Battling against host phagocytes: the wherefore of the RTX family of toxins?

The RTX family of bacterial exotoxins is a group of related cytolytic proteins produced by a wide variety of gram-negative human and animal pathogens. While diverse in their associated diseases and in their target cell specificities, there remain several themes common to RTX toxins, including genetic organization, structural and functional features, and effects on target cells. In this review, we summarize and discuss the genetics, regulation, epidemiology, structure/function relationships, and in vivo and in vitro activities of the best characterized RTX toxins, and speculate on their roles in pathogenesis and their use in immunotherapy.