About the Authors
Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, California, United States of America
Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
The authors have declared that no competing interests exist.
The author(s) have made the following declarations about their contributions: Conceived and designed the experiments: LP SEE MT YAA JPB JCB. Performed the experiments: LP AJS SEE JPB. Analyzed the data: LP AJS SEE JPB. Contributed reagents/materials/analysis tools: MT YAA. Wrote the paper: LP JCB.