Epstein-Barr virus (EBV), a human herpesvirus, is a significant human pathogen. It is a candidate human cancer virus as it is strongly linked to nasopharyngeal carcinoma and Burkitt's lymphoma, two malignancies and it is oncogenic in subhuman primates. In vitro, EBV transforms human B lymphocytes thereby generating permanent polyclonal cell lines. EBV is the etiologic agent of infectious mononucleosis, a self-limited lymphoproliferative disease which represents a significant health hazard in immunocompromised individuals; it is also associated with human autoimmune diseases. EBV reactivation frequently occurs during AIDS. Although the entire EBV genome has been molecularly cloned and knowledge of genetic features which lead to transformation is rapidly accumulating, little is known of the viral and cellular factors which permit this virus to infect B lymphocytes and epithelial cells. The primary objective of this proposal is the understanding, on a molecular and biochemical level, of the early events involved in EBV infection of human cells. EBV receptor (CR2) expression in B lymphocytes will b down-regulated by B cell activation and by transfection with vectors encoding anti-sense CR2 mRNA. CR2 will be introduced into various eucaryotic cells which lack endogenous CR2 by transfection of CR2 cDNA. The consequences of such altered CR2 expression including ability to bind and internalize EBV and C3dg and susceptibility to EBV induced B cell activation and transformation will be ascertained. The role of CR2 in EBV infection of epithelial cells will also be addressed. Primary epithelial cell cultures and epithelial cell lines will be examined for CR2 and EBV expression by in situ hybridization with high specific activity 35S-labeled RNA or DNA probes. Another primary goal of this project is the elucidation of the structure of CR2 and its various functional and structural domains. These studies will be aided by the recent isolation of a full-length CR2 cDNA clone and will be supplemented by the use of proteolytic and chemically cleaved CR2 fragments and synthetic peptides representing functionally important portions of the molecule. Similar studies of the functionally relevant regions of EBV gp350 and C3dg, the CR2 ligands, are planned. These data will be used for formulate models for the CR2/EBV receptor ligand complexes. Physicochemical approaches and potentially x- ray crystallography will be used to test these models. These planned studies will reveal basic knowledge about virus-host cell interactions in a model system of human disease and they may potentially provide rationales for blocking the early stages of EBV infection.