The proposed research, is aimed at elucidating the cell receptor for the type D simian retrovirus (SRV-l) and at elucidating the interaction between the virus and the receptor. The proposed work will generate monoclonal anti-receptor antibodies which will be used for the isolation of the receptor. Moreover, these monoclonal antibodies will be tested for their immunogenic capacity to induce anti-idiotypic antibodies which mimic parts of the receptor, thus binding to the virus and inhibiting viral attachment to the cell receptor. The isolated cell receptor will be characterized biochemically as to molecular size and composition. The relationship between the binding of the virus or its envelope protein with the receptor, the binding of monoclonal antibodies with the receptor, and binding of synthetic peptides, representing various areas of the viral envelope protein, with the receptor will be established. Elucidation of structural features of the viral envelope protein and the cell receptor will provide a basis for analyzing interactions between these two components.