Immune system paralysis by anthrax lethal toxin: the roles of innate and adaptive immunity

Since the deliberate use of anthrax as a bioweapon in the USA in 2001, an enormous amount of attention has been focused on the biology of Bacillus anthracis, the causative bacterium of anthrax. Fatal systemic anthrax involves massive bacteraemia and toxaemia with non-descript early symptoms until the onset of shock and sudden death. The outbreak of fatal symptoms after the incubation period of B anthracis suggests an impairment of the host immune system against this pathogen. Thus, it is likely that B anthracis will possess certain strategies to escape from the host immune system. However, the mechanisms of such immune-evasion strategies are not fully characterised yet. Given the critical role of B anthracis toxins in anthrax pathogenesis, much effort has been made to understand the pathological nature of the toxins. Recent studies have shown the pleiotropic actions of anthrax lethal toxin on host innate immune cells, and that several effects of anthrax lethal toxin may directly account for the mechanism of immune intervention by B anthracis.