Suppressive Effects of Anthrax Lethal Toxin on Megakaryopoiesis

Abstract

Anthrax lethal toxin (LT) is a major virulence factor of Bacillus anthracis. LT challenge suppresses platelet counts and platelet function in mice, however, the mechanism responsible for thrombocytopenia remains unclear. LT inhibits cellular mitogen-activated protein kinases (MAPKs), which are vital pathways responsible for cell survival, differentiation, and maturation. One of the MAPKs, the MEK1/2-extracellular signal-regulated kinase pathway, is particularly important in megakaryopoiesis. This study evaluates the hypothesis that LT may suppress the progenitor cells of platelets, thereby inducing thrombocytopenic responses. Using cord blood-derived CD34+ cells and mouse bone marrow mononuclear cells to perform in vitro differentiation, this work shows that LT suppresses megakaryopoiesis by reducing the survival of megakaryocytes. Thrombopoietin treatments can reduce thrombocytopenia, megakaryocytic suppression, and the quick onset of lethality in LT-challenged mice. These results suggest that megakaryocytic suppression is one of the mechanisms by which LT induces thrombocytopenia. These findings may provide new insights for developing feasible approaches against anthrax.

Acquired coagulant factor VIII deficiency induced byBacillus anthracislethal toxin in mice

“…4,5,14,16,52,55,56 For cell and animal studies, high-performance liquid chromatography (HPLC)-purified LF and PA were reconstituted as LT in a ratio of 1:5, which resembles the ratio of PA and LF in the culture supernatants of B. anthracis. The LPS contamination was monitored using a Limulus Amoebocyte Lysate QCL -1000 kit (Lonza, Walkersville, MD, USA).…”

“…[7][8][9][10][11][12][13] Recent studies have shown that LT might contribute to hemorrhage by inducing thrombocytopenia and megakaryocytic suppression. [14][15][16] The mechanism underlying coagulation suppression, however, remains undetermined.…”

Platelet production proceeds independently of the intrinsic and extrinsic apoptosis pathways

“…Traditional chemotherapeutic agents are a prime example 11 . Megakaryocyte apoptosis has also been implicated in a range of infectionrelated thrombocytopenias, including those associated with arenaviruses 12 , HIV 13 , dengue 14 and anthrax 15 . Apoptosis is also thought to contribute to thrombocytopenia in myelodysplastic syndrome 16 , and in immune-mediated thrombocytopenia 17 .…”

Endothelial Cell Sensitization by Death Receptor Fractions of an Anti–Dengue Nonstructural Protein 1 Antibody Induced Plasma Leakage, Coagulopathy, and Mortality in Mice

“…The Abs used for ELISA (detecting soluble thrombomodulin) and flow cytometry (detecting endothelial surface TRAIL-R expression) analyses were anti-thrombomodulin Ig (Santa Cruz Biotechnology) and anti-TRAIL-R (1-4) Ig (R&D Systems), respectively. The endothelial cells were challenged with (+DENV) (multiplicity of infection [MOI] of 0.2, subcytotoxic) or without DENV (2DENV) in combination with or without preimmune Ig, anti-NS1 Ig, anti-NS1-DR4 Ig treatments (20 mg/ml, subcytotoxic; 24 and 48 h), and then the surface expression levels of TRAIL-Rs were analyzed by flow cytometry (FACSCalibur; BD Biosciences, San Jose, CA) (29)(30)(31). Fluorescence-labeled isotype-matched control Igs were used to determine the background staining levels in the flow cytometry analyses.…”