Shared VH1-46 gene usage by anti-desmoglein 3 antibodies in pemphigus vulgaris suggest a common mechanism for developing autoimmunity (BA2P.116)

Abstract Pemphigus vulgaris (PV) is a potentially fatal blistering disease caused by autoantibodies (autoAbs) to desmoglein 3 (Dsg3). To better understand the mechanism by which PV Abs develop, we cloned human anti-Dsg3 Abs from four PV patients using phage display (n=2) or heterohybridoma (n=2). We identified VH1-46 anti-Dsg3 Abs from all 4 patients, comprising 5 unique heavy chain complementarity determining region (CDR) 3 sequences. All 5 Abs caused suprabasal blisters in human skin explants. Surprisingly, most VH1-46 Abs had few replacement mutations and did not show evidence of antigen-driven positive selection by focused binomial testing of mutation patterns. To determine if somatic mutations are required for Dsg3 binding, we reverted mutated Abs to their germline (GL) VDJ sequences. Three GL Abs bound Dsg3 by ELISA, with a 2- to 80-fold decrease in affinity as measured by surface plasmon resonance. Analysis of mutation patterns in 2 other Abs which lost Dsg3 binding after mutation reversion revealed homologous acidic amino acid CDR mutations. Site-directed mutagenesis indicated that these acidic residues are necessary and sufficient for Dsg3 binding. Our data indicate that VH1-46 autoAb gene usage is shared among PV patients which may be due to naive autoreactivity of some VH1-46 Abs or the requirement for very few acidic amino acid mutations in the CDRs to confer Dsg3 binding. Common VH1-46 autoAb gene usage may suggest a common mechanism for developing autoimmunity in PV.