Henry M. Jackson Foundation 3 articles published in JoVE Immunology and Infection Pairwise Growth Competition Assay for Determining the Replication Fitness of Human Immunodeficiency Viruses Siriphan Manocheewa1, Erinn C. Lanxon-Cookson1, Yi Liu1, J. Victor Swain1, Jan McClure1, Ushnal Rao1, Brandon Maust1, Wenjie Deng1, Justine E. Sunshine1, Moon Kim1, Morgane Rolland3,4, James I. Mullins1,2 1Department of Microbiology, University of Washington, 2Departments of Medicine and Laboratory Medicine, University of Washington, 3U.S Military HIV Research Program, Walter Reed Army Institute of Research, 4Henry M. Jackson Foundation Growth competition between nearly isogenic viruses provides a sensitive measurement for determining relative replication fitness. The protocols described here include the construction of recombinant HIV-1 clones, virus propagation and growth competition and analysis methods optimized to yield sensitive and consistent results. Biology A Method for Selecting Structure-switching Aptamers Applied to a Colorimetric Gold Nanoparticle Assay Jennifer A. Martin1,2, Joshua E. Smith1,2, Mercedes Warren1, Jorge L. Chávez1,3, Joshua A. Hagen1, Nancy Kelley-Loughnane1 1711th Human Performance Wing, Human Effectiveness Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, 2The Henry M. Jackson Foundation, 3UES, Inc. A protocol is provided to select structure-switching aptamers for small molecule targets based on a tunable stringency magnetic bead selection method. Aptamers selected with structure-switching properties are beneficial for assays that require a conformational change to signal the presence of a target, such as the described gold nanoparticle assay. Neuroscience A High Content Imaging Assay for Identification of Botulinum Neurotoxin Inhibitors Krishna P. Kota1,6, Veronica Soloveva2,6,7, Laura M. Wanner3,6, Glenn Gomba4,6, Erkan Kiris3,5,6, Rekha G. Panchal6, Christopher D. Kane2,6,7, Sina Bavari6 1Perkin Elmer Inc., 2Henry M. Jackson Foundation, 3The Geneva Foundation, 4ORISE, 5Frederick National Laboratory for Cancer Research, 6Division of Molecular and Translational Sciences, US Army Medical Research Institute of Infectious Diseases, 7DoD Biotechnology High Performance Computing Software Applications Institute (BHSAI), Telemedicine and Advanced Technology Research Center (TATRC), US Army Medical Research and Materiel Command (USAMRMC) Botulinum neurotoxin is one of the most potent toxins among Category-A biothreat agents, yet a post-exposure therapeutic is not available. The high content imaging approach is a powerful methodology for identifying novel inhibitors as it enables multiparameter screening using biologically relevant motor neurons, the primary target of this toxin.