Model of the pathogenesis of bullous pemphigoid. Deposition of anti-BP180 Abs along the basement membrane zone led to complement fixation and release of C5a. The C5a activates resident mast cells, which in turn release proinflammatory mediators, such as TNF and IL-8, leading to neutrophil recruitment. Activated neutrophils release proteinases such as neutrophil elastase (NE) and MMP9, which digest the BP180, causing blister formation.