is suspect (HPA tissue IHC; UniProt O43464 localization; general IHC practice).
| Tissue and cell choice | HPA reports Medium staining in adrenal glandular cells, marrow hematopoietic cells and cerebral cortex neurons, but Not detected in cardiomyocytes and skeletal myocytes (HPA tissue IHC). Use the former as observed comparators, while retaining the Uncertain tissue IHC reliability caveat (HPA tissue IHC). |
| Processing and epitope position | The precursor contains a propeptide at residues 32–133 and a mature chain at 134–458 (UniProt O43464 processing). If an antibody recognizes the removed region, its staining may differ from an antibody recognizing the mature chain; the supplied antibody records give no epitope positions, so this remains conditional (UniProt O43464 processing; HPA antibody records). |
| Apoptotic state | HTRA2 can leave mitochondria for the cytosol after apoptotic stimuli (UniProt O43464 localization). A less punctate cytoplasmic pattern may therefore merit review alongside cell morphology; the tissue IHC profile alone does not identify apoptosis or validate such a shift (UniProt O43464 localization; HPA tissue IHC). |
| Antibody evidence | The two listed IHC antibodies, HPA027366 and CAB004004, each have Uncertain IHC validation, while HPA006602 has Supported ICC validation (HPA antibody records). Neither ICC support nor tissue expression by itself upgrades a particular IHC result (HPA antibody records; HPA tissue IHC). |
| IF/ICC Q: What pattern should I expect? | A: Mitochondrial localization is Supported in HPA ICC-IF, with images listed for HEK293, Rh30 and U2OS (HPA subcellular; HPA antibody records). That evidence informs the compartment call; this IHC section supplies no IF/ICC protocol (HPA subcellular; general guide scope). |
| Situation | Likely cause | Next action |
|---|---|---|
| Weak or absent signal in an HPA medium-staining comparator. | The stain may have failed, or the chosen section may not contain the reported cell population (HPA tissue IHC; general IHC practice). | Confirm the target cells on the counterstain, then check the IHC-validated antibody and a working detection control; optimize retrieval and antibody concentration within the selected IHC workflow (general IHC practice). |
| Signal appears mainly nuclear. | This does not match the reported mitochondrial and cytoplasmic pattern (UniProt O43464 localization; HPA tissue IHC). | Compare no-primary and positive controls, inspect morphology and repeat with an independently validated antibody if available before scoring it as HTRA2 (general IHC practice; HPA antibody validation). |
| Strong staining appears in HPA 'Not detected' cells. | Cross-reactivity or endogenous detection activity is possible; HPA's negative observation is not absolute ground truth (HPA tissue IHC; general IHC practice). | Run a no-primary control and an appropriate endogenous-activity block for the chromogenic system; compare the suspect cells with HPA-reported medium-staining cells (general IHC practice; HPA tissue IHC). |
| Diffuse brown haze obscures cellular boundaries. | Background from detection chemistry, insufficient blocking or overdevelopment can obscure a cytoplasmic pattern (general IHC practice; HPA tissue IHC). | Inspect a no-primary section, adjust blocking and washes, and shorten chromogen development as indicated by control staining (general IHC practice). |
| Cytoplasmic staining looks diffuse rather than granular. | HTRA2 can enter the cytosol after apoptotic stimuli, but a diffuse chromogenic pattern can also be background (UniProt O43464 localization; general IHC practice). | Review cell morphology and a no-primary control; report a localization shift only with supporting context, and retain HPA's Uncertain IHC caveat (general IHC practice; HPA tissue IHC). |
| Results disagree between two antibodies. | The listed IHC antibodies both have Uncertain validation, and their epitope positions are unspecified (HPA antibody records). | Compare each antibody's compartment pattern and controls in the same cell population; do not infer which recognizes the precursor or mature chain without epitope evidence (UniProt O43464 processing; HPA antibody records; general IHC practice). |
Experiment evidence
IHC & IF images showing HTRA2 staining
A01941-3 · IHCIHC analysis of HTRA2 using anti-HTRA2 antibody (A01941-3). HTRA2 was detected in a paraffin-embedded section of human liver cancer tissue.
A01941-3 · IHCIHC analysis of HTRA2 using anti-HTRA2 antibody (A01941-3). HTRA2 was detected in a paraffin-embedded section of human thyroid papillary car
A01941-3 · IFIF analysis of HTRA2 using anti-HTRA2 antibody (A01941-3). HTRA2 was detected in an immunocytochemical section of U2OS cells. Enzyme antigen
A01941 · IHCImmunohistochemistry of OMI in human liver tissue with OMI antibody at 2 μg/mL.
A01941 · IFImmunofluorescence of OMI in Human Liver cells with OMI antibody at 20 μg/mL.
A01941-1 · IHCImmunohistochemistry analysis of paraffin-embedded human brain tissue, using HtrA2 Antibody. The picture on the right is blocked with the sy
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000115317-HTRA2/tissue/cerebral+cortex#imid_6980888
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000115317-HTRA2/tissue/colon#imid_6931926
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000115317-HTRA2/tissue/liver#imid_6931927
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000115317-HTRA2/tissue/kidney#imid_6931928
HPA · ICC-IF HEK293Human Protein Atlas immunofluorescence, HEK293, antibody HPA006602; green = HTRA2, blue = nucleus, red = microtubules.
HPA · ICC-IF HEK293Human Protein Atlas immunofluorescence, HEK293, antibody HPA006602; green = HTRA2, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for HTRA2 IHC & IF
🧪Run adrenal gland first: its glandular cells should stain (HPA: Medium). Use heart muscle cardiomyocytes as the comparison negative (HPA: Not detected); on the adrenal slide, cells without specific staining should show counterstain alone, without brown DAB above the no-primary background.
Positive control tissue: Adrenal gland (Glandular cells, HPA Medium)
Negative control tissue: Heart muscle (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show HTRA2 in HEK293, Rh30, U2OS, with annotated localisation: Mitochondria (supported) (HPA subcellular).
Technical controls: Include a no-primary, secondary-only control; rabbit IgG matched to the primary antibody’s isotype and clonality where applicable; and identically processed HTRA2-knockout material as a biological negative (caption: rabbit anti-HTRA2 antibody). For HRP/DAB detection, quench endogenous peroxidase and assess residual color against the no-primary slide (caption: HRP/DAB detection).
⚠️Feasibility: A target-specific fixation window or fixation effect is unreported, and the exact A01941-3 paraffin-section caption does not state a fixative (caption: fixative not stated). That caption uses heat retrieval in EDTA at pH 8.0, but does not establish whether retrieval is required in adrenal gland; frozen sections cannot be ranked as easier from the supplied evidence (caption: liver cancer paraffin section). IF feasibility is supported by mitochondrial ICC-IF localization in HEK293, Rh30 and U2OS (HPA: Mitochondria supported); no adrenal-specific artefact is reported in the supplied evidence.
HPA tissue IHC evidence for HTRA2
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Uncertain — Low consistency between antibody staining and RNA expression data. Pending external verification.). 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 |
|---|---|---|---|---|
| Adrenal gland | Glandular cells | Medium | Protein (IHC) | HPA → |
| Appendix | Glandular cells | Medium | Protein (IHC) | HPA → |
| Bone marrow | Hematopoietic cells | Medium | Protein (IHC) | HPA → |
| Breast | Glandular cells | Medium | Protein (IHC) | HPA → |
| Bronchus | Respiratory epithelial cells | Medium | Protein (IHC) | HPA → |
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Heart muscle | Cardiomyocytes | Not detected | Protein (IHC) | HPA → |
| Ovary | Ovarian stroma cells | Not detected | Protein (IHC) | HPA → |
| Skeletal muscle | Myocytes | Not detected | Protein (IHC) | HPA → |
| Soft tissue | Chondrocytes | Not detected | Protein (IHC) | HPA → |
| Spleen | Cells in red pulp | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced HTRA2 IHC Tips
Use the catalog antibody’s paraffin-section conditions as a starting point, then interpret staining against HTRA2 localisation and the reported uncertainty in tissue staining (datasheet A01941-3; UniProt O43464; HPA tissue IHC).
What retrieval should I try first when HTRA2 staining is weak?
Start with heat-mediated EDTA retrieval at pH 8.0 for paraffin sections (datasheet A01941-3). The documented stain used 2 µg/mL primary antibody overnight at 4°C, so confirm those conditions before changing retrieval (datasheet A01941-3). If staining remains weak, test retrieval duration on adjacent sections while keeping detection and exposure to DAB development consistent (standard IHC practice). A different buffer or pH is a fallback to evaluate with controls, because the supplied product image documents EDTA pH 8.0 only (datasheet A01941-3). Excessively harsh retrieval can damage morphology and make compartment-level interpretation unreliable (standard IHC practice).
Could fixation explain weak or uneven HTRA2 staining?
Target-specific fixation sensitivity is unknown: the selected paraffin-section caption does not state a fixative (datasheet A01941-3). Record the fixative, fixation interval and processing history for each specimen before comparing HTRA2 intensity across sections (standard IHC practice). Uneven preservation or section lifting warrants inspection of morphology and a repeat stain on a well-preserved section before changing the antibody concentration (standard IHC practice). The documented starting conditions are 10% goat serum blocking and 2 µg/mL primary antibody overnight at 4°C (datasheet A01941-3). Neither tissue staining patterns nor HTRA2 membrane topology establishes how a particular fixative affects this epitope (HPA tissue IHC; UniProt O43464 topology).
How should I assess diffuse cytoplasmic staining instead of mitochondrial-looking signal?
Expect HTRA2 predominantly in the mitochondrial intermembrane space, with membrane and endoplasmic reticulum annotations also reported (UniProt O43464 subcellular). HPA reports cytoplasmic staining in most tissues and supported mitochondrial localisation by ICC/IF, so a diffuse chromogenic pattern alone cannot resolve organelles (HPA tissue IHC; HPA subcellular). Compare intact cells with adjacent sections and assess whether staining follows cellular morphology rather than section edges or damaged areas (standard IHC practice). Cytosolic redistribution is biologically plausible after apoptotic stimuli, but chromogenic IHC alone cannot establish that release has occurred (UniProt O43464 subcellular; standard IHC practice). Document the fraction of cells with diffuse versus granular cytoplasmic staining using the same scoring rules across specimens (standard IHC practice).
Can this stain distinguish mature HTRA2 from its precursor or splice isoforms?
Do not assign an IHC signal to a particular HTRA2 form without an antibody epitope map or independently validated form-specific assay (standard IHC practice). HTRA2 has 4 reported isoforms, a 32–133 propeptide and a mature 134–458 chain (UniProt O43464 processing and isoforms). Its transmembrane segment spans residues 105–125, while the PDZ domain spans 364–445; epitope position could therefore affect which processed species is detected (UniProt O43464 topology and domains). The supplied paraffin-section caption gives retrieval and staining conditions but no epitope position or isoform selectivity (datasheet A01941-3). Describe the result as HTRA2 immunoreactivity unless specificity for a particular form has been established (standard IHC practice).
How can IF help assess HTRA2 localisation alongside this IHC result?
Use IF as a separate localisation check, because this page’s documented antibody workflow is chromogenic staining of a paraffin section (datasheet A01941-3). Multiplex HTRA2 with a marker identifying the cell population being scored and, where useful, a mitochondrial marker to examine intracellular overlap (standard IF practice; HPA subcellular). Choose spectrally separated fluorophores and inspect unstained tissue for autofluorescence before assigning faint signal to HTRA2 (standard IF practice). Permeabilisation must allow antibody access to the relevant side of the mitochondrial membrane, but the supplied evidence does not map this antibody’s epitope (UniProt O43464 topology; standard IF practice). HPA lists ICC/IF images from HEK293, Rh30 and U2OS cells; those images do not establish this antibody’s IF conditions (HPA subcellular).
What should I check when DAB staining appears widespread or patchy?
Run a no-primary control and inspect it for secondary-reagent binding, endogenous peroxidase signal and nonspecific DAB deposition (standard IHC practice). Include a peroxidase-blocking step in the chromogenic workflow, then compare its result with the no-primary control before interpreting weak cytoplasmic colour (standard IHC practice). The documented section used 10% goat serum blocking, 2 µg/mL primary antibody overnight at 4°C, and a peroxidase-conjugated secondary for 30 minutes at 37°C (datasheet A01941-3). Keep DAB development consistent between sections and exclude folds, edges and damaged regions from assessment (standard IHC practice). HPA’s tissue-staining reliability is uncertain, making control-dependent interpretation especially important (HPA tissue IHC).
How should I quantify HTRA2 staining across paraffin sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the cell population and regions of interest before scoring, then use the same rules for every section (standard IHC practice). An H-score combines the percentages of cells at intensities 0–3 and ranges from 0–300; alternatively report percent positive cells or positive-cell density per mm² (standard IHC practice). Normalise counts to the number of eligible cells or measured tissue area, and report stromal and other cellular compartments separately when they are distinguishable (standard IHC practice). Keep retrieval, 2 µg/mL primary incubation and DAB development comparable across the series (datasheet A01941-3; standard IHC practice). Treat small intensity differences cautiously because HPA reports low consistency between antibody staining and RNA expression (HPA tissue IHC).
When is an apparent HTRA2-positive cell likely to be an artefact?
Assess intact-cell cytoplasmic staining in context: HTRA2 is predominantly mitochondrial, while release into cytosol can follow apoptotic stimuli (UniProt O43464 subcellular). Signal confined to section edges, necrotic regions or tissue folds warrants review against morphology and a no-primary control (standard IHC practice). Colour in an unexpected compartment or cell population should prompt checks for endogenous peroxidase activity, nonspecific binding and cell misidentification before a biological explanation is assigned (standard IHC practice). HPA reports medium staining in several cell populations but rates its tissue IHC reliability uncertain because staining and RNA expression have low consistency (HPA tissue IHC). Report the observed compartment and controls rather than equating DAB positivity with active protease or apoptosis (standard IHC practice; UniProt O43464 function).
Boster reagents
Best HTRA2 / Serine protease HTRA2, mitochondrial IHC Antibodies
Catalog antibodies have real IHC images from human liver, liver cancer and brain tissue, plus IF images from human liver cells and U2OS cells (catalog image captions).
Real IHC data
Anti-HTRA2 Antibody ®
Cat # A01941-3
Real IHC data
Anti-OMI HTRA2 Antibody
Cat # A01941
Real IHC data
Anti-HtrA2/Omi Antibody
Cat # A01941-1
A01941 shows IHC in human liver tissue and IF in human liver cells; A01941-1 shows IHC in paraffin-embedded human brain tissue with a peptide-blocked comparison (catalog image captions). A01941-3 shows IHC in paraffin-embedded human liver cancer tissue and IF/ICC in U2OS cells (catalog image captions).
Which to pick: For tissue IHC, start with A01941-3 at 2–5 μg/mL: its paraffin-section image documents EDTA retrieval at pH 8.0 and DAB detection (A01941-3 datasheet and IHC caption). For IF/ICC, choose A01941-3 at 5 μg/mL because its application list includes both and its IF image shows U2OS cells; for human liver-cell IF, A01941 has an image at 20 μg/mL (A01941-3 application list and IF caption; A01941 IF caption). For human, mouse or rat reactivity, consider the polyclonal A01941-1, but its IHC image documents only paraffin-embedded human brain tissue; the fixative is unreported in the IHC captions (A01941-1 catalog reactivity, dilution notes and IHC caption; A01941 and A01941-3 IHC captions).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry O43464 (HTRA2_HUMAN, Serine protease HTRA2, mitochondrial).
- Human Protein Atlas. HTRA2 tissue IHC expression (reliability: Uncertain).
- Human Protein Atlas. HTRA2 subcellular location (ICC-IF): Localized to the mitochondria..
- Human Protein Atlas. HTRA2 antibody validation summary (3 antibodies).
- Serine Protease HtrA2/Omi Deficiency Impairs Mitochondrial Homeostasis and Promotes Hepatic Fibrogenesis via Activation of Hepatic Stellate Cells. Cells 2019 — PMC6829542.
- Increased Active OMI/HTRA2 Serine Protease Displays a Positive Correlation with Cholinergic Alterations in the Alzheimer's Disease Brain. Molecular neurobiology 2019 — PMC6657433.
- Apoptin causes apoptosis in HepG-2 cells via Ca(2+) imbalance and activation of the mitochondrial apoptotic pathway. Cancer medicine 2023 — PMC10134343.
- Enhanced HtrA2/Omi expression in oxidative injury to retinal pigment epithelial cells and murine models of neurodegeneration. Investigative ophthalmology & visual science 2009 — PMC2903625.
- PubMed PMID:10644717 — UniProt-cited evidence.
- PubMed PMID:10971580 — UniProt-cited evidence.
- PubMed PMID:10995577 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for HTRA2 (Serine protease HTRA2, mitochondrial). Expected localisation Cytoplasmic in tissue (HPA tissue IHC); mitochondrial intermembrane space expected (UniProt). Antigen retrieval: EDTA pH 8.0 HIER, heat-mediated (datasheet A01941-3). Validated IHC antibody: A01941-3 at 2-5 μg/ml (the product's own IHC validation image is shown). Controls (HPA): positive Adrenal gland (Glandular cells); negative Heart muscle. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded human liver cancer tissue; fixative not specified (datasheet A01941-3); 2. Fixation: Image fixative and duration unreported (datasheet A01941-3); verify before use.; 3. Sectioning: 4–5 µm sections on charged slides (standard); 4. Deparaffinisation: Xylene, graded ethanol series to water (standard); 5. Antigen retrieval: Heat retrieval: EDTA pH 8.0 (datasheet A01941-3); 20 min, 95–100 °C (standard); 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% goat serum (datasheet A01941-3); 8. Primary antibody: Rabbit anti-HTRA2, 2-5 μg/ml (datasheet A01941-3); 9. Primary incubation: Overnight at 4 °C (datasheet A01941-3). Watch for: Fixation: Keep fixation conditions consistent across sections. (standard IHC practice; not target-specific); Caveat: Antibody staining has low consistency with RNA expression (HPA tissue IHC); Isoform / epitope: Four isoforms; maturation removes residues 32–133, so check epitope position (UniProt); Regulation: Apoptotic stimuli release HTRA2 into cytosol (UniProt). Evidence: UniProt O43464, HPA tissue IHC · Uncertain, HPA ICC-IF · mitochondria., Datasheet A01941-3, PMC6829542, PMC6657433. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/HTRA2/immunohistochemistry-ihc-guide.