Sublytic concentrations of Staphylococcus aureus Panton-Valentine leukocidin alter human PMN gene expression and enhance bactericidal capacity

Abstract

CA-MRSA infections are often caused by strains encoding PVL, which can cause lysis of PMNs and other myeloid cells in vitro, a function considered widely as the primary means by which PVL might contribute to disease. However, at sublytic concentrations, PVL can function as a PMN agonist. To better understand this phenomenon, we investigated the ability of PVL to alter human PMN function. PMNs exposed to PVL had enhanced capacity to produce O(2)(-) in response to fMLF, but unlike priming by LPS, this response did not require TLR signal transduction. On the other hand, there was subcellular redistribution of NADPH oxidase components in PMNs following exposure of these cells to PVL--a finding consistent with priming. Importantly, PMNs primed with PVL had an enhanced ability to bind/ingest and kill Staphylococcus aureus. Priming of PMNs with other agonists, such as IL-8 or GM-CSF, altered the ability of PVL to cause formation of pores in the plasma membranes of these cells. Microarray analysis revealed significant changes in the human PMN transcriptome following exposure to PVL, including up-regulation of molecules that regulate the inflammatory response. Consistent with the microarray data, mediators of the inflammatory response were released from PMNs after stimulation with PVL. We conclude that exposure of human PMNs to sublytic concentrations of PVL elicits a proinflammatory response that is regulated in part at the level of gene expression. We propose that PVL-mediated priming of PMNs enhances the host innate immune response.

The Bicomponent Pore-Forming Leucocidins of Staphylococcus aureus

“…By virtue of binding C5aR, LukS-PV not only exerts its lytic activity on target host cells but also can facilitate the priming of primary human PMNs for activation by proinflammatory stimuli such as N-formyl-Met-Leu-Phe (fMLP). This finding fully supports previous studies that suggested that PVL could promote the proinflammatory responsiveness of PMNs when applied at sublytic concentrations (199,252,253).…”

“…However, a substantial body of evidence now suggests that most, if not all, leucocidins have bona fide immune cell-activating properties and/or additional sublytic functions that occur in the absence of cell lysis (Fig. 6) (210,233,252,253,(264)(265)(266). Most studies evaluating the proinflammatory signaling properties of the leucocidins stem from work done with PVL and gamma-hemolysin (210,252,253,(264)(265)(266).…”

Staphylococcus aureusLukAB cytotoxin kills human neutrophils by targeting the CD11b subunit of the integrin Mac-1

“…A possible explanation is that LukAB may cause disease in the mouse through receptor-independent immunomodulatory mechanisms, as has been as shown for PVL. Similar to LukAB, PVL also displays cytolytic tropism toward human PMNs (16), but has been shown to elicit proinflammatory responses in human PMNs and macrophages (26,27) as well as murine PMNs and macrophages (35,36). These findings suggest that the roles of LukAB and PVL in the mouse may be better explained by immunomodulatory functions rather than cytolytic functions, and indicate that mouse models underestimate the true contribution of these toxins to S. aureus pathobiology in humans.…”

“…Despite the lack of overlap in cellular targets identified thus far, the staphylococcal leukotoxins have been shown to exhibit synergistic effects (26). The identification of CD11b as a cellular target for LukAB provides an explanation for the previously reported synergism between LukAB and PVL toward human PMNs (10,11), as sublytic concentrations of PVL increase CD11b surface levels on these cells (27). From an evolutionary standpoint, the use of multiple, nonoverlapping cellular targets provides an explanation for why S. aureus has such a large arsenal of cytotoxins and is such a welladapted pathogen when it comes to evading host PMNs.…”

Targeting fundamental pathways to disrupt Staphylococcus aureus survival: clinical implications of recent discoveries

“…At sublytic concentrations, LukAB and PVL alter cellular signaling by inflammasome activation, leading to IL-1β secretion (67,68), and PVL is capable of priming and activating human neutrophils, resulting in enhanced phagocytic function (69). In addition, toxin monomers appear to antagonize their receptors, which may interfere with phagocyte recruitment and function (61,62).…”