## Target Antigens in Bullous Pemphigoid **Key Point:** Bullous pemphigoid is characterized by IgG autoantibodies directed against two major hemidesmosomal antigens: BP180 (type XVII collagen) and BP230 (a 230 kDa protein). ### Antigen Characteristics | Antigen | Location | Function | Antibody Frequency | | --- | --- | --- | --- | | BP180 (Collagen XVII) | Hemidesmosomal transmembrane protein | Anchors hemidesmosomes to basement membrane | ~90% of cases | | BP230 | Intracellular hemidesmosomal protein | Structural support | ~70% of cases | | Desmoglein 1/3 | Desmosomal cadherin | Cell-cell adhesion | Pemphigus vulgaris (NOT BP) | | Envoplakin/Periplakin | Plakin family proteins | Intermediate filament anchoring | Paraneoplastic pemphigus | **High-Yield:** BP180 is the most clinically relevant antigen; anti-BP180 IgG correlates with disease activity and is present in nearly all BP patients. Anti-BP230 alone can cause a milder, non-inflammatory variant. **Clinical Pearl:** The presence of anti-BP180 IgG is associated with more severe, generalized disease, while anti-BP230 alone may present with localized disease. **Mnemonic:** **BP = Basement membrane Proteins** — think hemidesmosomal anchoring proteins (BP180, BP230), NOT desmosomal proteins (which are pemphigus targets). 
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