Project Summary/Abstract This project seeks to understand how T-B collaboration and specific autoantigens drive inflammation and fibrosis in IgG4-related disease. In order to define antigenic drivers of IgG4- related disease this proposal examines autoantigens that define IgG4-related disease. The antigen-specificity of clonally expanded CD4+ cytotoxic T cells that are likely drivers of the disease will also be determined. Cognate B cells will be identified in an antigen specific manner and T and B cells interactions will be examined. Based on information on specific autoantigens already obtained, autoantibodies and antigen specific B cells will be identified that are not only seen initially at the time of diagnosis but that also return at the time of relapse following B cell depletion induced remission. The autoantigens that dominate at the time of relapse are the likely source of peptides that disease-related memory CD4+ T cells recognize. Autoantibodies will be identified using HuProt protein arrays and validated by the Luciferase Immunoprecipitation System assays and by ELISAs. Autoantigens will be dually labeled in order to identify and characterize antigen-specific B cells. Overlapping peptides from key autoantigen proteins will be used to activate autoantigen specific T cells, which will be characterized by flow cytometry and transcriptomics. Mechanisms of inflammation and fibrosis driven by adaptive immune cells in tissues will be characterized by imaging tissues and using systems biology approaches for analysis.