Eosinophils have long been thought to function exclusively as "end stage effector" cells in asthma and other eosinophilic lung disorders, acting through the release of cytotoxic substances. However, mounting evidence has demonstrated that eosinophils have important immunoregulatory roles in mediating airways inflammation. One such well-established key immunoregulatory role is their function as anitgen-presenting cells (APCs). The purpose of this grant is to explore the organization of the antigen presentation machinery on the surface membrane of human eosinophils. Specifically, the involvement of tetraspanin molecules and lipid rafts may be important in allowing eosinophils to function as professional APCs. The specific aims of the research proposed will investigate the following hypotheses: 1) the tetraspanin CD9 is associatedwith antigen-presentation machinery in human eosinophils, 2) MHC Class II Is located predominantly in lipid rafts on the cell surface of human eosinophils, 3) CD9 associates with MHC Class II in lipid rafts of human eosinophils, and 4) other non-CD9 tetraspanins associate with MHC Class II in intracellular compartments in human eosinophils. The proposed research will utilize co-immunopreciptation, lipid raft isolation, immunofluoresecence microscopy, flow cytometry, and Western blot in order to establish the involvement of tetraspanins and lipid rafts in the antigen presentation complex of human eosinophils. Establishment of the association between antigen presentation proteins, tetraspanins, and lipid rafts would further establish eosinophils as unique antigen presenation cells with a likely pivotal immunoregulatory role in the perpetuation of asthma. Asthma is a common disorder that affects millions of Americans, but a complete understanding of the disease remains elusive. Eosinophils are inflammatory cells that have been noted to be associated with asthma and other lung diseases. Our research aims to better understand how eosinophils organize their surface proteins with the hope that this will provide insight into their true role in asthma.