Dengue Literature Review

Line Immunoassay ANA

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Line Immunoassay ANA

Overview

Line immunoassay (LIA) is a solid-phase immunoassay that simultaneously detects IgG antibodies against multiple specific nuclear and cytoplasmic antigens. Individual antigens are coated as parallel lines on a nitrocellulose membrane strip. Patient serum is incubated with the strip; bound antibodies are visualised using HRP-conjugated secondary antibodies. Results are read as presence/absence (and semi-quantitative intensity) for each antigen, generating a full antibody profile in a single test.

LIA is used as a confirmatory and differentiation test following positive IIFA screening. Where IIFA detects the presence of any antinuclear reactivity, LIA identifies which specific autoantibodies are present and thereby determines the relevant autoimmune disease association. This two-step workflow (IIFA screen → LIA confirmation) is standard practice in ANA diagnostics.

Key Points from Literature

Antigens Covered

The IMTEC-ANA-LIA-XL assay used in Chatterjee2024 - ANA Detection in Dengue Kolkata simultaneously detects 18 IgG autoantibody specificities in one assay:

AntigenPrimary Disease Association
dsDNASLE
NucleosomeSLE
HistoneDrug-induced SLE, SLE
SmD1SLE
PCNASLE (rare)
PO (RPP)SLE
SS-A/Ro60Sjögren’s syndrome, SLE, neonatal lupus
SS-A/Ro52Sjögren’s syndrome, inflammatory myopathy
SS-B/LaSjögren’s syndrome
CENP-BLimited systemic sclerosis (CREST)
Scl-70 (topoisomerase I)Diffuse systemic sclerosis
U1-snRNPMCTD, SLE
AMA M2Primary biliary cholangitis (PBC)
Jo-1Autoimmune myositis / anti-synthetase syndrome
PM-SclPolymyositis/dermatomyositis, systemic sclerosis overlap
Mi-2Dermatomyositis
KuMyositis-sclerosis overlap, SLE
DFS-70Exclusion marker (isolated DFS70 argues against systemic rheumatic disease)

LIA vs. IIFA: The Confirmation Gap in Dengue

Chatterjee2024 - ANA Detection in Dengue Kolkata provides direct data on IIFA → LIA confirmation rates in dengue:

  • ANA-IIFA positive: 54.8% of dengue-positive patients (74/135)
  • ANA-LIA positive: 18.5% of dengue-positive patients (25/135)
  • Confirmation rate: ~34% of IIFA-positive dengue patients confirmed by LIA; ~66% of IIFA positives were LIA-negative

This 3:1 IIFA:LIA ratio is diagnostically important. It means that dengue infection produces a high rate of non-specific nuclear reactivity detectable by IIFA (the most sensitive assay) that does not correspond to the targeted autoantibody specificities of established systemic autoimmune diseases. The LIA-negative IIFA-positive patients likely have low-titer, polyclonal, or non-disease-specific ANAs.

In controls (dengue-negative): 10.3% IIFA-positive, 7.1% LIA-positive — a much higher IIFA → LIA confirmation rate (~69%), suggesting that in the non-dengue febrile population, most IIFA positives do represent specific autoimmune reactivities.

DFS70 as Rheumatic Disease Exclusion Marker

Isolated anti-DFS70 (Dense Fine Speckled 70 kDa) antibody on LIA is used to flag ANA-positive individuals who are unlikely to have a systemic autoimmune rheumatic disease (SARD). When DFS70 is the only antibody detected on LIA (not co-occurring with disease-specific autoantibodies), it argues against a true SARD. In Chatterjee2024, one dengue patient had isolated DFS70, used to identify a “false-positive” ANA without underlying rheumatic disease.

Disease Association Categorisation

LIA output in Chatterjee2024 - ANA Detection in Dengue Kolkata was used to categorise patients into autoimmune disease groups:

  • MCTD (anti-U1-snRNP): significant in dengue (multivariate p = 0.041)
  • Autoimmune myositis (anti-Jo-1, anti-Mi-2, anti-PM-Scl): significant in dengue (multivariate p = 0.018)
  • SLE, Sjögren’s, CREST, PBC, Non-Rheumatic Disease: not significantly elevated

Contradictions & Debates

  • The MCTD/myositis association from this LIA-based study (Kolkata, hospital-based, n=135) was not replicated in Shih2023’s population-based study (Taiwan, n=63,814) — though Shih2023 did not specifically test LIA-based categories and used different outcome ascertainment (ICD codes). The discrepancy may reflect population, setting, or statistical power differences.
  • LIA sensitivity varies by manufacturer and antigen preparation; the IMTEC kit (Human GmbH, Germany) has not been independently validated in dengue-specific populations.

Sources

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