Background: Pemphigus is an antidesmoglein (Dsg) autoimmune disease that is divided into two major subtypes: pemphigus foliaceus (PF) and pemphigus vulgaris (PV). We previously developed enzyme-linked immunosorbent assays (ELISAs) using recombinant Dsg1 and Dsg3 to detect IgG autoantibodies in patients with pemphigus. The protocol for the ELISAs was optimized for serological diagnosis, but under the conditions used, these assays were not particularly useful for monitoring disease activity in certain patients. That is, the sera from some patients with high-titre antibodies continued to show high index values in the ELISA after clinical improvement. Objectives: In the study reported here, we modified the ELISA protocol to obtain 'true' index values that exhibit a better correlation with disease activity. Methods: We tested two cases of pemphigus foliaceus (PF) and four cases of pemphigus vulgaris (PV), each with ELISA index values greater than 150 for Dsg1 or Dsg3. We ran an ELISA with sera from these patients serially diluted from 1:100 to 1:12,800. We then performed ELISA with a series of PV No. 1 sera diluted to 1:800 and PV No. 2-4 and PF No. 1-2 sera diluted to 1:1600, after which we plotted the ELISA index values against the time course of disease activity. Results: In each of these cases, there was no apparent decline, over the course of the disease activity, in the ELISA index values at a serum dilution of 1:100, probably because the antigen-antibody reaction was saturated at that dilution. After running an ELISA with sera serially diluted from 1:100 to 1:12,800 we found that a linear dose-dependency between the dilution value and the index value was only observed when sera were diluted to 1:800 or more in one case (PV No. 1) and to 1:1600 or more in the other five cases (PV No. 2-4, PF No. 1-2). After performing ELISA with these series as outlined above we plotted the ELISA index values against the time course of disease activity and found that the index values obtained from these appropriately diluted sera fluctuated in parallel with disease activity, and declined with clinical improvement. Conclusions: These findings indicate that when appropriate dilutions are used in Dsg1 and Dsg3 ELISA, these assays can provide useful serological information for assessing disease activity in PF and PV.
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