NIH researchers have recently announced the isolation of a human B-lymphotropic virus (HBLV) from six individuals with various lymphoproliferative and immune disorders. HBLV appears to belong to the group of human herpes viruses and may be associated with B-lymphoproliferative disorders. Serological tests using indirect immunofluorescence methods revealed that only 4 of 220 random healthy blood donors were seropositive for HBLV antibodies. An ELISA-based assay for HBLV antibody detection would facilitate further study of the prevalence of infection with this virus and the relation of infection to human disease. So far, however, HBLV has not been seen to be infectious for any cells other than fresh B-lymphocytes. In this proposal, the investigators present their plan for using HBLV cultured in B-lymphocytes obtained from umbilical cords to demonstrate the feasibility of developing an ELISA-based test kit for HBLV antibody detection. They also discuss their plans for establishing a cell culture system other than fresh B-lymphocytes for virus proliferation, so that tests can be produced on a commercial scale.