The overall objective of this project is to understand the molecular mechanism of MHV neuropathogenesis. The major goal of this project is to understand the molecular basis of viral tissue and cellular tropism. The progress made in the previous grant period has identified several cellular receptors for MHV infection. However, these receptors cannot totally account for viral tissue tropism. In this grant period, we propose to identify and study additional cellular receptors for MHV and the process of virus entry. Three specific projects will be performed: (1) Characterization of brain-specific MHV receptors. We have identified a carcinoembryonic antigen (CEA) which is expressed only in the brain, the only CEA molecule of this kind identified so far. We will determine its function as an MHV receptor, its neurobiology and role in the development of brain. Its biochemical properties and temporal and spatial expression patterns in the brain also will be examined. (2) Identification of additional brain-specific receptors for MHV in mice, rats and humans. Our data suggested that more than one CEA molecule can also serve as an MHV receptor. We want to examine whether CEA molecules in other species and other CEA molecules in mice can serve as MHV receptors. These studies will reveal the potential mechanism of MHV infections in mice as well as rats and primates. (3) Identification of cellular proteins interacting with MHV receptors and MHV structural proteins. Our studies have indicated the receptors alone are not sufficient to allow virus to enter cells. Other cellular factors are required. Preliminary data suggested that these cellular factors might interact directly or indirectly with receptors or with viral structural proteins. Therefore, we will use biochemical methods and molecular biology approaches to identify cellular proteins interacting with either CEA molecules or MHV structural proteins. The functions of these proteins in the viral entry process will be studied. These three projects will allow us to understand the molecular basis of viral tissue tropism.