Paraneoplastic pemphigus (PNP) is an autoimmune blistering disease that occurs in association with underlying neoplasms. Patients with PNP develop characteristic IgG autoantibodies directed against multiple antigens, most of which have been identified as cytoplasmic proteins of the plakin family (desmoplakin I, II, BPAG1, envoplakin, and periplakin). This study identified cell surface target antigens of PNP. We focused on desmoglein (Dsg) 3 and Dsg1, the autoantigens of pemphigus vulgaris and pemphigus foliaceus. ELISA using baculovirus-expressed recombinant Dsgs (rDsg3, rDsg1) has revealed that 25 out of 25 PNP sera tested were positive against Dsg3 and 16 of 25 were positive against Dsg1. All of 12 PNP sera tested immunoprecipitated Dsg3. Removal of anti-Dsg3 autoantibodies by immunoadsorption was sufficient to eliminate the ability of PNP sera to induce cutaneous blisters in neonatal mice in vivo. Furthermore, anti-Dsg3-specific antibodies that were affinity purified from PNP sera were proven to be pathogenic and caused blisters in neonatal mice. These findings indicate that Dsg3 and Dsg1 are the cell surface target antigens in PNP and that IgG autoantibodies against Dsg3 in PNP sera play a pathogenic role in inducing loss of cell adhesion of keratinocytes and causing blister formation. ( J. Clin. Invest.

Patient 2 was a 39-year-old man who received chemotherapy with cyclophosphamide, doxorubicin, vincristine, and prednisone for low-grade B-cell non-Hodgkin's lymphoma in 1993. The lym-The New England Journal of Medicine Downloaded from nejm.org at UNIVERSITY OF PITTSBURGH -MAIN on August 11, 2015. For personal use only. No other uses without permission.

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PNP in children and adolescents is most often a presenting sign of occult Castleman's disease. It presents with severe oral mucositis and cutaneous lichenoid lesions. Serum autoantibodies against plakin proteins were the most constant diagnostic markers. Pulmonary injury appears to account for the very high mortality rates observed.