Early Circulating Edema Factor in Inhalational Anthrax Infection: Does It Matter?

Area of Science:

• Microbiology
• Cell Biology
• Toxicology

Background:

• Anthrax toxins, including protective antigen (PA), lethal factor (LF), and edema factor (EF), are key virulence factors of Bacillus anthracis.
• While PA mediates cellular entry of LF and EF, these enzymatic factors can disseminate independently after infection.

Purpose of the Study:

• To investigate the endocytosis and intracellular activity of edema factor (EF) in the absence of protective antigen (PA).
• To elucidate the role of PA in EF trafficking and function within host cells.

Main Methods:

• Utilized a fluorescent EF chimera to study endocytosis in various cell lines.
• Assessed intracellular cAMP levels to measure EF enzymatic activity.
• Investigated the effect of sequential EF and PA delivery on cellular response.

Main Results:

• Edema factor (EF) was observed to enter cells independently of protective antigen (PA) via pole-dependent endocytosis.
• Protective antigen (PA) remained essential for EF's enzymatic activity, indicated by increased intracellular cAMP levels.
• Sequential addition of EF followed by PA restored EF-mediated cAMP elevation, suggesting intracellular functional association.

Conclusions:

• Edema factor (EF) exhibits PA-independent cellular uptake.
• Protective antigen (PA) is crucial for EF's enzymatic function, likely through intracellular association during trafficking.
• Findings provide new insights into EF trafficking and the mechanisms of anthrax toxin action.