The production of pathogenic autoantibodies is the cause of a number of autoimmune disease. In man, the cellular and molecular mechanisms underlying the production of such pathogenic autoantibodies is incompletely understood. Part of the lack of information in this area relates to the inability to develop a full picture of the repertoire of autoantibody producing B cells in normal individuals and potential bias in that repertoire in individuals with autoimmune disease. Moreover, mechanisms by which autoantibodies occurring in normal individuals may become pathogenic in persons with autoimmune disease ar unknown. The purpose of the proposed research, therefore, is to develop a better understanding of the mechanisms underlying the generation of autoantibodies and the cellular and molecular basis by which autoantibodies with pathogenic potential might develop. The specific projects will examine individual aspects of this overall subject. The first project, of which Dr. Peter Lipsky is the principal investigator, will examine the full extent of the repertoire of autoantibody producing B cells in normal adults, preimmune cord blood B cells and B cells of patients with autoimmune diseases. The goal of this project is to gain an understanding of the nature of the B cells producing autoantibodies, the V(H) and V(L) genes involved in autoantibody production and the cytokines that might be involved in facilitating maturation of each of the subsets of B cells, including those producing autoantibodies. Finally, the proposed studies will examine the signals involved in Ig class switching, as well as the relationship of class switching to the development of autoantibodies. In Project 2, of which Dr. Capra is the principal investigator, the molecular basis of autoantibody production will be examined by determining V(H) and V(L) gene utilization by the autoantibody producing B cells. Additional mechanistic experiments will be carried out to examine at the role of somatic mutation in the development of high avidity autoantibodies. In Project 3, Dr. Katheryn Meek will look at the role of recombination in the generation of autoantibodies. Two specific areas will be examined. The first involves an analysis of recombinatorial rearrangement of D segment genes in individuals with autoimmune disease to determine whether alterations in this mechanism of diversity generation is involved in the production of autoantibodies. The second aspect of this work will examine switch recombination of Ig class switching to autoantibodies. The second aspect of this work will examine switch recombination of Ig class switching to determine mechanisms of Ig class switching and whether the generation of pathogenic autoantibodies occurs in association with isotype switching. Finally, hypotheses generated in Projects 1-3 concerning mechanisms of autoantibody generation in individuals with autoimmune diseases will be tested using transgenic technology in Project 4, of which Dr. Philip Tucker will be the principle investigator. In these experiments, transgenic animals will be employed to examine in vivo mechanisms of pathogenic autoantibody production. It is anticipated that as a result of the proposed work, new and important insights into the mechanisms of autoimmunity will arise that should provide approaches to therapeutic interventions in the future.