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C3AR1 / C3a anaphylatoxin chemotactic receptor · IHC design guide
Design Immunohistochemistry for C3AR1
Plan C3AR1 staining in paraffin sections using an IHC-validated antibody at 1:100–1:300 (datasheet). Use cytoplasmic staining in immune cells as the tissue reference (HPA tissue IHC), while considering the receptor’s membrane topology when interpreting the pattern (UniProt).
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 fixation consistent across sections (standard IHC practice; not target-specific) | |
| Caveat | Phosphorylation-associated internalization may shift staining (UniProt) | |
| Regulation | Expression regulation not specified (UniProt) | |
| Isoform / epitope | No isoforms or processing noted; epitope side matters (UniProt) |
Section 1
Recommended C3AR1 IHC & IF Protocols
The catalog antibody’s IHC-P protocol is accompanied by published protocols for placental, ovarian, and carotid tissues (PMC11780793; PMC10067206; 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 antigen retrieval rule); the carotid protocol reports a different heating schedule (PMC11061441).
Section 2
What Is the Expected C3AR1 Staining Pattern?
C3AR1 is a 7-transmembrane cell-membrane receptor (UniProt Q16581 topology). In tissue IHC, expect mainly cytoplasmic staining in immune cells, with medium staining reported in lymphoid tissue and non-germinal-center cells (HPA: tissue IHC profile and levels). HPA rates its tissue staining “Enhanced”: external characterization supports staining, but internal RNA data are unavailable for correlation (HPA: reliability description).
| Discrete staining in immune cells, including non-germinal-center cells in lymph node or tonsil (HPA: tissue IHC). | This fits the reported mainly cytoplasmic immune-cell profile; both named cell populations show medium staining (HPA: tissue IHC). A membrane rim may fit the receptor's topology, but HPA's tissue images do not require a crisp rim in every positive cell (UniProt Q16581 topology; HPA: tissue IHC profile). |
| Predominantly nuclear staining, without a convincing immune-cell pattern. | A nuclear-only result conflicts with the membrane receptor annotation and HPA's mainly cytoplasmic IHC profile (UniProt Q16581 subcellular location; HPA: tissue IHC). Treat it as suspect, then compare the positive control and detection controls before assigning a cause (general IHC practice). |
| Strong staining in a cell population reported as undetected, such as adipocytes. | Adipocytes are “Not detected” in the supplied HPA tissue IHC data (HPA: adipose tissue). Consider cross-reactivity or endogenous detection activity; the discrepancy alone cannot distinguish them (general IHC practice). Do not classify every nonimmune cell as false positive: HPA also reports medium staining in several named nonimmune populations (HPA: tissue IHC). |
| Uniform colour across tissue, stroma, or section edges, without cell-specific contrast. | A diffuse pattern does not resemble HPA's mainly cytoplasmic immune-cell profile (HPA: tissue IHC). Background from detection chemistry or nonspecific binding is plausible; check a control lacking primary antibody and inspect the staining distribution before scoring cells (general IHC practice). |
| No staining in lymph node or tonsil non-germinal-center cells. | Both populations are reported at medium intensity, so a blank result raises concern about the run or specimen (HPA: tissue IHC). Confirm that expected cells are present, then review the catalog antibody's IHC-P conditions and the run controls; one negative section does not establish C3AR1 absence (general IHC practice). |
💡Expected C3AR1 appearanceCall a result positive when identifiable immune cells show mainly cytoplasmic staining of roughly medium intensity in the named positive populations; isolated nuclear colour or uniform section-wide colour is suspect (HPA: tissue IHC profile and levels; UniProt Q16581 subcellular location).
| Compartment and receptor topology | UniProt places C3AR1 at the cell membrane with 7 transmembrane segments, while HPA describes tissue staining as mainly cytoplasmic (UniProt Q16581 topology; HPA: tissue IHC profile). Interpret both annotations together; cytoplasmic IHC colour alone is not proof of mislocalization or receptor internalization. |
| Choice of positive and comparison tissue | Lymph node and tonsil non-germinal-center cells, and appendix lymphoid tissue, are reported at medium staining (HPA: tissue IHC). Adipocytes are reported “Not detected,” making that named population a useful comparison; this does not certify the whole adipose section as C3AR1-free (HPA: adipose tissue). |
| Strength of the tissue evidence | HPA assigns “Enhanced” reliability to tissue staining and lists antibody CAB009405 as IHC Enhanced (HPA: reliability and antibody validation). Its reliability description also says internal RNA data are unavailable for correlation; use morphology and controls when evaluating an unexpected cell type (HPA: reliability description; general IHC practice). |
| Epitope and molecular modification limits | UniProt lists extracellular and cytoplasmic regions and 3 glycosylation sites (UniProt Q16581 topology and glycosylation). The supplied record does not locate the catalog antibody's epitope, so it cannot predict whether retrieval or permeabilisation will expose that epitope (UniProt Q16581 topology; supplied antibody data). |
| Situation | Likely cause | Next action |
|---|---|---|
| No signal in a named positive tissue. | The expected cell population may be absent, or the IHC run may have failed; the result alone cannot identify which (HPA: tissue IHC; general IHC practice). | Find non-germinal-center cells in lymph node or tonsil, review run controls, and check the catalog antibody's IHC-P instructions before changing conditions (HPA: tissue IHC; general IHC practice). |
| Colour is diffuse or appears on nearly every structure. | Nonspecific staining or detection background may obscure the reported mainly cytoplasmic immune-cell pattern (HPA: tissue IHC profile; general IHC practice). | Compare a control lacking primary antibody, examine section edges and tissue architecture, and adjust blocking or detection only in response to the control result (general IHC practice). |
| Nuclei dominate the staining. | A nuclear-only pattern conflicts with the reported membrane location and mainly cytoplasmic IHC profile; its mechanism is unresolved (UniProt Q16581 subcellular location; HPA: tissue IHC). | Check the counterstain and control without primary antibody, then judge whether any identifiable immune cells retain the expected cytoplasmic pattern (general IHC practice; HPA: tissue IHC profile). |
| An unexpected cell population stains strongly. | Cross-reactivity or endogenous detection activity is possible, but tissue context matters: HPA reports some nonimmune populations at medium intensity (HPA: tissue IHC; general IHC practice). | Name the stained cell type before scoring it. Compare its HPA entry, nearby expected cells, and detection controls; avoid calling all nonimmune staining erroneous (HPA: tissue IHC; general IHC practice). |
| Adipocytes stain despite the HPA comparison. | HPA reports adipocytes as “Not detected”; staining could reflect technical background or a sample difference, which one section cannot resolve (HPA: adipose tissue; general IHC practice). | Verify adipocyte identity and check a control lacking primary antibody; use a named positive cell population from the same run to assess whether the assay behaved as expected (HPA: tissue IHC; general IHC practice). |
| Q: Should IF/ICC show a clear membrane rim? | A: HPA summarizes subcellular location as “Membrane” but supplies no ICC-IF image cell lines or main-location detail (HPA: subcellular record). | Use the separate IF/ICC guide for that application. Here, treat a membrane signal as compatible with UniProt topology, without requiring an IF pattern that the supplied HPA record has not documented (UniProt Q16581 topology; HPA: subcellular record). |
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: lymphoid tissue should show C3AR1 staining at the HPA Medium level (HPA: Appendix, lymphoid tissue, Medium). Use adipose tissue as the biological comparison: adipocytes should show no specific staining (HPA: Adipose tissue, adipocytes, Not detected); other cells on the appendix slide should provide a background reference, though HPA does not identify a specific internal negative cell type (HPA: Appendix row).
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 no-primary (secondary-only) and antibody-matched controls: isotype-matched IgG for a monoclonal primary or host-matched nonimmune IgG for a polyclonal primary (standard IHC practice). Add a C3AR1 knockout control if available, or a peptide-block control as shown for the catalog antibody, and quench endogenous peroxidase when using chromogenic detection in lymphoid tissue (catalog antibody A06350 caption: peptide block; standard IHC practice).
⚠️Feasibility: A target-specific fixation window and the effect of antigen retrieval are unreported in the supplied evidence; optimize retrieval on paraffin sections and assess staining against the controls (supplied HPA rows and catalog antibody A06350 caption; standard IHC practice). The selected catalog caption shows paraffin-embedded brain tissue but does not state the fixative, so it does not establish fixation (catalog antibody A06350 caption). Frozen sections or IF cannot be judged easier from these sources; for appendix, watch for endogenous peroxidase signal in leukocyte-rich areas (HPA: Appendix, lymphoid tissue; standard IHC practice). The selected A06350 tissue-IHC caption documents paraffin sections, but does not specify the fixative (selected-SKU IHC image A06350).
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 distribution, controls and scoring against the available tissue evidence.
How should I retrieve C3AR1 in paraffin sections with weak staining?
Start with citrate buffer at pH 6.0, heated to 95–98 °C for 20 min (page retrieval rule). Run a known staining section beside the test section and keep section thickness, cooling time and antibody incubation consistent, so a retrieval change is interpretable (standard IHC practice). If staining remains weak, compare a longer citrate incubation or an alternative buffer on adjacent sections, watching for tissue damage and increased background (standard IHC practice). Interpret gains in the context of C3AR1's seven transmembrane segments and extensive extracellular loop, whose epitopes may respond differently to processing (UniProt Q16581 topology).
Could fixation explain weak or uneven C3AR1 staining?
C3AR1-specific sensitivity to fixation is unknown from the supplied evidence; the catalog image identifies paraffin-embedded human brain tissue but does not state its fixative (catalog antibody A06350 caption). Record the fixative, duration, tissue thickness and time to fixation for each specimen before comparing stain intensity across cases (standard IHC practice). If an uneven pattern tracks poorly preserved regions, compare well-preserved areas on the same section and review a routine morphology stain (standard IHC practice). Keep retrieval at citrate pH 6.0, 95–98 °C for 20 min while assessing fixation as a separate variable (page retrieval rule).
Should C3AR1 appear on the membrane or in the cytoplasm?
Expect a membrane component because C3AR1 is a seven transmembrane receptor assigned to the cell membrane (UniProt Q16581 subcellular location and topology). Cytoplasmic staining can also warrant examination: the tissue atlas describes mainly cytoplasmic expression in immune cells, while receptor internalization is associated with ARRB1 interaction after phosphorylation (HPA tissue IHC profile; UniProt Q16581 subunit). Compare intact cell borders with intracellular staining at high magnification, using the same chromogen exposure across sections (standard IHC practice). Do not classify diffuse staining as specific solely because it is cytoplasmic; check cell identity, morphology and controls, especially where immune cells are sparse (HPA tissue IHC profile; standard IHC practice).
How do epitope location and modifications affect C3AR1 IHC interpretation?
The supplied record lists 0 isoforms, so do not assign different staining patterns to a documented C3AR1 splice isoform (UniProt Q16581 isoforms). Ask which sequence the IHC-validated antibody recognizes before interpreting a membrane or cytoplasmic pattern: C3AR1 has extracellular residues 161–332 and a cytoplasmic tail at 436–482 (UniProt Q16581 topology). Glycosylation is annotated at residues 9, 194 and 266, with sulfotyrosines in the extracellular region and phosphorylation sites near the tail (UniProt Q16581 modifications). If the epitope is undisclosed, compare peptide blocking, tissue distribution and morphology without claiming that a particular modification caused staining loss (catalog antibody A06350 caption; standard IHC practice).
How can IF help resolve ambiguous chromogenic C3AR1 staining?
Use IF as a complementary localisation check and multiplex C3AR1 with a validated marker for the suspected immune cell population, because tissue IHC reports mainly cytoplasmic expression in immune cells (HPA tissue IHC profile; standard IF practice). Choose spectrally separated fluorophores after checking tissue autofluorescence with an unstained control, and acquire single stain controls before interpreting overlap (standard IF practice). Set permeabilisation according to the antibody's mapped epitope: an extracellular epitope may be accessible without it, whereas the cytoplasmic tail requires membrane access (UniProt Q16581 topology; standard IF practice). Compare IF with chromogenic IHC by cell type and compartment, rather than assuming identical signal intensity across detection methods (standard IHC/IF practice).
What controls help distinguish C3AR1 signal from background?
Include a no primary control and examine whether diffuse chromogen persists after primary antibody omission; persistent colour points to detection or tissue background (standard IHC practice). Apply the routine endogenous peroxidase block before chromogenic detection and inspect pigment, folds and damaged tissue separately from cellular staining (standard IHC practice). The catalog brain section has an accompanying synthetic peptide blocked image, which supports an antibody competition check for that image but does not establish every stained cell's identity (catalog antibody A06350 caption). Compare staining in lymphoid tissue with an appropriate low staining cell population, while keeping exposure and counterstain consistent (HPA tissue IHC profile; standard IHC practice).
How should C3AR1 staining be scored across tissue sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the cell population and compartment before scoring, since the tissue atlas describes mainly cytoplasmic staining in immune cells and medium staining in several lymphoid tissue populations (HPA tissue IHC profile). For a chromogenic assay, record the percentage of positive eligible cells and an H-score based on intensity categories; keep thresholds fixed across a batch (standard IHC practice). Where infiltrating cells are the question, count positive cells per mm² of viable tissue and normalise against all cells of the same lineage or the sampled area (standard IHC practice). Exclude folds and necrosis, then report section count, fields sampled and the chosen denominator (standard IHC practice).
When is apparent C3AR1 positivity likely to be an artefact?
A credible pattern fits cell identity and localisation: C3AR1 is assigned to the cell membrane, while tissue IHC reports mainly cytoplasmic expression in immune cells (UniProt Q16581 subcellular location; HPA tissue IHC profile). Be cautious with strong nuclear only colour, staining confined to section edges, or deposits over necrosis; compare intact central tissue and a no primary control (standard IHC practice). Check that endogenous peroxidase has been blocked before attributing residual chromogen to receptor staining (standard IHC practice). The catalog peptide blocked brain image offers a competition reference, but a positive call still needs preserved morphology and a plausible cell distribution (catalog antibody A06350 caption; standard IHC practice).
Boster reagents
Best C3AR1 / C3a anaphylatoxin chemotactic receptor IHC Antibodies
A06350 offers IHC data from paraffin-embedded human brain and IF data from COS7 cells (catalog image captions); its listed reactivity is human, mouse and rat (catalog reactivity).
Real IHC data
Anti-C3AR1/C3Ar Antibody
Cat # A06350
A06350 will render with its IHC image of paraffin-embedded human brain and a peptide-blocked comparison (catalog IHC caption). The same SKU lists IHC, IF and ICC applications and human, mouse and rat reactivity; its separate IF image shows COS7 cells (catalog applications, reactivity and IF caption).
Which to pick: Choose A06350 for paraffin-section IHC because its own IHC caption shows human brain tissue processed that way (catalog IHC caption); the fixative is unreported (catalog IHC caption). A06350 is also the listed IF/ICC option, supported by an IF image of COS7 cells and an ICC application listing (catalog IF caption and applications). For human, mouse or rat samples, A06350 is the listed cross-species choice, with rabbit polyclonal host and human, mouse and rat reactivity (catalog host, dilution_raw and reactivity).
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 fixation consistent across sections (standard IHC practice; not target-specific); Caveat: Phosphorylation-associated internalization may shift staining (UniProt); Isoform / epitope: No isoforms or processing noted; epitope side matters (UniProt); Regulation: Expression regulation not specified (UniProt). Evidence: UniProt Q16581, HPA tissue IHC · Enhanced, HPA ICC-IF · Membrane, Datasheet A06350, PMC11780793, PMC10067206. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/C3AR1/immunohistochemistry-ihc-guide.