The purpose of this proposal is to solicit support through the Physician Scientist Award for studies examining the relationship of the handling of self proteins by antigen presenting cells to self tolerance and presentation of foreign antigens. The results will then be applied to the study of alloreactivity with a long term goal of using the knowledge and insights from our studies to find a method of inducing specific unresponsiveness in an allograft model. The hallmark of the immune response is the ability to distinguish self from nonself. However, the mechanisms by which the immune system develops and maintains tolerance to self antigens, while maintaining reactivity toward foreign antigens, are poorly understood. On of the mechanisms of self tolerance appears to involve the deletion of self-reactive cells in the thymus during T cell maturation. However, this mechanism alone does not completely explain self tolerance. Self proteins, like foreign proteins, have been shown in vitro to be processed and presented by antigen presenting cells. Until recently, however, it was not known whether this phenomenon actually occurred in vivo. Lorenz and Allen have described a unique system for studying the in vivo presentation of the self hemoglobin molecule. Using this system, they were able to show not only that self macrophages were able to present self hemoglobin molecules, but that a variety of cells in different organs of the body had self hemoglobin/Ia molecules on their surfaces that could be recognized by appropriate T cell hybridomas. As the mice do not react to these self hemoglobin/Ia molecules in vivo, T cell tolerance has occurred. Research proposal. For the first two years of the Award, David Hagerty will work in the group of Emil Unanue in the laboratory of Paul M. Allen. He will learn the laboratory techniques of creating and maintaining T cell hybridomas, cell and tissue culture, sterile technique, antigen presentation assays, cell purification and how to set-up RIA and ELISA assays. During this time he proposes to study in more detail the processing and presentation of self proteins by macrophages and other antigen representing cells in an attempt to understand the relationship between the processing and presentation of self and foreign proteins and self tolerance. Using the murine T cell hybridoma YO1.6, the I-Ek restricted hybrid which detects the processed hemoglobin peptide fragment HbBdminor(67-76), he will isolate and purify different cells in each organ homogenate and determine which cells are expressing the self Hb/Ia complexes. He will then use self-Hb specific TH1 and TH2 T cell clones to study the ability of the identified APCs from the organ homogenates to stimulate the clones, especially with regard to any costimulators that may be required. He will then study the mechanisms of tolerance to other self antigens that are compartmentalized and tissue specific (GFAP) or developmentally regulated (sperm hsp70). He plans to apply the findings of the above experiments to the study of alloreactivity, and eventually to apply these results to the achievement of specific unresponsiveness in an organ transplant model.