ANA & IIFT Patterns — Bench to Bedside · Dr. Deepika Chakraborty

The basics

What is an antinuclear antibody?

Everything you need to understand before you look down a microscope.

Antibodies are proteins produced by the immune system to recognise and neutralise foreign threats — bacteria, viruses, and the like. Each antibody is highly specific: it targets one particular antigen and nothing else.

In autoimmune disease, the immune system begins producing antibodies directed against the body's own proteins — called autoantibodies (auto = self). An antinuclear antibody, or ANA, targets proteins inside the cell nucleus — DNA, histones, RNA-binding proteins, and their complexes.

ANAs are characteristically associated with systemic autoimmune rheumatic diseases — SLE, Sjögren's, systemic sclerosis, MCTD, inflammatory myopathies. Sensitivity of ANA by IIFT for active SLE is 95–100%. But up to 20–30% of healthy adults have a low-titre positive ANA. A positive ANA requires clinical context to mean anything at all.

The most common error: Ordering ANA for fatigue, back pain, diffuse musculoskeletal aches, or vague symptoms without clinical features of a connective tissue disease. Indiscriminate testing causes false positives, unnecessary anxiety, and costly downstream workup. ANA is a confirmatory test in the context of clinical suspicion — not a screening tool.

The method

How does IIFT actually work?

Step by step — from patient blood to the fluorescent pattern you read at the microscope.

The Indirect ImmunoFluorescence Test (IIFT) is the gold standard for ANA detection, recommended by the ACR ANA Task Force (2009). "Indirect" refers to the two-step antibody system at its core.

Step 1

Serum applied

Patient's diluted serum applied to HEp-2 cells. If ANA present, it binds to its nuclear antigen.

Step 2

Wash

Unbound antibody washed off. Only antibody stuck to its antigen remains.

Step 3

Secondary antibody

Anti-human IgG tagged with FITC fluorescein added. It binds to any patient ANA already on the cell.

Step 4

UV microscopy

Under UV, FITC fluoresces green. The pattern of green staining reveals the antigen's location.

Step 5

Pattern + titre

Pattern (where it glows) and titre (at what dilution it still glows) are recorded.

Why HEp-2 cells? Human epithelial laryngeal carcinoma cells are large, flat, and rapidly dividing. Their large nuclei make fluorescence patterns easy to resolve, and because they divide constantly, every slide contains cells in both interphase and mitosis — both stages are essential for pattern classification. HEp-2 cells present over 100 different autoantigens.

Solid-phase assays vs IIFT: ELISA, line blots, and multiplex bead arrays test only a fixed panel of antigens. IIFT sees all antigens present in HEp-2 cells. A negative ELISA-based ANA with strong clinical suspicion should still prompt IIFT. The ACR recommendation remains: IIFT as the gold standard.

Before you look down the microscope

Anatomy of a HEp-2 cell

The pattern you see always maps directly to where the antibody's target lives in the cell.

Nuclear envelope — Peripheral/rim pattern (AC-11/12).

Nucleolus — RNA Pol I, fibrillarin, PM-Scl → nucleolar pattern (AC-8/9/10) = SSc territory.

Nucleoplasm / chromatin — dsDNA, histones, Sm, U1-RNP → homogeneous or speckled patterns.

Centromeres — CENP-A/B/C on kinetochores. Align on metaphase plate in mitosis (AC-3).

Mitochondria — AMA targets PDC-E2 here. Cytoplasmic reticular pattern (AC-21) — not nuclear but reported as positive ANA.

The key skill

Why mitotic cells are the secret weapon

Two patterns can look identical in interphase. The mitotic cell tells you which one you're actually looking at.

Every HEp-2 slide contains cells in both interphase and mitosis. Whether chromosomes stain brightly or remain dark in mitosis is one of the most powerful pattern discriminators you have.

✓ Chromosomes positive (bright)

Target antigen stays bound to condensed chromosomes. Classic for AC-1 (homogeneous) and AC-2 (DFS70). Key: this is how you tell AC-2 from AC-4 — both are speckled, but only AC-2 has positive chromosomes in mitosis.

✗ Chromosomes negative (dark)

Target antigen disperses when chromosomes condense. Classic for AC-4 (fine speckled — SSA/Ro, SSB/La) and AC-5 (coarse speckled — Sm, U1-RNP).

★ Dots align on metaphase plate

Pathognomonic for centromere pattern (AC-3). CENP proteins follow chromosomes precisely — discrete dots line up along the equatorial plate. Unmistakable once you've seen it.

— Cytoplasmic / unchanged

Cytoplasmic patterns (AMA-AC-21, Jo-1-AC-20) don't meaningfully change in mitosis — they're not nuclear to begin with. Cytoplasm stains throughout.

The core library

The 9 patterns you need to know

Left panel: real IIFT micrograph. Right panel: large annotated doodle — the cell fills the square so every feature is clearly visible. Prose and clinical pearls below.

AC-1

Homogeneous

dsDNA · Histone · Nucleosome

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: ✓ Chromosomes POSITIVE (bright)

🔬 What you see

The entire nucleus glows with a uniform, solid fluorescence — like a filled green oval. In mitotic cells, the condensed chromosomes also glow brightly. That chromosome positivity is the key distinguishing feature.

🧠 Why this pattern

dsDNA and histones coat all chromatin, so the antibody stains the entire nuclear volume uniformly. During cell division, chromatin condenses into visible chromosomes — the antigen is still there, so they stay bright.

Associated diseases: SLE, drug-induced lupus, juvenile idiopathic arthritis

💡 Rising anti-dsDNA titre often precedes a lupus nephritis flare — track it over time, not just at diagnosis. Reflex: anti-dsDNA and anti-histone.

AC-2

Dense Fine Speckled (DFS70)

DFS70 / LEDGF p75

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: ✓ Chromosomes POSITIVE (granular)

🔬 What you see

Extremely dense, uniform tiny speckles filling the nucleus — more packed and finer than AC-4. The critical differentiator: mitotic chromosomes also stain granularly, unlike AC-4 where they are dark.

🧠 Why this pattern

DFS70 protein remains bound to chromosomes even as they condense in mitosis — hence the positive chromosome staining that separates this from all other fine-speckled patterns.

Associated diseases: Healthy individuals, atopic dermatitis — rarely CTD (≤11%)

💡 Isolated DFS70 without any other ANA strongly argues against systemic CTD — this is the 'reassurance pattern.' If DFS70 is the only antibody, the patient is very unlikely to have lupus or SSc.

AC-3

Centromere

CENP-A · CENP-B · CENP-C

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: ★ Dots ALIGN on metaphase plate — pathognomonic

🔬 What you see

46–92 discrete, evenly spaced bright dots scattered across the nucleus. The unmistakable moment: in mitotic cells, these dots line up perfectly along the metaphase plate like beads on a string.

🧠 Why this pattern

CENP proteins are permanently attached to every chromosome's centromere. When chromosomes align at the metaphase plate during division, the centromere dots align with them — perfectly and distinctively.

Associated diseases: Limited cutaneous SSc (lcSSc) / CREST syndrome

💡 No ENA reflex test needed — the pattern alone is diagnostic. These patients need periodic echocardiography: anti-centromere predicts pulmonary arterial hypertension in SSc.

AC-4

Fine Speckled

SSA/Ro52 · SSA/Ro60 · SSB/La

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: ✗ Chromosomes NEGATIVE (dark)

🔬 What you see

Uniform tiny speckles across the nucleus. The nucleolus appears as a visibly darker 'hole' within the speckled nucleus. In mitotic cells, chromosomes do NOT stain — they stay dark.

🧠 Why this pattern

SSA/Ro and SSB/La are RNA-binding proteins that disperse away from chromatin when cells divide, leaving chromosomes dark. They also don't concentrate in the nucleolus — hence nucleolar sparing.

Associated diseases: Sjögren's syndrome, subacute cutaneous lupus (SCLE), neonatal lupus, SLE

💡 SSA/Ro crosses the placenta → neonatal lupus + congenital heart block. Always ask: is the patient pregnant or planning pregnancy? If anti-SSA positive, fetal cardiac monitoring is needed from 16–24 weeks.

AC-5

Coarse Speckled

Sm · U1-RNP (snRNPs)

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: ✗ Chromosomes NEGATIVE (dark)

🔬 What you see

Fewer, larger, irregular clumps of fluorescence — noticeably coarser than AC-4. Nucleolus is still dark (spared). In mitosis, chromosomes are dark — just like AC-4.

🧠 Why this pattern

Sm and U1-RNP are spliceosomal particles — large macromolecular complexes. Being larger and fewer than SSA/Ro particles, they produce bigger, more irregular-looking speckles.

Associated diseases: SLE, mixed connective tissue disease (MCTD / Sharp syndrome)

💡 Anti-Sm is ~99% specific for SLE — an SLE classification criterion — though only ~25% sensitive. Very high-titre anti-U1RNP alone (no anti-Sm) points toward MCTD: Raynaud's + swollen fingers + overlap features.

AC-6

Nuclear Dots

Sp100 · Sp140 · PML protein

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: Dots dissolve in mitosis

🔬 What you see

6–20 discrete, large, bright dots scattered within an otherwise dark nucleus. These are larger than centromere dots and fewer. They dissolve during mitosis — unlike centromere dots which stay visible.

🧠 Why this pattern

These are PML bodies (nuclear domain 10 structures) — discrete protein complexes in the nucleus involved in gene regulation. They are distinct protein-rich compartments, not distributed throughout chromatin.

Associated diseases: Primary Biliary Cholangitis (PBC)

💡 AC-6 + AMA (cytoplasmic mitochondrial, AC-21) = very high specificity for PBC. In AMA-negative PBC (~10% of cases), nuclear dot staining may be the only serological clue — do not miss it.

AC-8/9/10

Nucleolar

PM-Scl · Fibrillarin (U3-RNP) · RNA Pol I

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: Nucleolus disperses in mitosis

🔬 What you see

Bright fluorescence confined to the nucleolus — the 1–3 round blobs inside the nucleus. The surrounding nucleoplasm is comparatively dark.

🧠 Why this pattern

The target antigens are all components of the RNA synthesis machinery concentrated in the nucleolus. The antibody stains wherever its target lives — in this case, the nucleolus.

Associated diseases: Diffuse cutaneous SSc (dcSSc), polymyositis-SSc overlap, polymyositis/DM

💡 Nucleolar pattern = think SSc first. Anti-RNA Pol III (AC-10) specifically predicts scleroderma renal crisis and is associated with concurrent malignancy in SSc. Monitor blood pressure obsessively.

AC-19/20

Cytoplasmic Speckled

Jo-1 · PL-7 · PL-12 · SRP

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: Perichromosomal staining in mitosis

🔬 What you see

Speckled fluorescence in the cytoplasm — outside the nucleus. The nucleus itself appears relatively dark. This is the opposite of most ANA patterns.

🧠 Why this pattern

Jo-1 and related aminoacyl-tRNA synthetases are translation enzymes that live in the cytoplasm. The antibody stains where its antigen lives — not in the nucleus, but around it.

Associated diseases: Antisynthetase syndrome, polymyositis/DM with ILD

💡 Never dismiss cytoplasmic staining as 'non-specific.' Antisynthetase triad: inflammatory myositis + ILD + mechanic's hands. Jo-1 is the most common; 7 other synthetases exist (PL-7, PL-12, EJ, OJ, KS, Zo, Ha).

AC-21

Cytoplasmic Mitochondrial (AMA)

AMA-M2 (anti-PDC-E2)

Real IIFT · HEp-2 cells · Euroimmun

Mitosis: Cytoplasmic — unchanged in mitosis

🔬 What you see

Reticular (net-like) staining fills the cytoplasm, outlining the mitochondria around a dark nucleus. It looks like a glowing mesh or fishnet encircling the nucleus.

🧠 Why this pattern

AMA targets PDC-E2, a protein on the inner mitochondrial membrane. Mitochondria are densely distributed throughout the cytoplasm — so the pattern appears as a reticular network surrounding the dark unstained nucleus.

Associated diseases: Primary Biliary Cholangitis (PBC)

💡 NEVER report cytoplasmic staining as ANA-negative. AMA is present in ~95% of PBC cases. Always report: 'ANA positive, cytoplasmic mitochondrial pattern (AC-21) — suggest AMA-M2 testing.'

Quantification

Understanding titre

Titre tells you how much antibody is present — but must always be read alongside pattern and clinical context.

Titre is the highest serial dilution at which fluorescence remains detectable. Higher titre = more antibody present.

1:40

Non-specific — up to 30% healthy adults

1:80

Low — interpret with clinical context

1:160

Borderline — significant by many labs

1:320

Significant — high suspicion of CTD

≥1:640

Strongly positive — almost always pathological

The titre trap: A 1:640 fine speckled in a 60-year-old asymptomatic woman is far less alarming than a 1:160 homogeneous in a 22-year-old with nephritis and arthritis. Pattern + titre + clinical picture — always all three.

Lab reporting

How to write a complete ANA IIFT report

A report without a pattern is half a report. A pattern without a titre is the other half missing.

Example — complete IIFT report

ANA: Positive

Titre: 1:320

Pattern: Nuclear coarse speckled (AC-5)

Mitotic cells: Condensed chromosomes negative

Suggested reflex: anti-Sm · anti-U1RNP

Findings consistent with anti-ENA antibodies. Please correlate with clinical features of connective tissue disease.

Never report cytoplasmic staining as ANA-negative. If the cytoplasm stains — AMA (AC-21), Jo-1 (AC-20), SRP, ribosomal-P — this is a positive ANA result. Report: "ANA positive, cytoplasmic mitochondrial pattern (AC-21). Suggest AMA-M2 testing." One of the most common reporting errors in clinical practice.

Quick reference

Pattern → Disease → Action

Pattern	ICAP	Mitosis	Think first	Reflex test
Homogeneous	AC-1	✓ Positive	SLE · Drug-induced lupus	anti-dsDNA · anti-histone
DFS70	AC-2	✓ Positive (granular)	Healthy / non-CTD	anti-DFS70 ELISA
Centromere	AC-3	★ Align on plate	lcSSc / CREST	None — pattern diagnostic
Fine Speckled	AC-4	✗ Negative	Sjögren's · SCLE · Neonatal lupus	anti-SSA/Ro · anti-SSB/La
Coarse Speckled	AC-5	✗ Negative	SLE · MCTD	anti-Sm · anti-U1RNP
Nuclear Dots	AC-6	Dots dissolve	PBC	AMA-M2 · anti-Sp100
Nucleolar	AC-8/9/10	Disperses	SSc (dcSSc)	anti-RNA Pol III · PM-Scl
Cyto. Speckled	AC-19/20	Perichromosomal	Antisynthetase syndrome	anti-Jo-1 · myositis panel
Cyto. Mito (AMA)	AC-21	Unchanged	PBC	AMA-M2 (ELISA)

When NOT to order ANA

ANA is a confirmatory test, not a screen. Ordering it without clinical suspicion causes harm — false positives in 5% of healthy adults at 1:160, unnecessary referrals, patient anxiety, and costly downstream testing.

❌ Do NOT order ANA for:Fatigue · Back or musculoskeletal pain · Headaches · Paraesthesias · Vague diffuse symptoms · Screening asymptomatic individuals · Confirming RA or OA · Monitoring known CTD activity

✓ DO order ANA if clinical features suggest:Systemic lupus · Sjögren's · Systemic sclerosis · MCTD · Inflammatory myopathy · Drug-induced lupus · PBC · Unexplained cytopenias + arthritis + rash

Conditions causing positive ANA — beyond CTDs

A positive ANA is not specific for rheumatological disease. Always interpret in clinical context.

Liver diseaseChronic hepatitis · PBC · AIH

InfectionsTB · Viral hepatitis · Syphilis · HIV · EBV

Skin diseasesPsoriasis · Lichen planus

MalignanciesBreast/prostate cancer · Hodgkin's · Leukaemia

Other autoimmuneType 1 DM · Addison's · Hashimoto's

Normal populationUp to 30% at 1:40 · ~5% at 1:160

Image credit: All IIFT micrographs reproduced from ANA Diagnostics Using Indirect Immunofluorescence by Euroimmun Medizinische Labordiagnostika AG, Lübeck, Germany (www.euroimmun.com), for educational purposes. Schematics are original illustrations created for Bench to Bedside.

References: Santhosh P, Ajithkumar K. J Skin Sex Transm Dis 2021;3:175–9 · Pisetsky DS. Nat Rev Rheumatol 2017;13:495–502 · Kumar Y et al. Diagn Pathol 2009;4:1 · Chan EK et al. Front Immunol 2015;6:412 · Abbott A, Gilbert AL. UNC Rheumatology ANA Guide 2024 · Tan EM et al. Arthritis Rheum 1997;40:1601–11

Disclaimer: Educational content only — not clinical advice.

ANA & IIFT Patterns —explained from the ground up

What is an antinuclear antibody?

How does IIFT actually work?

Serum applied

Wash

Secondary antibody

UV microscopy

Pattern + titre

Anatomy of a HEp-2 cell

Why mitotic cells are the secret weapon

✓ Chromosomes positive (bright)

✗ Chromosomes negative (dark)

★ Dots align on metaphase plate

— Cytoplasmic / unchanged

The 9 patterns you need to know

Homogeneous

Dense Fine Speckled (DFS70)

Centromere

Fine Speckled

Coarse Speckled

Nuclear Dots

Nucleolar

Cytoplasmic Speckled

Cytoplasmic Mitochondrial (AMA)

Understanding titre

How to write a complete ANA IIFT report

Example — complete IIFT report

Pattern → Disease → Action

When NOT to order ANA

Conditions causing positive ANA — beyond CTDs

ANA & IIFT Patterns —
explained from the ground up