Immunodiagnostic Techniques in Dermatology
Introduction
Immunodiagnostic techniques are essential tools in dermatology, enabling precise diagnosis of autoimmune blistering diseases, connective tissue disorders, vasculitis, and immunodeficiencies. These methods detect antibodies, immune complexes, and cellular markers that are invisible to routine histopathology.
This chapter covers the principles and applications of key immunodiagnostic techniques used in dermatologic practice.
Direct Immunofluorescence (DIF)
Principle
Direct immunofluorescence detects immune deposits in patient tissue using fluorescent-labeled antibodies.
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Key DIF Patterns
| Pattern | Location | Diseases |
|---|
| Intercellular (ICS) | Between keratinocytes ("chicken-wire") | Pemphigus vulgaris, foliaceus |
| Linear BMZ | Basement membrane zone | BP, EBA, linear IgA, cicatricial pemphigoid |
| Granular BMZ | Dermal papillae, BMZ | Dermatitis herpetiformis |
| Shaggy fibrin at DEJ | Basement membrane zone | Lupus erythematosus |
| Vessel wall | Small vessels | Leukocytoclastic vasculitis (IgA in HSP) |
| Lupus band | DEJ (granular IgG, IgM, C3) | Systemic lupus erythematosus |
Biopsy Selection for DIF
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Immunofluorescence Findings by Disease
| Disease | DIF Pattern | Key Antibody |
|---|
| Pemphigus vulgaris | Intercellular IgG + C3 | Anti-Dsg3 (± Dsg1) |
| Pemphigus foliaceus | Intercellular IgG | Anti-Dsg1 |
| Bullous pemphigoid | Linear BMZ IgG + C3 | Anti-BP180/230 |
| Epidermolysis bullosa acquisita | Linear BMZ IgG | Anti-type VII collagen |
| Linear IgA disease | Linear BMZ IgA | Anti-BP180 (LAD-1) |
| Dermatitis herpetiformis | Granular IgA at dermal papillae | Anti-eTG |
| Lupus (band) | Granular IgG, IgM, C3 at DEJ | ANA, anti-dsDNA |
| IgA vasculitis (HSP) | IgA in vessel walls | — |
Indirect Immunofluorescence (IIF)
Principle
Indirect immunofluorescence detects circulating antibodies in patient serum using a substrate tissue.
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Common Substrates
| Substrate | Use |
|---|
| Monkey esophagus | Pemphigus (ICS pattern) |
| Rat bladder | Pemphigus (sensitive) |
| Human salt-split skin | Distinguish BP (roof) from EBA (floor) |
| HEp-2 cells | ANA patterns (lupus) |
Salt-Split Skin Technique
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| Binding | Antigen | Diseases |
|---|
| Roof (epidermal) | BP180, BP230 | BP, LABD, CP, PG |
| Floor (dermal) | Type VII collagen, Laminin-332 | EBA, Anti-p200, Anti-laminin-332 |
ELISA for Autoantibodies
Principle
Enzyme-linked immunosorbent assay (ELISA) provides quantitative detection of specific autoantibodies.
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Available ELISA Tests
| Antigen | Disease | Utility |
|---|
| Desmoglein 1 | Pemphigus foliaceus | Diagnosis, monitoring |
| Desmoglein 3 | Pemphigus vulgaris | Diagnosis, monitoring |
| BP180 (NC16A domain) | Bullous pemphigoid | Diagnosis; correlates with activity |
| BP230 | Bullous pemphigoid | Less specific |
| Type VII collagen | EBA | Diagnosis |
| Endomysial/tTG | Celiac (for DH workup) | DH association |
Clinical Utility
| Application | Details |
|---|
| Diagnosis | Confirmatory when DIF positive |
| Monitoring | Dsg1/3 levels correlate with pemphigus activity |
| Prognosis | High titers may indicate more severe disease |
| Treatment decisions | Inform tapering of therapy |
Immunohistochemistry (IHC)
Principle
IHC uses antibodies to detect specific antigens in formalin-fixed tissue, allowing identification of cell types, proteins, and markers.
Applications in Dermatology
| Application | Markers | Use |
|---|
| Melanoma diagnosis | S100, HMB-45, Melan-A, SOX10 | Confirm melanocytic origin |
| Melanoma prognosis | Ki-67 (proliferation) | Mitotic activity |
| Lymphoma typing | CD3 (T cell), CD20 (B cell), CD30 | Classification |
| Merkel cell carcinoma | CK20, neurofilament | Diagnosis |
| Dermatofibrosarcoma | CD34 | DFSP vs. dermatofibroma |
| Langerhans cell histiocytosis | CD1a, S100, Langerin | Diagnosis |
| Mast cell disease | Tryptase, CD117 | Mastocytosis |
Melanoma Markers
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Flow Cytometry
Principle
Flow cytometry analyzes individual cells in suspension by detecting fluorescent-labeled antibody binding.
Applications
| Application | Markers | Clinical Use |
|---|
| Lymphocyte subsets | CD3, CD4, CD8, CD19, CD16/56 | Immunodeficiency evaluation |
| Cutaneous T cell lymphoma | CD4/CD8 ratio, aberrant loss of markers | Sézary syndrome (blood) |
| Mast cell disease | CD117, CD25, CD2 | Systemic mastocytosis |
| NK cell function | CD56, CD16 | NK deficiencies |
Sézary Syndrome Criteria
| Parameter | Criteria |
|---|
| Absolute Sézary count | ≥1,000/μL |
| CD4:CD8 ratio | ≥10 |
| CD4+CD7− | ≥40% |
| CD4+CD26− | ≥30% |
| T cell clone | Present by TCR gene rearrangement |
Autoantibody Panels
ANA and Specific Antibodies
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ANA Patterns and Associations
| Pattern | Associated Antibodies | Diseases |
|---|
| Homogeneous | Anti-dsDNA, anti-histone | SLE, drug-induced lupus |
| Speckled | Anti-Sm, anti-RNP, anti-Ro/La | SLE, MCTD, Sjögren's |
| Nucleolar | Anti-RNA polymerase, anti-fibrillarin | Systemic sclerosis |
| Centromere | Anti-centromere | Limited scleroderma (CREST) |
Dermatomyositis-Specific Antibodies
| Antibody | Phenotype | Malignancy Risk | ILD Risk |
|---|
| Anti-Mi-2 | Classic DM rash | Low | Low |
| Anti-TIF1-γ | Classic DM | High | Low |
| Anti-NXP-2 | Calcinosis, severe muscle | Moderate-high | Low |
| Anti-MDA5 | Amyopathic DM, ulcers, arthritis | Low | High |
| Anti-Jo-1 | Mechanic's hands, ILD, arthritis | Low | High |
| Anti-SAE | Dysphagia, skin before muscle | Moderate | Moderate |
Specialized Tests
Patch Testing
| Feature | Details |
|---|
| Purpose | Identify allergens in allergic contact dermatitis |
| Method | Apply allergens to back for 48 hours; read at 48, 72-96 hours |
| Standard series | TRUE Test or expanded panels |
| Positive result | Erythema, induration, vesicles |
Phototesting
| Test | Use |
|---|
| Minimal erythema dose (MED) | Photosensitivity, guide phototherapy dosing |
| Photo-patch testing | Photoallergic contact dermatitis |
| Provocation testing | PMLE, solar urticaria |
Algorithm for Blistering Disease Workup
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Summary
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Key Clinical Pearls
| Topic | Pearl |
|---|
| DIF biopsy | Perilesional, NOT from the blister |
| Transport | Michel's medium (NOT formalin) for DIF |
| Salt-split | Roof = BP, LABD; Floor = EBA |
| Dsg1/3 ELISA | Levels correlate with pemphigus activity |
| BP180 ELISA | Correlates with BP activity |
| ANA pattern | Speckled = anti-Ro/La; consider SCLE |
| MDA5 | Amyopathic DM + high ILD risk (poor prognosis) |
| TIF1-γ | Classic DM + high malignancy risk |
Cross-References