Effect of Bacillus anthracis lethal toxin on human peripheral blood mononuclear cells

Abstract

Lethal toxin (LeTx) plays a central role in anthrax pathogenesis, however a cytotoxicity of LeTx has been difficult to demonstrate in vitro. No cytolytic effect has been reported for human cells, in contrast to murine cell lines, indicating that cell lysis can not be considered as a marker of LeTx activity. We have recently shown that murine macrophage‐like RAW 264.7 cells treated with LeTx or infected with anthrax spores underwent changes typical of apoptotic death. Here we demonstrate that cells from human peripheral blood display a proapoptotic behavior similar to murine cells. TUNEL assay detected a nucleosomal degradation typical of apoptosis in peripheral blood mononuclear cells (PBMC) treated with LeTx. Membrane staining with apoptotic dyes was detected in macrophages derived from monocytes in presence of LeTx. The toxin inhibited production of proinflammatory cytokines in PBMC stimulated with a preparation of Bacillus anthracis cell wall. Infection of PBMC with anthrax spores led to the appearance of a large population of cells stained positively for apoptosis, with a reduced capacity to eliminate spores and vegetative bacteria. The aminopeptidase inhibitor, bestatin, capable of protecting cells from LeTx, restored a bactericidal activity of infected cells. These findings may be explained by LeTx expression within phagocytes and support an important role of LeTx as an early intracellular virulence factor contributing to bacterial dissemination and disease progression.

A dually active anthrax vaccine that confers protection against both bacilli and toxins

“…4 C and D). In vitro, lethal toxin induces apoptosis by cleaving mitogenactivated protein kinase kinases (23,24). Our analysis illustrates this specific pathologic damage caused by lethal toxin in vivo.…”

Anthrax Lethal Toxin Blocks MAPK Kinase-Dependent IL-2 Production in CD4+ T Cells

“…Recent studies have shown deleterious effects of the toxin not only on other types of APCs (e.g., dendritic cells) (25), but also on non-leukocytes such as human endothelial cells (26). Pro-apoptotic effects of anthrax LT treatment on unpurified human PBMC have been reported (14), but direct effects on purified T cells have not been previously demonstrated.…”

“…We next examined the effect of anthrax LT on a variety of functions of Jurkat cells in our culture conditions, because anthrax LT has been reported to have a pro-apoptotic effect on PBMC (14). As shown in Fig.…”

“…Validated anthrax LT bioassays that are based on human cell parameters would fill a critical void in the development of anthrax therapeutics. Anthrax LT is known to be a potent modulator of cytokine signaling networks, either enhancing (11,12) or inhibiting (7,13,14) production and/or extracellular release of proinflammatory cytokines from APCs depending on the stimulation conditions. Because MAPKK-dependent cytokine production is a feature common to a variety of cell types from anthrax-susceptible species, we investigated whether modulation of cytokine production by anthrax LT in non-APC could form an alternative basis for anthrax LT bioassays.…”

Exploiting death: apoptotic immunity in microbial pathogenesis

“…18,21,41,[55][56][57][58][59][60][61][62][63][64] Viruses exploit apoptotic processes as well, especially reducing the death of virally infected cells to facilitate intracellular viral replication. The viral reprogramming of cell death, in contrast, reflects a distinct approach.…”