Overlapping IgG4 Responses to Self- and Environmental Antigens in Endemic Pemphigus Foliaceus

The etiology of human autoimmune diseases in general remains largely unknown, although the genetic and environmental interplay may be relevant. This applies to the autoimmune diseases of the skin such as the pemphigus phenotypes and others. In this group, there is an endemic form of pemphigus foliaceus [also known as Fogo Selvagem (FS)] where the pathogenic IgG4 autoantibody response to the self-antigen, Desmoglein 1 (Dsg1) cross-react with the LJM11 sand fly salivary gland antigen. In this investigation we dissected the IgG4 autoantibody repertoires utilized by FS patients in response to endogenous self Dsg1 and exogenous LJM11 sand fly antigen. Based on analyses of the genetic clonal signatures of these antibodies, our results indicate that there is a significant overlap between these two responses as all identified IgG4 monoclonal antibodies cross-react to both Dsg1 and LJM11 antigens. Germline H and L chain V gene antibodies generated according to mutated cross-reactive monoclonal antibodies preserved their reactivity to both antigens. Our findings suggest that both Dsg1 autoantigen and LJM11 environmental antigen could be the initial antigenic stimulants for the IgG4 autoimmune responses in FS. These results support our hypothesis that LJM11 antigen plays a substantial role in triggering the IgG4 autoantibody development in FS, and provide new insights on how non-infectious environmental antigen(s) may drive the generation of autoantibodies in IgG4-related autoimmune diseases