Controversial role of antibodies against linear epitopes of desmoglein 3 in pemphigus vulgaris, as revealed by semiquantitative living cell immunofluorescence microscopy and in-cell ELISA

A novel explanation of pemphigus vulgaris (PV) pathogenesis suggests that serum autoantibodies may affect desmoglein 3 (Dsg3)-mediated adhesion by triggering depletion of Dsg3 from desmosomes. Furthermore, abrogation of Dsg3 from the cell seems to depend on anti-Dsg3 pemphigus IgG. In this study we sought to gain more insights into the role of PV IgG recognizing non-conformational epitopes of Dsg3 (anti-Dsg3-L IgG) by semi-quantitative living cell immunofluorescence (LCIF) microscopy, in-cell ELISA and morphometric analysis of acantholysis. Our data demonstrate that PV serum and PV IgG can induce acantholysis and reduce the total amount of Dsg3 in cultured keratinocytes, whereas anti- Dsg3-L IgG fail to do so when administered at concentrations comparable to those present in pathogenic PV sera. However, the Dsg3-depleting activity of such polyclonal anti-Dsg3 IgG was acquired when used at 1μg/ml. Interestingly, both PV sera and IgG, including anti-Dsg3-L IgG, caused early depletion of surface Dsg3 while slightly affecting the total cell content of Dsg3 until late acantholysis. This raises a possibility that depletion of Dsg3 from cell membrane and reduction of the total cellular levels of Dsg3 represent distinct phenomena in PV acantholysis. Taken together, our data demonstrate that anti-Dsg3 PV IgG against linear epitopes of Dsg3 can induce acantholytic changes of keratinocytes in a doseand time-dependent manner. Specifically, both morphological and biochemical changes suggestive of acantholysis are seen only at high concentrations. We conclude that anti-Dsg3L IgG play a minor role in PV under physiologic conditions.