Which of the following statements about the immunological findings in bullous pemphigoid is INCORRECT?

Explanation

## Immunological Basis of Bullous Pemphigoid **Key Point:** IgG (not IgE) is the primary pathogenic antibody in bullous pemphigoid. IgE plays a minor role and is NOT the main driver of disease pathogenesis. ### Correct Answer Analysis **IgE is NOT the primary pathogenic antibody in BP.** While IgE may be present in some patients, **IgG antibodies** directed against BP180 (NC16A domain) and BP230 are the major pathogenic antibodies. IgE has only a minor, supplementary role in BP pathogenesis. ### Immunological Cascade in BP ```mermaid flowchart TD A[IgG antibodies bind to BP180/BP230]:::action --> B[Complement activation via classical pathway]:::action B --> C[C3 deposition at BMZ]:::outcome C --> D[Eosinophil recruitment and activation]:::action D --> E[Release of proteolytic enzymes]:::action E --> F[Disruption of anchoring filaments]:::action F --> G[Subepidermal blister formation]:::outcome ``` ### Immunofluorescence Patterns in BP | Test | Finding | Interpretation | | --- | --- | --- | | **Direct IF (DIF)** | Linear IgG + C3 at BMZ | Diagnostic of BP | | **Indirect IF (IIF)** | Circulating IgG against BMZ | Detects pathogenic antibodies | | **ELISA** | Anti-BP180 and anti-BP230 IgG | Confirms diagnosis; correlates with disease activity | **High-Yield:** The **linear pattern** on DIF (not granular) is pathognomonic for BP and distinguishes it from IgA pemphigus or dermatitis herpetiformis. ### Role of IgE in BP - **Minor component:** IgE may be present in some BP sera - **Not pathogenic:** IgE does not drive the primary pathological mechanism - **Eosinophil recruitment:** IgE may contribute to eosinophil infiltration, but IgG-mediated complement activation is the main driver - **Contrast with IgE-mediated diseases:** Urticaria and angioedema are primarily IgE-mediated; BP is not **Warning:** Do NOT confuse BP (IgG-mediated) with IgA pemphigus or dermatitis herpetiformis (IgA-mediated) or with IgE-mediated urticaria. ### Why the Other Options Are Correct - **DIF findings:** Linear IgG and C3 deposits along the basement membrane zone are diagnostic and characteristic of BP [cite:Robbins 10e Ch 25] - **IIF findings:** Circulating IgG antibodies can be detected by indirect IF and correlate with disease activity - **Complement activation:** The classical pathway is activated by IgG-C1q interaction, leading to C3 deposition and eosinophil recruitment [cite:Robbins 10e Ch 25]