The Thymus Leukemia (TL) antigen and CD1 are mouse class I histocompatibility molecules that are expressed primarily by intestinal epithelial cells. In addition to their expression pattern, they share several other features in common. First, unlike the histocompatibility molecules expressed on all cell types, both the TL antigen and CD1 are nonpolymorphic or nonclassical class I molecules. Second, unlike the other class I histocompatibility molecules, TL antigen and CD1 do not require a functional peptide antigen transporter, called TAP, to assemble and reach the cell surface. Based upon their sequence similarity to classical class I molecules, and their expression by antigen presenting cells such as intestinal epithelial cells, it is most likely that these molecules have a specialized antigen presenting function. Consistent with this, peptide-specific and CD1-restricted T cell lines have been generated, an unusual peptide motif for CD1 binding has been characterized, and TL-specific alloresponses have been reported. Based upon their TAP independent expression, we speculate that these nonclassical class I molecules may have evolved to acquire peptides in a post-ER or Golgi site. The major aims are to: 1. Characterize the intracellular trafficking of the TL antigen and CD1, to determine if they have a pathway, and a site where they bind peptides, distinct from the classical class J molecules. Biochemical studies will be used to study the maturation and transport of these molecules in cells with and without TAP function, and in polarized epithelial cells in culture. Functional studies with TL and CD1 restricted clones and defined protein antigens will be carried out to determine where antigen may be acquired. 2. Determine the structure and diversity of peptide antigens bound to the TL antigen and CD1 using both a biochemical and molecular genetic strategy. Peptides loaded in cells with and without TAP function will be compared. 3. To generate and characterize peptide-specific and TL and CD1 restricted T-cell lines and clones. 4. To generate T cells that are TL antigen or CD1 restricted during the course of a natural infection. We will use L. monocytogenes as a model antigen, and to enhance the chance of recognition, we will generate transgenic mice that express these class I molecules on all their tissues. 5. To determine if IEL can react to the TL antigen and CD1 by measuring in vitro responses of short term IEL cultures. Because these class I molecules have novel properties, these studies should provide important insights into general issues concerning antigen presentation function and in particular, to novel pathways for class I antigen presentation. This studies also may provide further insight into unresolved problems of immune function and regulation in the gut including the surveillance for transformed epithelial cells, and the dysfunction that leads to inflammatory bowel disease.