Bacillus anthracis interacts with plasmin(ogen) to evade C3b-dependent innate immunity

Area of Science:

• Microbiology
• Immunology
• Proteomics

Background:

• Bacillus anthracis evades host immunity using toxins and other strategies.
• The interaction of B. anthracis spores with host proteins, particularly the complement system, is not well understood.
• Understanding these interactions is crucial for developing effective countermeasures against anthrax.

Purpose of the Study:

• To identify human serum proteins that bind to Bacillus anthracis spores.
• To elucidate the mechanisms by which B. anthracis spores interact with and evade the innate immune system.
• To investigate the role of plasminogen (PLG) in B. anthracis immune evasion.

Main Methods:

• Proteomic analysis was used to identify proteins interacting with B. anthracis spores.
• Binding assays were performed to confirm the interaction of plasminogen (PLG) with spores.
• In vitro assays were conducted to assess the effect of PLG-bound spores on complement system components and phagocytosis.

Main Results:

• Plasminogen (PLG) was identified as a major human serum protein bound to B. anthracis spores.
• PLG binding was dependent on lysine and the spore's exosporium, with alpha-enolase and elongation factor tu identified as PLG receptors.
• PLG-bound spores demonstrated anti-opsonic properties by cleaving C3b, reducing macrophage phagocytosis.

Conclusions:

• Bacillus anthracis spores recruit plasminogen (PLG) to evade innate immunity.
• PLG binding enhances the anti-complement and anti-opsonization properties of B. anthracis spores.
• This study provides novel insights into B. anthracis immune evasion mechanisms.