The complement system, by virtue of its dual effector and priming functions, is a major host defense against pathogens. Flavivirus nonstructural protein (NS)-1 has been speculated to have immune evasion activity, because it is a secreted glycoprotein, binds back to cell surfaces, and accumulates to high levels in the serum of infected patients. Herein, we demonstrate an immunomodulatory function of West Nile virus NS1. Soluble and cell-surface-associated NS1 binds to and recruits the complement regulatory protein factor H, resulting in decreased complement activation in solution and attenuated deposition of C3 fragments and C5b-9 membrane attack complexes on cell surfaces. Accordingly, extracellular NS1 may function to minimize immune system targeting of West Nile virus by decreasing complement recognition of infected cells.

Original languageEnglish
Pages (from-to)19111-19116
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number50
StatePublished - Dec 12 2006


  • Flavivirus
  • Immune evasion
  • Innate immunity
  • Pathogenesis


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