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APOC4 / Apolipoprotein C-IV · IHC design guide
Design Immunohistochemistry for APOC4
Plan chromogenic APOC4 IHC in paraffin sections using the catalog antibody at 1:50–1:200 (datasheet). Use liver hepatocytes as a positive control and assess cytoplasmic staining alongside the strong plasma signal (HPA tissue IHC).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
APOC4 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 and hepatocyte cytoplasm (HPA tissue IHC); secreted (UniProt) | |
| Staining pattern | Strong plasma signal; medium hepatocyte cytoplasmic staining (HPA tissue IHC) | |
| Antigen retrieval | Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen) | |
| Positive control | Liver | |
| Negative control | Adipose tissue+4 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep formalin fixation consistent across paraffin sections. (standard IHC practice; not target-specific) | |
| Caveat | Staining may include protein from another gene (HPA tissue IHC) | |
| Regulation | Regulation unreported (UniProt) | |
| Isoform / epitope | No isoforms; mature chain spans 28–127 (UniProt) |
Section 1
Recommended APOC4 IHC & IF Protocols
The catalog antibody protocol (datasheet) is accompanied by one published APOC4 tissue-section IHC protocol (PMC11994977).
| Sample | Paraffin-embedded human liver carcinoma tissue; fixative not specified (datasheet A08520) |
| Fixation | Image fixative and duration unreported (datasheet A08520); verify before use. |
| Sectioning | 4–5 µm sections on charged slides (standard) |
| Deparaffinisation | Xylene, graded ethanol series to water (standard) |
| Antigen retrieval | Heat-induced epitope retrieval in citrate buffer, pH 6.0, 20 min at 95–98 °C (standard rule: cytoplasmic / membrane antigen) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% normal serum of the secondary host, 30 min, room temperature (standard) |
| Primary antibody | Rabbit anti-APOC4, 1:50-1:200 (datasheet A08520) |
| Primary incubation | Overnight at 4 °C (standard) |
| Detection | HRP-polymer secondary, DAB chromogen 5–10 min (standard) |
| Counterstain | Hematoxylin, blue, dehydrate and mount (standard) |
| Expected result | APOC4-positive staining in hepatocytes of liver (HPA tissue IHC: Medium). HPA tissue profile: Strong positivity in plasma. Also cytoplasmic expression in liver. No signal in the no-primary control. |
💡Decision noteStart with citrate pH 6.0 HIER at 95–98 °C for 20 min (page retrieval rule); the published excerpt does not specify retrieval (PMC11994977).
Section 2
What Is the Expected APOC4 Staining Pattern?
APOC4 is secreted from liver into plasma and has no transmembrane segment (UniProt P55056). In paraffin-section IHC, expect medium cytoplasmic staining in hepatocytes and potentially strong staining in retained plasma (HPA tissue IHC). HPA rates the tissue pattern Supported, while cautioning that the antibodies used may target protein from more than one gene (HPA tissue IHC). Interpret staining with that specificity limit in mind.
| Hepatocyte cytoplasm stains at a moderate level; plasma within vessels may stain more strongly. | This matches medium hepatocyte staining and strong plasma positivity (HPA tissue IHC). Plasma signal can coexist with cellular staining because liver-secreted APOC4 enters plasma (UniProt P55056). Score the hepatocytes and plasma separately. |
| A sharply nuclear or exclusively crisp cell-membrane pattern replaces hepatocyte cytoplasmic staining. | That pattern does not match the reported hepatocyte cytoplasm (HPA tissue IHC). APOC4 is secreted and lacks a transmembrane segment (UniProt P55056). Treat the compartment mismatch as possible artefact; review morphology and detection controls before calling it APOC4. |
| Adipocytes or respiratory epithelial cells show convincing cellular staining. | HPA reports APOC4 as not detected in adipocytes of adipose tissue and respiratory epithelial cells of bronchus (HPA tissue IHC). Investigate cross-reactivity or endogenous detection activity, especially given HPA's caution that antibodies may target protein from more than one gene (HPA tissue IHC). |
| Color spreads across many structures without a discernible hepatocyte pattern. | Diffuse background cannot be scored as the reported cytoplasmic hepatocyte signal (HPA tissue IHC). Check whether staining persists in a no-primary control and whether chromogen deposit obscures cell boundaries; those checks assess the detection workflow, not APOC4-specific biology. |
| The liver section has no discernible hepatocyte staining. | A negative result conflicts with the reported medium hepatocyte signal (HPA tissue IHC). Confirm that intact hepatocytes are present, then review the antibody's IHC-P instructions and assay controls before interpreting the sample as biologically negative. |
💡Expected APOC4 appearanceCall a section positive when hepatocytes show medium cytoplasmic staining, with possible strong signal in retained plasma (HPA tissue IHC); isolated nuclear staining or widespread staining of HPA-negative cell types is suspect (HPA tissue IHC; UniProt P55056).
| Cellular versus plasma signal | Liver expresses APOC4 and secretes it into plasma (UniProt P55056). HPA reports cytoplasmic hepatocyte staining and strong plasma positivity (HPA tissue IHC). Record these as separate compartments; plasma signal alone does not demonstrate staining within a particular cell. |
| Signal-peptide processing | The annotated precursor has a signal peptide at residues 1–27 and a mature chain at 28–127 (UniProt P55056). Epitope placement is not supplied here, so this annotation cannot predict whether a particular antibody detects precursor, mature protein, or both. |
| Topology and compartment | APOC4 is annotated as secreted, with no transmembrane segment (UniProt P55056). A membrane-only IHC pattern would need independent support before being assigned to APOC4; the observed tissue pattern instead includes hepatocyte cytoplasm and plasma (HPA tissue IHC). |
| Glycosylation | UniProt annotates one glycosylation site at residue 63 (UniProt P55056). The supplied sources do not show whether this modification affects the IHC epitope or staining intensity. Do not infer a retrieval requirement or fixation sensitivity from the site alone. |
| Antibody evidence | The tissue IHC reliability is Supported, and antibody HPA055877 has Supported IHC status (HPA tissue IHC; HPA antibodies). HPA also cautions that antibodies may target protein from more than one gene (HPA tissue IHC). Use the reported pattern as a reference, with specificity controls for unexpected staining. |
| IF/ICC Q&A: Is membrane localization established? | HPA lists a membrane summary but gives no main location or ICC-IF image-bearing cell lines (HPA subcellular ICC-IF). Because APOC4 is secreted and lacks a transmembrane segment (UniProt P55056), that summary alone cannot establish membrane localization in an IF image. Evaluate IF/ICC on its separate guide page. |
| Antigen retrieval | No APOC4-specific retrieval condition or fixation effect is supplied by UniProt or HPA. For paraffin-section IHC, follow the IHC-validated antibody's stated retrieval procedure and compare controls when optimizing. Treat any change in signal as an assay observation, not a documented APOC4-specific fixation effect. |
| Situation | Likely cause | Next action |
|---|---|---|
| No hepatocyte signal in the liver positive control | The result conflicts with HPA's medium hepatocyte staining (HPA tissue IHC); the failed step is not identifiable from this observation alone. | Check hepatocyte preservation, antibody application, retrieval against the antibody's IHC-P instructions, and detection controls. Repeat the control before scoring an unknown sample as negative. |
| Hepatocytes stain weakly, while vascular plasma is conspicuous | Plasma is reported as strong and hepatocytes as medium (HPA tissue IHC), so unequal intensity may be expected. Excess background can further obscure cellular detail. | Score each compartment separately. Inspect hepatocyte boundaries and compare a no-primary control before changing assay conditions. |
| Only nuclei or crisp cell outlines stain | The compartment differs from the reported hepatocyte cytoplasm (HPA tissue IHC) and from the secreted, non-transmembrane annotation (UniProt P55056). | Check the counterstain, section morphology, and no-primary control. Do not score isolated nuclear or membrane-only staining as a validated APOC4 pattern without further evidence. |
| HPA-negative cell types appear positive | HPA reports not detected staining in several sampled cell types and cautions about antibodies targeting more than one gene (HPA tissue IHC). Cross-reactivity or endogenous detection activity is possible. | Compare matched positive and negative tissues, include a no-primary control, and investigate the detection chemistry before assigning the signal to APOC4. |
| Diffuse chromogen masks cell boundaries | A widespread deposit does not resolve the cytoplasmic hepatocyte pattern or plasma positivity reported by HPA (HPA tissue IHC). Non-target background or detection activity may be contributing. | Review blocking, washing, chromogen development, and no-primary staining as general IHC workflow checks; reassess only when hepatocytes and vascular spaces can be distinguished. |
| Plasma stains, but hepatocytes remain undetectable | Strong plasma staining can occur with APOC4 secretion (HPA tissue IHC; UniProt P55056), but HPA also reports medium hepatocyte staining (HPA tissue IHC). Plasma positivity alone does not validate cellular detection. | Record plasma and cellular results separately. Verify hepatocyte preservation and repeat the liver control using the antibody's IHC-P instructions before making a cell-level call. |
Experiment evidence
IHC & IF images showing APOC4 staining
A08520 · IHCImmunohistochemistry (IHC) analyzes of APOC4 pAb in paraffin-embedded human liver carcinoma tissue at 1:50,showing secreted staining.Negativ
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000224916-APOC4/tissue/cerebral+cortex#imid_15718891
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000224916-APOC4/tissue/colon#imid_15718801
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000224916-APOC4/tissue/liver#imid_15718802
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000224916-APOC4/tissue/kidney#imid_15718819
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for APOC4 IHC & IF
🧪Run liver first and score hepatocytes for APOC4 staining (HPA: hepatocytes Medium). Use adipose tissue as the negative tissue and compare hepatocytes with neighboring non-hepatocyte cells on the liver slide; the latter should show less cellular staining, although extracellular signal may occur because APOC4 is secreted (HPA: adipocytes Not detected; UniProt P55056: Secreted).
Positive control tissue: Liver (Hepatocytes, HPA Medium)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA carries no ICC-IF cell line for APOC4; derive a cell-line control from the positive tissue's cell type (Hepatocytes) and confirm it by RNA or western blot first.
Technical controls: Include a no-primary, secondary-only control and a host-matched nonimmune rabbit IgG control for the polyclonal primary; if available, use APOC4 knockout material or peptide preabsorption as a biological specificity control (selected caption: APOC4 pAb with goat anti-rabbit secondary; standard IHC practice). In liver, control endogenous peroxidase and, when using the caption’s avidin–biotin detection method, endogenous biotin (selected caption: avidin–peroxidase detection; standard IHC practice).
⚠️Feasibility: A target-specific fixation window and fixation effect are unreported, and the selected A08520 paraffin-section caption does not state its fixative (selected caption: fixative unreported). Retrieval dependency is unreported, so optimize antigen retrieval empirically; the caption supports paraffin-section IHC at 1:50, while the supplied HPA record lists no ICC-IF cell-line images and provides no basis to call frozen sections or IF easier (selected caption: 1:50; HPA subcellular: no ICC-IF cell-line images). In liver, secreted APOC4 may produce extracellular signal that needs to be distinguished from hepatocyte staining (UniProt P55056: Secreted; HPA: hepatocytes Medium).
HPA tissue IHC evidence for APOC4
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Supported — Pending RNA-based expert annotation. Caution, targets protein from more than one gene.). 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 |
|---|---|---|---|---|
| Liver | Hepatocytes | 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 → |
| Appendix | Glandular cells | Not detected | Protein (IHC) | HPA → |
| Bone marrow | Hematopoietic cells | Not detected | Protein (IHC) | HPA → |
| Breast | Adipocytes | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced APOC4 IHC Tips
Troubleshoot APOC4 staining in paraffin sections by comparing hepatocyte signal, plasma-associated staining and antibody-omission controls (HPA tissue IHC; A08520 caption).
How should I retrieve APOC4 antigen when paraffin sections stain weakly?
Start with citrate buffer at pH 6.0 and heat-induced retrieval at 95–98 °C for 20 minutes (page retrieval setting). Keep section thickness, cooling time and detection conditions consistent while comparing retrieval runs (general IHC practice). The A08520 image shows staining in paraffin-embedded human liver carcinoma at 1:50, but its caption does not report retrieval conditions (A08520 caption). If staining remains weak, test a longer citrate retrieval time on adjacent sections while watching for tissue damage (general IHC practice). Judge improvement by hepatocyte-associated cytoplasmic signal and the PBS-instead-of-primary control, while accounting for strong plasma positivity (HPA tissue IHC; A08520 caption).
Could fixation explain weak APOC4 staining in my paraffin sections?
APOC4-specific sensitivity to fixation is unknown from the supplied evidence; the A08520 paraffin-section caption does not state a fixative (A08520 caption). Record the fixative, fixation duration, tissue thickness and processing history for each block before comparing staining (general IHC practice). Use matched sections, the same citrate retrieval at pH 6.0 and 95–98 °C for 20 minutes, and the same antibody conditions to assess whether a processing difference tracks with signal (page retrieval setting; general IHC practice). Include a liver section with hepatocytes as a reference and compare its staining with the PBS-instead-of-primary control (HPA tissue IHC; A08520 caption).
Where should convincing APOC4 staining appear in liver sections?
Expect a hepatocyte-associated cytoplasmic component and assess plasma-associated staining separately: liver hepatocytes show medium positivity, while plasma shows strong positivity (HPA tissue IHC). APOC4 is expressed by the liver, secreted into plasma and lacks a transmembrane segment (UniProt P55056). The A08520 paraffin-section image describes a secreted staining pattern in human liver carcinoma, so diffuse extracellular color alone cannot establish the producing cell (A08520 caption; general IHC interpretation). Compare staining with cell outlines, vascular spaces and a counterstain at the same magnification (general IHC practice). Treat an exclusively sharp cell-membrane pattern cautiously because the HPA subcellular summary says “Membrane” but provides no ICC/IF image here (HPA subcellular payload).
How do APOC4 processing and glycosylation affect epitope interpretation?
APOC4 is a 127-amino-acid precursor with a signal sequence at residues 1–27 and a mature chain at residues 28–127 (UniProt P55056). It has one annotated glycosylation site at residue 63, no annotated isoforms and no transmembrane segment (UniProt P55056). If the antibody epitope is undisclosed, the section stain alone cannot show whether it recognizes the signal sequence, mature chain or a glycosylation-sensitive site (UniProt P55056; general IHC interpretation). Check the antibody’s stated immunogen region before comparing tissues, and keep retrieval at citrate pH 6.0 constant during that comparison (page retrieval setting; general IHC practice).
How can I use IF to investigate an ambiguous IHC pattern?
Use IF on matched sections to examine whether APOC4 signal overlaps a hepatocyte marker, the expected producing cell type in liver (HPA tissue IHC; UniProt P55056). Select spectrally separated fluorophores and include single-color and unstained controls to identify tissue autofluorescence before interpreting overlap (general IF practice). Because APOC4 is secreted and has no transmembrane segment, use gentle permeabilisation when testing intracellular signal from the mature protein; compare it with an unpermeabilised section if extracellular signal is the question (UniProt P55056; general IF practice). The supplied A08520 caption documents paraffin-section chromogenic IHC at 1:50, so establish IF antibody conditions separately (A08520 caption; general IF practice).
What should I check when APOC4 DAB staining is widespread?
First compare the tissue with a section processed using PBS instead of primary antibody, as in the A08520 image control (A08520 caption). Strong plasma positivity can produce broad signal that needs anatomical interpretation rather than automatic classification as cellular expression (HPA tissue IHC; general IHC interpretation). For peroxidase-based chromogenic detection, check the hydrogen peroxide block, secondary-only control, wash quality and DAB development time (general IHC practice). Keep the documented 1:50 A08520 image dilution as a reference point while titrating the antibody on matched sections (A08520 caption; general IHC practice). Examine section edges and necrotic areas separately, since staining there may reflect processing or trapping rather than APOC4 distribution (general IHC practice).
How should I score APOC4 when plasma and hepatocytes both stain? ⚠ ANSWER MARKED FOR VERIFICATION
Score hepatocyte staining and plasma-associated signal in separate compartments, because HPA reports medium positivity in hepatocytes and strong positivity in plasma (HPA tissue IHC). For hepatocytes, record percent positive cells and intensity, then calculate an H-score from the percentage at each intensity level (general IHC practice). Report the denominator as evaluable hepatocytes or tissue area, and exclude folds, necrosis and non-evaluable edges consistently across sections (general IHC practice). If measuring extracellular signal, report positive area or optical density per mm² of the defined compartment rather than adding it to a cellular H-score (general IHC practice). Apply one threshold and the same counterstain and imaging settings to every comparison (general IHC practice).
What evidence separates real APOC4 staining from an artefact?
A credible pattern includes hepatocyte-associated cytoplasmic staining with separately interpretable plasma signal, matching the reported liver and plasma profile (HPA tissue IHC). APOC4 is secreted and lacks a transmembrane segment, so isolated crisp membrane outlining warrants further checking (UniProt P55056). Compare the suspect area with the PBS-instead-of-primary control, and inspect tissue edges, necrosis and vascular spaces before assigning positivity (A08520 caption; general IHC practice). If color persists without primary antibody, investigate endogenous peroxidase activity and secondary-reagent background in the chromogenic workflow (general IHC practice). HPA marks its tissue result “Supported” but cautions that the antibody targets protein from more than one gene, so confirm identity before making an APOC4-specific claim (HPA tissue IHC).
Boster reagents
Best APOC4 / Apolipoprotein C-IV IHC Antibodies
A08520 has an IHC image from paraffin-embedded human liver carcinoma tissue (catalog image caption); human and mouse reactivity are listed (catalog: reactivity). No IF image is supplied (catalog: IF images).
Real IHC data
Anti-Apolipoprotein C-IV APOC4 Antibody
Cat # A08520
A08520 is listed for IHC and WB in human and mouse (catalog: applications and reactivity). Its IHC figure shows paraffin-embedded human liver carcinoma tissue at 1:50, with a PBS-instead-of-primary control (catalog image caption).
Which to pick: For tissue IHC, choose A08520: its IHC figure uses paraffin-embedded human liver carcinoma tissue (catalog image caption), and its listed IHC dilution is 1:50–1:200 (datasheet: IHC dilution). The caption does not report the fixative (catalog image caption). For cross-species work, A08520 lists human and mouse reactivity (catalog: reactivity), but the supplied IHC figure is human only (catalog image caption); no IF/ICC application or IF image is listed, so there is no IF/ICC pick in this payload (catalog: applications and IF images).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry P55056 (APOC4_HUMAN, Apolipoprotein C-IV).
- Human Protein Atlas. APOC4 tissue IHC expression (reliability: Supported).
- Human Protein Atlas. APOC4 subcellular location (ICC-IF): Membrane.
- Human Protein Atlas. APOC4 antibody validation summary (1 antibodies).
- Proteomic Analysis of Human Follicular Fluid-Derived Exosomes Reveals That Insufficient Folliculogenesis in Aging Women is Associated With Infertility. Molecular & cellular proteomics : MCP 2025 — PMC11994977.
- PubMed PMID:8530039 — UniProt-cited evidence.
- PubMed PMID:14702039 — UniProt-cited evidence.
- PubMed PMID:15489334 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for APOC4 (Apolipoprotein C-IV). Expected localisation Plasma and hepatocyte cytoplasm (HPA tissue IHC); secreted (UniProt). Antigen retrieval: Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen). Validated IHC antibody: A08520 at 1:50-1:200 (the product's own IHC validation image is shown). Controls (HPA): positive Liver (Hepatocytes); negative Adipose tissue. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded human liver carcinoma tissue; fixative not specified (datasheet A08520); 2. Fixation: Image fixative and duration unreported (datasheet A08520); 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-induced epitope retrieval in citrate buffer, pH 6.0 , 20 min at 95–98 °C…; 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% normal serum of the secondary host, 30 min , room temperature (standard); 8. Primary antibody: Rabbit anti-APOC4, 1:50-1:200 (datasheet A08520); 9. Primary incubation: Overnight at 4 °C (standard). Watch for: Fixation: Keep formalin fixation consistent across paraffin sections. (standard IHC practice; not target-specific); Caveat: Staining may include protein from another gene (HPA tissue IHC); Isoform / epitope: No isoforms; mature chain spans 28–127 (UniProt); Regulation: Regulation unreported (UniProt). Evidence: UniProt P55056, HPA tissue IHC · Supported, HPA ICC-IF · Membrane, Datasheet A08520, PMC11994977. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/APOC4/immunohistochemistry-ihc-guide.