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TRIM21 / E3 ubiquitin-protein ligase TRIM21 · IHC design guide
Design Immunohistochemistry for TRIM21
Plan TRIM21 IHC-P around cytoplasmic staining in most tissues, including high staining in bone marrow hematopoietic cells (HPA tissue IHC). This guide covers formaldehyde-fixed paraffin sections and 5 μg/mL catalog antibody for chromogenic detection (datasheet A02079).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
TRIM21 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 | Cytoplasm in tissue sections (HPA tissue IHC) | |
| Staining pattern | Cytoplasmic staining in most tissues; cell type varies (HPA tissue IHC) | |
| Antigen retrieval | Citrate pH 6 HIER, heat-mediated (datasheet A02079) | |
| Positive control | Bone marrow+4 more · see all | |
| Negative control | Adrenal gland+3 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Formaldehyde-fixed paraffin sections (selected-SKU IHC image A02079); keep fixation consistent (standard IHC practice; not target-specific) | |
| Caveat | Tissue staining has medium concordance with RNA levels (HPA tissue IHC) | |
| Regulation | Upregulated through IFN/JAK/STAT signaling (UniProt) | |
| Isoform / epitope | 2 isoforms; verify antibody epitope coverage (UniProt) |
Section 1
Recommended TRIM21 IHC & IF Protocols
The catalog antibody protocol (datasheet: A02079) is accompanied by published TRIM21 IHC methods for endometrial tissue microarrays (PMC13526992) and kidney samples (PMC13338432).
| Sample | Formaldehyde-fixed, paraffin-embedded human small intestine tissue (datasheet A02079) |
| Fixation | Image formalin-fixed; duration unreported (datasheet A02079); verify before use. |
| Sectioning | 4–5 µm sections on charged slides (standard) |
| Deparaffinisation | Xylene, graded ethanol series to water (standard) |
| Antigen retrieval | Heat retrieval: Citrate pH 6 (datasheet A02079); 20 min, 95–100 °C (standard) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% serum (datasheet A02079) |
| Primary antibody | Rabbit anti-TRIM21, 5 μg/mL (datasheet A02079) |
| 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 | TRIM21-positive staining in hematopoietic cells of bone marrow (HPA tissue IHC: High). HPA tissue profile: Cytoplasmic expression in most tissues. No signal in the no-primary control. |
💡Decision noteStart with heat mediated citrate retrieval at pH 6 (datasheet: A02079); the endometrial tissue study also used citrate buffer (PMC13526992: methods).
Section 2
What Is the Expected TRIM21 Staining Pattern?
In paraffin-section IHC, expect predominantly cytoplasmic TRIM21 staining across many tissues, including high staining in breast glandular cells, bronchial respiratory epithelium and bone-marrow hematopoietic cells (HPA: tissue IHC). HPA rates its tissue profile Enhanced, with medium consistency between staining and RNA data (HPA: tissue IHC). TRIM21 can also occupy the nucleus and cytoplasmic structures; it has no transmembrane segment (UniProt P19474: subcellular location and topology).
| Cytoplasmic signal in breast or colon glandular cells, or bronchial respiratory epithelial cells (HPA: High in each listed cell population). | This matches the reported tissue-IHC compartment and high-staining cell populations (HPA: cytoplasmic expression in most tissues; High in these cells). Judge intensity against a processed control, since HPA reports a staining category rather than a universal numeric threshold (HPA: tissue IHC; general IHC practice). |
| Signal confined to the cell surface, gland lumen or extracellular space. | A compartment-restricted pattern of that kind conflicts with the expected cytoplasmic tissue profile and the absence of a transmembrane segment (HPA: tissue IHC; UniProt P19474: topology). Treat it as a possible staining artefact and check morphology and controls before scoring it as TRIM21 (general IHC practice). |
| Strong signal in adrenal gland glandular cells or spleen red-pulp cells. | Those specific cell populations were reported as not detected; the designation does not make the entire organ a universal negative control (HPA: tissue IHC). Check whether the stained cells were identified correctly, then investigate cross-reactivity or endogenous detection activity (general IHC practice). |
| Broad, poorly defined colour covers cells and surrounding tissue. | Diffuse background obscures the cytoplasmic pattern needed for interpretation (HPA: tissue IHC; general IHC practice). Compare a no-primary control and examine blocking, washing and detection conditions to distinguish nonspecific deposition from cell-associated signal (general IHC practice). |
| No discernible signal in breast glandular cells or bone-marrow hematopoietic cells. | Both are listed as High, so a blank run calls for technical review before a biological absence claim (HPA: tissue IHC). Check the tissue's integrity, the antibody's IHC validation and the detection controls (HPA: antibody validation; general IHC practice). |
💡Expected TRIM21 appearanceA convincing positive is cell-associated, predominantly cytoplasmic staining in an HPA high-staining population such as breast glandular cells; isolated luminal or extracellular colour is suspect (HPA: tissue IHC; UniProt P19474: topology; general IHC practice).
| Choice of comparison cells | Use a listed High population for a positive comparison and identify the exact cells when using a not detected population for contrast (HPA: tissue IHC). Thyroid glandular cells are reported Low, so faint staining there has a different interpretation from a blank high-staining control (HPA: tissue IHC). |
| Antibody validation | HPA lists one IHC antibody as Enhanced and another as Approved; these are antibody-specific ratings (HPA: HPA005673 Approved; CAB004566 Enhanced). The overall tissue profile is Enhanced but has medium staining-to-RNA consistency, so retain cell and compartment controls when interpreting a new run (HPA: tissue IHC). |
| Topology and processing | TRIM21 has no transmembrane segment or signal peptide and is annotated as a single chain spanning residues 1–475 (UniProt P19474: topology and processing). These annotations support scrutiny of a purely membrane or extracellular pattern; they do not establish how fixation or retrieval affects staining. |
| Isoforms and epitope | Two isoforms are annotated, but the supplied record does not map the IHC antibody's epitope to either one (UniProt P19474: isoforms; HPA: antibody validation). An isoform-specific staining claim therefore needs separate epitope evidence; do not infer it from tissue intensity (UniProt P19474: isoforms; HPA: tissue IHC). |
| IF/ICC Q&A: should nuclear signal count? | Yes, nuclear localisation is biologically plausible: HPA reports approved nucleoplasmic ICC-IF localisation, and UniProt includes the nucleus (HPA: subcellular ICC-IF; UniProt P19474: subcellular location). For paraffin IHC, interpret that observation alongside HPA's predominantly cytoplasmic tissue profile; the ICC-IF result alone does not set an IHC scoring threshold (HPA: tissue IHC and ICC-IF). |
| Situation | Likely cause | Next action |
|---|---|---|
| The high-staining comparison is blank. | The result conflicts with the reported High staining in the chosen cells (HPA: tissue IHC); the cause is undetermined. | Confirm that the expected cells are present, then review the IHC antibody, retrieval conditions, detection reagents and a run control (HPA: antibody validation; general IHC practice). |
| Colour appears throughout a no-primary control. | Primary-antibody-independent colour suggests endogenous detection activity or a detection-system problem (general IHC practice). | Review the detection chemistry and its relevant endogenous-activity block, then repeat the control alongside the sample (general IHC practice). Do not score that colour as TRIM21. |
| Staining is concentrated in lumens or at cell borders. | That distribution differs from HPA's cytoplasmic tissue pattern and UniProt's non-membrane topology (HPA: tissue IHC; UniProt P19474: topology). | Check whether colour follows tissue edges, folds or debris; compare a no-primary control and reassess cellular localisation before scoring (general IHC practice). |
| A reported not-detected population stains strongly. | Cell identification, cross-reactivity or endogenous detection activity could explain the discrepancy; HPA's negative designation applies to the named cells (HPA: tissue IHC; general IHC practice). | Recheck the cell population and morphology, examine a no-primary control, and compare staining with an HPA high-staining population in the same run (HPA: tissue IHC; general IHC practice). |
| Nuclear colour dominates a paraffin section. | Nuclear TRIM21 is possible, but HPA describes tissue IHC as predominantly cytoplasmic and ICC-IF as nucleoplasmic (UniProt P19474: subcellular location; HPA: tissue IHC and ICC-IF). | Record nuclear and cytoplasmic compartments separately; compare controls and the antibody's IHC validation before calling a nuclear-only tissue pattern expected (HPA: antibody validation; general IHC practice). |
| All sections show weak, hazy staining. | A run-wide pattern is difficult to reconcile with distinct HPA High and not-detected cell populations; the underlying technical cause remains unknown (HPA: tissue IHC). | Compare the high-staining tissue and no-primary control, then review antibody concentration, washing and detection conditions as general IHC variables (HPA: tissue IHC; general IHC practice). |
Experiment evidence
IHC & IF images showing TRIM21 staining
A02079 · IHCImmunohistochemistry Validation of TRIM21 in Human Small Intestine Tissue Immunohistochemical analysis of paraffin-embedded human small inte
A02079 · IFImmunofluorescence Validation of TRIM21 in Human Small Intestine Tissue Immunofluorescent analysis of 4% paraformaldehyde-fixed human small
A02079-2 · IFIF analysis of TRIM21/SS-A using anti-TRIM21/SS-A antibody (A02079-2). TRIM21/SS-A was detected in immunocytochemical section of U20S cells.
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000132109-TRIM21/tissue/cerebral+cortex#imid_2249520
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000132109-TRIM21/tissue/colon#imid_2249462
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000132109-TRIM21/tissue/liver#imid_2249463
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000132109-TRIM21/tissue/kidney#imid_2249456
HPA · ICC-IF HUVEC/TERT2Human Protein Atlas immunofluorescence, HUVEC/TERT2, antibody HPA005673; green = TRIM21, blue = nucleus, red = microtubules.
HPA · ICC-IF HUVEC/TERT2Human Protein Atlas immunofluorescence, HUVEC/TERT2, antibody HPA005673; green = TRIM21, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for TRIM21 IHC & IF
🧪Run breast first: glandular cells should show strong staining (HPA: High in breast glandular cells). Use adrenal gland as the negative tissue (HPA: Not detected in adrenal gland glandular cells); on the breast slide, assess adjacent nonglandular cells for background-level staining, without assuming they are TRIM21-negative because HPA does not establish that.
Positive control tissue: Bone marrow (Hematopoietic cells, HPA High)
Negative control tissue: Adrenal gland (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show TRIM21 in HUVEC/TERT2, U-251MG, U2OS, with annotated localisation: Nucleoplasm (approved) (HPA subcellular).
Technical controls: Include a no-primary (secondary-only) slide, a host- and clonality-matched isotype control, and TRIM21-knockout material as a biological negative. Quench endogenous peroxidase before chromogenic detection and check the breast section for background signal in the controls (standard IHC practice).
⚠️Feasibility: The selected A02079 caption reports heat retrieval in citrate buffer at pH 6 for paraffin sections, but does not establish whether retrieval is required for TRIM21; no target-specific fixation window or fixation effect is reported. The caption describes formaldehyde fixation, while its structured fixative field says “not stated” (A02079 caption and fixative field). HPA shows approved nucleoplasmic ICC-IF localisation, but the supplied evidence does not establish that frozen sections or IF are easier than paraffin IHC (HPA: Nucleoplasm, approved).
HPA tissue IHC evidence for TRIM21
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 |
|---|---|---|---|---|
| Bone marrow | Hematopoietic cells | High | Protein (IHC) | HPA → |
| Breast | Glandular cells | High | Protein (IHC) | HPA → |
| Bronchus | Respiratory epithelial cells | High | Protein (IHC) | HPA → |
| Colon | Glandular cells | High | Protein (IHC) | HPA → |
| Duodenum | Glandular cells | High | Protein (IHC) | HPA → |
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Adrenal gland | Glandular cells | Not detected | Protein (IHC) | HPA → |
| Cerebellum | Cells in granular layer | Not detected | Protein (IHC) | HPA → |
| Soft tissue | Peripheral nerve | Not detected | Protein (IHC) | HPA → |
| Spleen | Cells in red pulp | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced TRIM21 IHC Tips
Troubleshoot TRIM21 staining in paraffin sections by checking retrieval, cell type, subcellular pattern and matched controls.
What retrieval should I try when TRIM21 staining is weak in paraffin sections?
Start with heat-mediated citrate buffer at pH 6 for paraffin sections (datasheet A02079). The selected tissue image used this retrieval with the catalog antibody at 5 µg/ml and overnight primary incubation at 4°C (datasheet A02079). If staining is weak, compare a carefully controlled alternative retrieval condition on adjacent sections while keeping antibody concentration and detection constant (standard IHC practice). Include a known positive glandular tissue and a matched negative control so improved staining can be distinguished from increased background (HPA: High in duodenal glandular cells; standard IHC practice). Record heating and cooling conditions for reproducibility (standard IHC practice).
Could fixation explain inconsistent TRIM21 staining between paraffin blocks?
TRIM21-specific sensitivity to fixation is unknown from the supplied evidence; neither a tolerated fixation duration nor a preferred fixative can be assigned (supplied evidence). Compare blocks only after documenting fixative, fixation duration, tissue thickness and processing, because these factors can change antigen accessibility in paraffin IHC (standard IHC practice). When possible, stain adjacent sections from similarly processed blocks in the same run and retain an internal tissue control (standard IHC practice). If one block stains weakly, check section preservation and retrieval before interpreting the difference as biological (standard IHC practice). Do not infer fixation sensitivity from TRIM21 localisation or phosphorylation (UniProt P19474; supplied evidence).
Which TRIM21 staining patterns should I accept in tissue sections?
Expect predominantly cytoplasmic staining across many tissues in chromogenic IHC (HPA: cytoplasmic expression in most tissues). TRIM21 can also occur in the nucleus, autophagosomes, P-bodies and stress granules, so a restricted punctate or nuclear pattern needs biological context and validation (UniProt P19474 localisation). Nitric oxide exposure is associated with nuclear entry, and oxidative stress with stress-granule localisation (UniProt P19474, PubMed:18361920; PubMed:36692217). HPA reports approved nucleoplasmic localisation from subcellular imaging, which is a useful comparison but does not establish the expected pattern in every paraffin tissue (HPA subcellular; standard IHC interpretation). Score compartments separately and inspect morphology before accepting puncta as specific (standard IHC practice).
Could epitope choice make one TRIM21 isoform appear absent?
TRIM21 has 2 listed isoforms, and its B30.2/SPRY domain spans residues 268–465 (UniProt P19474). The supplied material does not map the catalog antibody's epitope, so isoform coverage cannot be inferred from its tissue staining (supplied evidence; standard IHC interpretation). Check the immunogen or epitope documentation before claiming that a negative cell population lacks both isoforms (standard IHC practice). Phosphoserine at residue 266 is annotated, but no evidence here shows that it alters this antibody's binding or retrieval response (UniProt P19474; supplied evidence). Compare staining with an independently mapped reagent if isoform discrimination is essential (standard IHC practice).
How should I adapt TRIM21 localisation checks to multiplex IF?
Treat IF/ICC as a separate assay requiring its own antibody validation; the selected A02079 image documents chromogenic staining of paraffin tissue (datasheet A02079; standard IF practice). Multiplex TRIM21 with a marker that identifies the expected cell population, then inspect overlap and compartment assignment in individual channels (HPA: High in duodenal glandular cells; standard IF practice). Choose a fluorophore channel after checking tissue autofluorescence and single-stain controls, particularly where background may obscure weak puncta (standard IF practice). TRIM21 has no transmembrane segment and has cytoplasmic and nuclear locations, so permeabilisation should permit access to the intracellular epitope being tested (UniProt P19474 topology and localisation; standard IF practice). Verify the resulting pattern against controls (standard IF practice).
How can I separate TRIM21 signal from chromogenic background?
The selected paraffin-tissue workflow used 10% serum blocking for 1 hour at room temperature and an HRP secondary at 1:250 (datasheet A02079). Include a no-primary section and an appropriate positive section to reveal detection-system background without treating either as proof of antibody specificity (standard IHC practice). Quench endogenous peroxidase before HRP detection, and assess pigment or nonspecific DAB deposits against the no-primary control (standard IHC practice). If diffuse colour persists, adjust blocking, washing and antibody concentration one variable at a time (standard IHC practice). Compare viable tissue interiors with edges and damaged areas before calling cytoplasmic signal (standard IHC practice).
What is a defensible way to quantify TRIM21 IHC? ⚠ ANSWER MARKED FOR VERIFICATION
Define the cell population and cytoplasmic scoring compartment before reviewing treatment groups, because tissue IHC is predominantly cytoplasmic (HPA: cytoplasmic expression in most tissues; standard IHC practice). For a cell-based readout, report the percentage of positive viable cells and an H-score from 0–300 using percentages at intensity grades 0–3 (standard IHC practice). If punctate cells are the outcome, report positive cells per mm² of viable tissue instead (standard IHC practice). Normalise to the number of eligible cells or measured viable area, and use identical thresholds across sections (standard IHC practice). Report nuclear staining separately rather than combining compartments (UniProt P19474 localisation; standard IHC practice).
When is apparent TRIM21 positivity more likely to be artefact?
A plausible positive pattern is intracellular and commonly cytoplasmic, with the stained cell type checked against tissue context (UniProt P19474 topology and localisation; HPA tissue IHC). Strong isolated membrane outlines are less consistent with a protein lacking a transmembrane segment and warrant control review (UniProt P19474 topology; standard IHC interpretation). Edge-only colour, necrotic areas and no-primary staining suggest processing or detection artefact (standard IHC practice). Check endogenous peroxidase when HRP/DAB signal appears in unexpected cells, and compare adjacent viable cells before scoring (standard IHC practice). HPA reports both high staining in some glandular cells and undetected staining in specified populations, so a negative cell requires an appropriate positive control for interpretation (HPA tissue IHC; standard IHC practice).
Boster reagents
Best TRIM21 / E3 ubiquitin-protein ligase TRIM21 IHC Antibodies
A02079 has IHC and IF images from human small intestine; A02079-2 has an IF/ICC image from U20S cells and lists human, mouse and rat reactivity (catalog applications and image captions).
Real IHC data
Anti-TRIM21 Antibody
Cat # A02079
Real IF data
Anti-TRIM21/SS-A Antibody ®
Cat # A02079-2
A02079 will render with an IHC image from formaldehyde-fixed, paraffin-embedded human small intestine at 5 μg/mL (A02079 image caption). A02079-2 will render with an IF/ICC image from U20S cells at 2 μg/mL (A02079-2 image caption).
Which to pick: Choose A02079 for human paraffin-section IHC: its IHC-P application and formaldehyde-fixed small-intestine image support that use (A02079 application list and image caption). Choose A02079-2 for IF/ICC in human cells, as shown in its U20S image (A02079-2 application list and image caption). For mouse or rat work, A02079-2 lists those species as reactive, but its pictured IF/ICC result is from U20S cells and it has no listed IHC-P application (A02079-2 reactivity, image caption and application list).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry P19474 (RO52_HUMAN, E3 ubiquitin-protein ligase TRIM21).
- Human Protein Atlas. TRIM21 tissue IHC expression (reliability: Enhanced).
- Human Protein Atlas. TRIM21 subcellular location (ICC-IF): Localized to the nucleoplasm..
- Human Protein Atlas. TRIM21 antibody validation summary (2 antibodies).
- Targeting AQP5-mediated arginine deprivation in gastric cancer stem cells restores NK cell anti-tumor immunity. Cell reports. Medicine 2025 — PMC12490235.
- TRIM21 suppresses uterine corpus endometrial carcinoma progression by promoting K48 -linked ubiquitination and degradation of SOAT1. Frontiers in immunology 2026 — PMC13526992.
- Pro-inflammatory cytokine IFN-γ protects against renal fibrosis by promoting E3 ubiquitin ligase Trim21-mediated Loxl2 degradation in tubular epithelial cells. Cell death & disease 2026 — PMC13338432.
- TRIM21 Expression as a Prognostic Biomarker for Progression-Free Survival in HNSCC. International journal of molecular sciences 2023 — PMC10048917.
- PubMed PMID:1985094 — UniProt-cited evidence.
- PubMed PMID:1985112 — UniProt-cited evidence.
- PubMed PMID:7713506 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for TRIM21 (E3 ubiquitin-protein ligase TRIM21). Expected localisation Cytoplasm in tissue sections (HPA tissue IHC). Antigen retrieval: Citrate pH 6 HIER, heat-mediated (datasheet A02079). Validated IHC antibody: A02079 at 5 μg/mL (the product's own IHC validation image is shown). Controls (HPA): positive Bone marrow (Hematopoietic cells); negative Adrenal gland. IHC-P workflow on paraffin sections. Protocol steps: 1. Sample: Formaldehyde-fixed, paraffin-embedded human small intestine tissue (datasheet A02079); 2. Fixation: Image formalin-fixed; duration unreported (datasheet A02079); 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: Citrate pH 6 (datasheet A02079); 20 min, 95–100 °C (standard); 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% serum (datasheet A02079); 8. Primary antibody: Rabbit anti-TRIM21, 5 μg/mL (datasheet A02079); 9. Primary incubation: Overnight at 4 °C (standard). Watch for: Fixation: Formaldehyde-fixed paraffin sections (selected-SKU IHC image A02079); keep fixation consistent (standard IHC practice; not target-specific); Caveat: Tissue staining has medium concordance with RNA levels (HPA tissue IHC); Isoform / epitope: 2 isoforms; verify antibody epitope coverage (UniProt); Regulation: Upregulated through IFN/JAK/STAT signaling (UniProt). Evidence: UniProt P19474, HPA tissue IHC · Enhanced, HPA ICC-IF · nucleoplasm., Datasheet A02079, PMC13526992, PMC13338432. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/TRIM21/immunohistochemistry-ihc-guide.