PRECISE ULTRASTRUCTURAL-LOCALIZATION OF IN-VIVO DEPOSITED IGG ANTIBODIES IN FRESH PERILESIONAL SKIN OF PATIENTS WITH BULLOUS PEMPHIGOID

Bullous pemphigoid (BP) is a blistering skin disease in which the pati ent develops autoantibodies to the epidermal basement membrane zone, U sing postembedding immunogold electron microscopy, we previously demon strated that autoantibodies against the 230-kDa BP antigen (BPAG1) bin d to the intracellular hemidesmosomal component of normal skin, wherea s those against the 180-kDa BP antigen (BPAG2) bind only along the pla sma membrane of hemidesmosomes. The purpose of the present study was t o elucidate the precise localization of the in vivo deposited IgG anti bodies in fresh perilesional skin of patients with BP. Samples of fres h perilesional skin were obtained from three patients with BP whose se ra reacted only with BPAG1, only with BPAG2, and with both BPAG1 and B PAG2 upon immunoblotting using epidermal extracts. Cryofixed and cryos ubstituted skin samples were used as a substrate for on-surface immuno labelling, In all three cases, most of the gold particles were observe d close to the plasma membrane of the basal keratinocytes. A quantitat ive analysis revealed that most (> 80%) of the in vivo deposited IgG a ntibodies in the three cases were localized within 10 nm inside to 50 nm outside of the cell membrane, with a single peak observed 0-10 nm o utside of the cells (> 50%). This distribution corresponded to the loc ation of BPAG2, but not to that of BPAG1. These findings suggest that most, if not all, of the in vivo deposited IgG antibodies in the peril esional skin of BP are directed against BPAG2, rather than against BPA G1, thus further supporting the crucial role of anti-BPAG2 autoantibod y in the initial stage of blister formation in BP.