Summary Nociceptor sensory neurons are specialized to detect potentially damaging stimuli, protecting the organism by initiating the sensation of pain and eliciting defensive behaviors. Bacterial infections produce pain by unknown molecular mechanisms, although they are presumed secondary to immune activation. Here we demonstrate that bacteria directly activate nociceptors, and that the immune response mediated through TLR2, MyD88, T cells, B cells, and neutrophils/monocytes is not necessary for Staphylococcus aureus induced pain in mice. Mechanical and thermal hyperalgesia parallels live bacterial load rather than tissue swelling or immune activation. Bacteria induce calcium flux and action potentials in nociceptor neurons, in part via bacterial N-formylated peptides and the pore-forming toxin alpha-hemolysin through distinct mechanisms. Specific ablation of Nav1.8-lineage neurons, which include nociceptors, abrogated pain during bacterial infection, but concurrently increased local immune infiltration and lymphadenopathy of the draining lymph node. Thus, bacterial pathogens produce pain by directly activating sensory neurons that modulate inflammation, an unsuspected role for the nervous system in host-pathogen interactions.

Staphylococcus aureus secretes a number of host-injurious toxins, among the most prominent of which is the small β-barrel pore-forming toxin α-hemolysin. Initially named based on its properties as a red blood cell lytic toxin, early studies suggested a far greater complexity of α-hemolysin action as nucleated cells also exhibited distinct responses to intoxication. The hemolysin, most aptly referred to as α-toxin based on its broad range of cellular specificity, has long been recognized as an important cause of injury in the context of both skin necrosis and lethal infection. The recent identification of ADAM10 as a cellular receptor for α-toxin has provided keen insight on the biology of toxin action during disease pathogenesis, demonstrating the molecular mechanisms by which the toxin causes tissue barrier disruption at host interfaces lined by epithelial or endothelial cells. This review highlights both the historical studies that laid the groundwork for nearly a century of research on α-toxin and key findings on the structural and functional biology of the toxin, in addition to discussing emerging observations that have significantly expanded our understanding of this toxin in S. aureus disease. The identification of ADAM10 as a proteinaceous receptor for the toxin not only provides a greater appreciation of truths uncovered by many historic studies, but now affords the opportunity to more extensively probe and understand the role of α-toxin in modulation of the complex interaction of S. aureus with its human host.

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Staphylococcus aureus pneumonia causes signifi cant mortality in hospitalized or healthy individuals, and recent increases in morbidity are attributed to the rapid spread of methicillin-resistant S. aureus (MRSA) strains, which are often not susceptible to antibiotic therapy. ␣ -Hemolysin (Hla), a secreted pore-forming toxin, is an essential virulence factor of MRSA in a mouse model of S. aureus pneumonia. We show that the level of Hla expression by independent S. aureus strains directly correlates with their virulence. Active immunization with a mutant form of Hla (Hla H35L ), which cannot form pores, generates antigen-specifi c immunoglobulin G responses and affords protection against staphylococcal pneumonia. Moreover, transfer of Hla-specifi c antibodies protects naive animals against S. aureus challenge and prevents the injury of human lung epithelial cells during infection. Thus, Hla vaccination or immunotherapy may prevent S. aureus pneumonia in humans.

Staphylococcus aureus α-hemolysin (Hla), a potent cytotoxin, plays an important role in the pathogenesis of staphylococcal diseases, including those caused by methicillin-resistant epidemic strains. Hla is secreted as a water-soluble monomer that undergoes a series of conformational changes to generate a heptameric, β-barrel structure in host membranes. Structural maturation of Hla depends on its interaction with a previously unknown proteinaceous receptor in the context of the cell membrane. It is reported here that a disintegrin and metalloprotease 10 (ADAM10) interacts with Hla and is required to initiate the sequence of events whereby the toxin is transformed into a cytolytic pore. Hla binding to the eukaryotic cell requires ADAM10 expression. Further, ADAM10 is required for Hlamediated cytotoxicity, most notably when the toxin is present at low concentrations. These data thus implicate ADAM10 as the probable high-affinity toxin receptor. Upon Hla binding, ADAM10 relocalizes to caveolin 1-enriched lipid rafts that serve as a platform for the clustering of signaling molecules. It is demonstrated that the Hla-ADAM10 complex initiates intracellular signaling events that culminate in the disruption of focal adhesions.pore-forming cytotoxin | cellular receptor T he Gram-positive extracellular pathogen Staphylococcus aureus is one of the leading causes of human bacterial infection. As a commensal of the skin, S. aureus is well positioned to cause infection of the skin and soft tissues, the bloodstream, and the lower respiratory tract, which are the principal sites of clinically relevant infection (1, 2). To facilitate entry and spread through the host tissue, S. aureus encodes a number of virulence factors that allow the organism to breach structural and immunological barriers to infection. One of the most prominent and well-characterized virulence factors produced by S. aureus is α-hemolysin (Hla), a pore-forming cytotoxin implicated in the pathogenesis of sepsis, pneumonia, and severe skin infection (3-6). Pore formation on susceptible host cell membranes triggers alterations in ion gradients, loss of membrane integrity, activation of stress-signaling pathways, and cell death (3, 7). Hla binds to most eukaryotic cells, often by a nonspecific adsorptive mechanism requiring micromolar concentrations of toxin (8). However, a high-affinity interaction of the toxin with a proteinaceous eukaryotic receptor has been suggested because rabbit erythrocytes are significantly more sensitive to Hla than human erythrocytes, correlating with the identification of 1,200-5,000 toxin-binding sites per rabbit cell (8, 9). Binding is saturable and time dependent, consistent with a ligand-receptor interaction (8,10). In addition to these data, membrane lipids seem to be central to the interaction of the toxin with the eukaryotic cell. Membrane cholesterol or sphingomyelin depletion abrogates toxin binding and cytotoxicity, and the addition of exogenous phosphocholine disrupts toxin binding and impairs rabbit red cell hemolysis (11)....