1. From the Departments of Radiology (W.S., M.D.B., D.F.K., A.H.M.) and Neurosurgery (G.A.H.), and the Cardiovascular Research Center (W.S., M.D.B.), University of Virginia, Charlottesville, Va; and the Departments of Medicine and of Microbiology, Immunology, and Molecular Genetics (X.W., J.W., A.J.L.) and of Pathology (T.A.D.), University of California, Los Angeles.