SLE is a complex auto-immune disorder. Recent studies show that SNPs in the TNFAlP3 locus encoding A20 protein are associated with many autoimmune diseases including SLE. Understanding TNFAlP3 regulating mechanisms and effects of SLE-associated SNPs might lead to new treatments for SLE However, potential regulatory elements of TNFAIP3 gene and autoimmune disease-associated SNPs are distributed over 300 kb, making it difficult to study in a (patho)physiologically meaningful context. Recently-developed BAC modification technology can identify regulatory elements for large-size genes because it links two or more overlapping BACs to a single recombinant. We therefore propose to (1 ) develop a BAC reporter SLE-relevant cell types for testing the TNFAlP3 response to BCR or CD40 ligation in B cells and TLR ligands and TNF in dendritic cells; (2) generate humanized TNFAIP3 mouse models on A20-deficient background to identify the regulatory regions important to compensate for loss of TNFAIP3 function; (3) generate human BAC reporter cell lines with a deletion at TT>A polymorphic dinucleotide region to study its regulation. After completing this grant, we expect to gain initial insights of TNFAlP3 regulation. This work will lay a solid foundation for future studies to uncover new therapeutic approaches for SLE by modulating TNFAlP3 gene expression.