Activity of the Bacillus anthracis 20 kDa protective antigen component

Abstract

<p>Abstract</p> <p>Background</p> <p>Anthrax is caused by <it>Bacillus anthracis </it>that produce two exotoxins, lethal toxin and edema toxin. The lethal toxin is composed of the lethal factor (LF) complexed with the cell binding protective antigen (PA₈₃, 83 kDa). Likewise, the edema factor (EF) binds to the PA₈₃to form the edema toxin. Once PA83 is bound to the host cell surface, a furin-like protease cleaves the full-length, inactive protein into 63 kDa and 20 kDa antigens (PA₆₃and PA₂₀). PA₆₃forms a heptamer and is internalized via receptor mediated endocytosis forming a protease-stable pore, which allows EF and LF to enter the cell and exert their toxic effects.</p> <p>Both proteolytically cleaved protective antigens (PA₆₃and PA₂₀fragments) are found in the blood of infected animals. The 63 kDa protective antigen PA₆₃fragment has been thoroughly studied while little is known about the PA₂₀.</p> <p>Methods</p> <p>In this study we examined the role of PA₂₀using high throughput gene expression analysis of human peripheral blood mononuclear cells (PBMC) exposed to the PA₂₀. We constructed a PA mutant in which a Factor Xa proteolytic recognition site was genetically engineered into the protective antigen PA₈₃to obtain PA₂₀using limited digestion of this recombinant PA₈₃with trypsin.</p> <p>Results</p> <p>Global gene expression response studies indicated modulation of various immune functions and showed gene patterns indicative of apoptosis via the Fas pathway in a subset of the lymphoid cells. This finding was extended to include observations of increased Caspase-3 enzymatic activity and the identification of increases in the population of apoptotic, but not necrotic cells, based on differential staining methods. We identified a list of ~40 inflammatory mediators and heat-shock proteins that were altered similarly upon exposure of PBMC to either rPA₂₀or <it>B. anthracis </it>spores/vegetative cells.</p> <p>Conclusion</p> <p>This study shows that the PA₂₀has an effect on human peripheral blood leukocytes and can induce apoptosis in the absence of other PA components.</p