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CPE / Carboxypeptidase E · IHC design guide
Design Immunohistochemistry for CPE
Plan chromogenic CPE IHC in paraffin sections using the cytoplasmic tissue pattern reported for islets, enteroendocrine cells and brain (HPA tissue IHC). Use that pattern to select positive controls, and check whether the antibody epitope lies in a removed precursor segment (UniProt).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
CPE 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 islets, gut endocrine cells and brain (HPA tissue IHC) | |
| Staining pattern | Cytoplasmic signal in islets, enteroendocrine cells and brain (HPA tissue IHC) | |
| Antigen retrieval | Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen) | |
| Positive control | Appendix+4 more · see all | |
| Negative control | Adipose tissue+4 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep fixation consistent across paraffin sections. (standard IHC practice; not target-specific) | |
| Caveat | Secreted CPE may extend staining beyond secretory granules (UniProt) | |
| Regulation | Expression regulation is not annotated (UniProt) | |
| Isoform / epitope | 2 isoforms; signal peptide and propeptide are removed—check epitope (UniProt) |
Section 1
Recommended CPE IHC & IF Protocols
The catalog antibody’s IHC-P protocol is accompanied by published CPE IHC protocols for human liver and gastric tissue (PMC4542421; PMC11058891).
| Sample | Paraffin-embedded Rat Brain tissue; fixative not specified (datasheet A01407) |
| Fixation | Image fixative and duration unreported (datasheet A01407); 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-CPE, 1:100 (datasheet A01407) |
| 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 | CPE-positive staining in endocrine cells of appendix (HPA tissue IHC: High). HPA tissue profile: Distinct cytoplasmic expression mainly in islets of Langerhans, enteroendocrine cells and brain. 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). For gastric tissue, EDTA pH 9.0 is a published alternative (PMC11058891).
Section 2
What Is the Expected CPE Staining Pattern?
CPE should stain mainly in the cytoplasm of pancreatic islet cells, gut endocrine cells and selected brain cells (HPA: Supported tissue IHC; High in pancreatic endocrine cells, intestinal endocrine cells and hippocampal neurons). Its secretory-vesicle and secreted locations support a cytoplasmic granular pattern; CPE has no transmembrane segment, although it can associate with granule membranes (UniProt P16870 localisation and topology).
| Strong, distinct cytoplasmic staining in pancreatic islets, with much less staining in surrounding tissue. | This fits the strongest documented control: HPA reports High staining in pancreatic endocrine cells and says external characterization supports islet staining (HPA: Supported tissue IHC). Judge the cell distribution as well as intensity; a brown deposit across the whole section is less convincing (general IHC interpretation). |
| Cytoplasmic staining in scattered intestinal endocrine cells or hippocampal neurons. | These are additional expected positives: HPA reports High staining in endocrine cells of the colon, duodenum, rectum and small intestine, and in hippocampal neuronal cells (HPA: tissue IHC). A punctate cytoplasmic appearance is compatible with secretory-vesicle localisation, but granules need not be individually resolved by chromogenic IHC (UniProt P16870 localisation; general IHC interpretation). |
| Predominantly nuclear staining, or a continuous rim on most cell surfaces. | Neither is the expected tissue-IHC pattern: HPA describes distinct cytoplasmic expression, while UniProt lists secretory vesicles, vesicle membranes and secretion, with no transmembrane segment (HPA: tissue IHC profile; UniProt P16870 localisation and topology). Reassess morphology and controls before scoring this as CPE (general IHC practice). |
| Strong staining in adipocytes or esophageal squamous epithelium. | HPA reports CPE as Not detected in those specified cells (HPA: adipose tissue adipocytes; esophagus squamous epithelial cells). Unexpected signal can reflect nonspecific antibody binding or endogenous detection activity; compare a negative-control section before attributing it to CPE (general IHC practice). |
| Diffuse brown haze across positive and negative areas. | A widespread haze obscures the cell-selective pattern reported by HPA (HPA: distinct cytoplasmic tissue-IHC profile). It can arise from nonspecific binding, inadequate washing or endogenous detection activity (general IHC practice). Treat a faint haze separately from clear cytoplasmic staining in the documented positive cells. |
💡Expected CPE appearanceCall the result positive when distinct, preferably granular cytoplasmic staining is strongest in pancreatic endocrine cells or other documented endocrine or neuronal cells; HPA reports these cells as High, whereas uniform haze or dominant nuclear staining is unconvincing (HPA: tissue IHC; UniProt P16870 secretory-vesicle localisation; general IHC interpretation).
| Tissue choice and validation | Pancreatic islets provide the most directly characterized positive comparison: HPA rates tissue IHC Supported and cites external characterization of islet staining (HPA: reliability description). The listed HPA antibodies are IHC Supported; this does not establish identical performance for an untested catalog antibody (HPA: antibody validation). |
| Secretory pathway and processing | CPE has a signal peptide at residues 1–25, a propeptide at 26–42 and a mature chain at 43–476 (UniProt P16870 processing). It is found in secretory vesicles, on granule membranes and as secreted protein (UniProt P16870 localisation). Without an epitope map, these facts cannot predict which processed form the antibody detects. |
| Isoforms and glycosylation | UniProt lists two isoforms and glycosylation sites at residues 139 and 390 (UniProt P16870 isoforms and glycosylation). Their effects on this antibody’s IHC staining cannot be assigned without epitope and validation data; do not explain an unexpected tissue pattern by invoking an isoform alone. |
| Antigen retrieval | Use the catalog antibody’s validated IHC-P retrieval conditions if available, then assess the pancreatic-islet positive control (general IHC practice; HPA: Supported islet staining). The supplied HPA and UniProt records do not report a CPE-specific retrieval requirement or fixation sensitivity. |
| IF/ICC Q&A: should the same pattern be expected? | HPA reports vesicles and centrosome as approved ICC-IF locations, with images from A-431, U-251MG and U2OS (HPA: subcellular ICC-IF). These cell-image findings provide context for IF interpretation; they do not make centrosomal dots a required feature of paraffin-section IHC. |
| Chromogenic detection background | Endogenous enzyme activity or nonspecific reagent binding can create color unrelated to the primary antibody (general chromogenic IHC practice). A no-primary control helps distinguish that background from the HPA-supported, cell-selective cytoplasmic pattern (HPA: tissue IHC profile; general IHC practice). |
| Situation | Likely cause | Next action |
|---|---|---|
| Pancreatic islets show no convincing signal. | The positive-control pattern has failed; antibody performance, retrieval or detection may be inadequate (HPA: Supported islet staining; general IHC practice). | Confirm that islets are present, then check the catalog antibody’s IHC-P instructions, retrieval, dilution and detection controls (general IHC practice). Do not label another tissue negative until the positive control works. |
| Signal is mainly nuclear or outlines nearly every cell. | The compartment conflicts with HPA’s cytoplasmic tissue pattern and UniProt’s vesicle and secreted localisation (HPA: tissue IHC profile; UniProt P16870 localisation). | Review a no-primary control and staining distribution, and repeat with the antibody’s validated IHC-P conditions if needed (general IHC practice). Score only convincing signal in expected cells. |
| Adipocytes or esophageal squamous cells stain strongly. | Those cell types are listed as Not detected by HPA; cross-reactivity or detection background is possible (HPA: adipose tissue and esophagus IHC; general IHC practice). | Compare with a no-primary control and a documented positive area such as pancreatic islets; reassess antibody specificity if the unexpected cell staining persists (general IHC practice; HPA: Supported islet staining). |
| Brown haze covers both positive and negative areas. | Diffuse background can reflect nonspecific binding, washing or endogenous detection activity (general IHC practice). | Inspect the no-primary control, blocking and wash steps, and detection reagents; accept a result only when the expected cells remain distinguishable (general IHC practice; HPA: distinct cytoplasmic tissue-IHC profile). |
| Intestinal staining appears only in scattered cells. | A scattered pattern can be appropriate because HPA assigns High staining specifically to intestinal endocrine cells, rather than to every epithelial cell (HPA: colon, duodenum, rectum and small-intestine IHC). | Check whether the stained cells have endocrine-cell morphology and cytoplasmic signal; compare them with the pancreatic-islet control before calling the section weak (HPA: tissue IHC; general IHC interpretation). |
| IF shows centrosomal dots that are absent from chromogenic IHC. | Centrosome is an approved HPA ICC-IF location, while the tissue-IHC profile emphasizes cytoplasmic staining (HPA: subcellular ICC-IF; tissue IHC profile). | Interpret each application against its own HPA evidence. Do not require visible centrosomal dots to accept cell-selective cytoplasmic staining in paraffin-section IHC (HPA: ICC-IF and tissue IHC; general IHC interpretation). |
Experiment evidence
IHC & IF images showing CPE staining
A01407 · IHCImmunohistochemistry (IHC) analysis of paraffin-embedded Rat Brain, antibody was diluted at 1:100.
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000109472-CPE/tissue/cerebral+cortex#imid_1337060
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000109472-CPE/tissue/colon#imid_1336994
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000109472-CPE/tissue/liver#imid_1336995
HPA · PancreasHuman Protein Atlas IHC, Pancreas. Source: https://www.proteinatlas.org/ENSG00000109472-CPE/tissue/pancreas#imid_1336938
HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody HPA003819; green = CPE, blue = nucleus, red = microtubules.
HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody HPA003819; green = CPE, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for CPE IHC & IF
🧪Run appendix first: its endocrine cells must show specific staining (HPA: High in appendix endocrine cells). Use adipose tissue as the negative, where adipocytes should lack specific staining (HPA: Not detected in adipocytes); on the appendix slide, adjacent non-endocrine cells should show only background staining relative to the endocrine cells (HPA: High in appendix endocrine cells).
Positive control tissue: Appendix (Endocrine cells, HPA High)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show CPE in A-431, U-251MG, U2OS, with annotated localisation: Vesicles (approved), Centrosome (approved) (HPA subcellular).
Technical controls: Include a no-primary (secondary-only) control and a nonimmune isotype control matched to the primary antibody’s host species and clonality; use CPE-knockout tissue or a validated immunizing-peptide block as a biological specificity control (standard IHC practice). For chromogenic staining of appendix, quench endogenous peroxidase and, if using avidin–biotin detection, control for endogenous biotin (standard IHC practice).
⚠️Feasibility: A target-specific fixation window and the effect of antigen retrieval are unreported in the supplied evidence; optimize retrieval empirically (standard IHC practice). The selected catalog antibody caption shows paraffin-section staining of rat brain at 1:100, but its fixative is unreported (A01407 tissue-IHC caption). The evidence does not establish that frozen sections or IF are easier for CPE; in appendix, endogenous peroxidase can cause background in chromogenic IHC (standard IHC practice).
HPA tissue IHC evidence for CPE
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Supported — External characterization data supports antibody staining in islets of Langerhans.). 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 | Endocrine cells | High | Protein (IHC) | HPA → |
| Cerebellum | Bergmann glia - cytoplasm/membrane | High | Protein (IHC) | HPA → |
| Colon | Endocrine cells | High | Protein (IHC) | HPA → |
| Duodenum | Endocrine cells | High | Protein (IHC) | HPA → |
| Hippocampus | Neuronal cells | High | 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 → |
| Caudate | Glial cells | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced CPE IHC Tips
Troubleshoot CPE staining in paraffin sections by checking retrieval, cell type and compartment before comparing chromogenic signal across samples.
How should I retrieve CPE in paraffin sections when staining is weak?
Start with citrate buffer at pH 6.0, heated to 95–98 °C for 20 min (page retrieval rule: cytoplasmic/membrane antigen). Keep section thickness, cooling and wash steps consistent across runs so differences in staining can be interpreted alongside the same positive control (standard IHC practice). CPE occurs in secretory vesicles, at their membranes and in secreted form, without a transmembrane segment; retrieval conditions therefore cannot be chosen from topology alone (UniProt P16870 localisation and topology). If staining remains weak, compare a separately optimised retrieval condition while monitoring tissue damage and background (standard IHC practice).
Could fixation explain inconsistent CPE staining between paraffin blocks?
Target-specific fixation sensitivity is unknown from the supplied evidence, and the selected rat brain paraffin caption does not state its fixative (selected A01407 tissue-IHC caption). Record the fixative, fixation duration and processing history for each block before attributing a signal difference to CPE biology (standard IHC practice). Run blocks with comparable handling together, using the same retrieval, antibody dilution and chromogenic development conditions (standard IHC practice). Compare endocrine-rich positive areas and a low-expression comparator on each run, while treating any fixation explanation as a hypothesis until controlled specimens support it (HPA tissue IHC; standard IHC practice).
Which staining compartments are plausible for CPE in chromogenic IHC?
Expect predominantly cytoplasmic staining in appropriate cells, consistent with the reported tissue pattern and CPE's secretory-vesicle localisation (HPA tissue IHC; UniProt P16870 localisation). Vesicle-associated signal may appear granular or perinuclear at light-microscope resolution, but chromogenic deposits alone cannot establish precise vesicle identity (UniProt P16870 localisation; standard IHC interpretation). CPE can associate with secretory-granule membranes without a transmembrane segment and can also be secreted, so a purely membranous scoring rule would be too restrictive (UniProt P16870 topology and localisation). Record diffuse, granular and membrane-adjacent patterns separately, and compare them with the expected cell distribution (HPA tissue IHC; standard IHC practice).
Can this antibody distinguish CPE isoforms or processing states in tissue?
CPE has 2 annotated isoforms, a signal peptide at residues 1–25, a propeptide at 26–42 and a mature chain beginning at 43 (UniProt P16870 processing and isoforms). The supplied A01407 caption reports staining of paraffin-embedded rat brain at 1:100 but does not identify the antibody epitope (selected A01407 tissue-IHC caption). Consequently, tissue staining cannot by itself assign an isoform or distinguish precursor from processed CPE (UniProt P16870 processing; standard IHC interpretation). Check documented epitope coverage before making those claims, particularly near the processing regions or glycosylation sites at residues 139 and 390 (UniProt P16870 processing and glycosylation; standard IHC practice).
How should I use IF to check a disputed CPE IHC pattern?
Use IF as a complementary localisation check, pairing CPE with a marker for the expected endocrine or neuronal cell population and including single-label controls (HPA tissue IHC; standard IF practice). Choose fluorophores in spectral regions with low measured tissue autofluorescence, and set exposures using unstained tissue and single-label controls (standard IF practice). If the antibody epitope faces the vesicle lumen or lies in the cytoplasm, optimise permeabilisation to expose that side; the supplied caption does not establish epitope orientation (UniProt P16870 localisation; selected A01407 tissue-IHC caption; standard IF practice). Compare the IF cell and compartment pattern with chromogenic IHC without treating IF intensity as an equivalent DAB score (standard IHC/IF interpretation).
What should I change when CPE staining spreads across the whole section?
First inspect a no-primary control and the tissue edge to separate reagent or development background from antibody-dependent staining (standard IHC practice). Use an appropriate protein block, thorough washes and a titration around the caption's 1:100 dilution, keeping development time identical across comparisons (selected A01407 tissue-IHC caption; standard IHC practice). For peroxidase detection, include an endogenous peroxidase block and check whether residual colour appears without primary antibody (standard chromogenic IHC practice). Judge any remaining signal against the expected endocrine and brain distribution; widespread uniform colour is less convincing than a cell-restricted cytoplasmic pattern (HPA tissue IHC; standard IHC interpretation).
How can I quantify CPE staining across tissue sections reproducibly? ⚠ ANSWER MARKED FOR VERIFICATION
Define the relevant cell population and tissue area before scoring, such as pancreatic endocrine cells or hippocampal neuronal cells (HPA tissue IHC; standard IHC practice). An H-score combines the percentage of cells at intensity levels 0–3 into a 0–300 score; alternatively report percent positive cells or positive-cell density per mm² (standard IHC scoring practice). Normalise cell counts to the number of eligible cells, or area measurements to viable annotated tissue area, using the same threshold and imaging settings across samples (standard IHC quantification practice). Exclude folds, edges and necrotic regions consistently, and report replicate-level variation rather than pooling all fields as independent samples (standard IHC quantification practice).
How do I distinguish genuine CPE staining from an artefact?
A convincing positive has cytoplasmic, potentially vesicle-associated staining in an expected cell population, such as pancreatic endocrine or hippocampal neuronal cells (UniProt P16870 localisation; HPA tissue IHC). Centrosomal signal is also reported in subcellular IF data, so compartment assessment should consider the imaging method and resolution (HPA subcellular). Treat isolated edge staining, necrotic deposits or colour persisting in a no-primary control as artefact candidates, including possible endogenous enzyme activity (standard chromogenic IHC interpretation). Compare matched positive and low-expression areas on the same run, then confirm disputed patterns with an independent specificity control before drawing a biological conclusion (HPA tissue IHC; standard IHC practice).
Boster reagents
Best CPE / Carboxypeptidase E IHC Antibodies
The IHC-validated anti-CPE antibody has a paraffin-section rat-brain image (A01407 catalog image caption); IF is listed without an image (A01407 catalog applications and image records).
Real IHC data
Anti-CPE/Carboxypeptidase E Antibody
Cat # A01407
A01407 will render with its rat-brain paraffin-section IHC image at 1:100 (A01407 catalog image caption); its listed reactivity is human, mouse and rat (A01407 catalog reactivity). A01407-2 is listed for IHC, with paraffin-section use specified for human and rat, but has no IHC image and will not render as a card (A01407-2 catalog application and image records).
Which to pick: Choose A01407 for tissue IHC when an imaged paraffin-section example matters; its caption reports rat brain at 1:100 and does not report the fixative (A01407 catalog image caption). Choose A01407 for IF because IF is listed at 1:50, while no IF image or separate ICC validation is reported (A01407 catalog applications, dilution and image records). Both antibodies are rabbit polyclonals with human, mouse and rat reactivity listed, but the IHC image documents only A01407 in rat brain (A01407 and A01407-2 catalog host, clonality and reactivity; A01407 catalog image caption).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry P16870 (CBPE_HUMAN, Carboxypeptidase E).
- Human Protein Atlas. CPE tissue IHC expression (reliability: Supported).
- Human Protein Atlas. CPE subcellular location (ICC-IF): Mainly localized to vesicles and centrosome..
- Human Protein Atlas. CPE antibody validation summary (3 antibodies).
- The expression of hepatic carboxypeptidase E is decreased in patients with cholesterol gallstone. Saudi journal of gastroenterology : official journal of the Saudi Gastroenterology Association 2015 — PMC4542421.
- SCG2 and CPE may be novel markers for the identification of pancreatic neuroendocrine tumors and solid pseudopapillary neoplasms. Translational cancer research 2024 — PMC11319939.
- CPE correlates with poor prognosis in gastric cancer by promoting tumourigenesis. Heliyon 2024 — PMC11058891.
- The Importance of Stromal Endometriosis in Thoracic Endometriosis. Cells 2021 — PMC7831500.
- PubMed PMID:2334405 — UniProt-cited evidence.
- PubMed PMID:9662053 — UniProt-cited evidence.
- PubMed PMID:14702039 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for CPE (Carboxypeptidase E). Expected localisation Cytoplasmic staining in islets, gut endocrine cells and brain (HPA tissue IHC). Antigen retrieval: Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen). Validated IHC antibody: A01407 at 1:100 (the product's own IHC validation image is shown). Controls (HPA): positive Appendix (Endocrine cells); negative Adipose tissue. IHC workflow; specimen preparation unspecified. Protocol steps: 1. Sample: Paraffin-embedded Rat Brain tissue; fixative not specified (datasheet A01407); 2. Fixation: Image fixative and duration unreported (datasheet A01407); 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-CPE, 1:100 (datasheet A01407); 9. Primary incubation: Overnight at 4 °C (standard). Watch for: Fixation: Keep fixation consistent across paraffin sections. (standard IHC practice; not target-specific); Caveat: Secreted CPE may extend staining beyond secretory granules (UniProt); Isoform / epitope: 2 isoforms; signal peptide and propeptide are removed—check epitope (UniProt); Regulation: Expression regulation is not annotated (UniProt). Evidence: UniProt P16870, HPA tissue IHC · Supported, HPA ICC-IF · Mainly localized to vesicles and centrosome., Datasheet A01407, PMC4542421, PMC11058891. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/CPE/immunohistochemistry-ihc-guide.