Dengue Literature Review

Indirect Immunofluorescence ANA Test

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Indirect Immunofluorescence ANA Test

Overview

Indirect immunofluorescence (IIF) on HEp-2 (human epithelial type 2) cells is the standard method for detecting antinuclear antibodies (ANAs). Patient serum is incubated with HEp-2 cell substrate slides; any antibodies present bind to nuclear and cytoplasmic antigens. A fluorochrome-conjugated anti-human IgG secondary antibody then reveals the binding pattern under fluorescence microscopy. The cellular staining pattern (nuclear, cytoplasmic, nucleolar, mitotic) and staining intensity are recorded, and results are reported as positive/negative with a titer (the highest serum dilution still giving positive fluorescence) and pattern description.

HEp-2 cells are preferred because they are large, proliferating human cells with well-defined nuclear structures, making a wide range of antigens accessible. They replaced earlier substrates (mouse liver/kidney) and provide higher sensitivity for clinically important autoantibodies.

Key Points from Literature

Dilution Thresholds Used Across Studies

Different dilution cutoffs are used in different contexts, with important implications for prevalence estimates:

Scoring and Positivity Criteria

Staining intensity is typically graded on a 0–4 scale (0=negative; 1=borderline; 2=weak positive; 3=moderate positive; 4=strong positive). Studies differ in their positivity threshold:

Inter-Laboratory Variability

Tan1997 - ANA Range in Healthy Individuals demonstrated ~50% coefficient of variation between laboratories at 1:40, declining at higher dilutions. This inter-laboratory variability (~3× greater than intra-laboratory variability) is a major limitation for cross-study comparisons. The variability reflects differences in HEp-2 cell lots, secondary antibody conjugates, fluorescence microscope settings, and reader experience.

ANA Patterns

IIF on HEp-2 cells generates characteristic staining patterns linked to specific autoantibodies and diseases:

  • Nuclear patterns: Most common in healthy populations (84.6% of ANA+ individuals; Satoh2012 - ANA Prevalence in United States); associated with anti-dsDNA, anti-histone, anti-Sm/RNP, anti-Ro/La
  • Cytoplasmic patterns: 21.8% of ANA+ individuals (Satoh2012); anti-Jo-1, anti-mitochondrial
  • Nucleolar patterns: 6.1% of ANA+ individuals (Satoh2012); strongly associated with systemic sclerosis
  • Dense fine speckled (DFS): Associated with anti-DFS70 antibodies; possibly more common in healthy individuals than in autoimmune disease patients

HEp-2 IIFA in Acute Dengue

Chatterjee2024 - ANA Detection in Dengue Kolkata is the first study in this wiki to apply HEp-2 IIFA directly to acute dengue patients, yielding a 54.8% ANA-positive rate in dengue-confirmed patients vs. 10.3% in dengue-negative controls. The study used the Immunoconcepts HEp-2000® ANA Test System (transfected with mitotic cells for enhanced Ro antigen detection). Semi-quantitative fluorescence scoring (1+–4+) was used per CDC guidelines.

The high rate (54.8%) is consistent with the expected sensitivity advantage of HEp-2 over the rat liver substrate used by Garcia2009 - Long-term Clinical Symptoms Post-Dengue (23.1% at 2 years). However, a direct comparison is confounded by the different time points (acute vs. 2 years post-dengue). The critical interpretive finding is that only ~34% of IIFA-positive dengue patients confirmed by LIA — meaning HEp-2 IIFA over-reads in dengue due to non-specific or low-titer reactivity not captured by disease-specific confirmatory assays.

Contradictions & Debates

  • Substrate incompatibility with Garcia2009: Garcia2009 - Long-term Clinical Symptoms Post-Dengue performed ANA testing on rat liver tissue, not HEp-2 cells. Rat/mouse liver tissue is an older, less sensitive substrate that was standard prior to the 1980s adoption of HEp-2. Its lower antigen density and absence of nuclear mitotic figures means it detects fewer ANA specificities and at lower sensitivity than HEp-2. All healthy-population ANA reference studies in this wiki (Tan1997, Satoh2012, Li2019, Dinse2022) use HEp-2 cells. The 23.1% ANA rate in Garcia2009 is therefore an underestimate relative to what would be found if HEp-2 cells had been used — the true rate might be higher still, making comparisons with HEp-2-based references conservative.
  • Sensitivity creep: HEp-2 cell substrates have become increasingly sensitive over time as manufacturers optimise for proliferating cells. This may partly explain rising ANA prevalence observed in temporal studies (see Dinse2022 - Increasing ANA Prevalence in United States), though Dinse2022 used a single-lab, single-kit design to minimise this confound.
  • Automated vs. manual reading: Automated fluorescence microscope systems (e.g., NOVA View) improve throughput and reproducibility but may capture patterns not identified by manual reading. Dinse2022 used automated reading; most prior studies used manual dual-reader review.
  • Solid-phase immunoassays vs. IIF: Enzyme immunoassays and multiplex bead assays are increasingly used as alternatives; the 2019 EULAR/ACR criteria permit “equivalent performance” alternatives, but IIF on HEp-2 remains the gold standard for pattern information.

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