FAMA Antibody
Description
Definition and Principle
FAMA detects IgG antibodies targeting VZV glycoproteins on infected cell membranes. The assay involves incubating serum with VZV-infected cells, followed by fluorescein-conjugated anti-human IgG. Positive results show ring-like fluorescence on cell membranes, with titers ≥1:4 indicating protection .
Classic FAMA
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Procedure: Live VZV-infected cells are incubated with serum, washed, and stained with fluorescent antibodies. Results are assessed via microscopy .
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Limitations: Labor-intensive, subjective interpretation, and biosafety requirements for live virus handling .
Adaptations
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Flow-FAMA: Uses flow cytometry for automated, quantitative results. Achieved 90.32% accuracy (ROC AUC: 0.9125) versus standard FAMA .
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Fixed-Cell FAMA: Acetone- or glutaraldehyde-fixed cells enable batch processing. Correlation with gpELISA: r = 0.795 (P < 0.001) .
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gE FAMA: Recombinant glycoprotein E (gE)-expressing cells eliminate live virus use. Titers correlate with gpELISA (r = 0.987) .
Sensitivity and Specificity
| Assay | Sensitivity | Specificity | AUC | Source |
|---|---|---|---|---|
| Standard FAMA | 99.4% | 79.3% | 0.995 | |
| Flow-FAMA | 90.32% | - | 0.9125 | |
| gpELISA | 88.9% | 95.1% | - |
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Protective Thresholds:
FAMA vs. gpELISA
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Discrepancies: FAMA detects 98.6% seropositivity in adults versus 95% for gpELISA, highlighting superior sensitivity .
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ROC Analysis: FAMA’s AUC reached 0.995 when benchmarked against gpELISA .
Flow-FAMA Variability
| Sample Type | Intra-Assay CV | Inter-Assay CV |
|---|---|---|
| Positive Controls | 7.94% | 14.97% |
| Negative Controls | 42.51% | 46.32% |
CV = Coefficient of Variation; Data from 62 serum samples .
Limitations and Challenges
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Subjectivity: Requires trained technicians for fluorescence interpretation .
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Cutoff Variability: Protective thresholds differ between populations (e.g., 1:4 for natural infection vs. 1:16 for vaccination) .
Clinical Applications
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Vaccine Efficacy: FAMA confirms seroconversion in 76% of vaccinees, outperforming gpELISA in identifying low responders .
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Epidemiology: Korean studies show 98.6% seropositivity in adults, supporting universal vaccination strategies .
Future Directions
Product Specs
Constituents: 50% Glycerol, 0.01M PBS, pH 7.4
Target Background
- Research indicates that loss of function in the basic helix-loop-helix transcription factor FAMA eliminates myrosin idioblasts (MIs) fate, as well as the expression of the myrosinase genes TGG1 and TGG2. PMID: 25304201
- Evidence suggests that the basic helix-loop-helix transcription factor FAMA is an essential component for myrosin cell development along leaf veins. PMID: 25304202
- Data suggest that the MYB transcription factor FOUR LIPS (FLP) and the bHLH transcription factor FAMA complement respective mutant phenotypes. PMID: 24571519
- Research indicates that the bHLH transcription factor FAMA and the MYB transcription factor FOUR LIPS (FLP) genes contribute to stabilizing guard cell fate. PMID: 24654956
- Low humidity induces DNA methylation and transcription repression of SPCH and FAMA. PMID: 22442411
- Studies report transcriptional changes in response to inducible expression of Arabidopsis FAMA, a basic helix-loop-helix protein whose actions during the final stage in stomatal development regulate both cell division and cell fate. PMID: 21245191
Q&A
Basic Research Questions
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What methodological advantages does the FAMA assay offer over gpELISA for VZV immunity assessment?
The fluorescent antibody to membrane antigen (FAMA) assay is considered the gold standard for detecting protective antibodies against varicella-zoster virus (VZV) due to its high sensitivity (99.4%) and specificity (79.3%) compared to glycoprotein enzyme-linked immunosorbent assay (gpELISA) . Unlike gpELISA, which measures total antibody binding to viral lysates, FAMA directly detects antibodies targeting viral membrane antigens, correlating better with functional immunity . For example, in a study of 300 subjects, FAMA demonstrated an area under the ROC curve of 0.995 (95% CI: 0.990–1.000) when validated against gpELISA .
Table 1: Key Performance Metrics of FAMA vs. gpELISA
| Metric | FAMA Assay | gpELISA |
|---|---|---|
| Sensitivity | 99.4% | 80.0% (1–4 yrs) |
| Specificity | 79.3% | 52.0% (5–9 yrs) |
| Correlation Coefficient | 0.795 (P < 0.001) | — |
Advanced Research Questions
Table 2: Protocol Variants and Outcomes
| Protocol | Sensitivity | Specificity | Kappa Value |
|---|---|---|---|
| Live-cell FAMA | 99.4% | 82.1% | 0.91 |
| Acetone-fixed FAMA | 95.6% | 79.3% | 0.84 |
| Flow-adapted FAMA | 90.3% | 93.9% | 0.87 |
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What statistical approaches resolve contradictions in seroprevalence data across age groups?
Age-stratified seroprevalence studies reveal declining immunity in 5–9-year-olds (52.0% by gpELISA vs. 80.0% in 1–4-year-olds) . Multivariate logistic regression and ROC analysis (AUC >0.9) are critical for adjusting cutoffs in pediatric cohorts . For example, a cutoff of 34.3 mIU/mL in gpELISA aligns with FAMA ≥1:4, achieving 77.9% sensitivity and 92.0% specificity . -
How does FAMA address limitations in ELISA for immunocompromised populations?
In post-HSCT patients, ELISA fails to detect 43.9% of FAMA-positive cases, risking unnecessary revaccination . FAMA’s granular titration (e.g., 1:4 to 1:512 dilutions) identifies patients with residual immunity, optimizing vaccine strategies. For instance, patients with FAMA titers <1:16 show a 4-fold GMT increase post-vaccination, whereas those ≥1:16 exhibit minimal response .
Methodological Challenges
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What steps validate FAMA assays in multi-center studies?
Validation requires:
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Inter-laboratory calibration using reference sera (e.g., WHO 1st IS VZV)
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Blinded interpretation by two independent observers to reduce subjectivity .
A 62-sample validation study achieved 90.3% concordance between flow-FAMA and traditional FAMA .
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How are conflicting results between FAMA and neutralization assays reconciled?
Discrepancies often arise from non-neutralizing antibodies detected by FAMA. Complementary assays (e.g., plaque reduction neutralization) resolve these, as FAMA titers ≥1:16 correlate with PRNT₅₀ ≥8 .
Emerging Applications
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Can FAMA guide two-dose vaccination policies?
Data from South Korea’s UVV program show waning immunity in 5–9-year-olds (seropositivity: 52.0% gpELISA, 44.2–70.6% FAMA), supporting second-dose implementation . Post-dose 2, FAMA seropositivity reaches 100% in adults .
Table 3: Age-Specific Seroprevalence Post-Vaccination
| Age Group | FAMA Seropositivity | gpELISA Seropositivity |
|---|---|---|
| 1–4 years | 80.0% (67.0–88.8) | 69.2–90.2% |
| 5–9 years | 52.0% (38.5–65.2) | 44.2–70.6% |
| ≥20 years | 95–100% | 95–100% |
