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CPXM2 / Inactive carboxypeptidase-like protein X2 · IHC design guide
Design Immunohistochemistry for CPXM2
Plan CPXM2 paraffin IHC with the catalog antibody’s 1:100–1:300 dilution range (datasheet A14237) and epididymal glandular cells as a medium-staining reference (HPA tissue IHC). Interpret cytoplasmic or membranous staining cautiously because secreted CPXM2 may differ from its tissue RNA distribution (HPA tissue IHC; UniProt).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
CPXM2 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 or membranous in selected tissues (HPA tissue IHC) | |
| Staining pattern | Selected tissues show cytoplasmic or membranous staining (HPA tissue IHC) | |
| Antigen retrieval | Tris-EDTA pH 9.0 HIER, heat-mediated (datasheet A14237) | |
| Positive control | Epididymis | |
| 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 | Secretion may separate tissue RNA and protein patterns (HPA tissue IHC) | |
| Regulation | Expression regulators unannotated (UniProt) | |
| Isoform / epitope | No isoforms; no cytoplasmic domain; mature chain 26–756 (UniProt) |
Section 1
Recommended CPXM2 IHC & IF Protocols
The catalog antibody protocol uses Tris-EDTA pH 9.0 retrieval (datasheet A14237). The published CPXM2 IHC protocols below provide four additional study-specific workflows (PMC6718098; PMC6138928; PMC7127851; PMC9293992).
| Sample | Paraffin-embedded human tonsil tissue; fixative not specified (datasheet A14237) |
| Fixation | Image fixative and duration unreported (datasheet A14237); verify before use. |
| Sectioning | 4–5 µm sections on charged slides (standard) |
| Deparaffinisation | Xylene, graded ethanol series to water (standard) |
| Antigen retrieval | Heat retrieval: Tris-EDTA pH 9.0 (datasheet A14237); 20 min, 95–100 °C (standard) |
| 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-CPXM2, 1:100-1:300 (datasheet A14237) |
| 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 | CPXM2-positive staining in glandular cells of epididymis (HPA tissue IHC: Medium). HPA tissue profile: Cytoplasmic or membranous expression in selected tissues. No signal in the no-primary control. |
💡Decision noteStart with heat-mediated Tris-EDTA pH 9.0 retrieval (datasheet A14237); a published brain-tissue protocol also uses microwave retrieval at pH 9 (PMC6138928).
Section 2
What Is the Expected CPXM2 Staining Pattern?
CPXM2 is a secreted protein with a signal peptide and no transmembrane segment (UniProt Q8N436). In tissue IHC, HPA describes cytoplasmic or membranous staining in selected tissues, including medium staining of epididymal glandular cells (HPA tissue IHC). Treat that appearance as a reference pattern, not a definitive compartment assignment: HPA rates the tissue staining Uncertain and cautions that secreted protein and RNA locations may differ (HPA tissue IHC).
| Epididymal glandular cells show moderate cytoplasmic or cell-edge chromogen, with discernible unstained areas. | This matches the reported medium glandular-cell signal and selected-tissue cytoplasmic or membranous pattern (HPA tissue IHC). Because CPXM2 is secreted, a cell-edge appearance alone does not establish membrane anchoring (UniProt Q8N436). |
| Strong, sharply nuclear staining dominates the section. | Nuclear staining falls outside HPA’s reported cytoplasmic or membranous tissue pattern (HPA tissue IHC). Check counterstain overlap, detection background, and antibody specificity before scoring it as CPXM2; the available record does not validate a nuclear pattern. |
| Adipocytes or bone-marrow hematopoietic cells stain prominently. | HPA reports CPXM2 as not detected in those sampled cells (HPA tissue IHC). An unexpected signal raises concern for cross-reactivity or endogenous chromogen activity; confirm the cell identity and compare antibody-omission and detection controls (general IHC practice). |
| Brown signal coats most cells, extracellular spaces, and blank regions without a clear cell pattern. | That distribution is difficult to reconcile with HPA’s selected-tissue pattern (HPA tissue IHC). Diffuse chromogen may reflect background from detection chemistry or inadequate blocking; assess a matched negative control before interpreting extracellular signal (general IHC practice). |
| Epididymal glandular cells have no visible signal. | A missing signal conflicts with HPA’s medium reference staining, but its reliability is Uncertain (HPA tissue IHC). First check tissue preservation, antibody and detection controls, and whether the sampled section contains the relevant glandular cells (general IHC practice). |
💡Expected CPXM2 appearanceScore a plausible positive as medium cytoplasmic or cell-edge staining in epididymal glandular cells (HPA tissue IHC); dominant nuclear staining or uniform staining of cells reported as negative is a suspect result requiring controls (HPA tissue IHC; general IHC practice).
| Secretion and apparent cell-edge signal | CPXM2 has a cleaved signal peptide, residues 1–25, and a secreted chain beginning at residue 26, with no transmembrane segment (UniProt Q8N436). Interpret cell-edge chromogen in that context; morphology alone cannot prove surface retention. |
| Reported tissue distribution | Epididymal glandular cells are medium; respiratory and several gastrointestinal epithelial or glandular cells are low (HPA tissue IHC). Use the reported level for the exact sampled cell type, rather than expecting equal staining across tissues. |
| RNA versus tissue protein | HPA lists RNA as tissue enhanced in blood vessel and choroid plexus, while warning that secreted variants can make RNA and protein locations differ (HPA tissue IHC). Do not treat RNA enrichment as an IHC positive-control result. |
| Antibody-validation limit | The listed rabbit polyclonal antibody HPA048375 has Uncertain IHC validation (HPA antibodies). Use staining morphology and appropriate controls together; the supplied record does not provide an independently confirmed IHC pattern. |
| Processing and glycosylation | UniProt annotates a signal peptide and five glycosylation sites (UniProt Q8N436). These features describe the protein, but the supplied sources do not establish their effect on antigen retrieval, staining intensity, or antibody epitope access. |
| IF/ICC Q&A: Is a cellular IF pattern established? | No ICC-IF image-bearing cell line or main subcellular location is supplied; HPA’s subcellular summary says Secreted (HPA subcellular). This IHC tissue pattern cannot by itself validate an IF/ICC compartment. |
| Situation | Likely cause | Next action |
|---|---|---|
| No staining in epididymal glandular cells | The result differs from HPA’s medium observation, although its reliability is Uncertain (HPA tissue IHC). A failed detection step or missing target cells is also possible (general IHC practice). | Verify glandular-cell presence and section quality; run antibody and detection controls, then review the chosen retrieval and antibody conditions as general IHC variables. No CPXM2-specific retrieval condition is established by the supplied sources. |
| Weak staining in bronchus, colon, or stomach | HPA reports low staining in the listed respiratory or gastrointestinal cells (HPA tissue IHC). Weak signal can therefore fit the reference pattern; judge it against background and the exact cell type. | Compare cells within the section and a matched negative control; record intensity and distribution without upgrading faint, nonspecific chromogen to a strong positive (general IHC practice). |
| Prominent nuclear signal | HPA describes cytoplasmic or membranous expression in selected tissues, not a nuclear pattern (HPA tissue IHC). Counterstain overlap or nonspecific detection can complicate visual assignment (general IHC practice). | Inspect the chromogen separately from the counterstain, compare antibody-omission controls, and avoid scoring nuclear signal as CPXM2 until independently supported (general IHC practice). |
| Widespread staining in reported negative cells | HPA reports adipocytes and bone-marrow hematopoietic cells as not detected in its sampled tissues (HPA tissue IHC). Cross-reactivity or endogenous detection activity could explain unexpected chromogen (general IHC practice). | Confirm cell identity and compare a no-primary control; check endogenous activity blocking and detection reagents before interpreting the signal (general IHC practice). |
| Diffuse brown haze obscures cell boundaries | A broad haze prevents comparison with HPA’s cell-specific reference pattern (HPA tissue IHC). In IHC, inadequate blocking, residual detection reagent, or excessive chromogen development may contribute to background (general IHC practice). | Review blocking, wash, and chromogen-development steps against a matched negative control; score only signal that remains spatially interpretable (general IHC practice). |
| An IF/ICC image seems to show a precise organelle location | HPA supplies no ICC-IF image-bearing cell line or main subcellular location for CPXM2; its summary is Secreted (HPA subcellular). | Treat the organelle assignment as unverified and seek independent localisation evidence before using it to interpret this tissue IHC result (HPA subcellular; general IF practice). |
Experiment evidence
IHC & IF images showing CPXM2 staining
A14237 · IHCImmunohistochemical analysis of paraffin-embedded human tonsil. 1, Antibody was diluted at 1:200 (4° overnight). 2, Tris-EDTA, pH9.0 was use
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000121898-CPXM2/tissue/cerebral+cortex#imid_13339399
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000121898-CPXM2/tissue/colon#imid_13339333
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000121898-CPXM2/tissue/liver#imid_13339326
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000121898-CPXM2/tissue/kidney#imid_13339327
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for CPXM2 IHC & IF
🧪Run epididymis first and assess glandular cells for CPXM2 staining (HPA: Medium in epididymal glandular cells); run adrenal gland as a negative tissue (HPA: Not detected in adrenal glandular cells). On the epididymis slide, compare glandular staining with unstained neighboring cells as candidate internal negatives, without assuming those cells are confirmed CPXM2-negative (HPA: Medium is reported only for glandular cells).
Positive control tissue: Epididymis (Glandular cells, 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 CPXM2; derive a cell-line control from the positive tissue's cell type (Glandular cells) and confirm it by RNA or western blot first.
Technical controls: Include no-primary (secondary-only) and primary host species-, immunoglobulin class-, and clonality-matched isotype controls; use CPXM2 knockout material or immunogen peptide competition as a biological specificity control when available. Block endogenous peroxidase for chromogenic IHC, and check the epididymis section for background signal in control slides (standard IHC practice).
⚠️Feasibility: A target-specific fixation window and fixation effect are unreported in the supplied evidence; the selected A14237 paraffin-section caption does not state a fixative (A14237 tissue-IHC caption: fixative not stated). The caption uses Tris-EDTA at pH 9.0 for antigen retrieval and a 1:200 primary dilution, but does not establish that retrieval is required for CPXM2 across specimens (A14237 tissue-IHC caption). Frozen sections and IF cannot be judged easier from the supplied evidence; because CPXM2 is secreted, examine epididymal luminal signal carefully before assigning staining to glandular cells (UniProt Q8N436: Secreted; HPA: Medium in epididymal glandular cells).
HPA tissue IHC evidence for CPXM2
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Uncertain — At least one protein variant secreted, tissue location of RNA and protein might differ and correlation is complex.). 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 |
|---|---|---|---|---|
| Epididymis | Glandular cells | 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 → |
| Caudate | Glial cells | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced CPXM2 IHC Tips
Troubleshoot CPXM2 chromogenic IHC in paraffin sections using the catalog antibody’s tonsil image and the reported localisation evidence.
Which retrieval conditions should I try first for weak CPXM2 staining?
Start with heat-mediated retrieval in Tris-EDTA at pH 9.0 (datasheet A14237). The paraffin-section tonsil image used that buffer, with primary antibody at 1:200 overnight at 4°C (caption A14237). If staining remains weak, compare a milder retrieval condition on adjacent sections while keeping antibody concentration and detection constant (standard IHC practice). Score signal and tissue preservation together, since stronger retrieval can increase nonspecific staining or damage section morphology (standard IHC practice). Include a no-primary control so added chromogen deposition is not mistaken for recovered CPXM2 signal (standard IHC practice).
How should I handle fixation when the CPXM2 image gives no fixative?
The selected image identifies paraffin-embedded human tonsil but does not state its fixative (caption A14237). Target-specific sensitivity to fixation is therefore unknown; neither the tissue staining pattern nor CPXM2 topology establishes it (caption A14237; UniProt Q8N436). Record the fixative, duration and processing schedule for every specimen, then compare similarly processed sections when investigating signal loss (standard IHC practice). Use the documented pH 9.0 retrieval and 1:200 primary dilution as starting conditions, rather than treating them as proof of fixation tolerance (caption A14237). If fixation varies across samples, validate staining consistency before comparing scores (standard IHC practice).
Where should CPXM2 staining appear in tissue sections?
Interpret CPXM2 as a secreted protein without a transmembrane segment, so staining need not trace a stable cell surface (UniProt Q8N436). The tissue atlas describes cytoplasmic or membranous staining in selected tissues, but rates its IHC reliability uncertain because secreted protein and RNA locations can differ (HPA: tissue IHC). Use glandular cells in epididymis, reported at medium intensity, as a contextual positive reference rather than a universal localisation rule (HPA: epididymis). Compare cellular and extracellular signal with section morphology and no-primary controls before assigning its source (standard IHC practice). Avoid calling staining nuclear CPXM2 without independent validation (UniProt Q8N436; standard IHC practice).
How do I assess whether epitope placement affects CPXM2 IHC?
CPXM2 has a signal peptide at residues 1–25 and a mature chain spanning 26–756 (UniProt Q8N436). Its annotated glycosylation sites are 231, 241, 281, 337 and 491, and no isoforms are listed (UniProt Q8N436). Check the antibody’s stated immunogen against these features before attributing weak staining to epitope masking; the supplied caption does not identify an epitope (caption A14237). If comparing antibodies, select independently mapped epitopes and apply each antibody’s validated retrieval conditions (standard IHC practice). Agreement in anatomical distribution provides useful corroboration, while discordance needs investigation of specificity and processing (standard IHC practice).
How can I investigate CPXM2 by IF alongside this chromogenic IHC guide?
Treat IF as a separate application: the supplied product evidence documents paraffin-section chromogenic IHC, not IF performance (caption A14237). For multiplex IF, pair CPXM2 with a validated glandular-cell marker when examining the reported epididymal signal, and confirm spectral separation with single-stain controls (HPA: epididymis; standard IF practice). Choose a fluorophore channel with low background in the tissue under study, measuring unstained-section autofluorescence first (standard IF practice). Match permeabilisation to the mapped epitope and its accessibility; CPXM2 is secreted and has no transmembrane segment, but this antibody’s epitope is unspecified (UniProt Q8N436; caption A14237). Do not transfer the IHC dilution to IF without validation (caption A14237; standard IF practice).
What should I check when CPXM2 chromogenic staining is diffuse?
Start with a no-primary control and inspect whether diffuse chromogen also appears there (standard IHC practice). Block endogenous peroxidase before an HRP and DAB workflow, and compare primary and secondary-only controls to separate detection background from antibody-dependent staining (standard IHC practice). The documented tonsil image used primary and secondary antibodies at 1:200, with secondary incubation for 30 minutes at room temperature (caption A14237). If controls are clean but tissue remains diffuse, titrate antibody and examine wash and blocking conditions on matched sections (standard IHC practice). Consider extracellular signal cautiously because CPXM2 is secreted (UniProt Q8N436).
How should I quantify CPXM2 across paraffin sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the anatomical region and eligible cell population before scoring, then keep those definitions fixed across specimens (standard IHC practice). For cellular staining, report the percentage of positive cells and an H-score using intensity classes 0–3; for extracellular signal, report stained area or density per mm² (standard IHC practice). Normalise cell counts to eligible cells and area measurements to analysed tissue area, excluding folds, necrosis and section edges (standard IHC practice). Keep stain development, imaging and thresholds consistent, with blinded review where feasible (standard IHC practice). State the scoring compartment because CPXM2 is secreted and tissue staining may be cytoplasmic or membranous (UniProt Q8N436; HPA: tissue IHC).
How can I distinguish convincing CPXM2 staining from artefact?
Look for reproducible staining in intact anatomy that exceeds matched no-primary and detection controls (standard IHC practice). Glandular cells in epididymis have reported medium staining, whereas adipocytes in adipose tissue were reported as not detected; neither observation alone establishes antibody specificity (HPA: tissue IHC). Treat exclusively nuclear signal as suspect because CPXM2 is annotated as secreted, while allowing carefully verified extracellular signal (UniProt Q8N436). Check edge staining, necrotic areas and endogenous peroxidase before calling a section positive (standard IHC practice). Interpret cell assignment cautiously because the tissue atlas labels its CPXM2 IHC reliability uncertain (HPA: tissue IHC).
Boster reagents
Best CPXM2 / Inactive carboxypeptidase-like protein X2 IHC Antibodies
A14237 has IHC image data from paraffin-embedded human tonsil (catalog IHC image caption). IF is listed without an image (catalog applications; catalog IF image alts); human and mouse reactivity is listed (catalog reactivity).
Real IHC data
Anti-CPXM2 Antibody
Cat # A14237
A14237 is listed for IHC and IF, with human and mouse reactivity (catalog applications; catalog reactivity). Its supplied image shows paraffin-embedded human tonsil IHC at 1:200 with Tris-EDTA pH 9.0 retrieval; no IF image is supplied (catalog IHC image caption; catalog IF image alts).
Which to pick: For tissue IHC, choose A14237 based on its human paraffin-section image; the fixative is unreported (catalog IHC image caption). For IF, A14237 is listed at 1:50, but ICC validation and an IF image are unreported, and clonality is unspecified (catalog applications; catalog IF dilution; catalog IF image alts; catalog clone field). For mouse work, A14237 lists mouse reactivity, though its supplied IHC image shows human tonsil (catalog reactivity; catalog IHC image caption).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry Q8N436 (CPXM2_HUMAN, Inactive carboxypeptidase-like protein X2).
- Human Protein Atlas. CPXM2 tissue IHC expression (reliability: Uncertain).
- Human Protein Atlas. CPXM2 subcellular location (ICC-IF): Secreted.
- Human Protein Atlas. CPXM2 antibody validation summary (1 antibodies).
- Overexpression of CPXM2 predicts an unfavorable prognosis and promotes the proliferation and migration of gastric cancer. Oncology reports 2019 — PMC6718098.
- Exome sequencing study in patients with multiple sclerosis reveals variants associated with disease course. Journal of neuroinflammation 2018 — PMC6138928.
- Expression of Carboxypeptidase X M14 Family Member 2 Accelerates the Progression of Hepatocellular Carcinoma via Regulation of the gp130/JAK2/Stat1 Pathway. Cancer management and research 2020 — PMC7127851.
- Proteomic analysis reveals key differences between squamous cell carcinomas and adenocarcinomas across multiple tissues. Nature communications 2022 — PMC9293992.
- PubMed PMID:12975309 — UniProt-cited evidence.
- PubMed PMID:14702039 — UniProt-cited evidence.
- PubMed PMID:15164054 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for CPXM2 (Inactive carboxypeptidase-like protein X2). Expected localisation Cytoplasmic or membranous in selected tissues (HPA tissue IHC). Antigen retrieval: Tris-EDTA pH 9.0 HIER, heat-mediated (datasheet A14237). Validated IHC antibody: A14237 at 1:100-1:300 (the product's own IHC validation image is shown). Controls (HPA): positive Epididymis (Glandular cells); negative Adipose tissue. IHC workflow; specimen preparation unspecified. Protocol steps: 1. Sample: Paraffin-embedded human tonsil tissue; fixative not specified (datasheet A14237); 2. Fixation: Image fixative and duration unreported (datasheet A14237); verify before use.; 3. Sectioning: 4–5 µm sections on charged slides (standard); 4. Deparaffinisation: Xylene, graded ethanol series to water (standard); 5. Antigen retrieval: Heat retrieval: Tris-EDTA pH 9.0 (datasheet A14237); 20 min, 95–100 °C (standard); 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-CPXM2, 1:100-1:300 (datasheet A14237); 9. Primary incubation: Overnight at 4 °C (standard). Watch for: Fixation: Keep fixation consistent across sections (standard IHC practice; not target-specific); Caveat: Secretion may separate tissue RNA and protein patterns (HPA tissue IHC); Isoform / epitope: No isoforms; no cytoplasmic domain; mature chain 26–756 (UniProt); Regulation: Expression regulators unannotated (UniProt). Evidence: UniProt Q8N436, HPA tissue IHC · Uncertain, HPA ICC-IF · Secreted, Datasheet A14237, PMC6718098, PMC6138928. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/CPXM2/immunohistochemistry-ihc-guide.