1. Analytical Chemistry Laboratory and Laboratory of Immunopathogenesis and Bioinformatics, SAIC-Frederick, Inc., National Cancer Institute at Frederick, P.O. Box B, Frederick, Maryland 21702-1201, and Critical Care Medicine Department, Clinical Center, and Clinical and Molecular Retrovirology Section, National Institute of Allergies and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892