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| Fig. 60.3 Pemphigoid gestationis. Direct immunofluorescent study demonstrating linear C3 along the basement membrane zone. Less commonly, linear IgG is also seen. |
Bullous pemphigoid antigen 2 (BPAG2) is a 180 kDal transcellular glycoprotein that is part of the hemidesmosome (a structure that binds epithelial cells to the basement membrane of the epidermis). IgG binds to BPAG2 and triggers the classic complement pathway leading to a deposition of C3 along the basement membrane zone (Fig. 60-3). Deposition of complement along the basement membrane zone leads to a recruitment of inflammatory cells, particularly eosinophils. This cascade ultimately leads to a release of proteolytic enzymes that cleave portions of the epidermis from the dermis.
