Host and pathogen hyaluronan signal through human siglec-9 to suppress neutrophil activation.

UNLABELLED: Inhibitory CD33-related Siglec receptors regulate immune cell activation upon engaging ubiquitous sialic acids (Sias) on host cell surface glycans. Through molecular mimicry, Sia-expressing pathogen group B Streptococcus binds inhibitory human Siglec-9 (hSiglec-9) to blunt neutrophil activation and promote bacterial survival. We unexpectedly discovered that hSiglec-9 also specifically binds high molecular weight hyaluronan (HMW-HA), another ubiquitous host glycan, through a region of its terminal Ig-like V-set domain distinct from the Sia-binding site. HMW-HA recognition by hSiglec-9 limited neutrophil extracellular trap (NET) formation, oxidative burst, and apoptosis, defining HMW-HA as a regulator of neutrophil activation. However, the pathogen group A Streptococcus (GAS) expresses a HMW-HA capsule that engages hSiglec-9, blocking NET formation and oxidative burst, thereby promoting bacterial survival. Thus, a single inhibitory lectin receptor detects two distinct glycan "self-associated molecular patterns" to maintain neutrophil homeostasis, and two leading human bacterial pathogens have independently evolved molecular mimicry to exploit this immunoregulatory mechanism. KEY MESSAGE: HMW-HA is the first example of a non-sialic acid containing glycan to be recognized by CD33-related Siglecs. HMW-HA engagement of hSiglec-9 attenuates neutrophil activation. Group A Streptococcus exploits hSiglec-9 recognition via its polysaccharide HMW-HA capsule to subvert neutrophil killing.

A rigid disc for protection of exposed blood vessels during negative pressure wound therapy.

BACKGROUND: There are increasing reports of serious complications and deaths associated with negative pressure wound therapy (NPWT). Bleeding may occur when NPWT is applied to a wound with exposed blood vessels. Inserting a rigid disc in the wound may protect these structures. The authors examined the effects of rigid discs on wound bed tissue pressure and blood flow through a large blood vessel in the wound bed during NPWT. METHODS: Wounds were created over the femoral artery in the groin of 8 pigs. Rigid discs were inserted. Wound bed pressures and arterial blood flow were measured during NPWT. RESULTS: Pressure transduction to the wound bed was similar for control wounds and wounds with discs. Blood flow through the femoral artery decreased in control wounds. When a disc was inserted, the blood flow was restored. CONCLUSIONS: NPWT causes hypoperfusion in the wound bed tissue, presumably as a result of mechanical deformation. The insertion of a rigid barrier alleviates this effect and restores blood flow.

The use of a rigid disc to protect exposed structures in wounds treated with negative pressure wound therapy: effects on wound bed pressure and microvascular blood flow.

There are increasing reports of deaths and serious complications associated with the use of negative pressure wound therapy (NPWT). Bleeding may occur in patients when NPWT is applied to a wound with exposed blood vessels or vascular grafts, possibly due to mechanical deformation and hypoperfusion of the vessel walls. Recent evidence suggests that using a rigid barrier disc to protect underlying tissue can prevent this mechanical deformation. The aim of this study was to examine the effect of rigid discs on the tissue exposed to negative pressure with regard to tissue pressure and microvascular blood flow. Peripheral wounds were created on the backs of eight pigs. The pressure and microvascular blood flow in the wound bed were measured when NPWT was applied. The wound was filled with foam, and rigid discs of different designs were inserted between the wound bed and the foam. The discs were created with or without channels (to accommodate exposed sensitive structures such as blood vessels and nerves), perforations, or a porous dressing that covered the underside of the discs (to facilitate pressure transduction and fluid evacuation). When comparing the results for pressure transduction to the wound bed, no significant differences were found using different discs covered with dressing, whereas pressure transduction was lower with bare discs. Microvascular blood flow in the wound bed decreased by 49 ± 7% when NPWT was applied to control wounds. The reduction in blood flow was less in the presence of a protective disc (e.g., -6 ± 5% for a dressing-covered, perforated disc, p = 0.006). In conclusion, NPWT causes hypoperfusion of superficial tissue in the wound bed. The insertion of a rigid barrier counteracts this effect. The placement of a rigid disc over exposed blood vessels or nerves may protect these structures from rupture and damage.

The influence on wound contraction and fluid evacuation of a rigid disc inserted to protect exposed organs during negative pressure wound therapy.

The use of a rigid disc as a barrier between the wound bed and the wound filler during negative pressure wound therapy (NPWT) has been suggested to prevent damage to exposed organs. However, it is important to determine that the effects of NPWT, such as wound contraction and fluid removal, are maintained during treatment despite the use of a barrier. This study was performed to examine the effect of NPWT on wound contraction and fluid evacuation in the presence of a rigid disc. Peripheral wounds were created on the backs of eight pigs. The wounds were filled with foam, and rigid discs of different designs were inserted between the wound bed and the foam. Wound contraction and fluid evacuation were measured after application of continuous NPWT at -80 mmHg. Wound contraction was similar in the presence and the absence of a rigid disc (84 ± 4% and 83 ± 3%, respectively, compared with baseline). Furthermore, the rigid disc did not affect wound fluid removal compared with ordinary NPWT (e.g. after 120 seconds, 71 ± 4 ml was removed in the presence and 73 ± 3 ml was removed in the absence of a disc). This study shows that a rigid barrier may be placed under the wound filler to protect exposed structures during NPWT without affecting wound contraction and fluid removal, which are two crucial features of NPWT.

Gene expression demonstrates increased resilience toward harmful inflammatory stimuli in the proliferating epidermis of human skin wounds.

We examined the epidermal gene expression during the proliferative phase of wound healing. Matrix metalloproteases were the group of proteases most prominently up-regulated in skin wounds, whereas serine protease inhibitors were the most strongly up-regulated protease inhibitors. Furthermore, we found down-regulation of genes involved in the extrinsic pathway of apoptosis. This together with the up-regulation of inhibitors of leukocyte serine proteases likely represents a protective step to ensure survival of keratinocytes in the inflammatory wound environment. The down-regulation of proapoptotic genes in the extrinsic pathway of apoptosis was not accompanied by a down-regulation of receptors indicating that the keratinocytes in skin wounds did not become less responsive to external stimuli. Examining the transcription factor binding sites in the promoters of the most differentially expressed genes between normal skin and skin wounds a significant overrepresentation of binding sites were found for STAT-5, SRY and members of the FOXO-family of transcription factors.

Injury is a major inducer of epidermal innate immune responses during wound healing.

We examined the importance of injury for the epidermal innate immune response in human skin wounds. We found that injury, independent of infiltrating inflammatory cells, generated prominent chemotactic activity toward neutrophils in injured skin because of IL-8 production. Furthermore, injury was a major inducer of the expression of antimicrobial (poly)peptides (AMPs) in skin wounds. In human skin, these injury-induced innate immune responses were mediated by activation of the epidermal growth factor receptor (EGFR). Consequently, inhibition of the EGFR blocked both the chemotactic activity generated in injured skin and the expression of the majority of the AMPs. The importance of injury was confirmed in mouse experiments in vivo, in which injury independent of infection was a potent inducer of AMPs in skin wounds. To our knowledge, these data thereby provide a previously unreported molecular link between injury and neutrophil accumulation and identify the molecular background for the vast expression of IL-8 and AMPs in wounded epidermis. Conceptually, these data show that the growth factor response elicited by injury is important for the recruitment of neutrophils in skin wounds.

Injury-induced innate immune response in human skin mediated by transactivation of the epidermal growth factor receptor.

We found that sterile wounding of human skin induced epidermal expression of the antimicrobial (poly)peptides human beta-defensin-3, neutrophil gelatinase-associated lipocalin, and secretory leukocyte protease inhibitor through activation of the epidermal growth factor receptor. After skin wounding, the receptor was activated by heparin-binding epidermal growth factor that was released by a metalloprotease-dependent mechanism. Activation of the epidermal growth factor receptor generated antimicrobial concentrations of human beta-defensin-3 and increased the activity of organotypic epidermal cultures against Staphylococcus aureus. These data demonstrate that sterile wounding initiates an innate immune response that increases resistance to overt infection and microbial colonization.