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CLDN1 / Claudin-1 · IHC design guide
Design Immunohistochemistry for CLDN1
Plan chromogenic paraffin IHC with the IHC-validated antibody at 2–5 μg/mL (datasheet A01585-2). Use skin granular-layer cells as a high-staining reference and colon glandular cells as an undetected comparator (HPA tissue IHC).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
CLDN1 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 | Membranous tissue staining (HPA tissue IHC) | |
| Staining pattern | Membranous staining, most abundant in squamous epithelium (HPA tissue IHC) | |
| Antigen retrieval | EDTA pH 8.0 HIER, heat-mediated (datasheet A01585-2) | |
| Positive control | Kidney+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 conditions consistent across paraffin sections. (standard IHC practice; not target-specific) | |
| Caveat | Antibody staining and RNA show medium consistency (HPA tissue IHC) | |
| Regulation | RNA is tissue enhanced in liver and skin (HPA tissue RNA) | |
| Isoform / epitope | No annotated isoforms; map extracellular vs cytoplasmic epitope (UniProt) |
Section 1
Recommended CLDN1 IHC & IF Protocols
Start with the catalog antibody’s IHC-P protocol (datasheet A01585-2). These four published CLDN1 IHC protocols provide conditions for breast, colorectal, mouse colonic, and paraffin-embedded tissue sections (PMC1064136; PMC4202803; PMC7571313; PMC12624041).
| Sample | Paraffin-embedded human lung cancer tissue; fixative not specified (datasheet A01585-2) |
| Fixation | Image fixative and duration unreported (datasheet A01585-2); 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 A01585-2); 20 min, 95–100 °C (standard) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% goat serum (datasheet A01585-2) |
| Primary antibody | Rabbit anti-CLDN1, 2μg/ml (datasheet A01585-2) |
| Primary incubation | Overnight at 4 °C (datasheet A01585-2) |
| Detection | Streptavidin-biotin complex (SABC), DAB chromogen (datasheet A01585-2) |
| Counterstain | Hematoxylin, blue, dehydrate and mount (standard) |
| Expected result | CLDN1-positive staining in bowman's capsule of kidney (HPA tissue IHC: High). HPA tissue profile: Membranous expression in several tissues, most abundant in squamous epithelium. No signal in the no-primary control. |
💡Decision noteTry heat-mediated EDTA at pH 8.0 first with the catalog antibody (datasheet A01585-2); citrate-based retrieval is reported with other antibodies (PMC4202803; PMC7571313; PMC12624041).
Section 2
What Is the Expected CLDN1 Staining Pattern?
CLDN1 is a four-pass membrane protein found at tight junctions and cell membranes, with a reported basolateral location in its CD81 complex (UniProt O95832 topology and subcellular location). In paraffin-section IHC, expect membranous staining in epithelial cells, especially skin granular-layer cells, tonsillar squamous epithelium, and kidney Bowman’s capsule (HPA: High in each). HPA rates its tissue IHC profile Enhanced, with medium consistency between staining and RNA expression (HPA tissue IHC).
| Membranous outlines in skin granular-layer cells, tonsillar squamous epithelium, or Bowman’s capsule. | This matches the expected compartment and High staining in these cells (UniProt O95832 subcellular location; HPA tissue IHC). Judge cell identity and membrane pattern together: a dark chromogenic deposit alone does not establish a correct CLDN1 result (general IHC practice). |
| Predominantly nuclear staining, or widespread cytoplasmic staining without clear cell borders. | This does not fit the annotated junctional and membrane location (UniProt O95832 subcellular location). Review morphology, detection controls, and antibody conditions before assigning it to CLDN1; the supplied sources do not establish a normal nuclear pattern (general IHC interpretation). |
| Strong staining in adipocytes, bone-marrow hematopoietic cells, or colon glandular cells. | HPA reports CLDN1 as not detected in these cell populations (HPA tissue IHC). If staining persists after confirming the cell type, consider nonspecific antibody binding or endogenous detection activity; a discordant result alone cannot distinguish them (general IHC practice). |
| Diffuse color across tissue, stroma, and slide, with little separation between cells. | A diffuse deposit cannot be scored as the epithelial membrane pattern described by HPA (HPA tissue IHC). Uneven reagent coverage, nonspecific binding, or detection background are general IHC possibilities; inspect a no-primary control and compare matched processing before interpreting tissue expression (general IHC practice). |
| No signal in a well-preserved skin granular layer, tonsillar squamous epithelium, or Bowman’s capsule. | These are expected High cell-specific positive references (HPA tissue IHC). First verify that the named cells are present and the section is interpretable; then review the catalog antibody’s IHC-P instructions, reagent activity, and detection controls. Absence in one section alone does not establish biological loss (general IHC practice). |
💡Expected CLDN1 appearanceCall a result positive when epithelial cell borders show clear membranous staining, especially High signal in skin granular-layer cells, tonsillar squamous cells, or Bowman’s capsule; isolated nuclear color or staining in HPA-negative cell populations is suspect (UniProt O95832 subcellular location; HPA tissue IHC).
| Membrane topology and epitope location | CLDN1 has 4 transmembrane segments, two extracellular regions, and cytoplasmic termini and loop (UniProt O95832 topology). The antibody epitope is unspecified here, so topology cannot justify a CLDN1-specific retrieval, permeabilisation, or fixation-sensitivity claim. |
| Cell-specific reference pattern | Skin granular-layer cells, tonsillar squamous cells, and Bowman’s capsule are High; breast glandular and bronchial respiratory epithelial cells are Medium (HPA tissue IHC). Compare the named cells, not whole-tissue color, when choosing positive references. |
| Strength of tissue evidence | HPA labels the tissue profile Enhanced but notes medium consistency with RNA expression; its listed antibodies have IHC ratings Enhanced and Supported (HPA tissue IHC; HPA antibodies). Treat an unexpected pattern as a finding to verify, rather than proof of absence or ectopic expression. |
| IF/ICC question: should the same pattern be expected? | Membrane localization is biologically expected (UniProt O95832 subcellular location; HPA subcellular summary: Membrane). HPA supplies no ICC-IF cell-line images or main-location assignment here, so this record cannot validate an IF/ICC staining pattern or supply an IF protocol (HPA subcellular). |
| Situation | Likely cause | Next action |
|---|---|---|
| Expected positive epithelium is blank. | The target cells may be absent from the section, or the IHC detection run may have failed; HPA reports High staining in the specified skin, tonsil, and kidney cells (HPA tissue IHC; general IHC practice). | Confirm cell identity and section integrity, then check the catalog antibody’s IHC-P instructions, reagent activity, and a run control. Change retrieval conditions only as a general optimization step; no CLDN1-specific retrieval effect is supplied (general IHC practice). |
| Signal is mainly nuclear or diffuse cytoplasmic. | The compartment conflicts with CLDN1’s junctional and membrane annotation (UniProt O95832 subcellular location). A mismatch can reflect staining or interpretation problems but does not identify one specific cause (general IHC practice). | Recheck focus and cell boundaries, compare a no-primary control, and repeat using the catalog antibody’s validated IHC-P conditions. Score membrane signal separately from any other deposit (general IHC practice). |
| HPA-negative cells appear strongly positive. | Adipocytes, bone-marrow hematopoietic cells, and colon glandular cells are reported not detected (HPA tissue IHC). Nonspecific binding or endogenous detection activity may produce misleading color (general IHC practice). | Verify morphology and compare no-primary and detection controls. If the deposit remains antibody dependent, reassess antibody conditions and seek independent confirmation before reporting CLDN1 in those cells (general IHC practice). |
| The entire section has a colored haze. | Broad background obscures the membranous epithelial pattern reported by HPA (HPA tissue IHC). Blocking, washing, or detection conditions can contribute to background in chromogenic IHC (general IHC practice). | Check a no-primary control and inspect reagent coverage. Review blocking, wash steps, primary-antibody concentration, and detection timing under the catalog IHC-P procedure; retain conditions that preserve interpretable positive-cell borders (general IHC practice). |
| A moderate-staining tissue is treated as a failed positive control. | HPA rates breast glandular and bronchial respiratory epithelial cells Medium, below its High examples (HPA tissue IHC). A weaker result in these named cells alone does not show that the run failed. | Compare like cell populations and include a High reference such as skin granular-layer cells, tonsillar squamous epithelium, or Bowman’s capsule when available (HPA tissue IHC). Interpret control intensity with morphology and run controls (general IHC practice). |
Experiment evidence
IHC & IF images showing CLDN1 staining
A01585-2 · IHCIHC analysis of Claudin 1/CLDN1 using anti Claudin 1/CLDN1 antibody (A01585-2). Claudin 1/CLDN1 was detected in paraffin-embedded section of
A01585-2 · IHCIHC analysis of Claudin 1/CLDN1 using anti Claudin 1/CLDN1 antibody (A01585-2). Claudin 1/CLDN1 was detected in paraffin-embedded section of
A01585-2 · IFIF analysis of Claudin 1/CLDN1 using anti-Claudin 1/CLDN1 antibody (A01585-2). Claudin 1/CLDN1 was detected in immunocytochemical section of
M01585-3 · IHCMouse stomach was stained with anti-Claudin 1 rabbit antibody
M01585-3 · IHCRat stomach was stained with anti-Claudin 1 rabbit antibody
M01585-2 · IHCRat stomach tissue was stained with anti-Claudin 1 rabbit Antibody
M01585-2 · IHCRat esophagus tissue was stained with anti-Claudin 1 rabbit Antibody
A01585-1 · IFImmunofluorescence Validation of CLDN1 in HepG2 Cells Immunofluorescent analysis of 4% paraformaldehyde-fixed HepG2 cells labeling CLDN1 wit
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000163347-CLDN1/tissue/cerebral+cortex#imid_15107034
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000163347-CLDN1/tissue/colon#imid_15106966
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000163347-CLDN1/tissue/liver#imid_15106959
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000163347-CLDN1/tissue/kidney#imid_15106960
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for CLDN1 IHC & IF
🧪Run skin first: cells in the granular layer should show junctional staining (HPA: High in skin granular-layer cells). Use adipose tissue as the negative tissue (HPA: Not detected in adipocytes); on the skin slide, non-epithelial stromal cells should lack the crisp junctional pattern expected in positive epithelial cells (UniProt O95832: tight-junction localization).
Positive control tissue: Kidney (Bowman's capsule, HPA High)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA carries no ICC-IF cell line for CLDN1; derive a cell-line control from the positive tissue's cell type (Bowman's capsule) and confirm it by RNA or western blot first.
Technical controls: Include a no-primary, secondary-only control, a concentration-matched rabbit IgG isotype control, and CLDN1-knockout tissue or cells as a biological negative (selected-SKU caption: rabbit primary antibody; standard IHC controls). Quench endogenous peroxidase and check for endogenous biotin staining when using the caption’s biotin-based DAB detection; inspect skin pigment separately from chromogen signal (selected-SKU caption: biotinylated secondary, SABC and DAB; standard IHC practice).
⚠️Feasibility: A target-specific fixation window and fixation effect are unreported in the supplied evidence; the selected-SKU paraffin-section caption does not state a fixative (selected-SKU caption: fixative unreported). Heat retrieval in EDTA at pH 8.0 was used for the caption’s lung-cancer section, so retrieval conditions for the selected skin control need optimization (selected-SKU caption: heat-mediated EDTA retrieval). The evidence does not establish that frozen-section IHC or IF is easier than paraffin IHC; for skin, distinguish junctional signal from pigment during chromogenic scoring (UniProt O95832: tight-junction localization; standard IHC practice).
HPA tissue IHC evidence for CLDN1
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Enhanced — Medium consistency between antibody staining and RNA expression data.). 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 |
|---|---|---|---|---|
| Kidney | Bowman's capsule | High | Protein (IHC) | HPA → |
| Skin | Cells in granular layer | High | Protein (IHC) | HPA → |
| Tonsil | Squamous epithelial cells | High | Protein (IHC) | HPA → |
| Breast | Glandular cells | Medium | Protein (IHC) | HPA → |
| Bronchus | Respiratory epithelial cells | Medium | Protein (IHC) | HPA → |
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Adipose tissue | Adipocytes | Not detected | Protein (IHC) | HPA → |
| Bone marrow | Hematopoietic cells | Not detected | Protein (IHC) | HPA → |
| Caudate | Glial cells | Not detected | Protein (IHC) | HPA → |
| Cerebellum | Cells in granular layer | Not detected | Protein (IHC) | HPA → |
| Cerebral cortex | Endothelial cells | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced CLDN1 IHC Tips
Troubleshoot CLDN1 staining by checking membrane localisation, cell identity and controls alongside retrieval and detection conditions (UniProt O95832; HPA tissue IHC).
What retrieval should I try when CLDN1 staining is weak in paraffin sections?
Use heat mediated retrieval in EDTA at pH 8.0 first (datasheet A01585-2). The selected paraffin section example used that retrieval before incubation with 2 µg/ml antibody overnight at 4°C, so check those conditions before changing several variables together (datasheet A01585-2). If staining remains weak, compare a modest increase in heating time on adjacent sections while monitoring tissue integrity (standard IHC practice). Include a positive squamous epithelial control, where membranous CLDN1 is abundant, and a no primary control in the same run (HPA tissue IHC; standard IHC practice). Score restored junctional staining rather than a general increase in chromogen (UniProt O95832 localisation; standard IHC practice).
Could fixation explain weak or uneven CLDN1 staining?
CLDN1 specific sensitivity to fixative type or fixation duration is unknown from the supplied evidence; the selected paraffin section caption does not state a fixative (datasheet A01585-2). Record the actual fixative, time to fixation and duration for each specimen before comparing staining intensity (standard IHC practice). On adjacent sections, keep EDTA at pH 8.0, antibody concentration at 2 µg/ml and overnight incubation at 4°C constant while assessing specimen variation (datasheet A01585-2; standard IHC practice). Compare intact epithelium with a positive control processed in the same batch, and inspect tissue morphology before attributing a weak signal to fixation (HPA tissue IHC; standard IHC practice). Do not infer a fixation effect from tissue expression patterns (HPA tissue IHC).
Where should convincing CLDN1 staining appear in an IHC section?
Expect a predominantly membranous pattern, especially at epithelial cell contacts, because CLDN1 is a tight junction and cell membrane protein (UniProt O95832 localisation; HPA tissue IHC). Basolateral membrane staining can also be plausible: the CLDN1–CD81 complex localises there (UniProt O95832 localisation). Examine the pattern at high magnification and compare it with preserved cell borders rather than scoring diffuse cytoplasmic DAB as equivalent (standard IHC practice). HPA reports abundant membranous expression in squamous epithelium, with high staining in the skin granular layer and tonsil squamous epithelial cells (HPA tissue IHC). Keep the tissue and cell type in the annotation, since a positive membrane pattern alone does not establish its cellular source (standard IHC practice).
How can epitope position affect my CLDN1 IHC result?
CLDN1 has 4 annotated transmembrane segments, extracellular regions at residues 29–81 and 137–163, and a cytoplasmic tail at 185–211 (UniProt O95832 topology). The supplied evidence does not identify this antibody’s epitope, so do not assign its staining behaviour to either membrane side (datasheet A01585-2). UniProt lists no isoforms, glycosylation sites or modified residues for this record; those annotations cannot explain a particular staining difference without further evidence (UniProt O95832 record). If results disagree across antibodies, obtain each antibody’s immunogen or epitope information and compare staining on adjacent sections under matched retrieval and detection conditions (standard IHC practice). Interpret concordant epithelial membrane staining alongside controls (HPA tissue IHC; standard IHC practice).
How should I adapt this CLDN1 experiment for multiplex IF?
Treat IF as a separate assay requiring its own validation; the supplied product example establishes chromogenic staining of a paraffin section, not IF performance (datasheet A01585-2). Pair CLDN1 with a marker for the epithelial cell population being examined and assess whether their signals occupy the expected cells and membrane boundaries (HPA tissue IHC; standard IF practice). Choose a fluorophore channel after checking unstained tissue for autofluorescence, and include single colour controls to assess bleed through (standard IF practice). If the epitope is cytoplasmic, test gentle permeabilisation; an extracellular epitope may be accessible without it, depending on specimen preparation (UniProt O95832 topology; standard IF practice). The antibody epitope is not specified here, so test access empirically (datasheet A01585-2).
How can I reduce diffuse brown staining without losing junctional CLDN1 signal?
First compare the stained section with a no primary control to distinguish antibody related signal from background caused by the detection workflow (standard IHC practice). The selected example used 10% goat serum blocking, 2 µg/ml primary antibody overnight at 4°C, and a biotinylated secondary for 30 minutes at 37°C before DAB development (datasheet A01585-2). Check peroxidase blocking and shorten chromogen development if the control also becomes brown (standard chromogenic IHC practice). If background appears only with primary antibody, titrate concentration and strengthen washes on matched sections (standard IHC practice). Preserve crisp epithelial membrane staining as the endpoint, since that matches the expected CLDN1 distribution (HPA tissue IHC; UniProt O95832 localisation).
What should I quantify when CLDN1 membrane staining varies between samples? ⚠ ANSWER MARKED FOR VERIFICATION
Define the eligible epithelial compartment on morphology before scoring, because HPA reports cell type dependent tissue staining (HPA tissue IHC; standard IHC practice). Record the percentage of cells with convincing membrane staining and, when intensity is reproducible, calculate a membrane specific H-score from intensity categories and their percentages (standard IHC practice). Normalise cell counts to the number of evaluable epithelial cells; for a spatial analysis, report positive cell density per mm² of viable eligible tissue (standard IHC practice). Apply the same threshold, region selection and DAB development conditions to all samples (standard IHC practice). Report cytoplasmic signal separately rather than adding it to the membrane score (UniProt O95832 localisation; standard IHC practice).
How do I distinguish genuine CLDN1 staining from IHC artefact?
A convincing result follows epithelial membranes or cell contacts, consistent with CLDN1 tight junction localisation and HPA membranous staining (UniProt O95832 localisation; HPA tissue IHC). Confirm that the stained cells are the intended population: HPA reports high signal in tonsil squamous epithelial cells and skin granular layer cells, while colon glandular cells are listed as not detected in its tissue profile (HPA tissue IHC). Discount staining confined to cut edges, folds or necrotic areas until it reproduces in intact tissue (standard IHC practice). Compare a no primary control for endogenous enzyme or detection background, and inspect the counterstain for preserved morphology (standard chromogenic IHC practice). Interpret an unexpected compartment or cell type as requiring corroboration, not as proof of altered CLDN1 biology (UniProt O95832 localisation; standard IHC practice).
Boster reagents
Best CLDN1 / Claudin-1 IHC Antibodies
Anti-CLDN1 antibodies have IHC images from human, mouse, and rat tissues and IF images from human cells and tissue (catalog image captions).
Real IHC data
Anti-Claudin 1/CLDN1 Antibody
Cat # A01585-2
Real IHC data
Anti-Claudin 1 Rabbit Monoclonal Antibody
Cat # M01585-3
Real IHC data
Anti-Claudin 1 Rabbit Monoclonal Antibody
Cat # M01585-2
Real IF data
Anti-Claudin-1 CLDN1 Antibody
Cat # A01585-1
A01585-2 has IHC images from paraffin sections of human lung and rectal cancers; M01585-3 has IHC images from mouse and rat stomach and human breast (catalog IHC image captions). M01585-2 has IHC images from rat stomach and esophagus; A01585-1 has an IF image from human HepG2 cells (catalog image captions).
Which to pick: For human paraffin-section IHC, choose A01585-2: its IHC captions document EDTA pH 8.0 retrieval and 2 μg/mL primary antibody, but do not report the fixative (A01585-2 IHC image captions). For IHC across human, mouse, and rat samples, consider M01585-3, a monoclonal antibody listed as reactive with all three species and validated for IHC (M01585-3 catalog); its IHC captions do not report fixation or section processing (M01585-3 IHC image captions). For IF/ICC, choose A01585-1, which lists both applications and has an IF image in human HepG2 cells (A01585-1 catalog and IF image caption).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry O95832 (CLD1_HUMAN, Claudin-1).
- Human Protein Atlas. CLDN1 tissue IHC expression (reliability: Enhanced).
- Human Protein Atlas. CLDN1 subcellular location (ICC-IF): Membrane.
- Human Protein Atlas. CLDN1 antibody validation summary (2 antibodies).
- Claudin-1, -3 and -4 proteins and mRNA expression in benign and malignant breast lesions: a research study. Breast cancer research : BCR 2005 — PMC1064136.
- Claudin-1 Expression Is Elevated in Colorectal Cancer Precursor Lesions Harboring the BRAF V600E Mutation. Translational oncology 2014 — PMC4202803.
- Inhibition of miRNA-29a regulates intestinal barrier function in diarrhea-predominant irritable bowel syndrome by upregulating ZO-1 and CLDN1. Experimental and therapeutic medicine 2020 — PMC7571313.
- PABPC3 drives ovarian cancer metastasis and drug sensitivity by downregulating CLDN1 expression. Cell death & disease 2025 — PMC12624041.
- PubMed PMID:9931503 — UniProt-cited evidence.
- PubMed PMID:10828592 — UniProt-cited evidence.
- PubMed PMID:11071387 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for CLDN1 (Claudin-1). Expected localisation Membranous tissue staining (HPA tissue IHC). Antigen retrieval: EDTA pH 8.0 HIER, heat-mediated (datasheet A01585-2). Validated IHC antibody: A01585-2 at 2μg/ml (the product's own IHC validation image is shown). Controls (HPA): positive Kidney (Bowman's capsule); negative Adipose tissue. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded human lung cancer tissue; fixative not specified (datasheet A01585-2); 2. Fixation: Image fixative and duration unreported (datasheet A01585-2); 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 A01585-2); 20 min, 95–100 °C (standard); 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% goat serum (datasheet A01585-2); 8. Primary antibody: Rabbit anti-CLDN1, 2μg/ml (datasheet A01585-2); 9. Primary incubation: Overnight at 4 °C (datasheet A01585-2). Watch for: Fixation: Keep fixation conditions consistent across paraffin sections. (standard IHC practice; not target-specific); Caveat: Antibody staining and RNA show medium consistency (HPA tissue IHC); Isoform / epitope: No annotated isoforms; map extracellular vs cytoplasmic epitope (UniProt); Regulation: RNA is tissue enhanced in liver and skin (HPA tissue RNA). Evidence: UniProt O95832, HPA tissue IHC · Enhanced, HPA ICC-IF · Membrane, Datasheet A01585-2, PMC1064136, PMC4202803. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/CLDN1/immunohistochemistry-ihc-guide.