Ultraviolet photoelectron spectra (UPS) were recorded for mass-selected negative clusters of copper (1–411 atoms), silver (1–60 atoms), and gold (1–233 atoms), using photodetachment lasers at 6.4 and 7.9 eV photon energy. The results provide a direct estimate of the vertical electron affinity (EA) of these clusters and information on the evolution of the d bands of copper and gold as a function of cluster size. The large even/odd alternation of EA in small clusters of these metals in earlier work is found to largely disappear as the cluster size exceeds 40 atoms. The ellipsoidal shell model is shown to be consistent with the observed EA behavior of all three metals, the predicted spherical shell closing at cluster 58 being evident for silver and gold. The UPS data show a smooth evolution of the d band toward that of the bulk metal.

Glycosaminoglycans, linear carbohydrates such as heparan sulfate and hyaluronan, participate in a variety of biological processes including cell-matrix interactions and activation of chemokines, enzymes and growth factors. This review will discuss progress in immunology and the science of wound repair that has revealed the importance of glycosaminoglycans, and their proteoglycans, in the inflammatory process. Heparan sulfate enables growth factor function and modifies enzyme/inhibitor functions, such as antithrombin III and heparin cofactor II. Heparan sulfate also interacts with cytokines/chemokines and participates in leukocyte selectin binding to promote the recruitment of leukocytes. Chondroitin sulfate/dermatan sulfate regulates growth factor activity and is an alternate modulator of heparin cofactor II. In addition, dermatan sulfate induces ICAM-1 expression on endothelial cells and also recruits leukocytes via selectin interactions. Hyaluronan alternatively participates in leukocyte recruitment via interaction with CD44, while activating various inflammatory cells, such as macrophages, through CD44-dependent signaling. Hyaluronan also signals through Toll-like receptor 4 to induce dendritic cell maturation and promote cytokine release by dendritic cells and endothelial cells. Taken together, the field of glycosaminoglycan biology provides new clues and explanations of the process of inflammation and suggests new therapeutic approaches to human disease.

Tissues must quickly recognize injury to respond to the rapid pace of microbial growth. In skin, dermal microvascular endothelial cells must also react to danger signals from the surrounding tissue and immediately participate by initiating the wound repair process. Components of the extracellular matrix such as hyaluronan are rapidly broken down into smaller molecular weight oligosaccharides in a wound, and these can activate a variety of biological processes. This study set out to determine if hyaluronan fragments released following injury can stimulate endothelial cells and what mechanism is responsible for this response. Using genechip microarray analysis, a response to hyaluronan fragments was detected in endothelial cells with the most significant increase observed for the chemokine IL-8. This observation was verified with qualitative reverse transcriptase-PCR and ELISA in human endothelial cell culture, and in a mouse model by observing serum levels of MIP-2 and KC following hyaluronan fragment administration in vivo. Activation was TLR4-dependent, as shown by use of TLR4 blocking antibody and TLR4-deficient mice, but not due to the presence of undetected contaminants as shown by inactivation following digestion with the hyaluronan-degrading enzyme chondroitinase ABC or incubation with the hyaluronan-specific blocking peptide Pep-1. Inactivation of LPS activity failed to diminish the action of hyaluronan fragments. These observations suggest that endogenous components of the extracellular matrix can stimulate endothelia to trigger recognition of injury in the initial stages of the wound defense and repair response.

Inflammation under sterile conditions is not well understood despite its importance in trauma and autoimmune disease. To investigate this process we established mouse models of sterile injury and explored the role of hyaluronan in mediating inflammation following injury. The response of cultured monocytes to hyaluronan was different than the response to lipopolysaccharide (LPS) despite both being dependent on Toll-like receptor 4 (TLR4). Cultured cells exposed to hyaluronan showed a pattern of gene induction that mimics the response seen in mouse skin after sterile injury with an increase in molecules such as transforming growth factor-␤2 and matrix metalloproteinase-13. These factors were not induced by LPS despite the mutual dependence of both hyaluronan and LPS on TLR4. Explanation for the unique response to hyaluronan was provided by observations that a lack of TLR4 or CD44 in mice diminished the response to sterile injury, and together with MD-2, was required for responsiveness to hyaluronan in vitro. Thus, a unique complex of TLR4, MD-2, and CD44 recognizes hyaluronan. Immunoprecipitation experiments confirmed the physical association of TLR4 and CD44. Taken together, our results define a previously unknown mechanism for initiation of sterile inflammation that involves recognition of released hyaluronan fragments as an endogenous signal of tissue injury.

Epidermal T cells have been shown to play unique roles in tissue homeostasis and repair in mice through local secretion of distinct growth factors in the skin. Human epidermis contains both αβ+ and γδ+ T cells whose functional capabilities are not understood. We demonstrate that human epidermal T cells are able to produce insulin-like growth factor 1 (IGF-1) upon activation and promote wound healing in a skin organ culture model. Moreover, an analysis of the functional capabilities of T cells isolated from acute versus chronic wounds revealed a striking difference. Both αβ+ and Vδ1+ T cells isolated from acute wounds actively produced IGF-1, demonstrating that they are activated during tissue damage to participate in wound repair. In contrast, IGF-1 production could not be detected in T cells isolated from chronic wounds. In fact, skin T cells isolated from chronic wounds were refractory to further stimulation, suggesting an unresponsive state. Collectively, these results define a novel role for human epidermis–resident T cells in wound healing and provide new insight into our understanding of chronic wound persistence.