Immune dysregulation of pemphigus in humans and mice

Pemphigus vulgaris is an autoimmune blistering disease of the skin and mucous membranes that is caused by immunoglobulin (Ig)G autoantibodies against the cadherin-type adhesion molecule desmoglein (Dsg)3 expressed on stratified epithelial cells. Interaction between antigen-specific T and B cells, which is selectively achieved through T-cell receptor/major histocompatibility complex-peptide complex association and subsequently corroborated by co-stimulatory molecules such as CD40/CD154, is required for production of pathological anti-desmoglein 3 antibody. Some genetically and environmentally susceptible individuals harbor desmoglein reactive B and T cells, and anti-desmoglein antibodies were detected in their serum. Analysis of the anti-desmoglein antibody clones derived from pemphigus patients or pemphigus model mice revealed that pathogenic antibodies mostly react with conformational epitopes on mature form desmogleins, whereas non-pathogenic ones tend to react with non-conformational epitopes. Surprisingly, antibodies to the Dsg1 precursor pro-protein are also cloned from individuals without pemphigus. These observations suggest that active suppression by regulatory cell subsets is dominant in these susceptible individuals. In fact, Dsg-reactive T-inducible regulatory type 1 (Tr1) cells are readily detected in healthy carriers of pemphigus-related human leukocyte antigen haplotypes, but rarely in pemphigus patients. These Tr1 cells can be functionally converted to T-helper 2-like cells which secrete interleukin-2 by inactivation of Foxp3 through antisense oligonucleotides. Thus, delicate balance between self-reactive lymphocytes and regulatory T cells may be a key element in determining whether individuals produce pathogenic antibodies and develop pemphigus phenotypes or not.