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CALD1 / Caldesmon · IHC design guide
Design Immunohistochemistry for CALD1
Plan CALD1 staining in paraffin sections around the expected cytoplasmic signal in smooth muscle (HPA tissue IHC). This guide covers IHC antibody use and interpretation alongside other strongly staining cell populations (datasheet PB9922; HPA tissue IHC).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
CALD1 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 | Smooth-muscle cytoplasm (HPA tissue IHC) | |
| Staining pattern | Cytoplasmic staining most abundant in smooth muscle (HPA tissue IHC) | |
| Antigen retrieval | EDTA pH 8.0 HIER, heat-mediated (datasheet PB9922) | |
| Positive control | Endometrium+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 | Ciliated epithelial cells can also stain strongly (HPA tissue IHC) | |
| Regulation | Isoform 1 predominates in smooth muscle (UniProt) | |
| Isoform / epitope | 6 isoforms; antibody epitope coverage is unspecified (UniProt; datasheet PB9922) |
Section 1
Recommended CALD1 IHC & IF Protocols
Compare the catalog antibody’s IHC-P protocol with 2 published CALD1 IHC protocols for aortic valve and breast tumor sections (PMC13003078; PMC4823093).
| Sample | Paraffin-embedded mouse intestine tissue; fixative not specified (datasheet PB9922) |
| Fixation | Image fixative and duration unreported (datasheet PB9922); verify before use. |
| Sectioning | 4–5 µm sections on charged slides (standard) |
| Deparaffinisation | Xylene, graded ethanol series to water (standard) |
| Antigen retrieval | Heat retrieval: EDTA pH 8.0 (datasheet PB9922); 20 min, 95–100 °C (standard) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% goat serum (datasheet PB9922) |
| Primary antibody | Rabbit anti-CALD1, 0.5-1μg/ml (datasheet PB9922) |
| Primary incubation | Overnight at 4 °C (datasheet PB9922) |
| Detection | HRP-conjugated secondary, DAB chromogen (datasheet PB9922) |
| Counterstain | Hematoxylin, blue, dehydrate and mount (standard) |
| Expected result | CALD1-positive staining in ciliated epithelial cells of endometrium (HPA tissue IHC: High). HPA tissue profile: Cytoplasmic expression most abundant in smooth muscle. No signal in the no-primary control. |
💡Decision noteStart with EDTA pH 8.0 heat retrieval for the catalog antibody (datasheet PB9922). Match each published retrieval and dilution to its stated antibody (PMC13003078; PMC4823093).
Section 2
What Is the Expected CALD1 Staining Pattern?
CALD1 should produce predominantly cytoplasmic staining, most abundant in smooth muscle cells (HPA tissue IHC: Enhanced). In smooth muscle, it associates with thin filaments; in nonmuscle cells, it can associate with stress fibers (UniProt Q05682: subcellular location). CALD1 has no transmembrane segment, so a purely membrane-restricted IHC pattern warrants review (UniProt Q05682: topology).
| Strong cytoplasmic staining in smooth muscle cells, with recognizable cell boundaries and little background. | This matches the most abundant tissue IHC pattern (HPA: High in smooth muscle cells; tissue IHC reliability: Enhanced). Compare staining in the intended cell population with the section’s morphology; nearby unstained cells can help reveal nonspecific color (general IHC practice). |
| Cytoplasmic staining in ovarian stroma, placental decidual cells, endometrial ciliated epithelium, or testicular peritubular cells. | These are also reported High cell populations (HPA tissue IHC). A positive result outside smooth muscle is therefore plausible when its location and cell identity fit the section. Broad distribution of nonmuscle isoforms supports this interpretation but does not identify which isoform the antibody detects (UniProt Q05682: tissue specificity). |
| Predominantly nuclear staining, or a sharp membrane-only rim without the expected cytoplasmic pattern. | Treat this as a discordant IHC pattern and investigate artefact or nonspecific detection: the tissue profile is cytoplasmic, and the protein lacks a transmembrane segment (HPA tissue IHC; UniProt Q05682: topology). Plasma membrane localization reported by ICC-IF means membrane signal alone cannot prove cross-reactivity (HPA subcellular). |
| Strong staining in a cell population reported as Not detected, or color that follows no recognizable cell structure. | Check cross-reactivity and endogenous detection activity (general IHC practice). HPA’s Not detected calls apply to named cells, such as adipocytes in adipose tissue and respiratory epithelial cells in bronchus; they do not declare every cell in those tissues negative (HPA tissue IHC). |
| Diffuse color across cells and extracellular spaces, or no signal in a smooth muscle positive control. | Diffuse color limits localization and scoring; assess background with a primary-omission control (general IHC practice). A blank smooth muscle control conflicts with the reported High signal and should prompt assay checks before interpreting a study specimen as CALD1-negative (HPA tissue IHC: smooth muscle cells High). |
💡Expected CALD1 appearanceCall an IHC result positive when convincing cytoplasmic signal is strongest in morphologically identified smooth muscle cells (HPA tissue IHC: High; reliability Enhanced); diffuse deposit or predominantly nuclear color is suspect and needs controls (general IHC practice; HPA tissue IHC: cytoplasmic profile).
| Cell population and isoforms | High-molecular-weight isoform 1 predominates in smooth muscle; lower-molecular-weight isoforms 2–5 are widespread in nonmuscle cells (UniProt Q05682: tissue specificity). Interpret nonmuscle cytoplasmic staining using HPA’s cell-level observations; the supplied record does not establish isoform-specific antibody recognition. |
| Subcellular context and topology | Thin-filament association in smooth muscle and stress-fiber association in fibroblasts support structured cytoplasmic signal (UniProt Q05682: subcellular location). CALD1 has no transmembrane segment (UniProt Q05682: topology); topology alone cannot rule out peripheral membrane localization. |
| IHC evidence and antibody choice | The tissue profile is rated Enhanced for agreement between staining and RNA data, with external characterization support (HPA tissue IHC: reliability). HPA008066, HPA017330, and CAB000006 each have Enhanced IHC status (HPA antibodies). These ratings support pattern comparison, not a guaranteed result under every staining condition. |
| IF/ICC Q&A: where should signal appear? | In ICC-IF, HPA reports plasma membrane and actin-filament localization, both rated Enhanced (HPA subcellular). Use that as an IF/ICC interpretation reference; it does not replace the predominantly cytoplasmic tissue IHC profile (HPA tissue IHC). |
| Situation | Likely cause | Next action |
|---|---|---|
| Smooth muscle positive control is blank or very weak. | The control disagrees with the reported High smooth muscle signal; inadequate assay performance or an unsuitable control section is possible (HPA tissue IHC: smooth muscle cells High; general IHC practice). | Confirm smooth muscle is present on the section, then review antigen retrieval, primary-antibody conditions, detection reagents, and run controls (general IHC practice). Do not assign a biological negative result until the positive control works. |
| Signal is predominantly nuclear. | Nuclear predominance does not fit the cytoplasmic tissue profile or filament-associated localization (HPA tissue IHC; UniProt Q05682: subcellular location). | Compare with morphology and a primary-omission control; inspect counterstain and chromogen deposits, then reassess detection specificity (general IHC practice). Record the result as discordant if it persists. |
| Unexpected cells stain strongly. | The named population may differ from the expected HPA cell type, or detection may be nonspecific (HPA tissue IHC; general IHC practice). A tissue label alone cannot establish a mismatch. | Identify the stained cells on the section first. Compare that exact population with HPA’s cell-level calls, then assess cross-reactivity or endogenous enzyme activity using appropriate detection controls (general IHC practice). |
| Color is widespread and obscures cell boundaries. | Diffuse background can arise during blocking, washing, or chromogenic detection (general IHC practice); it cannot establish CALD1 localization. | Review blocking and wash conditions, inspect the primary-omission control, and score only signal that can be assigned confidently to cells and compartments (general IHC practice). |
| A reportedly negative population shows faint color. | HPA’s Not detected designation is cell-specific; faint color may reflect background or a difference between specimens (HPA tissue IHC; general IHC practice). | Compare the named population with adjacent cells and controls. Avoid calling an entire tissue positive or negative from one population; document intensity and location separately (general IHC practice). |
| A nonmuscle population stains, but less strongly than smooth muscle. | This can fit the reported distribution: some nonmuscle populations are High, others Medium or Low, and nonmuscle isoforms are widespread (HPA tissue IHC; UniProt Q05682: tissue specificity). | Score the specific cell population and its cytoplasmic localization against the relevant HPA entry. Avoid treating weaker nonmuscle staining as assay failure solely because smooth muscle is stronger (HPA tissue IHC). |
Experiment evidence
IHC & IF images showing CALD1 staining
PB9922 · IHCIHC analysis of Caldesmon using anti-Caldesmon antibody (PB9922). Caldesmon was detected in a paraffin-embedded section of mouse intestine t
PB9922 · IHCIHC analysis of Caldesmon using anti-Caldesmon antibody (PB9922). Caldesmon was detected in a paraffin-embedded section of rat intestine tis
PB9922 · IFIF analysis of Caldesmon using anti-Caldesmon antibody (PB9922). Caldesmon was detected in an immunocytochemical section of SiHa cells. Enzy
M04578-2 · IHCHuman colon was stained with anti-Caldesmon rabbit antibody
M04578-2 · IHCMouse colon was stained with anti-Caldesmon rabbit antibody
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000122786-CALD1/tissue/cerebral+cortex#imid_308070
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000122786-CALD1/tissue/colon#imid_252496
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000122786-CALD1/tissue/liver#imid_252505
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000122786-CALD1/tissue/kidney#imid_252506
HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody HPA017330; green = CALD1, blue = nucleus, red = microtubules.
HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody HPA017330; green = CALD1, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for CALD1 IHC & IF
🧪Run smooth muscle first: smooth muscle cells should stain (High; HPA: smooth muscle). Use adipose tissue as the negative tissue and score adipocytes, which HPA lists as Not detected (HPA: adipose tissue). Internal negative cells, if independently identified on the positive slide, should show background DAB without specific filamentous staining; other nonmuscle cells cannot automatically serve as negatives because low-molecular-weight isoforms are widely distributed (UniProt Q05682 tissue specificity).
Positive control tissue: Endometrium (Ciliated epithelial cells, HPA High)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show CALD1 in A-431, U-251MG, U2OS, ASC52telo, HEK293, U2OS, siRNA 1, U2OS, siRNA 2, U2OS, scrambled, with annotated localisation: Plasma membrane (enhanced), Actin filaments (enhanced) (HPA subcellular).
Technical controls: Include a no-primary, secondary-only control; a concentration-matched rabbit IgG isotype control matched to the primary antibody’s clonality; and a CALD1 knockout or validated peptide-block control (selected-SKU caption: rabbit primary antibody). For chromogenic detection, block endogenous peroxidase and inspect smooth muscle sections for background before scoring DAB (selected-SKU caption: peroxidase secondary and DAB).
⚠️Feasibility: A target-specific fixation window or fixation effect is unreported, and the exact PB9922 tissue-IHC caption does not state a fixative (selected-SKU caption: fixative unreported). The reported paraffin-section procedure uses heat retrieval in EDTA at pH 8.0; the supplied evidence does not establish that frozen sections or IF are easier (selected-SKU caption: EDTA retrieval; HPA: ICC-IF images). In smooth muscle, closely packed positive cells can make individual cell boundaries difficult to score, so interpret DAB against tissue morphology (HPA: High in smooth muscle cells).
HPA tissue IHC evidence for CALD1
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Enhanced — High consistency between antibody staining and RNA expression data. External characterization data supports antibody staining.). 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 |
|---|---|---|---|---|
| Endometrium | Ciliated epithelial cells | High | Protein (IHC) | HPA → |
| Ovary | Ovarian stroma cells | High | Protein (IHC) | HPA → |
| Placenta | Decidual cells | High | Protein (IHC) | HPA → |
| Smooth muscle | Smooth muscle cells | High | Protein (IHC) | HPA → |
| Testis | Peritubular 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 → |
| Appendix | Endocrine cells | Not detected | Protein (IHC) | HPA → |
| Bronchus | Respiratory epithelial cells | Not detected | Protein (IHC) | HPA → |
| Caudate | Glial cells | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced CALD1 IHC Tips
Troubleshoot CALD1 staining in paraffin sections by checking retrieval, cell type, cytoskeletal localisation and detection controls before interpreting signal.
What retrieval should I try when CALD1 staining is weak in paraffin sections?
Start with heat-mediated antigen retrieval in EDTA pH 8.0 for paraffin sections (datasheet PB9922). The selected image used this retrieval before overnight incubation at 4°C with 1 μg/ml catalog antibody and DAB detection (datasheet PB9922). If staining remains weak, compare a second retrieval condition on adjacent sections while holding antibody concentration, detection and development constant (standard IHC practice). Include smooth muscle cells as a positive reference because CALD1 staining is most abundant there (HPA tissue IHC). Check tissue preservation and the no-primary control before treating stronger diffuse staining as improved antigen recovery (standard IHC practice).
Could fixation explain weak or uneven CALD1 IHC staining?
The selected paraffin-section caption does not report a fixative, so target-specific CALD1 sensitivity to fixation is unknown (datasheet PB9922). Record the fixative, fixation duration and processing history for each specimen before comparing staining intensity across samples (standard IHC practice). If preservation varies, compare similarly processed sections and inspect morphology alongside the smooth muscle reference, where CALD1 staining is most abundant (standard IHC practice; HPA tissue IHC). Keep the documented EDTA pH 8.0 retrieval and 1 μg/ml primary concentration constant during that comparison (datasheet PB9922). Do not attribute an apparent difference to fixation until processing and detection controls have been checked (standard IHC practice).
Where should convincing CALD1 staining appear in tissue sections?
Expect predominantly cytoplasmic staining in smooth muscle cells, with a pattern compatible with their contractile filaments (HPA tissue IHC; UniProt Q05682 localisation). CALD1 is associated with thin filaments in smooth muscle and stress fibers in nonmuscle cells (UniProt Q05682 localisation). HPA subcellular imaging also reports actin-filament and plasma-membrane localisation, so peripheral signal can be plausible when it accompanies the expected cellular pattern (HPA subcellular). Predominantly nuclear or extracellular DAB signal should trigger review of morphology, background and the no-primary control before scoring it as CALD1 (UniProt Q05682 localisation; standard IHC practice). Compare neighbouring expected cell populations within the same section rather than judging colour intensity alone (standard IHC practice).
Why might CALD1 staining differ between smooth muscle and other cells?
CALD1 has 6 annotated isoforms, and isoform 1 predominates in smooth muscle while isoforms 2–5 are widely distributed in nonmuscle tissues and cells (UniProt Q05682 isoforms and tissue specificity). An antibody’s recognised epitope determines which isoforms it can detect, so confirm epitope coverage before treating negative nonmuscle staining as absent CALD1 (standard IHC practice). The supplied caption documents staining conditions but does not identify the PB9922 epitope or establish isoform selectivity (datasheet PB9922). CALD1 also has annotated phosphorylation sites, including serine 643 and serine 656; their effect on this antibody’s binding is unknown (UniProt Q05682 modified residues; datasheet PB9922). Interpret cell-type differences alongside morphology and controls (standard IHC practice).
How should I assess CALD1 in a complementary IF experiment?
For IF/ICC, multiplex CALD1 with a marker identifying the expected cell type, then ask whether its signal follows actin-rich structures within those cells (UniProt Q05682 localisation; standard IF practice). Choose fluorophores after examining tissue autofluorescence in an unstained control, and assign the cleaner channel to the weaker signal (standard IF practice). CALD1 has no transmembrane segment and is associated with cytoplasmic filaments, so use controlled permeabilisation when the intended epitope is intracellular (UniProt Q05682 topology and localisation; standard IF practice). Check whether permeabilisation changes morphology or nonspecific staining with matched controls (standard IF practice). Do not transfer the paraffin-section antibody concentration or retrieval conditions directly to IF/ICC; validate IF conditions separately (datasheet PB9922; standard IF practice).
How can I reduce diffuse or misleading DAB background?
First compare the stained section with a no-primary control to distinguish antibody-dependent signal from detection-system background (standard IHC practice). The selected protocol used 10% goat serum blocking, 1 μg/ml primary antibody overnight at 4°C, and peroxidase-linked detection with DAB (datasheet PB9922). If background persists, check the peroxidase block, washes and DAB development time, changing one variable at a time (standard IHC practice). Review tissue edges, folds and damaged regions separately because they can distort apparent staining intensity (standard IHC practice). Judge any adjustment against the expected cytoplasmic smooth muscle pattern, not simply a paler slide (HPA tissue IHC; standard IHC practice).
How should I score CALD1 IHC across samples? ⚠ ANSWER MARKED FOR VERIFICATION
Define the cell population and anatomical region before scoring, since CALD1 expression varies among cell types (HPA tissue IHC). For a mixed section, report the percentage of positive cells and staining intensity by cell type, or calculate an H-score from the percentage in each intensity category (standard IHC practice). If counting positive profiles, report density per mm² of viable, analysable tissue and exclude folds, edges and necrotic regions by a prespecified rule (standard IHC practice). Normalise comparisons to the same cell population or viable tissue area, staining batch and exposure or DAB assessment criteria (standard IHC practice). Keep cytoplasmic signal separate from nonspecific background when setting positivity thresholds (HPA tissue IHC; standard IHC practice).
What distinguishes true CALD1 positivity from an IHC artefact?
Convincing CALD1 signal should fit cytoplasmic, filament-associated staining in an appropriate cell population, especially smooth muscle cells (UniProt Q05682 localisation; HPA tissue IHC). HPA reports high staining in smooth muscle cells and ovarian stroma cells, but no detected staining in adipocytes, providing context for cell-level interpretation (HPA tissue IHC). Be cautious with isolated nuclear or extracellular colour, intense section edges, necrotic areas, and deposits that also appear in a no-primary control (UniProt Q05682 localisation; standard IHC practice). Check a peroxidase-block control when endogenous enzyme activity could explain DAB colour (standard IHC practice). Resolve uncertain staining through morphology, matched controls and repeat sections before assigning biological meaning (standard IHC practice).
Boster reagents
Best CALD1 / Caldesmon IHC Antibodies
The catalog shows CALD1 staining in paraffin mouse intestine and human colon, plus IF in SiHa cells; both antibodies list human, mouse, and rat reactivity (IHC/IF captions; catalog reactivity).
Real IHC data
Anti-Caldesmon/CALD1 Antibody ®
Cat # PB9922
Real IHC data
Anti-Caldesmon Rabbit Monoclonal Antibody
Cat # M04578-2
PB9922 has IHC images from paraffin mouse and rat intestine and human intestinal cancer tissue, plus an IF image from SiHa cells (PB9922 IHC/IF captions). M04578-2 has IHC images from human, mouse, and rat colon and lists IF among its applications (M04578-2 IHC captions; catalog applications).
Which to pick: Choose PB9922 for paraffin-section IHC when its documented EDTA pH 8.0 retrieval and 1 μg/ml primary incubation suit the sample; its IHC caption does not report the fixative (PB9922 IHC caption). PB9922 also lists IF and ICC and has a SiHa-cell IF image (PB9922 catalog applications; IF caption). For colon IHC across species, M04578-2 is a rabbit monoclonal with human, mouse, and rat colon images; its captions do not report section processing or fixative (M04578-2 catalog description; IHC captions).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry Q05682 (CALD1_HUMAN, Caldesmon).
- Human Protein Atlas. CALD1 tissue IHC expression (reliability: Enhanced).
- Human Protein Atlas. CALD1 subcellular location (ICC-IF): Localized to the plasma membrane and actin filaments..
- Human Protein Atlas. CALD1 antibody validation summary (3 antibodies).
- Caldesmon-1-mediated actin dynamics is essential for osteogenic differentiation of aortic valve interstitial cells. Scientific reports 2026 — PMC13003078.
- Upregulation of CALD1 predicted a poor prognosis for platinum-treated ovarian cancer and revealed it as a potential therapeutic resistance target. BMC genomics 2024 — PMC10870461.
- Annexin-A1 and caldesmon are associated with resistance to tamoxifen in estrogen receptor positive recurrent breast cancer. Oncotarget 2016 — PMC4823093.
- The cancer-associated fibroblasts related gene CALD1 is a prognostic biomarker and correlated with immune infiltration in bladder cancer. Cancer cell international 2021 — PMC8164301.
- PubMed PMID:1885618 — UniProt-cited evidence.
- PubMed PMID:1555769 — UniProt-cited evidence.
- PubMed PMID:1465449 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for CALD1 (Caldesmon). Expected localisation Smooth-muscle cytoplasm (HPA tissue IHC). Antigen retrieval: EDTA pH 8.0 HIER, heat-mediated (datasheet PB9922). Validated IHC antibody: PB9922 at 0.5-1μg/ml (the product's own IHC validation image is shown). Controls (HPA): positive Endometrium (Ciliated epithelial cells); negative Adipose tissue. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded mouse intestine tissue; fixative not specified (datasheet PB9922); 2. Fixation: Image fixative and duration unreported (datasheet PB9922); 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: EDTA pH 8.0 (datasheet PB9922); 20 min, 95–100 °C (standard); 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% goat serum (datasheet PB9922); 8. Primary antibody: Rabbit anti-CALD1, 0.5-1μg/ml (datasheet PB9922); 9. Primary incubation: Overnight at 4 °C (datasheet PB9922). Watch for: Fixation: Keep fixation consistent across sections (standard IHC practice; not target-specific); Caveat: Ciliated epithelial cells can also stain strongly (HPA tissue IHC); Isoform / epitope: 6 isoforms; antibody epitope coverage is unspecified (UniProt; datasheet PB9922); Regulation: Isoform 1 predominates in smooth muscle (UniProt). Evidence: UniProt Q05682, HPA tissue IHC · Enhanced, HPA ICC-IF · plasma membrane and actin filaments., Datasheet PB9922, PMC13003078, PMC4823093. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/CALD1/immunohistochemistry-ihc-guide.