The use of two substrates to improve the sensitivity of indirect immunofluorescence in the diagnosis of pemphigus.

The aim of this study was to re-evaluate indirect immunofluorescence (IIF) comparing two substrates, normal human skin (HS) and monkey oesophagus (MO) using serum from 29 pemphigus patients classified according to the presence of serum autoantibodies to either desmoglein (Dsg) 1 or Dsg3 detected by enzyme-linked immunosorbent assay (ELISA). Overall, the sensitivity of IIF was 83% on HS and 90% on MO. When data from both substrates were combined, the sensitivity increased to 100%. When sera from pemphigus foliaceus (PF) patients were studied, which contained Dsg1 antibodies only, the sensitivity of IIF was greatest on HS and titres were on average 4.8 doubling dilutions higher than on MO. In contrast, when sera containing autoantibodies only to Dsg3 from pemphigus vulgaris (PV) patients was studied, the sensitivity was greatest on MO and titres were on average 4.4 doubling dilutions higher than on HS. There was a significant correlation between Dsg1 antibody levels and IIF titres on HS and between Dsg3 antibody levels and IIF titres on MO. The investigation of immunobullous disorders in the future is likely to move towards antigen-specific techniques such as the Dsg ELISAs used in this study. However, in laboratories which currently rely on IIF for detecting pemphigus autoantibodies, the data presented in this study strongly suggest that two substrates should be used for IIF screening: one rich in Dsg1, such as HS, and the other rich in Dsg3, such as MO. This combination of substrates should not only increase the sensitivity of detecting pemphigus antibodies, but will aid in the differentiation of PV from PF. It is also possible that the data might be more useful for disease monitoring.