Anthrax is a disease caused by the aerobic spore-forming Bacillus anthracis (BA), a Gram positive, rod-shaped bacterium. In the past few years it has made world news due to its use as a bioterrorist weapon. Dr. Rest’s Lab has recently been involved in characterizing a new BA toxin called Anthrolysin O (ALO). It is a cholesterol dependent cytolysin that has proven cytotoxic to many cell types in vitro such as human polymorphonuclear leukocytes (PMN), monocytes, monocyte-derived macrophages, and the THP-1 monocytic human cell line. Further, at sublethal concentrations, it inhibits neutrophil chemotaxis, induces p38 phosphorylation, and causes an LPS-like cytokine production in neutrophils and macrophages. We believe that one or more of three different mechanisms can be responsible for these phenomena. ALO could be a TLR4 agonist, binding directly to it and activating the TLR4 cell signaling pathway. ALO could be aggregating lipid rafts, which promotes tyrosine phosphorylation and recruitment of signaling proteins. Finally, ALO could be producing small pores which bring about calcium fluxes. Studies are in progress to validate one or more of these.