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APOA1 / Apolipoprotein A-I · IHC design guide
Design Immunohistochemistry for APOA1
Plan APOA1 paraffin-section IHC around its secreted biology and the plasma staining observed across several tissues (UniProt; HPA tissue IHC). This guide covers the catalog antibody’s 0.5–1 μg/ml IHC dilution and the reported medium staining of appendix enterocyte microvilli (datasheet PB9916; HPA tissue IHC).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
APOA1 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 | Secreted (UniProt); tissue plasma staining (HPA tissue IHC) | |
| Staining pattern | Distinct plasma positivity across several tissues (HPA tissue IHC) | |
| Antigen retrieval | EDTA pH 8.0 HIER, heat-mediated (datasheet PB9916) | |
| Positive control | Appendix | |
| Negative control | Adipose tissue+4 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep fixation consistent across samples (standard IHC practice; not target-specific) | |
| Caveat | Plasma staining can complicate attribution to local cells (UniProt; HPA tissue IHC) | |
| Regulation | Liver-enriched RNA expression (HPA tissue RNA) | |
| Isoform / epitope | No isoforms; processing changes terminal epitopes (UniProt) |
Section 1
Recommended APOA1 IHC & IF Protocols
The catalog antibody protocol uses EDTA retrieval (datasheet: PB9916). The published APOA1 IHC protocols below cover paraffin sections and fresh-frozen placenta (PMC8798787; PMC2742651; PMC10014468).
| Sample | Paraffin-embedded human renal cancer tissue; fixative not specified (datasheet PB9916) |
| Fixation | Image fixative and duration unreported (datasheet PB9916); 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 PB9916); 20 min, 95–100 °C (standard) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% goat serum (datasheet PB9916) |
| Primary antibody | Rabbit anti-APOA1, 0.5-1μg/ml (datasheet PB9916) |
| Primary incubation | Overnight at 4 °C (datasheet PB9916) |
| Detection | Streptavidin-biotin complex (SABC), DAB chromogen (datasheet PB9916) |
| Counterstain | Hematoxylin, blue, dehydrate and mount (standard) |
| Expected result | APOA1-positive staining in enterocytes - Microvilli of appendix (HPA tissue IHC: Medium). HPA tissue profile: Distinct plasma positivity in several tissues. No signal in the no-primary control. |
💡Decision noteStart with heat-mediated EDTA pH 8.0 for the catalog antibody (datasheet: PB9916). Citrate pH 6.0 is a published alternative for mouse yolk sac (PMC10014468).
Section 2
What Is the Expected APOA1 Staining Pattern?
APOA1 is secreted and has no transmembrane segment (UniProt P02647 topology). In paraffin IHC, expect plasma-associated staining across several tissues, with Medium staining at appendix enterocyte microvilli (HPA tissue IHC). Interpret cellular staining alongside extracellular signal: a secreted protein can appear away from its site of synthesis (HPA tissue IHC reliability: Supported; UniProt P02647 tissue specificity).
| Distinct plasma staining across several tissues, with Medium staining at appendix enterocyte microvilli (HPA tissue IHC). | This matches the reported tissue pattern (HPA tissue IHC). APOA1 is a major protein of plasma HDL (UniProt P02647 tissue specificity). Score the stained structure as well as intensity; extracellular staining alone does not identify a producing cell (HPA tissue IHC reliability: Supported). |
| Predominantly nuclear staining, or a membrane outline presented as the expected APOA1 compartment (UniProt P02647 topology). | Treat the pattern as suspect: APOA1 is secreted and has no transmembrane segment (UniProt P02647 topology). Recheck morphology and controls before assigning the signal to APOA1; the supplied tissue IHC profile does not establish nuclear or membrane-outline staining (HPA tissue IHC). |
| Strong staining in adipocytes or respiratory epithelial cells, reported as APOA1-positive cells (HPA tissue IHC). | HPA reports those cell types as Not detected (HPA tissue IHC). Consider cross-reactivity or endogenous detection activity, while distinguishing cell staining from nearby plasma signal; a negative cell annotation does not mean its whole tissue section must be unstained (HPA tissue IHC reliability: Supported; standard IHC practice). |
| Weak colour spread across most structures, without a distinct plasma or microvillus pattern (HPA tissue IHC). | Diffuse background limits interpretation (standard IHC practice). Compare a no-primary control, inspect washing and blocking, and review the detection reaction before scoring cells; nonspecific colour cannot establish APOA1 localisation (standard IHC practice). |
| No signal at appendix enterocyte microvilli in a section expected to show the reported pattern (HPA tissue IHC). | HPA reports Medium staining there, so an absent signal warrants a technical check (HPA tissue IHC). Review tissue integrity, antibody and detection controls, and the validated IHC conditions before calling the sample negative (standard IHC practice). |
💡Expected APOA1 appearanceCall a result positive when it shows distinct plasma-associated staining and, in appendix, Medium enterocyte-microvillus staining; widespread nuclear or indiscriminate cellular colour is suspect (HPA tissue IHC; UniProt P02647 topology).
| Secretion and tissue attribution (UniProt P02647 topology; HPA tissue IHC reliability: Supported) | APOA1 is secreted and found in plasma HDL (UniProt P02647). Its staining site need not match its synthesis site; HPA notes that tissue RNA and protein can differ for secreted variants (HPA tissue IHC reliability: Supported). |
| Maturation and epitope coverage (UniProt P02647 processing) | The precursor has a signal peptide at residues 1–18; listed APOA1 chains begin at residues 19 or 25 (UniProt P02647 processing). The antibody epitope is unspecified here, so staining of each processed form cannot be inferred. |
| Observed tissue specificity (HPA tissue IHC; UniProt P02647 tissue specificity) | Appendix enterocyte microvilli show Medium staining, while listed adipocytes and respiratory epithelial cells are Not detected (HPA tissue IHC). Liver and small intestine synthesize APOA1 (UniProt P02647), but this payload supplies no hepatocyte IHC intensity. |
| Antibody validation (HPA antibodies) | Both listed antibodies have IHC status Supported (HPA antibodies). That status supports use of the reported pattern; it does not supply a dilution, retrieval setting, or evidence that every stained cell is a synthesis site (HPA antibodies; HPA tissue IHC reliability: Supported). |
| Does IF/ICC show the same compartment? (HPA subcellular ICC-IF) | HPA ICC-IF reports mainly vesicles, with additional cytosol (HPA subcellular ICC-IF). Use that as IF/ICC context only; it does not replace the plasma and microvillus observations used to read paraffin IHC (HPA tissue IHC). |
| Situation | Likely cause | Next action |
|---|---|---|
| No appendix microvillus signal despite adequate tissue morphology (HPA tissue IHC). | The reported Medium signal may have been missed, or the staining run may have failed; the supplied record does not identify a target-specific fixation effect (HPA tissue IHC; standard IHC practice). | Check the positive section, antibody and detection controls, then review the IHC-validated antibody's documented conditions. Optimise retrieval only as a general IHC variable; do not presume APOA1-specific fixation sensitivity (standard IHC practice). |
| Broad brown signal obscures plasma and cell boundaries (HPA tissue IHC). | Nonspecific primary or detection background can make a structured pattern unreadable (standard IHC practice). The supplied HPA profile calls for distinct plasma positivity, not uniform colour (HPA tissue IHC). | Compare a no-primary control, then review blocking, washing, antibody concentration and chromogen development one variable at a time (standard IHC practice). Rescore only when structures remain identifiable. |
| Colour persists in the no-primary control (standard IHC practice). | Endogenous detection activity or the detection reagents can contribute signal independently of primary-antibody binding (standard IHC practice). | Address the relevant endogenous activity and review the detection system before attributing colour to APOA1 (standard IHC practice). Use the control to locate background in the same tissue compartment. |
| A predominantly nuclear or sharply membrane-outline pattern is reported (UniProt P02647 topology). | That assignment conflicts with APOA1 secretion and its lack of a transmembrane segment (UniProt P02647 topology). The supplied HPA tissue profile does not validate those compartments (HPA tissue IHC). | Inspect the counterstain and morphology, compare controls, and confirm the pattern with an independently validated antibody if available (standard IHC practice). Do not score the unexpected compartment as established APOA1 localisation. |
| Adipocytes appear positive in an adipose section (HPA tissue IHC). | HPA lists adipocytes as Not detected; extracellular plasma signal, background or cross-reactivity may be mistaken for cellular staining (HPA tissue IHC; standard IHC practice). | Identify cell borders before scoring, compare a no-primary control, and record extracellular and cellular signal separately (standard IHC practice; HPA tissue IHC reliability: Supported). |
| ICC-IF vesicles seem inconsistent with an IHC section dominated by plasma staining (HPA subcellular ICC-IF; HPA tissue IHC). | The supplied observations come from different assay contexts: ICC-IF reports vesicles and cytosol, while tissue IHC reports distinct plasma positivity (HPA subcellular ICC-IF; HPA tissue IHC). | Interpret each image using its own assay and controls. For this paraffin IHC readout, use the HPA tissue pattern; consult the separate IF/ICC guide for imaging decisions (HPA tissue IHC; HPA subcellular ICC-IF). |
Experiment evidence
IHC & IF images showing APOA1 staining
PB9916 · IHCIHC analysis of APOA1 using anti-APOA1 antibody (PB9916). APOA1 was detected in a paraffin-embedded section of human renal cancer tissue. He
PB9916 · IHCIHC analysis of APOA1 using anti-APOA1 antibody (PB9916). APOA1 was detected in a paraffin-embedded section of human liver cancer tissue. He
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000118137-APOA1/tissue/cerebral+cortex#imid_15543843
HPA · DuodenumHuman Protein Atlas IHC, Duodenum. Source: https://www.proteinatlas.org/ENSG00000118137-APOA1/tissue/duodenum#imid_15518624
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000118137-APOA1/tissue/colon#imid_15518617
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000118137-APOA1/tissue/liver#imid_15518618
HPA · ICC-IF CACO-2Human Protein Atlas immunofluorescence, CACO-2, antibody HPA046715; green = APOA1, blue = nucleus, red = microtubules.
HPA · ICC-IF CACO-2Human Protein Atlas immunofluorescence, CACO-2, antibody HPA046715; green = APOA1, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for APOA1 IHC & IF
🧪Run appendix first and expect staining at enterocyte microvilli (HPA: Appendix enterocytes–microvilli, Medium); use adipose tissue adipocytes as a negative comparator (HPA: Adipose tissue adipocytes, Not detected). On the appendix slide, use areas without the enterocyte microvillar pattern to assess background, but establish their staining status by inspection because the supplied HPA row identifies only the positive cell type (HPA: Appendix enterocytes–microvilli, Medium).
Positive control tissue: Appendix (Enterocytes - Microvilli, HPA Medium)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show APOA1 in CACO-2, Hep-G2, U2OS, with annotated localisation: Vesicles (approved) (HPA subcellular).
Technical controls: Include no-primary (secondary-only) and matched rabbit IgG isotype controls, plus APOA1-knockout material or validated peptide competition as a specificity control (caption: rabbit primary; standard IHC control practice). Quench endogenous peroxidase and check for endogenous biotin signal in appendix when using the caption’s biotinylated secondary and SABC/DAB detection (caption: PB9916; standard IHC control practice).
⚠️Feasibility: A target-specific fixation window or fixation effect is unreported, and the selected paraffin-section caption does not state a fixative (caption: PB9916). Heat retrieval in EDTA at pH 8.0 is a documented starting condition, but retrieval dependency is unreported (caption: PB9916). Whether frozen sections or IF are easier is unreported; assess possible apical or luminal background when scoring appendix enterocyte microvilli (HPA: Appendix enterocytes–microvilli, Medium; standard IHC practice).
HPA tissue IHC evidence for APOA1
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Supported — At least one protein variant secreted, tissue location of RNA and protein might differ and correlation is complex. Antibody staining in cells/structures not annotated, view images.). 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 |
|---|---|---|---|---|
| Appendix | Enterocytes - Microvilli | Medium | 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 → |
| 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 APOA1 IHC Tips
Troubleshoot APOA1 staining in paraffin sections by separating tissue signal from circulating protein, then checking retrieval, detection controls, and scoring compartments.
What retrieval should I start with when APOA1 staining is weak in paraffin sections?
Start with heat-mediated retrieval in EDTA, pH 8.0 (datasheet PB9916). The catalog antibody produced chromogenic staining in a paraffin-embedded human renal cancer section after that retrieval, followed by 1 μg/ml primary antibody overnight at 4°C (datasheet PB9916). Compare a known staining control and a no-primary control in the same run to distinguish weak antigen signal from detection background (standard IHC practice). If signal remains weak, vary heating duration and antibody concentration in separate titrations while keeping section thickness and detection conditions consistent (standard IHC practice). The image caption does not report the fixative, so retrieval performance in differently fixed specimens remains uncertain (datasheet PB9916).
How should I troubleshoot fixation-related variation in APOA1 IHC?
The selected paraffin-section caption does not state a fixative, and target-specific fixation sensitivity is unknown (datasheet PB9916). Record each specimen’s fixative, time in fixative, processing history, and section age before comparing staining intensity across cases (standard IHC practice). Run specimens with different processing histories alongside the same control section, using EDTA, pH 8.0 retrieval and the established 1 μg/ml primary concentration as the starting conditions (datasheet PB9916; standard IHC practice). If results diverge, change retrieval or primary incubation conditions one variable at a time and assess morphology together with signal (standard IHC practice). Do not attribute a difference to an APOA1-specific fixation effect without a controlled comparison (standard IHC practice).
Where should APOA1 staining appear, and what does unexpected cellular staining mean?
APOA1 is secreted, lacks a transmembrane segment, and is a major protein of plasma HDL; liver and small intestine synthesize it (UniProt P02647). In tissue IHC, plasma-associated staining can therefore appear away from its site of synthesis; HPA describes distinct plasma positivity in several tissues (UniProt P02647; HPA tissue IHC). HPA also reports medium staining of appendix enterocyte microvilli, while its ICC/IF observations place APOA1 mainly in vesicles and additionally in cytosol (HPA tissue IHC; HPA subcellular). Evaluate extracellular, luminal, and cellular staining separately against local morphology and controls (standard IHC practice). A stained renal cancer section demonstrates detection in that specimen, but does not by itself establish production by tumor cells (datasheet PB9916; UniProt P02647).
Could processing or chemical modification explain discordant APOA1 staining?
The supplied record lists 0 isoforms but several processed APOA1 chains, including residues 19–267, 25–267, and 25–266 (UniProt P02647). It also annotates glycosylation at residue 263 and oxidative or nitrative modifications at other residues (UniProt P02647). Because the catalog antibody’s epitope is not specified in the supplied caption, staining cannot establish which processed or modified form it recognizes (datasheet PB9916; UniProt P02647). Compare staining across similarly processed sections with an independent antibody whose epitope is known, if available, and keep retrieval constant during that comparison (standard IHC practice). Interpret differences in staining as possible epitope-accessibility effects until specificity is tested directly (standard IHC practice).
How can I compare APOA1 immunofluorescence with the chromogenic IHC result?
Treat IF/ICC as a separate assay: the supplied EDTA, pH 8.0 retrieval and 1 μg/ml overnight incubation document paraffin-section chromogenic IHC with this antibody (datasheet PB9916). For multiplex IF, pair APOA1 with an independently validated marker of the expected producing cell type, such as a liver or small-intestine cell marker, and check whether signals occupy the same cells (UniProt P02647; standard IF practice). Choose fluorophores and exposure settings after measuring tissue autofluorescence in an unstained section (standard IF practice). Determine whether the antibody epitope is accessible extracellularly or requires access to vesicles or cytosol before deciding on permeabilisation; the supplied caption does not map that epitope (HPA subcellular; datasheet PB9916). Include single-label and no-primary controls when assessing apparent overlap (standard IF practice).
How do I reduce diffuse or vessel-associated APOA1 background?
First distinguish plausible plasma-associated APOA1 from nonspecific stain: APOA1 is a plasma HDL protein, and HPA reports distinct plasma positivity in several tissues (UniProt P02647; HPA tissue IHC). Compare the pattern with tissue architecture, a no-primary control, and a matched control section before increasing wash stringency or reducing primary concentration (standard IHC practice). The selected image used 10% goat serum, 1 μg/ml primary antibody overnight at 4°C, and biotin-based DAB detection (datasheet PB9916). With that detection chemistry, assess endogenous peroxidase and biotin-related background using appropriate reagent controls and blocking steps (datasheet PB9916; standard IHC practice). Record extracellular and cellular signal separately so removal of background does not erase a biologically plausible plasma pattern (UniProt P02647; standard IHC practice).
How should I score APOA1 when plasma and cellular compartments both stain? ⚠ ANSWER MARKED FOR VERIFICATION
Define compartments before scoring, because secreted APOA1 can yield plasma-associated signal apart from the cells that synthesize it (UniProt P02647; HPA tissue IHC). For cellular DAB staining, report the percentage of positive cells and an intensity-weighted H-score, with the counted cell population and threshold stated explicitly (standard IHC practice). For extracellular signal, measure positive area or optical density per mm² of evaluable tissue, rather than including it in a cellular H-score (standard IHC practice). Normalize cell counts to eligible cells and area measurements to analyzed tissue area, excluding folds, necrosis, and slide edges by prespecified rules (standard IHC practice). Apply identical illumination, color separation, and threshold settings across sections and verify automated classifications by visual review (standard IHC practice).
How can I distinguish a true APOA1 pattern from staining artefact?
Interpret staining against APOA1’s secreted topology and plasma HDL association, so vessel or extracellular signal alone does not identify the producing cell (UniProt P02647). HPA documents plasma positivity in several tissues and medium appendix enterocyte-microvillus staining, providing compartment-specific reference patterns rather than a universal positive-cell rule (HPA tissue IHC). Scrutinize isolated intense staining at section edges, folds, or necrotic areas, and check a no-primary control for detection-system signal (standard IHC practice). With DAB, assess endogenous peroxidase activity before calling a dark deposit antigen-specific (standard IHC practice). The renal cancer image shows APOA1 detection after EDTA, pH 8.0 retrieval, but its caption does not establish which cells synthesized the detected protein (datasheet PB9916; UniProt P02647).
Boster reagents
Best APOA1 / Apolipoprotein A-I IHC Antibodies
PB9916 has real IHC data from human paraffin sections (PB9916 IHC captions: renal and liver cancer). ICC is listed, but no IF figure is supplied (catalog: applications; IF image alts).
Real IHC data
Anti-Apolipoprotein A I/APOA1 Antibody ®
Cat # PB9916
PB9916 will render with its human renal cancer paraffin-section IHC figure (PB9916 IHC caption). Its catalog lists human reactivity and IHC and ICC applications; a second IHC caption describes a human liver cancer paraffin section (catalog: reactivity and applications; PB9916 IHC captions).
Which to pick: Choose PB9916 for human tissue IHC: its own figure documents staining of a paraffin section, but does not report the fixative (PB9916 IHC caption: human renal cancer). For ICC, PB9916 is listed, although no IF figure is supplied and clonality is unreported (catalog: applications, IF image alts, clone). No cross-species choice is supported because PB9916 lists human reactivity only (catalog: reactivity).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry P02647 (APOA1_HUMAN, Apolipoprotein A-I).
- Human Protein Atlas. APOA1 tissue IHC expression (reliability: Supported).
- Human Protein Atlas. APOA1 subcellular location (ICC-IF): Mainly localized to vesicles. In addition localized to the cytosol..
- Human Protein Atlas. APOA1 antibody validation summary (2 antibodies).
- The expression of apolipoproteina1 and its correlation with infiltration of urologic neoplasm. Translational cancer research 2020 — PMC8798787.
- Apolipoprotein A1 reduces blood-spinal cord barrier leakage, improves astrocytic coverage, and enhances motor neuron survival to restore the neurovascular unit in ALS mice. Frontiers in aging neuroscience 2025 — PMC12832854.
- Differential proteome analysis of the preeclamptic placenta using optimized protein extraction. Journal of biomedicine & biotechnology 2010 — PMC2742651.
- Aberrant lipid accumulation in the mouse visceral yolk sac resulting from maternal diabetes and obesity. Frontiers in cell and developmental biology 2023 — PMC10014468.
- PubMed PMID:6406984 — UniProt-cited evidence.
- PubMed PMID:6304641 — UniProt-cited evidence.
- PubMed PMID:6413973 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for APOA1 (Apolipoprotein A-I). Expected localisation Secreted (UniProt); tissue plasma staining (HPA tissue IHC). Antigen retrieval: EDTA pH 8.0 HIER, heat-mediated (datasheet PB9916). Validated IHC antibody: PB9916 at 0.5-1μg/ml (the product's own IHC validation image is shown). Controls (HPA): positive Appendix (Enterocytes - Microvilli); negative Adipose tissue. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded human renal cancer tissue; fixative not specified (datasheet PB9916); 2. Fixation: Image fixative and duration unreported (datasheet PB9916); 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 PB9916); 20 min, 95–100 °C (standard); 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% goat serum (datasheet PB9916); 8. Primary antibody: Rabbit anti-APOA1, 0.5-1μg/ml (datasheet PB9916); 9. Primary incubation: Overnight at 4 °C (datasheet PB9916). Watch for: Fixation: Keep fixation consistent across samples (standard IHC practice; not target-specific); Caveat: Plasma staining can complicate attribution to local cells (UniProt; HPA tissue IHC); Isoform / epitope: No isoforms; processing changes terminal epitopes (UniProt); Regulation: Liver-enriched RNA expression (HPA tissue RNA). Evidence: UniProt P02647, HPA tissue IHC · Supported, HPA ICC-IF · Mainly localized to vesicles. In addition localized to the cytosol., Datasheet PB9916, PMC8798787, PMC2742651. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/APOA1/immunohistochemistry-ihc-guide.