Cryptosporidium parvum is a gastrointestinal parasite that causes chronic, severe, and frequently fatal diarrheal disease in immunocompromised hosts, for which there is no treatment. Current strategies for the development of therapies to treat this parasitic infection have focused on disruption of the processes of sporozoite attachment and invasion into intestinal epithelial cells. These studies have identified two sporozoite ligands, gp900 and gp40/15, that adhere to epithelial cells and mediate attachment and invasion. The genes encoding these glycoproteins have been identified, cloned, and expressed, but production of functional recombinant C. parvum ligands requires expression in eukaryotic systems to generate the particular carbohydrate epitopes critical for epithelial cell binding. The lack of functional recombinant C. parvum ligands has hampered identification of the epithelial cell receptors used by the parasite to invade cells. The major goal of this project is to isolate and identify the epithelial cell receptors for gp900 and gp40/15. The specific aims of this project are:Specific Aim 1: To generate recombinant gp900 glycoproteins and characterize binding of native and recombinant gp900 to intestinal epithelial cells in vitro.Specific Aim 2: To identify intestinal epithelial cell receptors for gp900 and gp40/15Results from these experiments will provide greater insight into the processes of C. parvum sporozoite attachment and invasion and will advance the goal of developing treatment strategies for cryptosporidiosis. This award will provide the candidate, Dr. O'Connor, with the opportunity to study C. parvum ligand-epithelial cell receptor interactions at the molecular level, and provide the groundwork for her to establish an independent research program in the field of host-parasite interactions. Dr. O'Connor will be advised by her sponsor, Dr. Ward, a gastroenterologist and a recognized expert on enteric parasites. Her co-mentor, Dr. Kopin, has extensive experience identifying and characterizing gastrointestinal receptors. New England Medical Center, in association with Tufts University and the wider Boston scientific community provides researchers with diverse and excellent scientific resources, and is exceptional environment for a young scientist.