Evaluating efficacy of plasmapheresis for patients with pemphigus using desmoglein enzyme-linked immunosorbent assay

Background: Pemphigus is an autoimmune bullous disease caused by circulating IgG autoantibodies against cell-cell adhesion molecules between keratinocytes: desmoglein (Dsg) 3 and Dsg1. Plasmapheresis is often used to treat severe cases of pemphigus. Enzyme-linked immunosorbent assays (ELISAs) against recombinant Dsg3 and Dsg1 have recently become available, allowing us to quantify IgG autoantibodies against Dsg3 and Dsg1. Objectives: Using ELISA against recombinant Dsg3 and Dsg1, to evaluate the efficacy of plasmapheresis in pemphigus. Methods: Sera obtained from 10 patients with pemphigus vulgaris and one with pemphigus foliaceus following a total of 16 cycles of centrifugal plasmapheresis and 12 effluents from the plasmapheresis were subjected to ELISA against Dsgs. The percentage of IgG autoantibodies removed was calculated using two different formulae: one used serum titres before and immediately after plasmapheresis and the other used the absolute amounts of IgG autoantibodies in the effluents. The percentage fall of anti-Dsg antibody level was also calculated using the serum titres 1 day after plasmapheresis. Results: Using serum titres immediately after plasmapheresis, there was a mean fall per treatment in anti-Dsg 3 antibody level of 43.0% (n = 12) and in anti-Dsg1 antibody level of 48.4% (n = 7). By contrast, calculated from the effluents, on average one treatment removed only 14.6% of anti-Dsg3 antibodies (n = 12) and 16.4% of anti-Dsg1 antibodies (n = 7). This should reflect the correct percentage as it is based on the absolute amounts of IgG autoantibodies removed. Using serum titres 1 day after plasmapheresis, there was a mean fall per treatment in anti-Dsg 3 antibody level of 12.9% (n = 2) and in anti-Dsg1 antibody level of 8.4% (n = 4). The percentage of IgG autoantibodies removed 1 day after plasmapheresis was lower than that found to be removed immediately after plasmapheresis (n = 6). Conclusions: One centrifugal plasmapheresis procedure eliminates about 15% of the IgG autoantibodies from the whole body. The percentage fall of anti-Dsg IgG antibody level differed depending on when the serum samples were obtained after plasmapheresis. The change in the percentage fall of anti-Dsg antibody level within 1 day after plasmapheresis is thought to be attributable to the passive diffusion of the IgG autoantibodies from the extravascular space to the intravascular space. Therefore, removal of IgG autoantibodies calculated using serum titres only should be evaluated carefully considering the equilibration of the IgG autoantibodies between the different body spaces.