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HSD3B1 / 3 beta-hydroxysteroid dehydrogenase/Delta 5-->4-isomerase type 1 · IHC design guide
Design Immunohistochemistry for HSD3B1
Plan HSD3B1 paraffin IHC around strong cytoplasmic staining in placental syncytiotrophoblasts (HPA tissue IHC). Start with the IHC-validated antibody A02856-2 at 0.5–1 μg/mL and include a negative control (datasheet: A02856-2; standard IHC practice).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
HSD3B1 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 staining in placenta and adrenal gland (HPA tissue IHC) | |
| Staining pattern | Syncytiotrophoblast and adrenal cell cytoplasm (HPA tissue IHC) | |
| Antigen retrieval | EDTA pH 8.0 HIER, heat-mediated (datasheet A02856-2) | |
| Positive control | Placenta+1 more · see all | |
| Negative control | Adipose tissue+4 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep paraffin tissue fixation consistent across samples. (standard IHC practice; not target-specific) | |
| Caveat | Presumed off-target binding may mimic positivity (HPA tissue IHC) | |
| Regulation | Regulatory drivers are not specified (UniProt) | |
| Isoform / epitope | No annotated isoforms; epitope sidedness unresolved (UniProt) |
Section 1
Recommended HSD3B1 IHC & IF Protocols
The catalog antibody’s IHC-P protocol (datasheet: A02856-2) is accompanied by published HSD3B1 staining methods for human adenoma, rat testis, and cat testis (PMC4821076; PMC5643909; PMC13313884).
| Sample | Paraffin-embedded human placenta tissue; fixative not specified (datasheet A02856-2) |
| Fixation | Image fixative and duration unreported (datasheet A02856-2); 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 A02856-2); 20 min, 95–100 °C (standard) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% goat serum (datasheet A02856-2) |
| Primary antibody | Rabbit anti-HSD3B1, 0.5-1μg/ml (datasheet A02856-2) |
| Primary incubation | Overnight at 4 °C (datasheet A02856-2) |
| Detection | Streptavidin-biotin complex (SABC), DAB chromogen (datasheet A02856-2) |
| Counterstain | Hematoxylin, blue, dehydrate and mount (standard) |
| Expected result | HSD3B1-positive staining in syncytiotrophoblasts of placenta (HPA tissue IHC: High). HPA tissue profile: Cytoplasmic expression in placenta and adrenal gland. No signal in the no-primary control. |
💡Decision noteStart with heat-mediated EDTA pH 8.0 for the catalog antibody (datasheet: A02856-2); the rat testis protocol used citrate pH 6.0 (PMC5643909).
Section 2
What Is the Expected HSD3B1 Staining Pattern?
HSD3B1 is an endoplasmic reticulum and mitochondrial membrane protein with one transmembrane segment at residues 288–308 (UniProt P14060 topology). In paraffin-section IHC, expect cytoplasmic staining, strongest in placental syncytiotrophoblasts (HPA tissue IHC: High; reliability Supported). Interpret that pattern with caution: HPA reports antibodies targeting proteins from more than one gene and presumed off-target binding that was disregarded in its expression profile (HPA tissue IHC: reliability description).
| Strong cytoplasmic staining in placental syncytiotrophoblasts. | This is the clearest supplied positive-tissue pattern (HPA tissue IHC: Syncytiotrophoblasts High). Record the cell type and cytoplasmic distribution together; intensity alone is insufficient because HPA flags antibodies that target proteins from more than one gene (HPA tissue IHC: reliability description). |
| Predominantly nuclear or other noncytoplasmic staining in placental syncytiotrophoblasts. | A nuclear-only IHC pattern does not match the reported cytoplasmic tissue pattern or membrane localization (HPA tissue IHC: cytoplasmic expression; UniProt P14060 topology). Review staining controls and interpretation before calling it HSD3B1; the ICC-IF nucleolar annotation is uncertain (HPA subcellular: Nucleoli uncertain). |
| Strong staining in a cell population HPA reports as not detected, such as adipocytes in adipose tissue. | That result conflicts with the supplied cell-specific reference (HPA tissue IHC: Adipocytes Not detected). Consider antibody cross-reactivity, which is a particular concern given HPA's multi-gene targeting caution, or endogenous chromogenic detection activity as a general IHC cause (HPA tissue IHC: reliability description; general IHC practice). |
| Weak, widespread chromogen obscures cell boundaries across the section. | Treat this as background until controls establish a cell-specific signal (general IHC practice). It cannot be scored as the reported placental pattern merely because the section contains placenta (HPA tissue IHC: Syncytiotrophoblasts High); inspect a no-primary control and the distribution of staining (general IHC practice). |
| No cytoplasmic signal in placental syncytiotrophoblasts. | A blank known-positive cell population conflicts with the HPA reference pattern (HPA tissue IHC: Syncytiotrophoblasts High). Check section identity and IHC run controls, then review antigen retrieval, primary-antibody conditions and detection as general workflow variables; the supplied sources do not establish HSD3B1-specific fixation sensitivity (general IHC practice). |
💡Expected HSD3B1 appearanceCall a positive IHC result when placental syncytiotrophoblasts show strong cytoplasmic staining (HPA tissue IHC: High; cytoplasmic expression), while isolated nuclear staining or broad staining of HPA-negative cells warrants review as possible nonspecific signal (HPA tissue IHC: Not detected cell examples; HPA subcellular: Nucleoli uncertain).
| Membrane localization and topology | UniProt places HSD3B1 at endoplasmic reticulum and mitochondrial membranes and annotates one transmembrane segment, residues 288–308 (UniProt P14060 topology). These facts support a cytoplasmic IHC interpretation; they do not identify this antibody's epitope or predict an antigen-retrieval condition. |
| Cell-specific reference levels | HPA reports High staining in placental syncytiotrophoblasts, Medium in testicular spermatogonia and Low in adrenal zona fasciculata cells (HPA tissue IHC). Compare like cell populations when assessing intensity; do not expect uniform staining across a tissue from a cell-specific rating. |
| Strength and limit of IHC evidence | The tissue profile is rated Supported, and three listed antibodies have Supported IHC status (HPA tissue IHC: reliability Supported; HPA antibodies: HPA043261, HPA043264, HPA044028). HPA also warns of multi-gene targeting and presumed off-target binding, so agreement with the expected pattern supports interpretation without proving molecular specificity (HPA tissue IHC: reliability description). |
| IF/ICC Q&A: What localization should be expected? | The supported ICC-IF location is endoplasmic reticulum (HPA subcellular: Endoplasmic reticulum supported). Nucleoli, primary cilium and other listed locations are uncertain, with a multi-gene antibody caution (HPA subcellular). Use the separate IF/ICC guide for that application; these annotations are not an IHC protocol. |
| Situation | Likely cause | Next action |
|---|---|---|
| Placental syncytiotrophoblasts are unstained. | The expected High cell-specific signal is absent (HPA tissue IHC: Syncytiotrophoblasts High); a failed staining run or incorrect section identification are general IHC possibilities. | Confirm tissue and cell identity, examine run controls, then review retrieval, primary-antibody and detection steps using the validated IHC procedure (general IHC practice). Do not infer an HSD3B1-specific fixation problem from these sources. |
| Placenta shows staining, but it is chiefly nuclear. | This conflicts with the cytoplasmic tissue profile (HPA tissue IHC: cytoplasmic expression). The ICC-IF nucleolar report is uncertain and does not validate nuclear IHC staining (HPA subcellular: Nucleoli uncertain). | Check the counterstain and chromogen distribution, compare with the positive-tissue reference and repeat with appropriate controls if the compartment remains unclear (general IHC practice). |
| Adipocytes or other HPA-negative cell populations stain strongly. | Their staining conflicts with HPA's Not detected ratings; antibody cross-reactivity is plausible given the documented multi-gene targeting caution (HPA tissue IHC: negative cells; reliability description). | Compare the precise cell population with HPA's reference and examine a no-primary control for endogenous detection activity (general IHC practice). Avoid scoring unexpected staining as HSD3B1 without further specificity evidence. |
| Diffuse chromogen covers positive and negative areas. | Nonspecific background or endogenous detection activity can obscure a cell-specific IHC pattern (general IHC practice); HPA's reference is cytoplasmic and cell-specific (HPA tissue IHC). | Inspect no-primary and run controls, then review blocking, washes, primary-antibody conditions and chromogen development under the laboratory's standard IHC workflow (general IHC practice). |
| Adrenal signal is much fainter than placental signal. | That difference matches the supplied cell ratings: Low in adrenal zona fasciculata cells versus High in placental syncytiotrophoblasts (HPA tissue IHC). | Identify the scored adrenal cells and compare slides stained in the same run before treating the lower intensity as a technical failure (general IHC practice; HPA tissue IHC: cell-specific levels). |
| IF/ICC shows a prominent nucleolar or ciliary pattern. | HPA marks nucleoli and primary cilium as uncertain ICC-IF locations and cautions that the underlying antibodies target proteins from multiple genes (HPA subcellular). | Interpret those locations cautiously and consult the separate IF/ICC guide; the supported ICC-IF location is endoplasmic reticulum (HPA subcellular: Endoplasmic reticulum supported). |
Experiment evidence
IHC & IF images showing HSD3B1 staining
A02856-2 · IHCIHC analysis of HSD3B1 using anti-HSD3B1 antibody (A02856-2). HSD3B1 was detected in paraffin-embedded section of human placenta tissue. Hea
A02856-2 · IFIF analysis of HSD3B1 using anti-HSD3B1 antibody (A02856-2). HSD3B1 was detected in immunocytochemical section of U20S cells. Enzyme antigen
M02856 · IFIF analysis of HSD3B1 using anti-HSD3B1 antibody (M02856). HSD3B1 was detected in an immunocytochemical section of U20S cells. Enzyme antige
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000203857-HSD3B1/tissue/cerebral+cortex#imid_19831477
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000203857-HSD3B1/tissue/colon#imid_19831395
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000203857-HSD3B1/tissue/liver#imid_19831396
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000203857-HSD3B1/tissue/kidney#imid_19831397
HPA · ICC-IF CACO-2Human Protein Atlas immunofluorescence, CACO-2, antibody HPA044028; green = HSD3B1, blue = nucleus, red = microtubules.
HPA · ICC-IF CACO-2Human Protein Atlas immunofluorescence, CACO-2, antibody HPA044028; green = HSD3B1, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for HSD3B1 IHC & IF
🧪Run placenta first: syncytiotrophoblasts should stain (HPA: High in placenta syncytiotrophoblasts). Use adipose tissue as a negative, focusing on adipocytes (HPA: Not detected in adipocytes); other cells on the placenta slide provide an internal background comparison, but their HSD3B1 status is not specified by the supplied HPA row.
Positive control tissue: Placenta (Syncytiotrophoblasts, HPA High)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show HSD3B1 in CACO-2, U-251MG, U2OS, ASC52telo, RPTEC/TERT1, hTERT-RPE1 (serum starved), with annotated localisation: Nucleoli (uncertain), Endoplasmic reticulum (supported), Primary cilium (uncertain) (HPA subcellular).
Technical controls: Include a no-primary, secondary-only control and a concentration-matched rabbit IgG isotype control for the rabbit catalog antibody (selected-SKU caption: rabbit primary; standard IHC practice). Add HSD3B1-knockout material or a validated peptide-block control to assess target specificity, and check or block endogenous peroxidase and biotin in placenta when using the caption’s biotin-based DAB detection (selected-SKU caption: SABC/DAB; standard IHC practice).
⚠️Feasibility: No matched source reports a target-specific fixation window or fixation effect, and the selected A02856-2 tissue-IHC caption does not report a fixative (selected-SKU caption: fixative not stated). The caption uses heat-mediated EDTA retrieval at pH 8.0, but does not establish that retrieval is required (selected-SKU caption). The supplied evidence does not establish whether frozen sections or IF are easier; with the caption’s SABC/DAB method, assess placental endogenous biotin and peroxidase background (selected-SKU caption: SABC/DAB; standard IHC practice).
HPA tissue IHC evidence for HSD3B1
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Supported — Caution, targets protein from more than one gene. Presumed off target binding observed and disregarded. Paired antibodies with high similarity supports the expression profile.). 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 |
|---|---|---|---|---|
| Placenta | Syncytiotrophoblasts | High | Protein (IHC) | HPA → |
| Testis | Spermatogonia cells | Medium | Protein (IHC) | HPA → |
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Adipose tissue | Adipocytes | Not detected | Protein (IHC) | HPA → |
| Appendix | Glandular cells | Not detected | Protein (IHC) | HPA → |
| Bone marrow | Hematopoietic cells | Not detected | Protein (IHC) | HPA → |
| Breast | Adipocytes | Not detected | Protein (IHC) | HPA → |
| Bronchus | Respiratory epithelial cells | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced HSD3B1 IHC Tips
Troubleshoot HSD3B1 staining in paraffin sections using the catalog antibody’s tissue protocol, expected cellular distribution, and appropriate controls.
How should I optimise retrieval when HSD3B1 staining is weak?
Start with heat-mediated retrieval in EDTA at pH 8.0 for paraffin sections (datasheet A02856-2). The catalog antibody detected HSD3B1 in a human placenta section after this retrieval, followed by 1 μg/ml primary antibody overnight at 4°C (datasheet A02856-2). If staining remains weak, compare modest changes in heating and cooling conditions on adjacent sections while keeping antibody concentration and detection constant (standard IHC practice). Include placenta syncytiotrophoblasts as an expected positive reference and an omission control for detection background (HPA tissue IHC; standard IHC practice). Record morphology alongside signal, because excessive heat can damage sections and make apparent gains difficult to interpret (standard IHC practice).
Could fixation explain a negative HSD3B1 result?
Target-specific fixation sensitivity is unknown: the selected paraffin-section caption does not state a fixative (datasheet A02856-2). Record the actual fixative and fixation duration for each specimen, then compare sections processed together with the same EDTA pH 8.0 retrieval and 1 μg/ml primary concentration (datasheet A02856-2; standard IHC practice). A placenta reference section can show whether the staining run worked, but cannot establish that a test specimen retained its epitope (HPA tissue IHC; standard IHC practice). Review tissue preservation and section adhesion before changing detection chemistry (standard IHC practice). Do not assign a fixation mechanism to a negative result without a controlled comparison (standard IHC practice).
Which HSD3B1 staining pattern should I accept?
Assess staining within cell outlines and expect a cytoplasmic pattern in placenta, where syncytiotrophoblasts show high staining (HPA tissue IHC). HSD3B1 is annotated at endoplasmic reticulum and mitochondrial membranes, with a transmembrane segment at residues 288–308 (UniProt P14060 localisation and topology). Diffuse nuclear-only chromogen therefore needs independent validation before being scored as HSD3B1 (UniProt P14060 localisation; standard IHC practice). Compare the pattern with adjacent negative cells and a primary-antibody omission section at the same DAB development time (standard IHC practice). HPA also reports low staining in adrenal zona fasciculata cells, so intensity thresholds should reflect the tissue being examined (HPA tissue IHC).
How can I assess whether this antibody distinguishes HSD3B1?
Check the catalog antibody’s stated immunogen and cross-reactivity before interpreting its chromogenic signal as gene-specific (standard IHC practice). The supplied HSD3B1 record lists 0 annotated isoforms and one transmembrane segment at residues 288–308; neither fact identifies this antibody’s epitope (UniProt P14060 isoforms and topology). HPA cautions that its expression profile involves antibodies targeting proteins from more than one gene and presumed off-target binding (HPA tissue IHC). Compare independently validated antibodies against distinct epitopes where available, and examine whether both reproduce the expected placental cell pattern (HPA tissue IHC; standard IHC practice). Treat agreement in staining distribution as supporting evidence, not proof of molecular specificity (standard IHC practice).
How should I investigate HSD3B1 by IF after chromogenic IHC?
Use the chromogenic IHC pattern as a tissue-level reference when planning a separate IF experiment; the paraffin-section caption does not validate an IF protocol (datasheet A02856-2). Multiplex HSD3B1 with an independently validated marker of the expected syncytiotrophoblast population and inspect cellular overlap, rather than relying on fluorescence intensity alone (HPA tissue IHC; standard IF practice). Check unstained tissue autofluorescence and favour a spectrally separated red or far-red channel when its background is lower (standard IF practice). Because HSD3B1 spans a membrane at residues 288–308, choose permeabilisation after establishing which side contains the antibody epitope (UniProt P14060 topology; standard IF practice). Include single-colour controls to assess bleed-through (standard IF practice).
What should I check when DAB obscures HSD3B1 staining?
First compare a primary-antibody omission section with the test section to locate background from detection reagents or endogenous enzyme activity (standard IHC practice). The catalog example used biotinylated secondary antibody, a streptavidin-biotin complex, and DAB after 1 μg/ml primary antibody overnight at 4°C (datasheet A02856-2). Apply an appropriate peroxidase block and assess endogenous biotin background for this detection chemistry (standard IHC practice). If background persists, compare blocking and wash conditions while keeping EDTA retrieval at pH 8.0 fixed (datasheet A02856-2; standard IHC practice). Score only cell-associated signal above the omission control, excluding precipitate and tissue-edge deposits (standard IHC practice).
How should I quantify HSD3B1 across paraffin sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the cell population and regions of interest before measuring chromogenic staining, and keep imaging and DAB development settings consistent (standard IHC practice). For syncytiotrophoblasts, report the percentage of positive cells or an H-score that combines percentage with intensity; use positive-cell density per mm² when counting discrete cells is appropriate (HPA tissue IHC; standard IHC practice). Normalise to the number of evaluable target cells or their sampled area, and report excluded damaged or necrotic regions (standard IHC practice). Set positivity against a primary-antibody omission control and a shared reference section rather than changing thresholds between specimens (standard IHC practice). Report tissue compartment separately because HPA describes high placental and low adrenal staining (HPA tissue IHC).
When is apparent HSD3B1 positivity likely to be artefactual?
A convincing result places cytoplasmic staining in the expected cells, especially placental syncytiotrophoblasts, and exceeds the matched omission control (HPA tissue IHC; standard IHC practice). Question isolated nuclear staining because HSD3B1 is annotated at endoplasmic reticulum and mitochondrial membranes (UniProt P14060 localisation). Also question staining restricted to section edges, necrotic areas, or cells outside the expected population; inspect those areas against morphology and controls (HPA tissue IHC; standard IHC practice). Residual endogenous peroxidase or biotin-related detection signal can mimic DAB positivity with the catalog’s biotin-based workflow (datasheet A02856-2; standard IHC practice). HPA’s cross-gene antibody caution means a plausible pattern still needs orthogonal specificity evidence (HPA tissue IHC).
Boster reagents
Best HSD3B1 / 3 beta-hydroxysteroid dehydrogenase/Delta 5-->4-isomerase type 1 IHC Antibodies
The catalog shows HSD3B1 IHC in human placenta paraffin sections and IF/ICC in human U20S cells (catalog image captions); one IF/ICC antibody also lists mouse and rat reactivity (catalog reactivity).
Real IHC data
Anti-HSD3B1 Antibody ®
Cat # A02856-2
Real IF data
Anti-HSD3B1 Antibody ® (monoclonal, 3F3C/7F9C8)
Cat # M02856
A02856-2 renders with IHC data from human placenta paraffin sections and lists human reactivity (catalog IHC caption; catalog reactivity). M02856 renders with IF/ICC data from human U20S cells and lists human, mouse, and rat reactivity (catalog IF caption; catalog reactivity).
Which to pick: Choose A02856-2 for paraffin-section IHC: its own caption documents heat retrieval in EDTA at pH 8.0 and chromogenic DAB detection in human placenta; the fixative is unreported (catalog IHC caption). For IF/ICC, A02856-2 has human U20S-cell IF data and a listed concentration of 2 μg/ml, while mouse monoclonal M02856 has its own human U20S-cell IF data at 5 μg/ml (catalog IF captions; catalog host and clone). Choose M02856 when mouse or rat reactivity is needed for IF/ICC, while treating its demonstrated IF image as human-cell evidence (catalog applications, reactivity, and IF caption).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry P14060 (3BHS1_HUMAN, 3 beta-hydroxysteroid dehydrogenase/Delta 5-->4-isomerase type 1).
- Human Protein Atlas. HSD3B1 tissue IHC expression (reliability: Supported).
- Human Protein Atlas. HSD3B1 subcellular location (ICC-IF): Mainly localized to the nucleoli, endoplasmic reticulum and primary cilium. In addition localized to the microtubules, cytokinetic bridge and primary cilium transition zone. Caution: Based on antibodies targeting proteins from multiple genes..
- Human Protein Atlas. HSD3B1 antibody validation summary (3 antibodies).
- Effect of selenium-enriched Ganoderma lucidum powder in testicular tissues, oxidative stress biomarkers and antiapoptotic capacities in roosters. Poultry science 2026 — PMC12723041.
- 3β-Hydroxysteroid dehydrogenase isoforms in human aldosterone-producing adenoma. Molecular and cellular endocrinology 2015 — PMC4821076.
- A Short-Term Exposure to Tributyltin Blocks Leydig Cell Regeneration in the Adult Rat Testis. Frontiers in pharmacology 2017 — PMC5643909.
- Immunohistochemical evaluation of Sertoli and Leydig cells of scotch cat testis (Felis catus) at diverse ages. Open veterinary journal 2026 — PMC13313884.
- PubMed PMID:2779585 — UniProt-cited evidence.
- PubMed PMID:2139411 — UniProt-cited evidence.
- PubMed PMID:2082186 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for HSD3B1 (3 beta-hydroxysteroid dehydrogenase/Delta 5-->4-isomerase type 1). Expected localisation Cytoplasmic staining in placenta and adrenal gland (HPA tissue IHC). Antigen retrieval: EDTA pH 8.0 HIER, heat-mediated (datasheet A02856-2). Validated IHC antibody: A02856-2 at 0.5-1μg/ml (the product's own IHC validation image is shown). Controls (HPA): positive Placenta (Syncytiotrophoblasts); negative Adipose tissue. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded human placenta tissue; fixative not specified (datasheet A02856-2); 2. Fixation: Image fixative and duration unreported (datasheet A02856-2); 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 A02856-2); 20 min, 95–100 °C (standard); 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% goat serum (datasheet A02856-2); 8. Primary antibody: Rabbit anti-HSD3B1, 0.5-1μg/ml (datasheet A02856-2); 9. Primary incubation: Overnight at 4 °C (datasheet A02856-2). Watch for: Fixation: Keep paraffin tissue fixation consistent across samples. (standard IHC practice; not target-specific); Caveat: Presumed off-target binding may mimic positivity (HPA tissue IHC); Isoform / epitope: No annotated isoforms; epitope sidedness unresolved (UniProt); Regulation: Regulatory drivers are not specified (UniProt). Evidence: UniProt P14060, HPA tissue IHC · Supported, HPA ICC-IF · Mainly localized to the nucleoli, endoplasmic reticulum and primary…, Datasheet A02856-2, PMC4821076, PMC5643909. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/HSD3B1/immunohistochemistry-ihc-guide.