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CPE / Carboxypeptidase E · IHC design guide
Design Immunohistochemistry for CPE
Plan paraffin IHC for CPE using pancreatic islets as a positive control and scoring cytoplasmic staining in endocrine cells (HPA tissue IHC). The catalog antibody has a listed IHC dilution of 1:100 (datasheet: A01407).
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 | Endocrine-cell cytoplasm (HPA tissue IHC) | |
| Staining pattern | Distinct cytoplasmic staining in islets and enteroendocrine cells (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 sections. (standard IHC practice; not target-specific) | |
| Caveat | Secreted CPE may contribute to extracellular staining (UniProt) | |
| Regulation | No specific expression regulator annotated (UniProt) | |
| Isoform / epitope | 2 isoforms; mature chain starts at residue 43—check epitope (UniProt) |
Section 1
Recommended CPE IHC & IF Protocols
Compare the catalog antibody’s IHC-P protocol (datasheet) with published CPE staining methods for human liver (PMC4542421) and gastric tissue (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 antigen retrieval); the gastric tissue study used EDTA pH 9.0 (PMC11058891).
Section 2
What Is the Expected CPE Staining Pattern?
CPE staining in paraffin sections should be mainly cytoplasmic, concentrated in pancreatic islet cells, intestinal endocrine cells and selected brain cells (HPA: supported tissue IHC; HPA: high in those cell populations). A punctate or granular appearance is consistent with secretory vesicles and their membranes (UniProt P16870: secretory vesicle localisation). CPE has no transmembrane segment; membrane association reflects binding to granule lipids (UniProt P16870: topology and localisation).
| Strong cytoplasmic staining in pancreatic islet cells, with much less signal in surrounding tissue. | This is a suitable positive pattern: HPA reports high staining in pancreatic endocrine cells and describes distinct cytoplasmic expression mainly in islets, enteroendocrine cells and brain (HPA: tissue IHC). Assess the labelled cell population as well as intensity; a uniformly stained section loses that distinction. |
| Granular cytoplasmic staining in gut endocrine cells or hippocampal neuronal cells. | These are supported positive populations: appendix, colon, duodenum, rectum and small intestine endocrine cells, plus hippocampal neuronal cells, are reported high (HPA: tissue IHC). Granularity is compatible with secretory vesicle localisation (UniProt P16870: localisation), although chromogenic IHC alone cannot identify individual organelles. |
| Predominantly nuclear staining, or a continuous cell surface outline without the expected cytoplasmic signal. | Treat this as a compartment mismatch with the reported tissue pattern (HPA: distinct cytoplasmic expression) and secretory vesicle localisation (UniProt P16870: localisation). Review morphology, controls and detection background before interpreting it as CPE; compartment mismatch alone does not identify the source of the signal. |
| Strong staining in a population reported as undetected, such as adipocytes in adipose tissue. | HPA reports CPE as not detected in that specific population (HPA: adipose tissue adipocytes). Check cell identification, antibody specificity and endogenous detection activity. A discrepant result is a reason to investigate; the HPA observation does not prove that every cell in every specimen must be negative. |
| Diffuse chromogen across cells and extracellular areas, or no signal in a known positive islet control. | Diffuse signal obscures the expected cell and cytoplasm pattern (HPA: tissue IHC) and may reflect general staining background. An unstained islet control conflicts with HPA's high pancreatic endocrine cell staining (HPA: tissue IHC); first verify the control, run conditions and detection reagents before drawing a biological conclusion. |
💡Expected CPE appearanceCall a section positive when the relevant endocrine or neuronal cells show distinct cytoplasmic staining, often granular, with strong signal in HPA high populations; widespread nuclear, extracellular or cell type indiscriminate colour is suspect (HPA: tissue IHC; UniProt P16870: secretory vesicle localisation).
| Reference tissue and cell identity | Pancreatic endocrine cells, gut endocrine cells and hippocampal neuronal cells are high reference populations (HPA: tissue IHC). Adipose tissue adipocytes and bone marrow hematopoietic cells are reported not detected (HPA: tissue IHC). Score named cell types rather than assigning one expected intensity to the whole organ. |
| Compartment and processing | CPE is reported in secretory vesicles, on their membranes and as a secreted protein (UniProt P16870: localisation). Its signal peptide spans residues 1–25 and propeptide 26–42 (UniProt P16870: processing). Epitope position could affect recognition, but no antibody epitope or processing dependent IHC comparison is supplied. |
| Isoforms and antibody validation | UniProt lists 2 CPE isoforms (UniProt P16870: isoforms). HPA lists IHC as supported for HPA003819, CAB024907 and CAB080183; HPA003819 is also ICC approved (HPA: antibody validation). Those labels support the stated applications but do not establish identical staining, isoform recognition or epitope coverage for every reagent. |
| Antigen retrieval and detection | Retrieval and detection settings are general paraffin IHC variables; compare conditions against a known positive section and a negative reagent control (standard IHC practice). The supplied HPA and UniProt records give no CPE specific retrieval setting or fixation sensitivity, so a changed signal under those conditions cannot be attributed to a documented CPE fixation effect. |
| IF/ICC localisation scope | HPA reports vesicles and centrosome as approved ICC IF locations and shows images from A-431, U-251MG and U2OS cells (HPA: subcellular ICC IF). These cell based observations can inform localisation review, but they are separate from the supported tissue IHC pattern and do not provide an IF protocol for this paraffin IHC guide. |
| Situation | Likely cause | Next action |
|---|---|---|
| No chromogenic signal in pancreatic islet cells. | The positive reference has failed relative to HPA's high pancreatic endocrine cell staining (HPA: tissue IHC); the result alone cannot distinguish specimen, antibody and detection failures. | Confirm that islets are present on the section, then check the validated IHC workflow, reagent activity and positive control side by side (standard IHC practice). Reassess the sample only after the control stains. |
| Colour covers most cells or extends through empty background. | The distribution lacks HPA's distinct cytoplasmic, cell restricted tissue pattern (HPA: tissue IHC). Excess detection signal or nonspecific binding is possible (standard IHC practice). | Inspect a negative reagent control; review blocking, antibody concentration, wash steps and chromogen development (standard IHC practice). Restore a readable cell specific pattern before scoring CPE. |
| Nuclei dominate while expected cytoplasm is faint. | This differs from the cytoplasmic tissue pattern (HPA: tissue IHC) and the secretory vesicle localisation (UniProt P16870: localisation); the source of the nuclear colour is unresolved. | Check counterstain and detection controls, then compare the same run with a positive islet section (standard IHC practice). Do not classify nuclear colour alone as a confirmed CPE positive. |
| Strong colour appears in adipose tissue adipocytes or bone marrow hematopoietic cells. | Those named populations are reported not detected (HPA: tissue IHC). Misidentified cells, cross reactivity or endogenous detection activity may explain the discrepancy (standard IHC practice). | Verify cell identity on morphology and examine negative reagent and detection controls (standard IHC practice). If the discrepancy persists, compare an independently validated antibody; keep the finding separate from the HPA reference pattern. |
| A weak or patchy section seems negative despite some stained cells. | CPE intensity varies by named population: HPA reports high endocrine cells but low bronchial respiratory epithelial cells and lung macrophages (HPA: tissue IHC). Whole section averaging can conceal a restricted positive population. | Score the relevant cell type and compartment, and compare it with a high reference population processed in the same run (HPA: tissue IHC; standard IHC practice). Record weak staining without upgrading it to the high reference pattern. |
| Q: Does an IF/ICC centrosomal signal validate a paraffin IHC result? | A: Centrosome and vesicles are approved ICC IF locations (HPA: subcellular ICC IF), while tissue IHC is described mainly as cytoplasmic (HPA: tissue IHC). The applications have distinct evidence. | Use cell based IF/ICC as a localisation cross check only; judge paraffin IHC against its tissue and cell pattern and controls (HPA: tissue IHC; standard IHC practice). Consult the separate IF/ICC guide for that application. |
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 should stain strongly (HPA: High in appendix endocrine cells). Use adipose tissue as the negative tissue, with adipocytes expected to remain unstained (HPA: Not detected in adipocytes); on the appendix slide, compare endocrine cells with neighboring cells as an internal background reference, without assuming those neighbors are CPE-negative.
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 host- and isotype-matched control for a monoclonal primary, or host-matched nonimmune IgG for a polyclonal primary; use CPE knockout tissue or an immunizing-peptide block, if available, to test specificity (standard IHC practice). In appendix, control for endogenous peroxidase in chromogenic IHC and tissue autofluorescence in IF; block endogenous biotin if using avidin–biotin detection (standard IHC/IF practice).
⚠️Feasibility: Paraffin-section IHC has a reported example in rat brain at 1:100, but its fixative is unreported (selected A01407 tissue-IHC caption). A target-specific fixation window and antigen-retrieval dependence are unreported in the supplied evidence; frozen sections and IF are not established as easier options. Interpret punctate vesicular staining in light of CPE’s secretory-vesicle localization, and check diffuse appendix signal against the background controls (UniProt P16870 subcellular; 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, subcellular pattern and controls before comparing chromogenic signal.
How should I retrieve CPE when staining is weak in paraffin sections?
Start with citrate buffer at pH 6.0, heated to 95–98 °C for 20 min (page retrieval setting). If staining remains weak, compare a second retrieval condition on matched sections while keeping antibody dilution and detection constant; interpret any gain alongside tissue morphology and background (standard IHC practice). Use the catalog antibody’s 1:100 rat brain paraffin image as an application reference, while recognizing that its caption does not report fixation or retrieval conditions (A01407 image caption). Evaluate signal in neuronal cells and pancreatic endocrine cells, which have high tissue staining, rather than judging success from unstained adipocytes (HPA: hippocampus and pancreas high; adipocytes not detected).
Could fixation explain weak or patchy CPE staining?
The supplied CPE evidence does not establish target-specific fixation sensitivity, and the rat brain paraffin image does not state its fixative (A01407 image caption). Record fixative, fixation duration, processing and section age for each sample, then compare matched sections if those variables differ (standard IHC practice). Run a reliably staining control tissue through the same processing and retrieval workflow; pancreatic endocrine cells or hippocampal neuronal cells are evidence-supported candidates (HPA: pancreas and hippocampus high). If the control also fades, investigate processing, retrieval and detection before assigning the difference to CPE biology; retain an unstained or omission control to assess nonspecific chromogen deposition (standard IHC practice).
What CPE staining pattern should I expect within positive cells?
Expect predominantly cytoplasmic staining in appropriate cells, with a punctate vesicular component consistent with secretory vesicles and their membranes (HPA: distinct cytoplasmic expression; UniProt P16870 subcellular location). CPE can also be secreted and can associate with granule membranes through lipid-raft binding, despite having no transmembrane segment (UniProt P16870 subcellular location and topology). Examine pancreatic endocrine cells or hippocampal neuronal cells at sufficient magnification to separate cellular staining from diffuse extracellular chromogen (HPA: pancreas and hippocampus high; standard IHC practice). Strong isolated nuclear staining or uniform staining across unrelated cells warrants a review of controls, section quality and antibody dilution before interpretation (standard IHC practice).
Could CPE processing or isoforms affect what this antibody detects?
CPE has 2 annotated isoforms, a signal peptide at residues 1–25, a propeptide at 26–42 and a mature chain at 43–476 (UniProt P16870 processing and isoforms). Its peptidase M14 domain spans residues 52–372, and glycosylation is annotated at residues 139 and 390 (UniProt P16870 domains and glycosylation). The payload does not identify this antibody’s epitope, so staining cannot establish which isoform or processing state is present (supplied antibody evidence). Ask for an epitope map or test a separately validated reagent if that distinction drives the experiment; compare the resulting cellular patterns under matched IHC conditions (standard IHC practice).
How can I check a CPE pattern by multiplex immunofluorescence?
Pair CPE with a separately validated marker of the expected cell type, such as a pancreatic endocrine or neuronal marker, and include single-stain controls (HPA: pancreatic endocrine and hippocampal neuronal staining; standard IF practice). Choose spectrally separated fluorophores after checking tissue autofluorescence in an unstained section, particularly when measuring faint puncta (standard IF practice). For an intracellular CPE epitope, use controlled permeabilisation; for an epitope accessible without crossing a membrane, compare an unpermeabilised condition, since the catalog antibody’s epitope is unspecified (UniProt P16870 secretory vesicle and secreted locations; supplied antibody evidence; standard IF practice). HPA reports vesicle and centrosome IF localisation, but that observation does not specify an IF fixation or permeabilisation protocol for this antibody (HPA subcellular record).
How do I distinguish CPE signal from chromogenic background?
Inspect a primary-antibody omission control and a detection-only control to identify reagent-driven deposits; assess endogenous peroxidase blocking when using a peroxidase and DAB workflow (standard IHC practice). Check whether diffuse brown signal follows folds, torn edges or damaged tissue instead of the cytoplasm of expected cells (standard IHC practice; HPA: distinct cytoplasmic expression). Titrate the antibody around the captioned 1:100 starting point on matched sections, judging background and retained cellular contrast together rather than maximizing darkness (A01407 image caption; standard IHC practice). Because adipocytes were not detected in the HPA tissue profile, staining there calls for additional specificity checks without proving cross-reactivity by itself (HPA: adipocytes not detected; standard IHC practice).
How should I quantify CPE staining across specimens? ⚠ ANSWER MARKED FOR VERIFICATION
Define the eligible cell population before scoring, then record the percentage of positive cells and intensity on a consistent ordinal scale; calculate an H-score if intensity differences matter (standard IHC practice). For spatial questions, count positive cells per mm² of viable annotated tissue, excluding empty spaces, folds and necrosis (standard IHC practice). Normalize each specimen to its eligible cell count or viable tissue area and process comparison groups with the same retrieval, antibody dilution, chromogen development and imaging settings (standard IHC practice). Report pancreatic endocrine or neuronal compartments separately from surrounding cells, because HPA describes cell-restricted CPE staining in those sites (HPA: pancreas and hippocampus high).
When should an apparent CPE-positive result be questioned?
Give greater weight to cytoplasmic staining in expected endocrine or neuronal cells than to broad staining of unrelated compartments (HPA: endocrine and neuronal staining; UniProt P16870 secretory vesicle location). Question isolated nuclear signal, section-edge staining or deposits over necrotic regions, and compare each pattern with omission and detection controls (standard IHC practice). In a peroxidase and DAB assay, signal surviving primary-antibody omission can reflect endogenous enzyme activity or detection chemistry rather than CPE binding (standard IHC practice). Confirm an unexpected distribution with a separately validated antibody or an independent assay before treating it as new CPE localisation; HPA tissue patterns are reference observations, not proof for every specimen (standard IHC practice; HPA tissue profile).
Boster reagents
Best CPE / Carboxypeptidase E IHC Antibodies
A01407 has a rat brain paraffin-section IHC image (catalog image caption); IF is listed without an image, and Human, Mouse, and Rat reactivity is listed (catalog applications/reactivity).
Real IHC data
Anti-CPE/Carboxypeptidase E Antibody
Cat # A01407
A01407 is the card that renders, with IHC and IF listed for Human, Mouse, and Rat (catalog applications/reactivity). Its own image shows paraffin-embedded rat brain IHC at 1:100; no IF image is supplied (A01407 image captions).
Which to pick: For tissue IHC, choose A01407 when working with paraffin sections: its own image shows rat brain at 1:100, but the fixative is unreported (A01407 IHC image caption). For IF/ICC, A01407 is the IF-listed choice at 1:50; ICC validation and an IF image are not supplied (A01407 applications, IF dilution, image captions). For cross-species work, both A01407 and A01407-2 are rabbit polyclonals with listed Human, Mouse, and Rat reactivity; A01407 has the IHC image, while A01407-2 lists IHC without an image or IF application (catalog host, dilution details, applications, reactivity, image captions).
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 Endocrine-cell cytoplasm (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 sections. (standard IHC practice; not target-specific); Caveat: Secreted CPE may contribute to extracellular staining (UniProt); Isoform / epitope: 2 isoforms; mature chain starts at residue 43 —check epitope (UniProt); Regulation: No specific expression regulator 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.