Identification of desmoglein 1 as autoantigen in a patient with intraepidermal neutrophilic IgA dermatosis type of IgA pemphigus

In a 51-year-old female patient with intraepidermal neutrophilic IgA dermatosis (IEN) type of IgA pemphigus, circulating IgA, but not IgG, autoantibodies were detected to bind to the cell surface of the whole epidermis, being much stronger in the upper epidermis. In the patient's skin a heavy intraepidermal IgA staining was observed throughout the whole epidermis, accompanied by a weak IgG and a more prominent C3 staining. IgA from the patient's serum showed no reactivity either with epidermal proteins by immunoblot analysis, or with COS 7 cells transiently transfected with mammalian cell expression constructs containing full length human Dsc1, Dsc2 and Dsc3. Our patient's IgA specifically reacted with conformational epitopes of human desmoglein (Dsg) 1 but not Dsg 3, when studied in a previously established, here for IgA antibody detection modified enzyme-linked immunoabsorbent assay (ELISA) of baculovirus expression system. The immunoreactivity against keratinocyte cell surface was completely removed from the serum of the patient by pre-incubation with recombinant Dsg1 baculoprotein. This finding indicates that the sera possess only IgA antibodies against the extracellular domain of Dsg1 baculoprotein, but no antibodies against components of keratinocyte cell surface other than Dsg1. This is the first case of IgA pemphigus where Dsg1 has been identified as the autoantigen.