## Mechanism of Acantholysis in Pemphigus Vulgaris **Key Point:** Acantholysis (loss of cell-to-cell adhesion) in PV results from IgG autoantibodies binding to desmogleins and disrupting desmosomal adhesion, NOT from complement activation or direct cytotoxicity. ### Pathogenic Mechanism 1. **IgG autoantibodies** bind to desmoglein 3 (and desmoglein 1 in mucocutaneous disease) 2. **Disruption of desmosomal adhesion** occurs through: - Steric hindrance of adhesion molecule interaction - Possible signaling-mediated loss of adhesion 3. **Acantholysis results**: Keratinocytes lose contact with neighbors 4. **Intraepidermal blistering** forms (suprabasal in mucosal PV, superficial in cutaneous PV) **High-Yield:** Unlike bullous pemphigoid (which is complement-dependent), pemphigus vulgaris is **antibody-mediated without significant complement activation**. This is why complement levels are normal in PV. **Clinical Pearl:** Direct immunofluorescence (DIF) shows **intercellular IgG deposition** ("tombstone" pattern) around keratinocytes, confirming antibody-mediated pathology. ### Why Other Mechanisms Are Wrong - **Complement-mediated lysis**: PV is NOT complement-dependent; C3 is typically absent on DIF. - **Cytotoxic T-cell infiltration**: T cells are present but are secondary; the primary pathology is antibody-mediated. - **Basement membrane degradation**: This occurs in bullous pemphigoid and dermatitis herpetiformis, not PV (which has an intact basement membrane). 
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