## Autoantigen Targets in Bullous Pemphigoid **Key Point:** Bullous pemphigoid is an autoimmune blistering disorder caused by IgG autoantibodies directed against hemidesmosomal proteins, specifically BP180 (collagen XVII) and BP230. ### Molecular Basis BP180 and BP230 are integral components of the **hemidesmosome**, the adhesion structure that anchors basal keratinocytes to the basement membrane zone (BMZ). These proteins form the transmembrane and intracellular components of hemidesmosomes. ### Antibody Characteristics | Feature | BP Antibodies | | --- | --- | | Antibody type | IgG (circulating and tissue-bound) | | Primary targets | BP180 (most common), BP230 | | Location | Basement membrane zone (linear pattern on IF) | | Pathogenic mechanism | Complement activation → neutrophil infiltration → subepidermal blister | **High-Yield:** BP180 is the more clinically significant antigen; anti-BP180 antibodies correlate better with disease activity and severity than anti-BP230 antibodies. ### Immunofluorescence Pattern Direct immunofluorescence (DIF) shows **linear IgG and C3 deposition along the basement membrane zone** — this is the hallmark finding that distinguishes BP from pemphigus vulgaris (which shows intercellular IgG). **Clinical Pearl:** The presence of circulating anti-BP180 IgG can be detected by ELISA or immunoblotting, making serology a useful adjunct to diagnosis and monitoring. [cite:Robbins 10e Ch 25] 
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