Gram-positive bacterial pathogens that secrete cytotoxic pore-forming toxins, such as Staphylococcus aureus and Streptococcus pneumoniae, cause a substantial burden of disease. Inspired by the principles that govern natural toxin-host interactions, we have engineered artificial liposomes that are tailored to effectively compete with host cells for toxin binding. Liposome-bound toxins are unable to lyse mammalian cells in vitro. We use these artificial liposomes as decoy targets to sequester bacterial toxins that are produced during active infection in vivo. Administration of artificial liposomes within 10 h after infection rescues mice from septicemia caused by S. aureus and S. pneumoniae, whereas untreated mice die within 24-33 h. Furthermore, liposomes protect mice against invasive pneumococcal pneumonia. Composed exclusively of naturally occurring lipids, tailored liposomes are not bactericidal and could be used therapeutically either alone or in conjunction with antibiotics to combat bacterial infections and to minimize toxin-induced tissue damage that occurs during bacterial clearance.

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Pore-forming (poly)peptides originating from invading pathogens cause plasma membrane damage in target cells, with consequences as diverse as proliferation or cell death. However, the factors that define the outcome remain unknown. We show that in cells maintaining an intracellular Ca 2 þ concentration [Ca 2 þ ] i below a critical threshold of 10 lM, repair mechanisms seal off 'hot spots' of Ca 2 þ entry and shed them in the form of microparticles, leading to [ Plasma membrane pores formed by cytotoxic proteins and peptides disrupt the permeability barrier in a target cell. Pathogens gain access and kill host cells by secreting pore-forming toxins, whereas the blood complement system utilises the pore-forming proteins of membrane attack complexes to eliminate both pathogens and the pathogen-invaded cells. 1,2 As in particular, cells of the blood and the vascular systems are permanently exposed to potential deadly attacks by a variety of pore-forming (poly)peptides, it is not surprising that mechanisms repairing the damaged plasma membrane have evolved. [3][4][5][6] Biological effects occurring in the wake of membrane permeabilisation and its subsequent repair are multifaceted. Apart from the two obvious end points, complete recovery or death, recovering cells can newly acquire numerous (patho)physiological functions. 3,7,8 A rise in intracellular Ca 2 þ concentration [Ca 2 þ ] i is critical for successful plasma membrane repair and cell recovery, 9,10 whereas an intracellular Ca 2 þ overload is held responsible for the death of pore-bearing cells. 11 In addition, Ca 2 þ influx, followed by transcriptional activation, is thought to induce a variety of biological responses associated with sublytic effects of pore-forming toxins. 3,4,7,8 Thus, it appears that the extent of [Ca 2 þ ] i elevation following pore formation determines the fate of a targeted cell. Consequently, Morgan et al. 11 suggested that in nucleated cells, an initial increase in [Ca 2 þ ] i stimulates the recovery processes, allowing the cell to withstand a limited complement attack. The recovery might be associated with cellular activation and the production of inflammatory modulators, which, in turn, amplify an ongoing inflammatory response. 3,11 The authors further hypothesised that a more severe membrane damage causes a sharp rise in [Ca 2 þ ] i , which overwhelms all recovery processes. 11 However, how [Ca 2 þ ] i determines cell fate, how the acquisition of novel functions is initiated and how the 'point of no return' is defined remain unknown.In this study, we have undertaken a simultaneous, real-time characterisation of [Ca 2 þ ] i and plasma membrane dynamics in living cells permeabilised with the bacterial pore-forming toxin streptolysin O (SLO). Our data show that the fate of SLOperforated cells is dependent on their ability to control the extent of a pore-induced elevation in [Ca 2 þ ] i . We detail Ca 2 þ -dependent mechanisms that elicit either repair or irreversible structural changes in the plasma membrane and show how intracellula...

The plasma membrane constitutes a barrier that maintains the essential differences between the cytosol and the extracellular environment. Plasmalemmal injury is a common event during the life of many cells that often leads to their premature, necrotic death. Blebbing -a display of plasmalemmal protrusions -is a characteristic feature of injured cells. In this study, we disclose a previously unknown role for blebbing in furnishing resistance to plasmalemmal injury. Blebs serve as precursors for injuryinduced intracellular compartments that trap damaged segments of the plasma membrane. Hence, loss of cytosol and the detrimental influx of extracellular constituents are confined to blebs that are sealed off from the cell body by plugs of annexin A1 -a Ca 2 þ -and membrane-binding protein. Our findings shed light on a fundamental process that contributes to the survival of injured cells. By targeting annexin A1/blebbing, new therapeutic approaches could be developed to avert the necrotic loss of cells in a variety of human pathologies.

We have achieved a comprehensive view of a general plasma membrane repair mechanism after injury by a major bacterial toxin.