IgA pemphigus is a rare autoimmune bullous disease characterized by
IgA deposition at keratinocyte cell surfaces. Clinically and histologically,
IgA pemphigus is divided into two major subtypes:
subcorneal pustular dermatosis (SPD) type and intraepidermal neutrophilic
IgA dermatosis (IEN) type. Using
cDNA transfection and living cell immunofluorescence, we previously showed that
desmocollin 1, one of the
desmosomal cadherins, is the
autoantigen in SPD-type
IgA pemphigus, but the
autoantigen in IEN type is still unclear. In the present study we investigated
antigen localization by postembedding immunoelectron microscopy. We examined three sera each of SPD-type and IEN-type
IgA pemphigus. In SPD-type,
gold particles were observed predominantly in the extracellular spaces between keratinocytes at desmosomes, although a few particles were observed in the intracellular domain at the desmosomal attachment plaques. In IEN type, the
gold particles were observed mainly in the intercellular spaces in nondesmosomal areas. These results provide evidence that the
IgA in the sera of SPD-type
IgA pemphigus reacts with the extracellular domain of
desmocollins. In contrast, the
autoantigen for IEN type may in fact not be a component of desmosomes. IEN-type
IgA pemphigus may be the first member of the
pemphigus group of autoimmune
bullous dermatoses that reacts with a nondesmosomal transmembranous
protein.