Figure 1.

Differential phagocytosis of encapsulated and non-encapsulated strains of Bacillus anthracis active bacteria by human monocyte-derived macrophages. THP-1 macrophage cells were infected with B. anthracis in media supplemented with different concentrations of normal human serum (NHS; 12.5–50%) and heat-treated human serum (ΔNHS, 12.5–50%). (A) Internalized surviving bacteria obtained from lysed macrophages post-phagocytosis represented as percent of B. anthracis inoculum. (B) Percent of B. anthracis inoculum (non-internalized) surviving in the media post incubation with THP-1 macrophages. Black and gray bars represent non-encapsulated and encapsulated strains, respectively. Cytochalasin D (Cyto D)-treated THP-1 cells that have lost their phagocytic ability were considered as negative control. Each bar represents the mean of three independent experiments. Error bars represent standard error of the mean. WS, media without serum. Statistical significance is highlighted by the following denotations: * for P-value < 0.05, ** for P-value < 0.01, and *** for P-value < 0.001.