Persistent infections were established in suspension cultures of BHK21/13S cells with both Parana and lymphocytic choriomeningitis viruses. Four generations after infection with either virus, more than 90% of the cells scored as infective centers, with concomitant peaks in extracellular virus yields. In both cultures the synthesis of detectable plaque-forming units (PFU) ceased about the 50th generation postinfection, and this condition was maintained until the 350th cell generation when the cultures were discontinued. The generation time of each culture was identical to that of uninfected parent controls, and at no time were cytopathic effects evident. In spite of the absence of infectivity, over 90% of the cells sampled at various times contained viral antigen demonstrable by immunofluorescence. When either of these persistently infected cell lines was substituted for normal cells in the standard plaque assay, very low efficiencies of plating were observed for homotypic and heterotypic viruses. Plaque formation by several heterologous viruses was virtually unaffected.

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This ultrastructural study was undertaken to determine the localization ofcytochemically demonstrable blood-brain bartier (BBB)-associated enzymatic activities and ofsome nonenzymatic constituents in sheep brain microvascular endotheial cells (ECs) growing in vitro. Positive reactions for alkaline phosphatase (AP), 5'-nudeotidase (5'N), transport ATPase (Na ,K-ATPase), and adenosine diphosphatase (AD1 ase) were present on both apical and basolateral plasma membranes (PMs) ofthe ECs. The reaction for calcium-dependent ATPase (Ca2-ATPase) was less intense and was restricted to basolateral PM and associated plasmalemmal pits. These cells also revealed an abundance ofanionic siteslabeled with cationic colloidal gold (CCG) and Ricinus communis agglutifin 120 (RCA)-binding sites, specific forD -ga1aaosyl cal Retardation and Developmental Disabilities and the fund for the Center for Trace Metal Studies and Environmental Neurotoxicology.

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