PROJECT SUMMARY/ABSTRACT CEACAM1 is a single-pass type I transmembrane protein and the primordial member of the carcinoembryonic antigen (CEA) family of immunoglobulin molecules that is expressed on the apical and basolateral surfaces of intestinal epithelial cells (IEC) and on a wide range of immune cell types. However, its functions on intestinal epithelial cells (IECs) are unknown. The current research proposal addresses the unanswered question of whether CEACAM1 acts to convert microbial or host signals from the apical and/or basolateral surface into the production of antimicrobial peptides (AMP) by IECs. The ability of the IEC to sense the presence of microbes and deliver antimicrobial peptides (AMP) into the lumen represents a major mechanism of mucosal defense. Our long-term goals are to determine whether CEACAM1-mediated stimulation of AMPs protects from commensal and pathogenic microbe invasion of the IEC and susceptibility to colitis, the vectoral direction required for this stimulation (apical and/or basolateral), whether it is specifically dependent upon CEACAM1 isoforms with a short (S) cytoplasmic tail and if high-affinity ligands for CEACAM1 can be developed to stimulate these protective activities. The objective of this research is to elucidate how CEACAM1 stimulates AMP production and whether this information together can be co-opted for therapeutic purposes. Our central hypothesis is that CEACAM1 functions as a novel microbial sensor that responds to specific microbes or host ligands with production of AMPs that are important to barrier protection. This rationale is derived from recent studies that a specific deficiency of CEACAM1 in mouse IEC in vivo leads to decreased AMP expression by IECs coupled to increased susceptibility to colitis and invasion by pathogenic microbes. Our central hypothesis will be tested with three specific aims: 1) Determine whether IEC-associated CEACAM1 regulates the production of AMP and host susceptibility to colitis and enteropathogens; 2) Determine whether specific CEACAM1 isoforms are responsible for delivering activat- ing signals to induce AMPs, and; 3) Define a therapeutic strategy to enhance human CEACAM1 ligands that interact homophilically to induce these protective responses. In Aim 1, we will determine the innate and/or adap- tive origins of the intestinal inflammation that ensues from CEACAM1-deficiency in the IEC and whether this involves increased bacterial translocation of founding populations in the lumen. Aim 2 will determine whether CEACAM1-S isoforms can stimulate IECs to produce AMPs in response to pharmacologic and microbial signals and whether such stimulation can occur in response to ligation of CEACAM1 on the apical and basolateral sur- faces. In Aim 3, we seek to generate human CEACAM1 variants with enhanced ability to stimulate IEC produc- tion of AMP in vitro and in vivo and as such provide protection from experimental colitis. Overall, this proposal is significant because...