MOLECULAR MECHANISMS OF MHC LINKED SUSCEPTIBILITY

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DESCRIPTION: (Adapted from the applicant's abstract) - The major histocompatibility complex (MHC) is an important susceptibility locus for many human autoimmune diseases. Susceptibility to pemphigus vulgaris (PV), an autoimmune disease of the skin, is strongly associated with MHC class II alleles that are rare in the general population. In PV patients, autoantibodies against a keratinocyte adhesion molecule, desmoglein 3, inhibit desmoglein 3-mediated kearatinocyte adhesion and induce severe blister formation. The mechanisms by which MHC class II genes confer susceptibility to this antibody-mediated autoimmune disease will be studied in a DQ1 transgenic mouse model and in patients with PV. The PV-associated DQ1 molecule differs from a common DQ1 subtype that does not confer susceptibility to PV only at a single position of the DQbeta chain (aspartic acid/valine at DQbeta 57). This disease-associated polymorphism introduces a negative charge into the DQ1 peptide binding site. The functional consequences of the DQ(beta) 57 polymorphism will be examined using soluble DQ1 molecules that have been expressed in Drosphila Schneider cells. Peptides from the desmoglein 3 autoantigen that bind to the PV-associated DQ1 molecule will be sought, and the pathogenicity of DQ1 peptide ligands will be assessed. Transgenic mice that express the PV-associated DQalpha and DQbeta genes (DQA1*0101, DQB1*0503) will be generated as an animal model for PV; the bareskin (Bsk) mutation will be introduced into these mice to allow visual assessment of skin lesions. To determine if susceptibility in this model faithfully replicates the genetics of human disease, mice that express a DQ1 subtype that is not associated with PV will also be generated. DQ1 transgenic mice will be used to define the DQ1 peptide ligands that induce skin autoimmunity and to determine which T cell population(s) induce the production of pathogenic autoantibodies by B cells. NK1.1+ T cells are of particular interest because they are the major source of IL-4 for the differentiation of naive T cells into Th2 cells. The relevance of findings in the transgenic mouse model for the pathogenesis of the human disease will be investigated. It will be determined whether peptide(s) that induce disease in the transgenic mouse model are recognized by T cells from PV patients and whether these T cells induce the production of desmoglein 3 autoantibodies. The five specific aims are designed to study the interaction of DQ1-bound peptides in DQ1 transgenic mice and by studies in PV patients. Aim 1 is "to generate transgenic mice that express PV associated DQ1 molecule". Mice will be generated which express DQA1*0101 and DQB1*0503 and control transgenic animals with DQA1*0101 and DQB1*0501. This will be done in animals that have had the MHC class II knocked out (Ab superscript o/o). In addition, the bareskin mutation (Bsk) will also be moved into these animals so that the lesions of pemphigus can be directly observed. The second specific aim is to "find the structural requirements for peptide binding by the PV-associated DQ1 molecule and to identify desmoglein 3 peptides that are bound by DQ1." Peptide expression libraries will be constructed and an effort will be made to identify a motif for the peptide sequence which binds to this particular class II molecule. Soluble molecules have been generated after molecular engineering binding of the alpha and beta chains to one another in place of the transmembrane domains. A third specific aim is "to examine the induction of autoimmunity by desmoglein 3 peptides and DQ1 transgenic mice. Specific aim four is "to examine the role of NK1.1+/- T cells and other T cell subsets in the induction of a Th2-mediated autoimmune response against desmoglein 3." Cell transfer experiments are planned, as well as the use of T cell receptor alpha chain knock out mice. The fifth aim is "to examine the relevance of findings in the transgenic mouse model for the pathogenesis of the human disease." Here desmoglein 3 specific B cell lines will be developed as well as T cell lines that recognize desmoglein 3 peptides as presented by DQ1. The author hopes to reconstruct a system in which T cell clones induce production of desmoglein 3 autoantibodies. A number of cytokines will be explored in this system.