Complement protein C3 binding to Bacillus anthracis spores enhances phagocytosis by human macrophages

Christopher Premanandan, Craig A. Storozuk, Corey D. Clay, Michael Dale Lairmore, Larry S. Schlesinger, Andrew J. Phipps

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Alveolar macrophages are thought to play a central role in the pathogenesis of inhalational anthrax. Receptors present on macrophages that mediate phagocytosis of Bacillus anthracis spores have yet to be completely defined. To begin to determine if soluble factors that are present in the lung such as immunoglobulin and complement are involved, we characterized the binding of human IgG and C3 to the surface of B. anthracis spores at different concentrations of nonimmune human serum. Furthermore we investigated the uptake of B. anthracis spores by human monocyte-derived macrophages in the presence of nonimmune human serum. Here we show that C3b is bound to B. anthracis spores and is activated through the classical pathway by IgG bound to the spore surface. Furthermore, we show that C3 serves as an opsonin for B. anthracis spores resulting in enhanced phagocytosis by human macrophages. These studies provide evidence that nonimmune serum contains IgG which binds to B. anthracis spores but is not sufficient to initiate phagocytosis. However, surface-bound IgG does initiate the classical pathway of complement activation, which is active in the lung, resulting in deposition of the opsonin C3b on the spore surface.

Original languageEnglish (US)
Pages (from-to)306-314
Number of pages9
JournalMicrobial Pathogenesis
Issue number6
StatePublished - Jun 2009
Externally publishedYes


  • Anthrax
  • Bacillus anthracis
  • Complement
  • Macrophage

ASJC Scopus subject areas

  • Microbiology
  • Infectious Diseases


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