Activation of vascular endothelial cells (EC) plays a crucial role in the pathology of chronic inflammation. Our long-term research goal is to identify the specific intracellular signals that underlie EC activation as this will identify novel selective therapeutic strategies aimed at preventing or treating chronic inflammatory diseases. Many chronic inflammatory diseases (e.g. rheumatoid arthritis, multiple sclerosis) are accompanied by de novo formation of ectopic lymphoid microenvironments named tertiary lymphoid organs (TLOs) that optimize the immune response and exacerbate the inflammation. A defining feature of these TLOs is the distinct phenotype of the endothelium that resembles the high endothelial cells (HEC) in normal secondary lymph nodes. However the signals that activate normal EC to become HEC-like cells are not known. Genetic evidence and our preliminary studies lead us to hypothesize that the recently described non- canonical (NC) NF-kappa B (NF-kB) pathway plays a fundamental role in the genesis of HEC however this pathway has not yet been investigated in EC. We will address our hypothesis by accomplishing the following specific aims: 1. To identify the components of the NC NF-kB pathway in EC. We will identify the series of molecular events in the NC pathway in endothelial cells in vitro. 2. To identify the NC NF-kB-dependent genes activated in EC. We will selectively inhibit the NC pathway to identify the target genes in EC. 3. To determine the effects of NC NF-kB deletion in EC on lymph node development and tertiary lymphoid organ formation in vivo. We will use the Cre-loxP to selectively delete the NC pathway in EC in vivo and determine the effects that this has on HEC formation in lymph nodes and TLOs. Accomplishing these aims will establish the validity of therapeutically targeting the NC NF-kB pathway in chronic inflammatory diseases. Lay Statement: Chronic inflammation is a debilitating and potentially life threatening condition that occurs in a number of diseases. Cells of the blood vessel walls control chronic inflammation by allowing the recruitment the immune cells from the blood into tissues. This proposal will investigate the signals that control blood vessel activation and will therefore identify novel drug targets for preventing or treating chronic inflammation.