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C3AR1 / C3a anaphylatoxin chemotactic receptor · IHC design guide
Design Immunohistochemistry for C3AR1
Plan C3AR1 paraffin IHC around mainly cytoplasmic staining in immune cells (HPA tissue IHC). Use lymph-node non-germinal-center cells as a positive reference and adipocytes as a negative comparator (HPA tissue IHC); start the catalog antibody at 1:100–1:300 (datasheet: IHC dilution).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
C3AR1 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 | Immune-cell cytoplasm (HPA tissue IHC); cell membrane (UniProt) | |
| Staining pattern | Mainly cytoplasmic staining in immune cells (HPA tissue IHC) | |
| Antigen retrieval | Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen) | |
| Positive control | Appendix+4 more · see all | |
| Negative control | Adipose tissue+4 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep formalin fixation consistent across paraffin sections (standard IHC practice; not target-specific) | |
| Caveat | ARRB1-associated receptor internalization may alter the pattern (UniProt) | |
| Regulation | Expression regulators are not specified (UniProt) | |
| Isoform / epitope | 0 isoforms annotated; epitopes may face outside or cytoplasm (UniProt) |
Section 1
Recommended C3AR1 IHC & IF Protocols
The catalog antibody’s IHC-P protocol is accompanied by published C3AR1 staining protocols for placental tissue and carotid artery specimens (PMC11780793; PMC11061441).
| Sample | Paraffin-embedded human brain tissue; fixative not specified (datasheet A06350) |
| Fixation | Image fixative and duration unreported (datasheet A06350); verify before use. |
| Sectioning | 4–5 µm sections on charged slides (standard) |
| Deparaffinisation | Xylene, graded ethanol series to water (standard) |
| Antigen retrieval | Heat-induced epitope retrieval in citrate buffer, pH 6.0, 20 min at 95–98 °C (standard rule: cytoplasmic / membrane antigen) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% normal serum of the secondary host, 30 min, room temperature (standard) |
| Primary antibody | Rabbit anti-C3AR1, 1:100 - 1:300 (datasheet A06350) |
| 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 | C3AR1-positive staining in lymphoid tissue of appendix (HPA tissue IHC: Medium). HPA tissue profile: Mainly cytoplasmic expression in immune cells. No signal in the no-primary control. |
💡Decision noteStart with citrate pH 6.0 HIER at 95–98 °C for 20 min (page retrieval rule); adjust using the published tissue-specific conditions.
Section 2
What Is the Expected C3AR1 Staining Pattern?
C3AR1 is a cell membrane receptor with 7 transmembrane segments (UniProt Q16581 topology). In tissue IHC, expect staining mainly in the cytoplasm of immune cells (HPA tissue IHC). HPA rates its tissue staining reliability “Enhanced,” while noting that external characterization supports the staining and internal RNA correlation is unavailable (HPA tissue IHC). Read the observed cytoplasmic pattern alongside the receptor’s membrane assignment.
| Discrete staining in immune cells of appendix lymphoid tissue, lymph node, or tonsil. | This fits HPA’s mainly cytoplasmic immune-cell profile; the listed compartments have Medium staining (HPA tissue IHC). Assess individual cells and nearby unstained areas, since a tissue-wide brown haze does not establish cell-specific staining (standard IHC practice). |
| Cytoplasmic staining is more evident than a crisp cell outline. | Do not reject this solely because UniProt assigns C3AR1 to the membrane: HPA describes mainly cytoplasmic staining in immune cells (UniProt Q16581 subcellular location; HPA tissue IHC). UniProt also reports receptor internalization after interaction with ARRB1 when phosphorylated, but that mechanism does not prove the cause of cytoplasmic staining on a given slide (UniProt Q16581 subunit). |
| Strong, predominantly nuclear staining in the putative positive cells. | Treat this as an unexpected compartment, because UniProt assigns C3AR1 to the cell membrane and HPA describes mainly cytoplasmic tissue staining (UniProt Q16581 subcellular location; HPA tissue IHC). Review the negative control and detection background before assigning the nuclear signal to C3AR1 (standard IHC practice). |
| Prominent staining in adipocytes or adrenal glandular cells. | HPA reports C3AR1 as Not detected in those cell types (HPA tissue IHC). Relative to that reference pattern, investigate cross-reactivity or endogenous detection activity; the mismatch alone does not identify which cause applies (standard IHC practice). |
| Diffuse brown background, or no staining in an expected positive compartment. | Diffuse signal without identifiable cells is difficult to score as C3AR1 (standard IHC practice). Conversely, an unstained appendix lymphoid compartment, lymph-node non-germinal-center cells, or tonsil non-germinal-center cells conflicts with HPA’s Medium examples; check assay performance before interpreting absence (HPA tissue IHC; standard IHC practice). |
💡Expected C3AR1 appearanceCall a result positive when identifiable immune cells show mainly cytoplasmic staining, with membrane staining compatible with receptor location (HPA tissue IHC; UniProt Q16581 subcellular location). HPA’s listed lymphoid examples are Medium; a uniform brown haze or isolated strong nuclear signal is suspect (HPA tissue IHC; standard IHC practice).
| Topology and epitope location | C3AR1 has 7 transmembrane segments and extracellular and cytoplasmic regions (UniProt Q16581 topology). The supplied sources do not locate the catalog antibody’s epitope, so topology alone cannot specify its retrieval conditions or predict which receptor pool it detects. |
| Choice of comparison tissue | Appendix lymphoid tissue and lymph-node or tonsil non-germinal-center cells have Medium staining; adipocytes and adrenal glandular cells are Not detected (HPA tissue IHC). Compare the named cell compartments rather than treating an entire section as uniformly positive or negative. |
| Strength of staining evidence | HPA labels tissue IHC reliability “Enhanced” and lists one antibody, CAB009405, with IHC “Enhanced” status (HPA tissue IHC; HPA antibodies). Its reliability note cites external characterization and no internal RNA data for correlation, so match the observed cell pattern as well as the validation label (HPA tissue IHC). |
| Retrieval and detection controls | No target-specific antigen-retrieval or fixation-sensitivity result is supplied. For paraffin-section chromogenic IHC, assess retrieval and detection performance with an appropriate positive section and negative control (standard IHC practice); do not infer a C3AR1-specific fixation effect from HPA staining levels or UniProt topology. |
| IF/ICC Q: What localization should be expected? | A: Membrane localization is the stated expectation (HPA subcellular summary; UniProt Q16581 subcellular location). HPA supplies no ICC-IF cell-line images or main-location annotation, so it does not establish a finer IF/ICC staining pattern (HPA subcellular). |
| Situation | Likely cause | Next action |
|---|---|---|
| No signal in an expected positive lymphoid compartment. | The result conflicts with HPA’s Medium examples; the staining run may have failed (HPA tissue IHC; standard IHC practice). | Check the positive control, antigen-retrieval record, primary-antibody step, and chromogenic detection run (standard IHC practice). |
| Weak signal in small-intestine glandular cells. | HPA lists this compartment as Low, so weak staining can match its reference pattern (HPA tissue IHC). | Compare it with a listed Medium lymphoid compartment before calling the run insensitive (HPA tissue IHC; standard IHC practice). |
| Brown signal spreads across cells and extracellular areas. | Non-specific binding or detection background may obscure identifiable cell staining (standard IHC practice). | Inspect the negative control and review blocking, washing, and detection conditions; score only distinguishable cells (standard IHC practice). |
| Strong staining appears in adipocytes. | Adipocytes are Not detected in HPA’s tissue reference; cross-reactivity or endogenous detection activity is possible (HPA tissue IHC; standard IHC practice). | Compare the same compartment in the negative control and review endogenous enzyme blocking for chromogenic detection (standard IHC practice). |
| Signal is confined to nuclei. | That compartment conflicts with UniProt’s membrane assignment and HPA’s mainly cytoplasmic profile (UniProt Q16581 subcellular location; HPA tissue IHC). | Check counterstain and negative-control appearance, then reassess whether the signal is specific (standard IHC practice). |
| The whole section is scored positive despite staining in only scattered cells. | HPA describes an immune-cell pattern and reports staining levels for named cell compartments, not a uniform tissue signal (HPA tissue IHC). | Record the stained cell type, compartment, intensity, and proportion separately; compare each with the HPA reference (HPA tissue IHC; standard IHC practice). |
Experiment evidence
IHC & IF images showing C3AR1 staining
A06350 · IHCImmunohistochemistry analysis of paraffin-embedded human brain tissue, using C3AR1 Antibody. The picture on the right is blocked with the sy
A06350 · IFImmunofluorescence analysis of COS7 cells, using C3AR1 Antibody. The picture on the right is blocked with the synthesized peptide.
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000171860-C3AR1/tissue/cerebral+cortex#imid_3564428
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000171860-C3AR1/tissue/colon#imid_3538354
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000171860-C3AR1/tissue/liver#imid_3538371
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000171860-C3AR1/tissue/kidney#imid_3538364
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for C3AR1 IHC & IF
🧪Run appendix first and look for staining in its lymphoid tissue (HPA: Medium in appendix lymphoid tissue). Use adipose tissue as the negative tissue and expect adipocytes to remain unstained (HPA: Not detected in adipocytes); on the appendix slide, cells outside the stained lymphoid population can serve as an internal background reference, but should not be assumed C3AR1-negative without validation.
Positive control tissue: Appendix (Lymphoid tissue, 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 C3AR1; derive a cell-line control from the positive tissue's cell type (Lymphoid tissue) and confirm it by RNA or western blot first.
Technical controls: Include a no-primary, secondary-only slide; use an immunoglobulin control matched to the primary antibody’s host species and isotype or class, as appropriate for its clonality; and test specificity with peptide blocking (selected A06350 tissue-IHC caption: staining blocked with synthesized peptide) or a validated C3AR1 knockout sample. For chromogenic IHC in appendix, block endogenous peroxidase and check for residual signal in the no-primary control (standard IHC practice).
⚠️Feasibility: A target-specific fixation window or fixation effect is unreported in the supplied evidence; the selected A06350 paraffin-section caption does not state a fixative (selected A06350 tissue-IHC caption). Retrieval dependence is also unreported, so compare antigen-retrieval conditions empirically on the positive tissue (standard IHC practice). The evidence does not establish whether frozen sections or IF are easier for C3AR1; when assessing appendix, distinguish specific lymphoid-cell staining from endogenous peroxidase signal (HPA: Medium in appendix lymphoid tissue; standard IHC practice).
HPA tissue IHC evidence for C3AR1
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Enhanced — External characterization data supports antibody staining but no internal RNA data available for correlation. Antibody staining in cells/structures not annotated, view images.). Rows are taken directly from the HPA tissue chart — click any row's HPA link to view the source.
Positive expression · recommended positive controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Appendix | Lymphoid tissue | Medium | Protein (IHC) | HPA → |
| Endometrium | Cells in endometrial stroma | Medium | Protein (IHC) | HPA → |
| Lung | Alveolar cells type I | Medium | Protein (IHC) | HPA → |
| Lymph node | Non-germinal center cells | Medium | Protein (IHC) | HPA → |
| Nasopharynx | 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 → |
| Adrenal gland | Glandular 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 C3AR1 IHC Tips
Troubleshoot C3AR1 staining in paraffin sections by checking retrieval, cellular context and controls before comparing chromogenic scores.
How should I retrieve C3AR1 in paraffin sections when staining is weak?
Start with citrate buffer at pH 6.0, heated to 95–98 °C for 20 min (page retrieval rule). After cooling, compare retrieved and unretrieved sections of the same tissue using the same antibody dilution and chromogenic development time (standard IHC control practice). Judge improvement in annotated cell populations, such as non-germinal center cells in tonsil, rather than by stronger stain across the entire section (HPA: Medium in tonsil non-germinal center cells). Excessive retrieval can damage tissue morphology or increase background (standard IHC practice); if staining remains weak, vary heating time on matched sections before changing buffer conditions.
Could fixation explain weak or uneven C3AR1 staining?
Target-specific fixation sensitivity is unknown: the selected A06350 image describes paraffin-embedded human brain tissue but does not report its fixative (A06350 tissue-IHC caption). Record the actual fixative, fixation duration and tissue thickness for each specimen before attributing a weak stain to fixation (standard IHC practice). Compare identically processed sections and hold citrate retrieval at pH 6.0, 95–98 °C for 20 min while assessing that variable (page retrieval rule). Check whether poor staining coincides with damaged morphology or varies across a specimen, and include a reliably stained control section in each run (standard IHC control practice).
Should C3AR1 staining be membranous or cytoplasmic in tissue?
C3AR1 is a cell-membrane receptor with 7 transmembrane segments (UniProt Q16581: localisation and topology). Tissue IHC may show mainly cytoplasmic staining in immune cells (HPA: tissue-IHC profile), so cytoplasmic signal alone does not establish an incorrect result. Score membrane and cytoplasmic staining separately in the intended cell population, recording whether either pattern is reproducible across sections (standard IHC scoring practice). Receptor phosphorylation is associated with arrestin binding and internalisation, but a chromogenic localisation pattern alone cannot establish that mechanism in a specimen (UniProt Q16581: ARRB1 interaction; standard interpretation). Check compartment assignments against morphology and a matched control before calling diffuse tissue staining specific (standard IHC control practice).
How do epitope position and modifications affect C3AR1 IHC interpretation?
UniProt lists 0 alternative isoforms for the 482-residue C3AR1 record, so an isoform-specific explanation requires independent evidence (UniProt Q16581: isoforms and chain). Its extracellular regions include residues 161–332, whereas the C-terminal 436–482 region is cytoplasmic (UniProt Q16581: topology). Reported glycosylation sites at 9, 194 and 266, and sulfotyrosines at 174, 184 and 318, make epitope identity relevant to interpretation (UniProt Q16581: modifications). The supplied caption does not identify the antibody epitope (A06350 tissue-IHC caption); request its mapped sequence before assigning a negative stain to modification or epitope masking (standard antibody-validation practice).
How can IF help resolve ambiguous C3AR1 chromogenic staining?
Use IF on a matched specimen to compare C3AR1 with a validated marker for the cell population being assessed, such as an immune-cell marker when examining lymphoid tissue (HPA: mainly cytoplasmic expression in immune cells; standard multiplex IF practice). Choose spectrally separated fluorophores and inspect an unstained section for tissue autofluorescence before interpreting overlap (standard IF practice). If the antibody epitope is cytoplasmic, optimise mild permeabilisation; for an extracellular epitope, first assess staining without permeabilisation, since the supplied caption does not map the epitope (UniProt Q16581: topology; A06350 tissue-IHC caption; standard IF practice). Include single-label controls and compare compartment patterns with the chromogenic result, without treating fluorescence overlap alone as proof of receptor identity (standard IF control practice).
What controls distinguish C3AR1 staining from chromogenic background?
Run a no-primary control to reveal secondary-reagent or detection background, and block endogenous peroxidase before peroxidase-based DAB development (standard chromogenic IHC practice). Compare staining with a matched section incubated with the synthesized peptide: the selected A06350 brain-tissue caption shows a peptide-blocked image, although it does not report fixation (A06350 tissue-IHC caption). Assess whether brown signal tracks intact cells or instead pools at section edges, damaged areas or deposits (standard IHC interpretation). Use consistent antibody incubation, wash and DAB development conditions across control and test sections (standard IHC control practice). Peptide competition supports an epitope-dependent signal but does not alone prove cell-type specificity (standard antibody-validation practice).
How should I score C3AR1 across differently cellular tissue regions? ⚠ ANSWER MARKED FOR VERIFICATION
Define the anatomic region and eligible cell population before scoring; lymphoid tissue is a relevant context because C3AR1 RNA is tissue enhanced there (HPA: RNA specificity). For chromogenic IHC, report the percentage of positive eligible cells and, when intensity is reproducible, an H-score using intensity categories of 0–3 (standard IHC scoring practice). If cells are sparse, report positive-cell density per mm² of viable, evaluated tissue (standard image-analysis practice). Normalise positive counts to all eligible cells in that region, or density to measured viable area, rather than total slide area (standard image-analysis practice). Keep thresholds, counterstain and imaging settings consistent across specimens, and score membrane and cytoplasmic patterns separately (standard IHC scoring practice).
When is a C3AR1-positive IHC pattern convincing rather than artefactual?
A convincing call combines reproducible cellular staining, appropriate controls and a documented compartment pattern; C3AR1 is a membrane receptor while HPA reports mainly cytoplasmic tissue staining in immune cells (UniProt Q16581: localisation; HPA: tissue-IHC profile; standard IHC interpretation). Evaluate the exact cell population: HPA reports medium staining in tonsil non-germinal center cells, but does not detect staining in adipocytes (HPA: tissue IHC). Treat isolated nuclear signal, edge-restricted colour and staining confined to necrotic areas as suspect until controls support them (standard IHC interpretation). Check no-primary sections for endogenous enzyme or detection background, and compare peptide-blocked sections where available (standard IHC control practice; A06350 tissue-IHC caption). A positive chromogenic signal alone cannot establish receptor activity (UniProt Q16581: signaling function; standard IHC interpretation).
Boster reagents
Best C3AR1 / C3a anaphylatoxin chemotactic receptor IHC Antibodies
A06350 has IHC data from paraffin-embedded human brain tissue and IF data from COS7 cells (catalog image captions); listed reactivity covers human, mouse, and rat (catalog: reactivity).
Real IHC data
Anti-C3AR1/C3Ar Antibody
Cat # A06350
A06350 is listed for IHC, IF, ICC, and ELISA in human, mouse, and rat (catalog: applications and reactivity). Its IHC image shows paraffin-embedded human brain tissue with a peptide-blocked comparison, and its IF image shows COS7 cells with a peptide-blocked comparison (catalog image captions).
Which to pick: For tissue IHC, choose A06350 based on its paraffin-embedded human brain image; the caption does not report the fixative (catalog: IHC image caption). For IF/ICC, choose A06350 because both applications are listed and an IF image is provided for COS7 cells (catalog: applications and IF image caption). A06350 is a polyclonal option listed as reactive with human, mouse, and rat, though the IHC image documents human tissue only (catalog: dilution_raw, reactivity, and IHC image caption).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry Q16581 (C3AR_HUMAN, C3a anaphylatoxin chemotactic receptor).
- Human Protein Atlas. C3AR1 tissue IHC expression (reliability: Enhanced).
- Human Protein Atlas. C3AR1 subcellular location (ICC-IF): Membrane.
- Human Protein Atlas. C3AR1 antibody validation summary (1 antibodies).
- C3AR1 as a target for preeclampsia: from bioinformatics and network pharmacology to experimental validation. BMC pregnancy and childbirth 2025 — PMC11780793.
- Prognostic marker C3AR1 is associated with ovarian cancer cell proliferation and immunosuppression in the tumor microenvironment. Journal of ovarian research 2023 — PMC10067206.
- Complement 3a receptor in dorsal horn microglia mediates pronociceptive neuropeptide signaling. Glia 2017 — PMC5747931.
- Identification of pivotal genes and regulatory networks associated with atherosclerotic carotid artery stenosis based on comprehensive bioinformatics analysis and machine learning. Frontiers in pharmacology 2024 — PMC11061441.
- PubMed PMID:8605247 — UniProt-cited evidence.
- PubMed PMID:8765043 — UniProt-cited evidence.
- PubMed PMID:8702752 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for C3AR1 (C3a anaphylatoxin chemotactic receptor). Expected localisation Immune-cell cytoplasm (HPA tissue IHC); cell membrane (UniProt). Antigen retrieval: Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen). Validated IHC antibody: A06350 at 1:100 - 1:300 (the product's own IHC validation image is shown). Controls (HPA): positive Appendix (Lymphoid tissue); negative Adipose tissue. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded human brain tissue; fixative not specified (datasheet A06350); 2. Fixation: Image fixative and duration unreported (datasheet A06350); verify before use.; 3. Sectioning: 4–5 µm sections on charged slides (standard); 4. Deparaffinisation: Xylene, graded ethanol series to water (standard); 5. Antigen retrieval: Heat-induced epitope retrieval in citrate buffer, pH 6.0 , 20 min at 95–98 °C…; 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% normal serum of the secondary host, 30 min , room temperature (standard); 8. Primary antibody: Rabbit anti-C3AR1, 1:100 - 1:300 (datasheet A06350); 9. Primary incubation: Overnight at 4 °C (standard). Watch for: Fixation: Keep formalin fixation consistent across paraffin sections (standard IHC practice; not target-specific); Caveat: ARRB1-associated receptor internalization may alter the pattern (UniProt); Isoform / epitope: 0 isoforms annotated; epitopes may face outside or cytoplasm (UniProt); Regulation: Expression regulators are not specified (UniProt). Evidence: UniProt Q16581, HPA tissue IHC · Enhanced, HPA ICC-IF · Membrane, Datasheet A06350, PMC11780793, PMC11061441. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/C3AR1/immunohistochemistry-ihc-guide.