Research method
Immunofluorescence Staining
8 studies
Immunofluorescence uses antibodies (or fluorescent tags) to mark a protein, organelle, or pathogen antigen in fixed or live cells, then images where the signal sits. The output is a localisation pattern — surface versus endosome, apical pole, tissue-resident T cells — sometimes scored as a binary infected/uninfected well. Antibody cross-reactivity and fixation artifacts are part of the uncertainty.
Host–pathogen and trafficking papers reach for IF when they need to see a receptor, a viral protein, or a polarity marker in place rather than only on a blot. It answers 'where is this epitope, and does a mutation or drug move it?' Its main limitation is that staining intensity is not a binding affinity, and a Vero-cell antiviral screen or a permeabilized-sperm assay does not automatically generalise to human tissue.
Studies
8
Findings
5
7 supporting · 0 challenging · 0 qualifying citations
Open tensions
2
Currently
What we know
- Permeabilized sperm plus staged inhibitors and photolabile Ca2+ chelators ordered acrosome exocytosis: Rab3A acts before intra-acrosomal Ca2+ efflux; SNAREs and synaptotagmin act after to complete fusion. Immunofluorescence of fusion factors here is timed biochemistry in a stripped-down cell, not every in-vivo regulatory layer.
- A Vero E6 SARS-CoV-2 assay screened about 430 kinase inhibitors: the ATR inhibitor berzosertib showed strong antiviral activity, and 100 nM fully blocked replication at 48 hours post-infection in that assay. Infection staining or antigen IF is a screening endpoint, not a completed human COVID-19 efficacy trial.
- USP8 is required for Hedgehog-induced Smoothened surface accumulation and keeps Smo out of Rab5 early endosomes. Site-specific monoubiquitination of Rab5 at K140 and K165 (not K116) downregulates the endocytic pathway via disrupted effectors and nucleotide conversion. Both papers use localisation of Smo or Rab5 as a trafficking IF readout.
- In resected human TB lung from 35 patients, PD-1 marked tissue-resident T cells; infection models then showed that TNF-α is primarily responsible for anti-PD-1–driven reactivation and that TNF neutralization reverses the phenotype. Tissue IF here is a human spatial observation paired with mechanistic models, not a randomized oncology endpoint trial.
- Enteroid polarity reversed within hours without BME, with β1 integrin orienting apical pathogen access. Spike LYQD mutants altered S2 glycosylation mobility, and palmitoylation at cysteine clusters I/II was required for Golgi/plasma-membrane targeting and ACE2-mediated fusion. Those localisation phenotypes are IF/trafficking stains; enteroids are not a clinical gut, and much spike work uses pseudoviruses.
Largest unresolved question
IF is a screening camera in Vero cells (berzosertib 100 nM, 48 hpi), a tissue census in TB lung (35 patients), a trafficking assay for Smo/Rab5/spike, and a polarity assay in enteroids. 'Positive staining' in a drug screen is not the same claim as PD-1 on human tissue-resident T cells or as K140/K165 moving Rab5 off endosomes.
Procedure
How it works
The main stages of the method. Specific protocols and analysis choices vary between studies.
Fix, or keep the cells live
Fixation preserves an epitope at a moment and can also move or hide it. Live tagging avoids that artifact and introduces a different one: the tag itself.
Bind an antibody or a fluorescent tag
The reagent marks a protein, organelle, or pathogen antigen. Cross-reactivity is part of the result; a clean-looking pattern of the wrong epitope still looks like a localisation.
Image where the epitope sits
The output is a localisation pattern — surface versus endosome, apical pole, tissue-resident T cells — sometimes scored as a binary infected/uninfected well.
Compare a mutation, a drug, or a tissue
Host–pathogen and trafficking papers ask whether a mutation or inhibitor moves the signal. Staining intensity is not a binding affinity, and a Vero-cell screen is not a human tissue census.
Do not treat a stained well as a clinical result
Immunofluorescence answers where this epitope is, and whether a perturbation moved it. A blocked viral stain in Vero cells is a screen endpoint, not a proven drug, and a PD-1 pattern on resected lung is not automatically a T-cell–intrinsic therapy mechanism.
Common misconceptions
If 100 nM berzosertib fully blocks SARS-CoV-2 staining in Vero cells at 48 hpi, it is a proven COVID-19 drug.
That figure is a kinase-inhibitor screen endpoint in Vero E6 cells (~430 compounds). It is not a completed human clinical efficacy trial.
Any ubiquitin on Rab5 shuts the endocytic pathway down.
Rab5 is monoubiquitinated at K116, K140 and K165; K140/K165 modifications downregulate the pathway while K116 has little localisation effect. Site matters.
PD-1 staining on TB-lung T cells means anti-PD-1 cancer therapy always reactivates tuberculosis by a T-cell–intrinsic switch independent of TNF.
PD-1 is present on tissue-resident T cells in 35 patients' resected lung, but infection models found TNF-α primarily responsible and neutralization reversed the anti-PD-1 phenotype.
Related
Claim ledger
What the evidence shows
Drawn from 8 studies in this library. Mix labels say which citation roles are present; they are not a strength score. Supports means evidence for a finding; Challenges means evidence against a stated position; Qualifies marks scope.
Permeabilized sperm plus staged inhibitors and photolabile Ca2+ chelators ordered acrosome exocytosis: Rab3A acts before intra-acrosomal Ca2+ efflux; SNAREs and synaptotagmin act after to complete fusion. Immunofluorescence of fusion factors here is timed biochemistry in a stripped-down cell, not every in-vivo regulatory layer.
A Vero E6 SARS-CoV-2 assay screened about 430 kinase inhibitors: the ATR inhibitor berzosertib showed strong antiviral activity, and 100 nM fully blocked replication at 48 hours post-infection in that assay. Infection staining or antigen IF is a screening endpoint, not a completed human COVID-19 efficacy trial.
USP8 is required for Hedgehog-induced Smoothened surface accumulation and keeps Smo out of Rab5 early endosomes. Site-specific monoubiquitination of Rab5 at K140 and K165 (not K116) downregulates the endocytic pathway via disrupted effectors and nucleotide conversion. Both papers use localisation of Smo or Rab5 as a trafficking IF readout.
Study Role Design N Population Outcome How does USP8 turn on Smoothened? Supports Animal / in-vitroRNAi screen of Drosophila DUBs in wings and S2 cells focused on USP8–Smo regulation Drosophila genetics and S2 cell assays — no single sample N Drosophila tissues and S2 cells USP8 prevention of Smoothened ubiquitination promoting Hedgehog signaling How does monoubiquitin turn down Rab5? Supports Animal / in-vitroMapped Rab5 monoubiquitination sites and tested chemically monoubiquitinated Rab5 function Cell-biochemistry of Rab5 ubiquitin sites K116/K140/K165 — no single sample N Cultured cells expressing Rab5 variants Site-specific monoubiquitination downregulating Rab5 endocytic signaling In resected human TB lung from 35 patients, PD-1 marked tissue-resident T cells; infection models then showed that TNF-α is primarily responsible for anti-PD-1–driven reactivation and that TNF neutralization reverses the phenotype. Tissue IF here is a human spatial observation paired with mechanistic models, not a randomized oncology endpoint trial.
Enteroid polarity reversed within hours without BME, with β1 integrin orienting apical pathogen access. Spike LYQD mutants altered S2 glycosylation mobility, and palmitoylation at cysteine clusters I/II was required for Golgi/plasma-membrane targeting and ACE2-mediated fusion. Those localisation phenotypes are IF/trafficking stains; enteroids are not a clinical gut, and much spike work uses pseudoviruses.
Study Role Design N Population Outcome Apical-out enteroids for pathogen access Supports Animal / in-vitroHuman enteroids cultured in suspension without BME to reverse polarity for apical pathogen assays Enteroid lines from multiple donors; assays often scored ~10 enteroids per well across experiments — no single primary N Human intestinal enteroids β1-integrin–dependent epithelial polarity orientation for host–pathogen assays Spike glycosylation and palmitoylation trafficking Supports Animal / in-vitroMutagenesis and 2BP inhibition of SARS-CoV-2 spike glycosylation/palmitoylation trafficking Cell-based spike trafficking/fusion assays — no single primary analytic N Cells expressing wild-type or mutant SARS-CoV-2 spike Spike intracellular trafficking, packaging, and ACE2-mediated fusion
Debates
Tensions and limits
Some items are genuine disagreements on the same question. Others mark different assays, populations, or outcomes.
IF is a screening camera in Vero cells (berzosertib 100 nM, 48 hpi), a tissue census in TB lung (35 patients), a trafficking assay for Smo/Rab5/spike, and a polarity assay in enteroids. 'Positive staining' in a drug screen is not the same claim as PD-1 on human tissue-resident T cells or as K140/K165 moving Rab5 off endosomes.
IF is a screening camera in Vero cells (berzosertib 100 nM, 48 hpi), a tissue census in TB lung (35 patients), a trafficking assay for Smo/Rab5/spike, and a polarity assay in enteroids. 'Positive staining' in a drug screen is not the same claim as PD-1 on human tissue-resident T cells or as K140/K165 moving Rab5 off endosomes.
- ATR inhibitor blocks SARS-CoV-2
- PD-1 blockade reactivates TB via TNF
- How does monoubiquitin turn down Rab5?
- Apical-out enteroids for pathogen access
Study Role Design N Population Outcome ATR inhibitor blocks SARS-CoV-2 Supports Animal / in-vitroMedium-throughput SARS-CoV-2 antiviral screen of kinase inhibitors in Vero E6 cells ~430 kinase inhibitors screened; cell-assay study without a human sample N Vero E6 cells infected with SARS-CoV-2 Antiviral activity of kinase inhibitors (notably berzosertib/ATR) PD-1 blockade reactivates TB via TNF Supports OtherHuman TB lung PD-1+ T-cell profiling plus infection models of anti-PD-1 effects N=35 · 35 patients with medically indicated lung resection; matched blood for 23; animal/in-vitro models secondary Patients undergoing lung resection for TB or sequelae (plus infection models) PD-1 expression and TNF-dependent effects of PD-1 blockade in TB How does monoubiquitin turn down Rab5? Supports Animal / in-vitroMapped Rab5 monoubiquitination sites and tested chemically monoubiquitinated Rab5 function Cell-biochemistry of Rab5 ubiquitin sites K116/K140/K165 — no single sample N Cultured cells expressing Rab5 variants Site-specific monoubiquitination downregulating Rab5 endocytic signaling Apical-out enteroids for pathogen access Supports Animal / in-vitroHuman enteroids cultured in suspension without BME to reverse polarity for apical pathogen assays Enteroid lines from multiple donors; assays often scored ~10 enteroids per well across experiments — no single primary N Human intestinal enteroids β1-integrin–dependent epithelial polarity orientation for host–pathogen assays
PaperFren reads this as a limit on how far one study travels — different assays, populations, or outcomes — not a forced fight between papers.
Permeabilized-sperm SNARE timing and live epithelial polarity/spike trafficking disagree about how much native membrane regulation is still present. In-vitro sperm may miss in-vivo layers; enteroids and pseudovirus spike assays only approximate infection of a human airway or gut.
Permeabilized-sperm SNARE timing and live epithelial polarity/spike trafficking disagree about how much native membrane regulation is still present. In-vitro sperm may miss in-vivo layers; enteroids and pseudovirus spike assays only approximate infection of a human airway or gut.
- SNARE timing in sperm acrosome exocytosis
- Apical-out enteroids for pathogen access
- Spike glycosylation and palmitoylation trafficking
Study Role Design N Population Outcome SNARE timing in sperm acrosome exocytosis Supports Animal / in-vitroStaged inhibitors and photolabile Ca²⁺ chelators in permeabilized sperm to order fusion factors Cell-biology ordering experiments — no single primary analytic N in stored text Permeabilized sperm undergoing acrosomal exocytosis Temporal order of Rab3A and SNARE/synaptotagmin steps in acrosomal fusion Apical-out enteroids for pathogen access Supports Animal / in-vitroHuman enteroids cultured in suspension without BME to reverse polarity for apical pathogen assays Enteroid lines from multiple donors; assays often scored ~10 enteroids per well across experiments — no single primary N Human intestinal enteroids β1-integrin–dependent epithelial polarity orientation for host–pathogen assays Spike glycosylation and palmitoylation trafficking Supports Animal / in-vitroMutagenesis and 2BP inhibition of SARS-CoV-2 spike glycosylation/palmitoylation trafficking Cell-based spike trafficking/fusion assays — no single primary analytic N Cells expressing wild-type or mutant SARS-CoV-2 spike Spike intracellular trafficking, packaging, and ACE2-mediated fusion
PaperFren reads this as a limit on how far one study travels — different assays, populations, or outcomes — not a forced fight between papers.
Timeline
How understanding moved
Study years are when the paper was published. Evidence edits are dated changes to this page's claims. Explanations are when PaperFren added a Discovery — not a claim that the science happened that day.
2026
Concept page published
Immunofluorescence Staining
Change log
What changed
Dated edits to this page's evidence: studies added or removed from a claim, claims added or withdrawn, and new explanations tagged here. Coverage edits are distinct from reviewed research changes and corrections. Dates record PaperFren updates; study publication dates appear in the timeline.
- Coverage updated · Concept page published
Papers
8 studies in this library bear on Immunofluorescence Staining, ordered by citations.
- Apical-out enteroids for pathogen access
Suspending human enteroids without ECM flips polarity so microbes can meet the apical face.
- What marks definitive endoderm progenitors in hESCs?
Single-cell RNA-seq separates definitive endoderm progenitors and links metabolism/hypoxia to DE differentiation.
- How does USP8 turn on Smoothened?
USP8 deubiquitinates Smoothened, promoting Hh-dependent cell-surface accumulation and signaling while limiting early-endosome localization.
- ATR inhibitor blocks SARS-CoV-2
DDR/ATR inhibitor berzosertib potently blocks SARS-CoV-2 replication in cell culture.
- PD-1 blockade reactivates TB via TNF
Anti-PD-1 immunotherapy can reactivate tuberculosis through TNF-α dysregulation.
- SNARE timing in sperm acrosome exocytosis
Sperm acrosome exocytosis proceeds via ordered SNARE assembly/disassembly around intra-acrosomal Ca2+ release.
- How does monoubiquitin turn down Rab5?
Rab5 is monoubiquitinated at specific lysines; ubiquitin at K140/K165 disrupts effector binding and downregulates endocytic trafficking.
- Spike glycosylation and palmitoylation trafficking
Glycosylation motifs and cysteine palmitoylation steer SARS-CoV-2 spike maturation, Golgi trafficking, and fusion.
Compare studies
Select 2–10 studies. Design and N are labels, not a ranking.
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Questions
What is still open
IF is a screening camera in Vero cells (berzosertib 100 nM, 48 hpi), a tissue census in TB lung (35 patients), a trafficking assay for Smo/Rab5/spike, and a polarity assay in enteroids. 'Positive staining' in a drug screen is not the same claim as PD-1 on human tissue-resident T cells or as K140/K165 moving Rab5 off endosomes.
Permeabilized-sperm SNARE timing and live epithelial polarity/spike trafficking disagree about how much native membrane regulation is still present. In-vitro sperm may miss in-vivo layers; enteroids and pseudovirus spike assays only approximate infection of a human airway or gut.
Ask PaperFren about Immunofluorescence Staining
Study this conceptflashcards and short-answer questions
Rab3A acts before intra-acrosomal Ca2+ efflux, SNAREs after. What did immunofluorescence plus staged inhibitors allow that a single endpoint stain would miss?
Order. Photolabile chelators and inhibitors placed Rab3A upstream of Ca2+ efflux and SNAREs/synaptotagmin at fusion completion. A single stained snapshot cannot sequence those steps.
A colleague treats berzosertib's 100 nM full block at 48 hpi as equivalent to PD-1 IF in 35 TB lungs. How do the IF claims differ?
Berzosertib is a Vero-cell antiviral screen with low-toxicity filters, not a human trial. TB-lung IF shows PD-1 on tissue-resident T cells in patients, then models implicate TNF. One is a drug-hit image; the other is human tissue localisation plus mechanism.
Why does monoubiquitination at Rab5 K116 versus K140/K165 change what an IF localisation experiment can conclude?
K140/K165 disrupt effectors and nucleotide conversion and downregulate endocytic localisation; K116 has little localisation effect. A pan-ubiquitin stain without site mutants would blur those outcomes.
Spike palmitoylation at cysteine clusters I/II is required for Golgi/plasma-membrane targeting. What IF pattern would you expect if 2-bromopalmitate blocks that step, and what caveat remains?
Less efficient surface/Golgi targeting of S and weaker ACE2-mediated fusion. Much of the work uses spike pseudoviruses rather than full-virus genetics for every assay, so the IF pattern is a trafficking phenotype, not a clinical antiviral result.