Project Summary/Abstract (Collaborative Project) In this project a set of recently developed experimental and computational tools for antigen discovery will be utilized to identify antigens of microbial and self origin in IgG4-related disease and in systemic sclerosis. The focus will be to identify T cell antigens from the microbiome and from the host extracellular matrix. Detailed metagenomic analyses of the microbiome will be performed to identify microbial antigens of relevance. In addition, peptide antigens from the host extracellular matrix will be screened for presentation by MHCII and evidence of T cell immunogenicity. Finally, attempts will be made to identify shared T cell epitopes derived from host and microbial antigens that are targeted by B cells.