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ARHGAP18 / Rho GTPase-activating protein 18 · IHC design guide
Design Immunohistochemistry for ARHGAP18
This guide helps plan ARHGAP18 IHC in paraffin sections around cytoplasmic staining, with membranous staining in a few tissues (HPA tissue IHC). It covers fixation, tissue controls and compartment-based scoring, using A08418 at 1:100–1:300 as a starting dilution (datasheet: A08418).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
ARHGAP18 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 | Predominantly cytoplasmic; membranous in a few tissues (HPA tissue IHC) | |
| Staining pattern | General cytoplasmic staining; membranous in a few tissues (HPA tissue IHC) | |
| Antigen retrieval | Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen) | |
| Positive control | Adrenal gland+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 paraffin-section fixation consistent across samples. (standard IHC practice; not target-specific) | |
| Caveat | Staining and RNA expression show medium consistency (HPA tissue IHC) | |
| Regulation | Expression regulation is not annotated (UniProt) | |
| Isoform / epitope | Two isoforms; no extracellular domain; epitope map unknown (UniProt) |
Section 1
Recommended ARHGAP18 IHC & IF Protocols
Compare the catalog antibody’s IHC-P protocol with the published ARHGAP18 IHC protocol for human invasive breast carcinoma (PMC5674094).
| Sample | Paraffin-embedded human brain tissue; fixative not specified (datasheet A08418) |
| Fixation | Image fixative and duration unreported (datasheet A08418); 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-ARHGAP18, 1:100-1:300 (datasheet A08418) |
| 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 | ARHGAP18-positive staining in glandular cells of adrenal gland (HPA tissue IHC: High). HPA tissue profile: General cytoplasmic expression with additional membranous expression in a few tissues. 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); the published protocol used microwave heating (PMC5674094: IHC methods).
Section 2
What Is the Expected ARHGAP18 Staining Pattern?
ARHGAP18 is cytoplasmic, with no transmembrane segment (UniProt Q8N392 topology). In paraffin-section IHC, expect mainly cytoplasmic staining in selected glandular, basal and ciliated cells; a few tissues also show membranous staining (HPA tissue IHC). HPA rates the tissue profile Approved, with medium consistency between staining and RNA data and external verification pending (HPA tissue IHC).
| Cytoplasmic staining is strong in pancreatic exocrine glandular cells or duodenal glandular cells. | This matches two documented High cell populations (HPA tissue IHC). Assess the named cells rather than treating every cell in either section as a positive control (HPA tissue IHC). |
| Basal cells in bronchus or ciliated cell bodies in fallopian tube stain strongly. | Both are documented High populations (HPA tissue IHC). Cytoplasmic signal fits the principal location (UniProt Q8N392; HPA tissue IHC); signal limited to a different compartment warrants review. |
| A section shows only nuclear staining, with no convincing cytoplasmic signal. | A nuclear-only IHC pattern conflicts with the principal cytoplasmic profile (UniProt Q8N392; HPA tissue IHC). Review counterstain and detection artefacts before assigning it to ARHGAP18 (standard IHC practice). |
| Adipocytes or parathyroid glandular cells stain as strongly as the chosen positive cells. | Those cell populations are reported as Not detected (HPA tissue IHC). Unexpected staining raises possible cross-reactivity or endogenous detection activity; the Approved profile still awaits external verification (HPA tissue IHC). |
| Colour spreads across tissue and empty spaces, or a documented positive population has no signal. | A widespread deposit lacks the expected cell and compartment pattern (HPA tissue IHC); check background controls (standard IHC practice). Absence from a High population calls for a technical check, not an immediate biological conclusion (HPA tissue IHC; standard IHC practice). |
💡Expected ARHGAP18 appearanceA convincing positive shows predominantly cytoplasmic High staining in documented cells such as pancreatic exocrine or bronchial basal cells (HPA tissue IHC); nuclear-only signal or similarly strong staining in documented negative cells is suspect (UniProt Q8N392; HPA tissue IHC).
| Cell type and compartment | HPA describes general cytoplasmic expression with additional membranous staining in a few tissues (HPA tissue IHC). Score the documented cell population and its distribution together; membrane accent alone is insufficient to identify a positive cell (HPA tissue IHC). |
| Strength of reference tissue | Pancreatic exocrine, duodenal glandular and bronchial basal cells are High; adipocytes are Not detected (HPA tissue IHC). These observations guide comparison within an IHC run, while HPA's medium consistency limits certainty (HPA tissue IHC). |
| Antibody evidence | HPA031595 is IHC Approved, and the tissue profile has medium consistency with RNA data and awaits external verification (HPA antibodies; HPA tissue IHC). Treat an unexpected pattern as a finding to check, not as independently established specificity. |
| Isoforms and epitope scope | UniProt lists 2 ARHGAP18 isoforms (UniProt Q8N392). The supplied record gives no antibody epitope or isoform coverage, so staining alone cannot identify which isoform contributes to a positive cell. |
| Detection chemistry | Endogenous enzyme activity or residual reagent can create chromogenic background (standard IHC practice). Use appropriate detection controls when colour appears outside the documented cell and compartment pattern (HPA tissue IHC; standard IHC practice). |
| Situation | Likely cause | Next action |
|---|---|---|
| No signal in pancreatic exocrine glandular cells. | They are reported High (HPA tissue IHC); a failed stain is possible (standard IHC practice). | Check section integrity, antibody incubation, detection reagents and the IHC-P workflow used for this run (standard IHC practice). |
| Only weak signal appears in a documented high population. | The observed level differs from HPA's High call, though that call has medium consistency with RNA data (HPA tissue IHC). | Compare a second documented high population and review retrieval and antibody working conditions using the validated IHC-P procedure (HPA tissue IHC; standard IHC practice). |
| Staining is predominantly nuclear. | The principal location is cytoplasmic (UniProt Q8N392; HPA tissue IHC). | Compare with a documented positive cell population and review counterstain, detection controls and compartment scoring (HPA tissue IHC; standard IHC practice). |
| Adipocytes or parathyroid glandular cells stain strongly. | Both populations are Not detected in the HPA tissue profile (HPA tissue IHC). | Check background and endogenous-activity controls, then reassess antibody specificity before scoring these cells as positive (standard IHC practice; HPA tissue IHC). |
| Colour is diffuse across cells and tissue spaces. | That distribution lacks the expected cytoplasmic, cell-associated pattern (HPA tissue IHC). | Review blocking, washing and detection controls; compare cellular boundaries with the counterstain (standard IHC practice). |
| Q: Can ICC-IF establish the subcellular pattern? | HPA reports supported cytosolic localization; nuclear speckles and plasma membrane are uncertain additional locations (HPA subcellular ICC-IF). | A: Use the separate IF/ICC guide for that application; interpret its additional locations with HPA's stated uncertainty (HPA subcellular ICC-IF). |
Experiment evidence
IHC & IF images showing ARHGAP18 staining
A08418 · IHCImmunohistochemistryt analysis of paraffin-embedded human brain, using RHG18 Antibody. The lane on the right is blocked with the RHG18 pepti
A08418-1 · IFImmunocytochemistry of ARHGAP18 in 3T3 cells with ARHGAP18 antibody at 2.5 μg/mL.
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000146376-ARHGAP18/tissue/cerebral+cortex#imid_11205847
HPA · Adrenal glandHuman Protein Atlas IHC, Adrenal gland. Source: https://www.proteinatlas.org/ENSG00000146376-ARHGAP18/tissue/adrenal+gland#imid_11205823
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000146376-ARHGAP18/tissue/colon#imid_11205781
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000146376-ARHGAP18/tissue/liver#imid_11205782
HPA · ICC-IF Hep-G2Human Protein Atlas immunofluorescence, Hep-G2, antibody HPA031595; green = ARHGAP18, blue = nucleus, red = microtubules.
HPA · ICC-IF Hep-G2Human Protein Atlas immunofluorescence, Hep-G2, antibody HPA031595; green = ARHGAP18, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for ARHGAP18 IHC & IF
🧪Run adrenal gland first and require staining in its glandular cells (HPA: High in adrenal gland glandular cells); use adipose tissue as the negative comparator and score its adipocytes (HPA: Not detected in adipocytes). On the adrenal slide, non-glandular cells can serve as internal negatives if they show only counterstain and background chromogen; their negative status must be confirmed on that slide (HPA: High designation applies to glandular cells).
Positive control tissue: Adrenal gland (Glandular cells, HPA High)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show ARHGAP18 in Hep-G2, U-251MG, U2OS, RPTEC/TERT1, with annotated localisation: Cytosol (supported) (HPA subcellular).
Technical controls: Include no-primary/secondary-only and isotype controls matched to the primary antibody’s host species, immunoglobulin class, and clonality; assess specificity with knockout material or a peptide block (catalog caption: A08418 peptide-block condition). For adrenal chromogenic IHC, quench endogenous peroxidase and inspect tissue pigment before scoring; block endogenous biotin if using biotin-based detection (standard IHC practice).
⚠️Feasibility: A target-specific fixation window or fixation effect is unreported, and the selected A08418 paraffin-section caption does not state a fixative (catalog caption: fixative unreported). Retrieval dependence is unreported; compare retrieval conditions on paraffin sections and assess the expected cytoplasmic signal (UniProt: Cytoplasm; HPA: cytosol supported). The supplied evidence does not establish whether frozen sections or IF/ICC are easier, despite HPA ICC-IF images for this gene; adrenal pigment may complicate chromogen scoring and should be checked on the no-primary slide (HPA: ICC-IF cell lines listed; standard IHC practice).
HPA tissue IHC evidence for ARHGAP18
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Approved — Medium consistency between antibody staining and RNA expression data. Pending external verification.). 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 |
|---|---|---|---|---|
| Adrenal gland | Glandular cells | High | Protein (IHC) | HPA → |
| Bronchus | Basal cells | High | Protein (IHC) | HPA → |
| Cervix | Glandular cells | High | Protein (IHC) | HPA → |
| Duodenum | Glandular cells | High | Protein (IHC) | HPA → |
| Epididymis | Glandular cells | High | Protein (IHC) | HPA → |
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Adipose tissue | Adipocytes | Not detected | Protein (IHC) | HPA → |
| Cerebellum | Cells in granular layer | Not detected | Protein (IHC) | HPA → |
| Hippocampus | Glial cells | Not detected | Protein (IHC) | HPA → |
| Liver | Cholangiocytes | Not detected | Protein (IHC) | HPA → |
| Ovary | Ovarian stroma cells | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced ARHGAP18 IHC Tips
Troubleshoot ARHGAP18 staining in paraffin sections using compartment, cell type, and staining controls; interpret IF/ICC separately.
What should I adjust when ARHGAP18 staining is weak after retrieval?
Start with citrate buffer at pH 6.0 for heat-induced antigen retrieval at 95–98 °C for 20 minutes (page retrieval rule: cytoplasmic / membrane antigen). Keep section thickness, cooling, antibody incubation, and chromogen development consistent while comparing retrieval runs (standard IHC practice). If staining remains weak, test a more alkaline retrieval buffer on adjacent sections as a fallback, while checking whether tissue morphology or background deteriorates (standard IHC practice). Score cytoplasmic staining in an expected positive cell population, such as adrenal glandular cells, rather than treating any increase in overall brown signal as improvement (HPA: High in adrenal glandular cells; UniProt Q8N392: cytoplasm).
How can I troubleshoot variable ARHGAP18 staining between paraffin blocks?
Target-specific fixation sensitivity is unknown: the selected antibody caption identifies paraffin-embedded human brain but does not state the fixative (A08418 tissue-IHC caption). Record the fixative, fixation duration, tissue thickness, processing history, and block age for each specimen before attributing differences to ARHGAP18 biology (standard IHC practice). Compare adjacent sections under one retrieval and detection workflow, with a positive-control section in every run to reveal technical drift (standard IHC practice). If morphology is poor or staining varies across a block, inspect processing records and repeat on better-preserved material where available; HPA staining patterns and protein features do not establish this antigen’s fixation tolerance (standard IHC practice; HPA tissue IHC; UniProt Q8N392).
Should ARHGAP18 appear at the membrane or in the nucleus?
Expect predominantly cytoplasmic staining in chromogenic sections (UniProt Q8N392: cytoplasm; HPA tissue IHC: general cytoplasmic expression). HPA also reports membranous staining in a few tissues, while its cell-imaging data support cytosol and mark plasma membrane and nuclear speckles as uncertain additional locations (HPA tissue IHC; HPA subcellular). Compare any sharp membrane or nuclear pattern with adjacent-cell staining, morphology, and a no-primary control before calling it specific (standard IHC practice). ARHGAP18 has no transmembrane segment, so membrane-associated staining should be interpreted cautiously rather than assumed to represent an integral membrane protein (UniProt Q8N392 topology; standard IHC practice).
Could isoforms or epitope accessibility explain inconsistent ARHGAP18 staining?
ARHGAP18 has 2 annotated isoforms, but the supplied record does not map this antibody’s epitope onto either one (UniProt Q8N392: isoforms 1 and 2; A08418 tissue-IHC caption). Check the antibody’s documented immunogen or epitope before interpreting a negative section as absence of both isoforms (standard IHC practice). The Rho-GAP domain spans residues 324–523, and several phosphorylation sites are annotated; neither fact establishes that this antibody recognizes a particular domain or modification (UniProt Q8N392). For uncertain staining, compare the catalog antibody with an independently validated antibody against a documented distinct epitope, using matched sections and the same scoring rules (standard IHC practice).
How should I check ARHGAP18 localisation by IF alongside tissue IHC?
Treat IF/ICC as a separate validation experiment; the supplied A08418 tissue caption documents paraffin-section IHC only (A08418 tissue-IHC caption). Multiplex ARHGAP18 with a validated marker for the expected cell population, such as glandular cells in adrenal tissue, and assess colocalisation within individual cells (HPA: High in adrenal glandular cells; standard IF practice). Choose a fluorophore and imaging channel after measuring tissue autofluorescence, favoring a longer-wavelength channel when shorter wavelengths have substantial background (standard IF practice). Because ARHGAP18 is mainly cytosolic and has no transmembrane segment, use controlled permeabilisation to expose intracellular epitopes, then compare permeabilised and minimally permeabilised preparations with appropriate single-stain controls (HPA subcellular: supported cytosol; UniProt Q8N392 topology; standard IF practice).
What causes diffuse brown background in ARHGAP18 paraffin sections?
First distinguish diffuse deposit from the predominantly cytoplasmic cellular pattern expected for ARHGAP18 (HPA tissue IHC; UniProt Q8N392: cytoplasm). Run no-primary and detection-only controls, inspect reagent carryover, and verify that washes remove unbound antibody between steps (standard chromogenic IHC practice). With peroxidase-based detection, check the endogenous peroxidase block and shorten chromogen development if control sections also darken; these are general workflow checks, not ARHGAP18-specific evidence (standard chromogenic IHC practice). Compare background in morphologically intact cells with staining at folds, torn edges, or necrotic areas, and adjust blocking or antibody concentration only after identifying which component produces the signal (standard IHC practice).
How should I quantify ARHGAP18 staining across tissue sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the cell population and compartment before scoring: ARHGAP18 is mainly cytoplasmic, and HPA reports different levels among specified cell types (UniProt Q8N392: cytoplasm; HPA tissue IHC). For comparable regions, use an H-score based on staining intensity and percentage of positive target cells, or report percentage positive alone when intensity cannot be measured reproducibly (standard IHC practice). Normalize cell counts to the number of eligible cells; if measuring stained-cell density, report cells per mm² of viable tissue and use the same region-selection rule across sections (standard IHC practice). Keep retrieval, imaging, counterstain, and scoring thresholds consistent, and record excluded folds and necrosis before comparing groups (standard IHC practice).
When is a brown ARHGAP18 signal credible rather than artefactual?
A credible result has cellular staining in the expected compartment and cell type, such as cytoplasmic signal in adrenal glandular cells (UniProt Q8N392: cytoplasm; HPA: High in adrenal glandular cells). Check unexpected strong nuclear-only staining or signal assigned to a cell population reported as undetected, such as adipocytes, against morphology and controls before calling it positive (HPA: Not detected in adipocytes; standard IHC practice). Discount isolated staining at section edges, folds, and necrotic areas, and exclude residual endogenous enzyme signal using a no-primary control (standard chromogenic IHC practice). The selected paraffin-brain image includes a peptide-blocked comparison, but that control alone does not establish staining specificity in every tissue (A08418 tissue-IHC caption; standard IHC practice).
Boster reagents
Best ARHGAP18 / Rho GTPase-activating protein 18 IHC Antibodies
The catalog includes human- and mouse-reactive antibodies for IHC and IF (catalog: A08418 applications/reactivity), plus a rat-reactive IF/ICC option (catalog: A08418-1 applications/reactivity). Figures show paraffin-section IHC and cell IF/ICC (image captions).
Real IHC data
Anti-ARHGAP18 Antibody
Cat # A08418
Real IF data
Anti-ARHGAP18 Antibody
Cat # A08418-1
A08418 is listed for human and mouse IHC and IF; its IHC figure shows paraffin-embedded human brain (catalog: A08418 applications/reactivity; A08418 IHC image caption). A08418-1 is listed for human, mouse and rat IF/ICC, with IF/ICC figures in 3T3 cells (catalog: A08418-1 applications/reactivity; A08418-1 IF image captions).
Which to pick: Choose A08418 for paraffin-section tissue IHC: IHC is listed and its own figure shows paraffin-embedded human brain; the fixative is unreported (catalog: A08418 applications; A08418 IHC image caption). Choose A08418-1 for IF/ICC in cells because those applications are listed and its own figures show 3T3 cells; it also has the broader listed species reactivity, including rat (catalog: A08418-1 applications/reactivity; A08418-1 IF image captions). Both antibodies are rabbit-hosted, with no clone reported (catalog: A08418 and A08418-1 host/clone).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry Q8N392 (RHG18_HUMAN, Rho GTPase-activating protein 18).
- Human Protein Atlas. ARHGAP18 tissue IHC expression (reliability: Approved).
- Human Protein Atlas. ARHGAP18 subcellular location (ICC-IF): Mainly localized to the cytosol. In addition localized to the nuclear speckles and plasma membrane..
- Human Protein Atlas. ARHGAP18 antibody validation summary (1 antibodies).
- Rho-GTPase activating-protein 18: a biomarker associated with good prognosis in invasive breast cancer. British journal of cancer 2017 — PMC5674094.
- The somatostatin analogue octreotide inhibits growth of small intestine neuroendocrine tumour cells. PloS one 2012 — PMC3485222.
- Thiopurines correct the effects of autophagy impairment on intestinal healing - a potential role for ARHGAP18/RhoA. Disease models & mechanisms 2021 — PMC8084572.
- Tenofovir Modulates Semaphorin 4D Signaling and Regulates Bone Homeostasis, Which Can Be Counteracted by Dipyridamole and Adenosine A2A Receptor. International journal of molecular sciences 2021 — PMC8583797.
- PubMed PMID:17974005 — UniProt-cited evidence.
- PubMed PMID:14574404 — UniProt-cited evidence.
- PubMed PMID:15489334 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for ARHGAP18 (Rho GTPase-activating protein 18). Expected localisation Predominantly cytoplasmic; membranous in a few tissues (HPA tissue IHC). Antigen retrieval: Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen). Validated IHC antibody: A08418 at 1:100-1:300 (the product's own IHC validation image is shown). Controls (HPA): positive Adrenal gland (Glandular cells); negative Adipose tissue. IHC workflow; specimen preparation unspecified. Protocol steps: 1. Sample: Paraffin-embedded human brain tissue; fixative not specified (datasheet A08418); 2. Fixation: Image fixative and duration unreported (datasheet A08418); 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-ARHGAP18, 1:100-1:300 (datasheet A08418); 9. Primary incubation: Overnight at 4 °C (standard). Watch for: Fixation: Keep paraffin-section fixation consistent across samples. (standard IHC practice; not target-specific); Caveat: Staining and RNA expression show medium consistency (HPA tissue IHC); Isoform / epitope: Two isoforms; no extracellular domain; epitope map unknown (UniProt); Regulation: Expression regulation is not annotated (UniProt). Evidence: UniProt Q8N392, HPA tissue IHC · Approved, HPA ICC-IF · Mainly localized to the cytosol. In addition localized to the…, Datasheet A08418, PMC5674094. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/ARHGAP18/immunohistochemistry-ihc-guide.