APOA1 / Apolipoprotein A-I · IHC design guide

Design Immunohistochemistry for APOA1

Plan APOA1 chromogenic IHC in paraffin sections using the catalog antibody at 0.5–1 μg/ml (datasheet PB9916). Compare plasma staining and appendix enterocyte microvilli with the tissue IHC reference pattern (HPA tissue IHC).

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

Immunohistochemistry protocol sheet for APOA1 (IHC for APOA1): expected localisation Plasma positivity in several tissues (HPA tissue IHC), antibody PB9916, validated IHC image, and IHC protocol steps — Printable **APOA1** IHC protocol sheet — expected localisation Plasma positivity in several tissues (HPA tissue IHC), antibody PB9916, controls and protocol steps. Open the full APOA1 IHC guide →

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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	Plasma positivity in several tissues (HPA tissue IHC)
	Staining pattern	Distinct plasma staining; appendix enterocyte microvilli stain (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	Secreted APOA1 may stain plasma away from synthesis sites (UniProt; HPA tissue IHC)
	Regulation	Hepatic and intestinal synthesis (UniProt)
	Isoform / epitope	0 isoforms; mature chain starts at residue 25; no cytoplasmic domain (UniProt)

Section 1

Recommended APOA1 IHC & IF Protocols

The catalog antibody’s IHC-P protocol is accompanied by three published APOA1 IHC protocols covering urologic neoplasm, frozen placenta, and mouse yolk sac sections (PMC8798787; PMC2742651; PMC10014468).

Recommended immunohistochemistry (IHC-P) protocol parameters
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 retrieval for the catalog antibody (PB9916 datasheet); the published mouse yolk sac protocol used citrate pH 6.0 (PMC10014468).

Section 2

What Is the Expected APOA1 Staining Pattern?

APOA1 is secreted and has no transmembrane segment (UniProt P02647 topology). In paraffin-section IHC, expect plasma-associated staining across several tissues (HPA: distinct plasma positivity; Supported reliability). Appendix enterocyte microvilli show medium staining (HPA: Appendix, Medium). Liver and small intestine synthesize APOA1 (UniProt P02647 tissue specificity), but synthesis alone does not establish an IHC staining pattern for their cells.

What am I looking at on my slide?
Plasma-associated staining is distinct, with medium staining at appendix enterocyte microvilli.	This matches the reported tissue IHC pattern (HPA: distinct plasma positivity; Appendix enterocytes–microvilli, Medium). Score the microvillar signal separately from nearby plasma staining so that extracellular signal is not assigned to enterocyte cytoplasm (general IHC interpretation practice).
Strong, sharply nuclear staining dominates the section.	A dominant nuclear pattern conflicts with APOA1 secretion (UniProt P02647 subcellular location) and the reported plasma and microvillar IHC pattern (HPA: tissue IHC). Treat it as suspect; compare antibody-omission and detection controls before assigning it to APOA1 (general IHC practice).
Adipocytes or adrenal glandular cells stain strongly, while the expected structures remain weak.	Those cell types are reported as not detected (HPA: adipose adipocytes; adrenal glandular cells). Investigate cross-reactivity or endogenous detection activity; a negative cellular annotation does not rule out plasma-associated signal elsewhere in the same tissue (HPA: distinct plasma positivity).
A uniform haze covers cells and extracellular spaces, obscuring tissue boundaries.	Diffuse background cannot be scored as the distinct plasma signal or appendix microvillar staining reported by HPA (HPA: tissue IHC). Check nonspecific primary binding, detection background, and wash conditions with matched controls (general IHC practice).
No signal is visible at appendix enterocyte microvilli in an otherwise interpretable section.	The reported medium microvillar signal is absent (HPA: Appendix enterocytes–microvilli, Medium). Confirm the structure is present and compare a known-positive section processed in the same run; absence in one preparation alone does not establish that APOA1 is absent (general IHC practice).

💡Expected APOA1 appearanceCall the IHC result positive when distinct plasma-associated signal is present, with medium staining at appendix enterocyte microvilli where sampled (HPA: tissue IHC; Appendix, Medium); dominant nuclear staining or uniform haze warrants investigation as possible false-positive signal (UniProt P02647: Secreted; general IHC practice).

How each factor affects the staining
Secreted protein and tissue location	APOA1 is a major plasma HDL protein and is secreted (UniProt P02647 tissue specificity; subcellular location); HPA reports distinct plasma positivity in several tissues (HPA: tissue IHC). Interpret extracellular signal separately from staining assigned to resident cells.
Precursor processing	The 267-aa precursor has a signal peptide at residues 1–18; mature apolipoprotein A-I is annotated at residues 25–267 (UniProt P02647 processing). Antibody epitope details are absent here, so these annotations cannot predict whether processing changes this antibody's staining.
IHC evidence and controls	The tissue profile is rated Supported, and both listed antibodies have Supported IHC status (HPA: tissue IHC; HPA046715; CAB016778). Use the reported appendix microvilli as a positive-pattern reference and reported not-detected cell types as comparison points, while allowing for plasma signal.
Fixation and antigen retrieval	APOA1-specific fixation sensitivity and retrieval requirements are unreported in these payloads (HPA: tissue IHC scope; UniProt P02647 record). If optimizing paraffin IHC, compare retrieval conditions against matched positive tissue and background controls without assuming a target-specific effect (general IHC practice).
IF/ICC Q: What localization should be assessed?	A: HPA reports mainly vesicles, with additional cytosol, in ICC-IF (HPA: subcellular, approved locations). This is cellular IF evidence; it does not replace the plasma and appendix microvillar pattern used to interpret tissue IHC (HPA: tissue IHC).

Why is my staining missing, weak or wrong?
Situation	Likely cause	Next action
Appendix microvilli lack signal.	The reported medium-positive structure may be absent from the sampled section, or the staining run may have failed (HPA: Appendix, Medium; general IHC practice).	Verify identifiable enterocyte microvilli and repeat alongside a previously positive appendix section under the same staining conditions (general IHC practice).
Only broad plasma-associated signal is visible.	Extracellular APOA1 can contribute distinct plasma positivity across tissues (UniProt P02647: Secreted; HPA: tissue IHC).	Record plasma signal as its own pattern; assess appendix microvilli only when that structure is present and distinguishable (HPA: Appendix enterocytes–microvilli; general IHC interpretation practice).
Strong staining appears in a reported negative cell type.	Cross-reactivity or endogenous detection activity is possible; HPA reports adipocytes and adrenal glandular cells as not detected (HPA: tissue IHC).	Compare with a primary-antibody omission control and an appropriate detection control, then reassess the signal's cell and extracellular location (general IHC practice; HPA: distinct plasma positivity).
Nuclear signal dominates.	This conflicts with the secreted annotation and reported tissue pattern (UniProt P02647: Secreted; HPA: tissue IHC); its cause is unresolved.	Check omission and detection controls, then compare the section with reported plasma and microvillar locations before scoring it as APOA1 (general IHC practice; HPA: tissue IHC).
Diffuse chromogen obscures the section.	Nonspecific binding, detection background, or inadequate washing may obscure a discrete pattern (general IHC practice).	Inspect omission controls and reagent background; adjust blocking, washing, or detection conditions as indicated by those controls (general IHC practice).
Retrieval changes staining between runs.	The supplied sources do not establish APOA1-specific fixation sensitivity or a required retrieval condition (HPA: tissue IHC scope; UniProt P02647 record).	Compare retrieval conditions using matched sections, the same positive-pattern reference, and background controls; report the observed result without attributing it to an established APOA1 fixation effect (general IHC practice).

Source: UniProt P02647 Human Protein Atlas tissue Human Protein Atlas subcellular

Experiment evidence

IHC & IF images showing APOA1 staining

IHC analysis of APOA1 using anti-APOA1 antibody (PB9916). APOA1 was detected in a paraffin-embedded section of human renal 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 1 μg/ml rabbit anti-APOA1 Antibody (PB9916) overnight at 4°C. Biotinylated goat anti-rabbit IgG was used as secondary antibody and incubated for 30 minutes at 37°C. The tissue section was developed using Strepavidin-Biotin-Complex (SABC) (Catalog # SA1022) with DAB as the chromogen.

PB9916 · IHCIHC analysis of APOA1 using anti-APOA1 antibody (PB9916). APOA1 was detected in a paraffin-embedded section of human renal cancer tissue. He

IHC analysis of APOA1 using anti-APOA1 antibody (PB9916). APOA1 was detected in a paraffin-embedded section of human liver 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 1 μg/ml rabbit anti-APOA1 Antibody (PB9916) overnight at 4°C. Biotinylated goat anti-rabbit IgG was used as secondary antibody and incubated for 30 minutes at 37°C. The tissue section was developed using Strepavidin-Biotin-Complex (SABC) (Catalog # SA1022) with DAB as the chromogen.

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.

← 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: enterocyte microvilli should stain at the HPA Medium level (HPA: Appendix, Enterocytes - Microvilli, Medium). Use adipose tissue as the negative comparator (HPA: Adipocytes, Not detected); on the appendix slide, assess cells outside the annotated enterocyte microvilli for background rather than assuming they are biologically negative (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 a no-primary (secondary-only) slide, a matched nonimmune rabbit IgG isotype control appropriate to the antibody’s clonality, and a validated APOA1 knockout or peptide-block control (caption: rabbit anti-APOA1 antibody). For appendix IHC, block endogenous peroxidase and check endogenous biotin background before interpreting SABC–DAB staining (caption: biotinylated secondary, SABC–DAB detection).

⚠️Feasibility: The selected PB9916 paraffin-section caption reports EDTA retrieval at pH 8.0 and overnight primary incubation at 1 μg/ml, but its fixative is unreported; no target-specific fixation window or fixation effect is supplied (PB9916 tissue-IHC caption). Retrieval was used in that example, but whether APOA1 staining depends on it, or whether frozen sections or IF are easier, is unreported (PB9916 tissue-IHC caption). Because APOA1 is secreted and occurs in plasma HDL, assess microvillar staining against possible extracellular or luminal signal in the appendix section (UniProt P02647: Secreted; major protein of plasma HDL; HPA: Appendix, Enterocytes - Microvilli).

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 by checking retrieval, compartment, and plasma-associated signal before assigning cells as APOA1 producers (UniProt P02647; HPA tissue IHC).

Which retrieval condition should I start with for APOA1 paraffin-section IHC?

Start with heat-mediated EDTA pH 8.0 antigen retrieval for paraffin sections (datasheet PB9916). The documented tissue procedure then uses 1 μg/ml primary antibody overnight at 4°C, so keep those conditions fixed while assessing retrieval (caption PB9916). Compare staining within intact tissue and include a section processed without primary antibody to identify detection background (standard IHC practice). If staining remains weak, adjust heating duration on matched sections before considering another buffer, while recording tissue preservation and background (standard IHC practice). Do not infer retrieval success solely from plasma staining, which occurs across several tissues (HPA tissue IHC).

How should I troubleshoot fixation-related loss of APOA1 staining?

The selected paraffin-section image does not report its fixative, so APOA1-specific fixation sensitivity is unknown for this antibody (caption PB9916). Record the fixative, time in fixative, tissue thickness, and processing history for each specimen before comparing staining intensity (standard IHC practice). If a case stains weakly, compare similarly processed sections using the documented EDTA pH 8.0 retrieval and 1 μg/ml primary concentration (datasheet PB9916; caption PB9916). Test a matched, well-preserved control alongside the case to distinguish specimen handling from assay failure (standard IHC practice). Neither plasma positivity nor APOA1 processing establishes how fixation changes this epitope (HPA tissue IHC; UniProt P02647).

Where should APOA1 signal appear in tissue sections?

Interpret APOA1 as a secreted protein without a transmembrane segment, so extracellular or plasma-associated staining is plausible (UniProt P02647). Distinct plasma positivity occurs in several tissues, and tissue RNA and protein locations can differ for secreted variants (HPA tissue IHC). Examine vascular lumina, extracellular deposits, and cellular profiles separately before assigning a positive cell type (standard IHC practice; HPA tissue IHC). Enterocyte microvilli show medium staining in appendix, whereas adipocytes in adipose tissue were not detected in the cited profile (HPA tissue IHC). Cytoplasmic staining alone does not prove local synthesis; compare morphology and an appropriate cell marker where that conclusion matters (UniProt P02647; standard IHC practice).

Could APOA1 processing or modification change the epitope detected by IHC?

APOA1 has no annotated isoforms, but its precursor and processed chains have different termini (UniProt P02647). The signal peptide occupies residues 1–18, while annotated chains span 19–267, 25–267, or 25–266 (UniProt P02647). A terminal epitope could therefore differ across processed forms; check the antibody’s stated immunogen before interpreting selective staining (UniProt P02647; standard IHC practice). APOA1 also has an annotated glycosylation site at residue 263 and oxidation or nitration modifications at specified residues (UniProt P02647). Without an epitope map, tissue staining cannot identify a particular processed or modified form (UniProt P02647; standard IHC practice).

How can I adapt the IHC interpretation to multiplex APOA1 immunofluorescence?

Treat IF as a separate assay: the selected antibody evidence describes paraffin-section chromogenic detection, not an IF staining condition (caption PB9916). Multiplex APOA1 with a marker for the cell type being assessed, then inspect both cellular and extracellular signal because APOA1 is secreted (UniProt P02647; standard IF practice). Select fluorophores after checking the tissue’s autofluorescence in unstained sections, and include single-label controls for channel bleed-through (standard IF practice). For an intracellular epitope, evaluate permeabilisation; for an accessible extracellular epitope, begin without it, since APOA1 has no transmembrane segment (UniProt P02647; standard IF practice). Vesicular and cytosolic IF locations have been reported, but they do not establish tissue-cell origin (HPA subcellular; UniProt P02647).

How do I separate APOA1 signal from chromogenic IHC background?

The documented procedure uses 10% goat-serum block, biotinylated secondary antibody, a streptavidin–biotin complex, and DAB (caption PB9916). Include a no-primary section and inspect diffuse colour, edge staining, and pigment before assigning APOA1 positivity (standard IHC practice). Check endogenous peroxidase and biotin contributions with appropriate controls, particularly when background follows tissue structures rather than expected localisation (standard IHC practice). Plasma-associated staining may be genuine because APOA1 is a major plasma HDL protein and distinct plasma positivity appears in tissues (UniProt P02647; HPA tissue IHC). Reduce nonspecific detection background before changing the documented 1 μg/ml primary concentration, and compare matched sections (caption PB9916; standard IHC practice).

What should I score when APOA1 staining includes plasma and tissue structures? ⚠ ANSWER MARKED FOR VERIFICATION

Define the scored compartment before analysis, since APOA1 is secreted and several tissues show distinct plasma positivity (UniProt P02647; HPA tissue IHC). For identifiable cells, report percent positive cells and an intensity-weighted H-score; for extracellular deposits, report stained area or optical density per mm² of evaluable tissue (standard IHC practice). Normalise cell counts to the relevant cell population and extracellular measurements to intact, non-necrotic tissue area (standard IHC practice). Keep acquisition, DAB development, counterstain, and threshold settings consistent across compared sections (standard IHC practice). Report vascular or plasma signal separately so differences in blood content do not masquerade as changes in cellular expression (UniProt P02647; standard IHC practice).

What would make an APOA1-positive IHC result convincing rather than artefactual?

A convincing result follows interpretable tissue structures, survives comparison with a no-primary control, and is reproducible in matched sections (standard IHC practice). Plasma-associated signal is compatible with secreted APOA1, but does not by itself identify the cells that synthesized it (UniProt P02647; HPA tissue IHC). Examine unexpected nuclear staining, section-edge colour, necrotic regions, and pigment or residual endogenous-enzyme signal before calling a positive cell (standard IHC practice; UniProt P02647). Compare any proposed cellular localisation with morphology and a cell-type marker; appendix enterocyte microvilli are an observed positive structure (HPA tissue IHC; standard IHC practice). Describe staining as protein distribution rather than local gene expression unless independent evidence supports synthesis there (HPA tissue IHC; standard IHC practice).

Boster reagents

Best APOA1 / Apolipoprotein A-I IHC Antibodies

PB9916 is human-reactive for IHC and ICC (catalog: applications/reactivity), with IHC images from paraffin-embedded human renal and liver cancer tissue (IHC image captions); no IF image is supplied (catalog: IF images).

Real IHC data

Anti-Apolipoprotein A I/APOA1 Antibody ®

Cat # PB9916

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PB9916 will render with its IHC figure from paraffin-embedded human renal cancer tissue (IHC figure caption). A second catalog IHC image shows paraffin-embedded human liver cancer tissue, and ICC is listed without an image (catalog: IHC image captions and applications).

Which to pick: Choose PB9916 for human paraffin-section IHC; its figure documents EDTA retrieval at pH 8.0 and primary antibody at 1 μg/ml (IHC figure caption). For IF/ICC, PB9916 lists ICC at 0.5–1 μg/ml, but supplies no IF image; its clonality is unreported (catalog: applications, ICC dilution, IF images, clone). No cross-species option is supported because PB9916 lists human reactivity only; the paraffin-section caption does not report the fixative (catalog: reactivity; IHC figure caption).

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.