Autoantibodies against the 3 desmocollin (Dsc; Dsc1-Dsc3) isoforms have been described in different pemphigus variants. Here, we developed state-of-the-art detection systems for serum anti-Dsc1, Dsc2and Dsc1 IgG and IgA. These assays were applied in 5 different cohorts including pemphigus vulgaris (PV) patients with compatible direct immunofluorescence (IF) microscopy but no reactivity against desmogleins 1 and 3 (n = 24) and sera from patients with autoimmune blistering diseases with positive direct IF microscopy taken at the time of diagnosis (n = 749). We found that detection of anti-Dsc serum reactivity is not helpful in the routine diagnosis of PV, pemphigus foliaceus and paraneoplastic pemphigus but may be valuable in pemphigus vegetans.
| BACKGROUNDDesmocollins (Dsc) and desmogleins (Dsg) belong to the Ca 2+ -dependent cadherin adhesion protein family. They are part of the desmosomes and provide proper cohesion between neighbouring cells of various tissues including skin and surface-close epithelia. The 4 Dsg (Dsg1-Dsg4) and 3 Dsc (Dsc1-Dsc3) isoforms share a similar architecture with approximately 30% sequence identity ( Figure 1A). By both homo-and heterophilic transinteraction of the outmost extracellular N-termini and binding to proteins of the desmosomal plaque, Dsc and Dsg mediate connection between the intermediate filaments of neighbouring cells.In pemphigus vulgaris (PV), the major target antigen is Dsg3. [2,3] In patients with the mucocutaneous phenotype of PV, autoantibodies against Dsg1 in addition to Dsg3 reactivity are found. [2,3] In contrast, autoantibody reactivity in paraneoplastic pemphigus (PNP) is more diverse. In addition to antibodies against Dsg3, reactivity against proteins of the plakin family comprising desmoplakins I and II, periplakin, envoplakin, plectin, and BP230 as well as Dsg1, and, more recently, α2-macroglobulin-like 1 and epiplakin has been described. [4,5] Autoantibodies against all 3 Dsc isoforms have been reported in various pemphigus subtypes including PV, pemphigus foliaceus, pemphigus vegetans, pemphigus herpetiformis, IgA pemphigus and PNP.  A pathogenic relevance of anti-Dsc antibodies has been suggested by different in vitro models based on the incubation of cultured human keratinocytes and human skin with anti-Dsc3 IgG. These data are supported by the finding of intra-epidermal splitting resulting in erosions and hair loss in mice with Dsc3-null skin.
| QUESTIONS ADDRESSEDWhile Dsc1 has been identified as major target antigen in the subcorneal pustular dermatosis type of IgA pemphigus,  the diagnostic value of detecting serum anti-Dsc antibodies in PV is still unclear.
| EXPERIMENTAL DESIGNTo address this open question, we cloned and expressed the ectodo- This strategy has recently led to highly sensitive and specific test systems for serum autoantibodies against Dsg1, Dsg3, BP230 and the NC1 domain of type VII collagen.To evaluate the diagnostic relevance of detecting anti-Dsc antibodies in pemphigus sera, 5 distinct cohorts we...