Polarized Th2 cytokine production in patients with hypertrophic scar following thermal injury

Macrophages in skin injury and repair

After recruitment to the wound bed, monocytes differentiate into macrophages. Macrophages play a central role in all stages of wound healing and orchestrate the wound healing process. Their functional phenotype is dependent on the wound microenvironment, which changes during healing, hereby altering macrophage phenotype. During the early and short inflammatory phase macrophages exert pro-inflammatory functions like antigen-presenting, phagocytosis and the production of inflammatory cytokines and growth factors that facilitate the wound healing process. As such, the phenotype of wound macrophages in this phase is probably the classically activated or the so-called M1 phenotype. During the proliferative phase, macrophages stimulate proliferation of connective, endothelial and epithelial tissue directly and indirectly. Especially fibroblasts, keratinocytes and endothelial cells are stimulated by macrophages during this phase to induce and complete ECM formation, reepithelialization and neovascularization. Subsequently, macrophages can change the composition of the ECM both during angiogenesis and in the remodelling phase by release of degrading enzymes and by synthesizing ECM molecules. This suggests an important role for alternatively activated macrophages in this phase of wound healing. Pathological functioning of macrophages in the wound healing process can result in derailed wound healing, like the formation of ulcers, chronic wounds, hypertrophic scars and keloids. However, the exact role of macrophages in these processes is still incompletely understood. For treating wound repair disorders more should be elucidated on the role of macrophages in these conditions, especially their functional phenotype, to find more therapeutic opportunities. This review summarizes macrophage function in skin injury repair, thereby providing more insight in macrophage function in wound healing and possible interventions in this process.

Perioperative conditions affect long-term hypertrophic scar formation

Corticosteroids are widely used as treatment for excessive scarring by intralesional injection with variable success rates. It is conceivable that systemically administered corticosteroids affect a wider range of inflammatory processes that influence wound healing and may be more successful in preventing hypertrophic scar formation. To study this presumption, we have used a standardized model of presternal scars caused by cardiothoracic surgery through a median sternotomy incision. During cardiac surgery with cardiopulmonary bypass, 1 mg/kg dexamethasone was administered preoperatively, and 0.5 mg/kg 8 hours postoperatively. The presternal scars were evaluated prospectively 2, 4, 6, 12, and 52 weeks postoperatively at standardized measuring points. The height and width of the scars were measured 12 and 52 weeks postoperatively using both a slide caliper and a 7.5-MHz ultrasound probe. Cardiopulmonary bypass was used in 31 of the 43 participants. Eleven patients (35%) in the dexamethasone group developed clinical hypertrophic scars compared with 4 patients (33%) in the control group. These differences were not statistically significant. However, cranial scars became significantly wider in the dexamethasone group compared with the control group (P = 0.04). Twelve weeks postoperatively scars were significantly higher in the dexamethasone group, both cranial (P = 0.05) and caudal (P = 0.03). The differences in scar width and height were mainly present in patients that developed hypertrophic scars. The present results suggest that administration of high-dose perioperative dexamethasone does not prevent hypertrophic scar formation. Its use together with the cardiopulmonary bypass, however, did affect scar dimensions negatively up to 52 weeks after surgery. These findings contribute to the concept of the involvement of perioperative immunologic responses in the etiology of hypertrophic scar formation.

Reprogrammed fibrocytes induce a mixed Th1/Th2 cytokine response of naïve CD4(+) T cells

Naïve CD4(+) T cells develop different effector T cells and cytokine profiles after antigenic stimulation. It has been previously documented that fibrocytes function as antigen presenting cells inducing proliferation as well as Th2 cytokine response in naïve CD4(+) T cells. Our group has reported that several circulating cell types recruited to the wound site can be transformed into anti-fibrotic profile cells, which subsequently induce MMP-1 stimulation in dermal fibroblasts. Here, we report how similar reprogramming pathway of fibrocytes could modify the CD4(+) T cell response. Our findings confirmed that reprogrammed fibrocytes induce CD4(+) T cell activation with a mixed Th1/Th2 cytokine response. Since a reciprocal positive feedback between Th2 cells and fibrocytes exist to amplify and perpetuate the pro-fibrotic stimulation in dermal fibroblasts, the novel transdifferentiation of regular mature fibrocytes into reprogrammed fibrocytes appears to be a promising strategy to reverse the Th2 cytokine overproduction, and subsequently control the local fibrogenesis.

Cutaneous scarring: a clinical review

Cutaneous scarring can cause patients symptoms ranging from the psychological to physical pain. Although the process of normal scarring is well described the ultimate cause of pathological scarring remains unknown. Similarly, exactly how early gestation fetuses can heal scarlessly remains unsolved. These questions are crucial in the search for a preventative or curative antiscarring agent. Such a discovery would be of enormous medical and commercial importance, not least because it may have application in other tissues. In the clinical context the assessment of scars is becoming more sophisticated and new physical, medical and surgical therapies are being introduced. This review aims to summarise some of the recent developments in scarring research for non-specialists and specialists alike.

Pathophysiology and management of the burn scar

Fibroproliferative disorders (FPDs) are common and serious disorders. Hypertrophic scar (HSc) and keloids represent the dermal equivalents of FPD and impose lower mortality but great morbidity. This article reviews current knowledge in the pathophysiology and molecular and cellular characteristics of postburn HSc. Additionally, current treatment modalities and future treatment options based on advancements in the understanding of the pathophysiology of HSc are discussed.

Scar and contracture: biological principles

Dysregulated wound healing and pathologic fibrosis cause abnormal scarring, leading to poor functional and aesthetic results in hand burns. Understanding the underlying biologic mechanisms involved allows the hand surgeon to better address these issues, and suggests new avenues of research to improve patient outcomes. In this article, the authors review the biology of scar and contracture by focusing on potential causes of abnormal wound healing, including depth of injury, cytokines, cells, the immune system, and extracellular matrix, and explore therapeutic measures designed to target the various biologic causes of poor scar.

[Opioid-induced pruritus. Mechanisms and treatment regimens]

Substantial progress has been achieved in recent years in research on the interaction between pain and pruritus. Over and above the known inhibition of pruritus by painful stimuli (e.g. scratching), a foundation for the explanation of opioid-induced pruritus was laid through the discovery of pruritus-specific neuronal processing channels. Although traditionally the degranulating effect of opioids on mast cells was assumed to be the essential mechanism, it is now clear that opioids can also induce itching at the spinal level. Neurons of the dorsal horn of the pain system inhibit spinal itch neurons. If this inhibition is weakened by opioids, the disinhibited itch neurons become active and mediate itching, without stimulation of the primary afferent peripheral nerves. Spinal triggering of itching is observed in particular by activation of mu-opioid receptors (mu-OR), while kappa-OR surprisingly suppress itch. The therapeutic implications of this interaction will be described.

Deep dermal fibroblasts contribute to hypertrophic scarring

Hypertrophic scar (HTS) following thermal injury is a dermal fibroproliferative disorder that leads to considerable morbidity. The development of HTS involves numerous cell types and cytokines with dermal fibroblasts being a key cell. We have previously reported that the phenotype of fibroblasts isolated from HTS was altered compared to fibroblasts from normal skin. In this study, normal skin was horizontally sectioned into five layers using a dermatome from which fibroblasts were isolated and cultured. Cells from the deeper layers were observed to proliferate at a slow rate, but were morphologically larger. In ELISA and FACS assays, cells from the deeper layers produced more TGF-beta1 and TGF-beta1 producing cells were higher. In quantitative RT-PCR, the cells from the deeper layers had higher CTGF and HSP47 mRNA levels compared to those from superficial layers. In western blot, FACS and collagen gel assays, fibroblasts from the deeper layers produced more alpha-smooth muscle actin (alpha-SMA), had higher alpha-SMA positive cells and contracted collagen gels more. Fibroblasts from the deeper layers were also found to produce more collagen, but less collagenase by mass spectrometry and collagenase assay. Interestingly, cells from the deeper layers also produced more of the proteoglycan, versican, but less decorin. Taken together, these data strongly demonstrate that fibroblasts from the deeper layers of the dermis resemble HTS fibroblasts, suggesting that the deeper layer fibroblasts may be critical in the formation of HTS.

Potential cellular and molecular causes of hypertrophic scar formation

A scar is an expected result of wound healing. However, in some individuals, and particularly in burn victims, the wound healing processes may lead to a fibrotic hypertrophic scar, which is raised, red, inflexible and responsible for serious functional and cosmetic problems. It seems that a wide array of subsequent processes are involved in hypertrophic scar formation, like an affected haemostasis, exaggerated inflammation, prolonged reepithelialization, overabundant extracellular matrix production, augmented neovascularization, atypical extracellular matrix remodeling and reduced apoptosis. Platelets, macrophages, T-lymphocytes, mast cells, Langerhans cells and keratinocytes are directly and indirectly involved in the activation of fibroblasts, which in turn produce excess extracellular matrix. Following the chronology of normal wound healing, we unravel, clarify and reorganize the complex molecular and cellular key processes that may be responsible for hypertrophic scars. It remains unclear whether these processes are a cause or a consequence of unusual scar tissue formation, but raising evidence exists that immunological responses early following wounding play an important role. Therefore, when developing preventive treatment modalities, one should aim to put the early affected wound healing processes back on track as quickly as possible.

Pivotal Advance: Th-1 cytokines inhibit, and Th-2 cytokines promote fibrocyte differentiation

CD14+ peripheral blood monocytes can differentiate into fibroblast-like cells called fibrocytes, which are associated with and are at least partially responsible for wound healing and fibrosis in multiple organ systems. Signals regulating fibrocyte differentiation are poorly understood. In this study, we find that when added to human PBMCs cultured in serum-free medium, the profibrotic cytokines IL-4 and IL-13 promote fibrocyte differentiation without inducing fibrocyte or fibrocyte precursor proliferation. We also find that the potent, antifibrotic cytokines IFN-gamma and IL-12 inhibit fibrocyte differentiation. In our culture system, IL-1beta, IL-3, IL-6, IL-7, IL-16, GM-CSF, M-CSF, fetal liver tyrosine kinase 3, insulin growth factor 1, vascular endothelial growth factor, and TNF-alpha had no significant effect on fibrocyte differentiation. IL-4, IL-13, and IFN-gamma act directly on monocytes to regulate fibrocyte differentiation, and IL-12 acts indirectly, possibly through CD16-positive NK cells. We previously identified the plasma protein serum amyloid P (SAP) as a potent inhibitor of fibrocyte differentiation. When added together, the fibrocyte-inhibitory activity of SAP dominates the profibrocyte activities of IL-4 and IL-13. The profibrocyte activities of IL-4 and IL-13 and the fibrocyte-inhibitory activities of IFN-gamma and IL-12 counteract each other in a concentration-dependent manner. These results indicate that the complex mix of cytokines and plasma proteins present in inflammatory lesions, wounds, and fibrosis will influence fibrocyte differentiation.

Improvement in postburn hypertrophic scar after treatment with IFN-alpha2b is associated with decreased fibrocytes

Hypertrophic scar (HTS) following thermal injury is a dermal fibroproliferative disorder that leads to considerable morbidity. Previous clinical studies from our laboratory have suggested that interferon-alpha2b (IFN-alpha2b) improves scar quality as a result of suppression of fibroblast functions. Fibrocytes, which constitute a unique cell population, have recently been reported to contribute to wound healing and to a variety of fibrotic conditions, including HTS. Therefore, we hypothesize that improvement of scar in HTS patients after IFN-alpha2b treatment may be associated with a decreased number of fibrocytes or altered fibrocyte function. Using flow cytometry, immunofluorescent staining, and confocal microscopy, we demonstrate here that the marker protein leukocyte-specific protein 1 (LSP1) is stably expressed by fibrocytes for at least 2 months, whereas other potential fibrocyte markers, such as CD34 and CD45, gradually disappear. Using dual staining immunohistochemistry for LSP1 and procollagen, we demonstrated a significant reduction in numbers of fibrocytes in HTS tissue from patients after treatment with systemic IFN-alpha2b. IFN-alpha2b was shown to abolish fibrocyte differentiation from peripheral blood mononuclear cells (PBMCs) in vitro in a dose-dependent fashion. In addition, IFN-alpha2b inhibits proliferation of fibrocytes and T lymphocytes and reduces transforming growth factor-beta (TGF-beta)-mediated alpha-smooth muscle actin (alpha-SMA) expression in fibrocytes. Taken together with our previous study in which we showed that fibrocytes could indirectly regulate dermal fibroblasts in burn patients, the present study suggests that the improvement of scar quality in HTS patients after IFN-alpha2b treatment is associated with decreased numbers and activities of fibrocytes.

Cellular and molecular pathology of HTS: basis for treatment

Hypertrophic scar and keloids are fibroproliferative disorders of the skin which occur often unpredictably, following trauma and inflammation that compromise cosmesis and function and commonly recur following surgical attempts for improvement. Despite decades of research in these fibrotic conditions, current non-surgical methods of treatment are slow, inconvenient and often only partially effective. Fibroblasts from these conditions are activated to produce extracellular matrix proteins such as collagen I and III, proteoglycans such as versican and biglycan and growth factors, including transforming growth factor-beta and insulin like growth factor I. However, more consistently these cells produce less remodeling enzymes including collagenase and other matrix metalloproteinases, as well as the small proteoglycan decorin which is important for normal collagen fibrillogenesis. Recently, the systemic response to injury appears to influence the local healing process whereby increases in Th2 and possibly Th3 cytokines such as IL-2, IL-4 and IL-10 and TGF-beta are present in the circulating lymphocytes in these fibrotic conditions. Finally, unique bone marrow derived cells including mesenchymal and endothelial stem cells as well as fibrocytes appear to traffic into healing wounds and influence the healing tissue. On this background, clinicians are faced with patients who require treatment and the pathophysiologic basis as currently understood is reviewed for a number of emerging modalities.

Increased TGF-??producing CD4+ T lymphocytes in postburn patients and their potential interaction with dermal fibroblasts in hypertrophic scarring

The development of hypertrophic scar involves a complex interplay between cells and cytokines. Although the mechanism underlying its pathogenesis is not well understood, a polarized T-helper type 2 immune response has been reported, indicating a role for CD4+ T lymphocytes in hypertrophic scarring. Here, we report an increased frequency of CD4+/transforming growth factor-beta (TGF-beta)-producing T cells in the peripheral blood and hypertrophic scar tissue of burn patients. These cells may play an indirect regulatory role in hypertrophic scar by affecting the functions of dermal fibroblasts. Our results show an increase in cell proliferation and collagen synthesis by dermal fibroblasts treated with medium derived from burn patient CD4+ T lymphocytes but not from the CD4+ T cells of normal subjects. Using confocal microscopy and immunoblotting, we found the level of alpha-smooth muscle actin to be elevated in these treated dermal fibroblasts, which also showed an enhanced ability to contract collagen lattices. TGF-beta levels in medium conditioned by the culture of CD4+ T lymphocytes from burn patients were significantly higher than in the conditioned medium from CD4+ T lymphocytes of normal subjects. In addition, the application of a TGF-beta-neutralizing antibody significantly reduced the effect of burn patient CD4+ T lymphocyte medium on dermal fibroblast proliferation and collagen lattice contraction. Our study suggests that CD4+/TGF-beta-producing T lymphocytes may play an important role in postburn hypertrophic scarring.

Fibrocytes from burn patients regulate the activities of fibroblasts

Wound healing requires an elaborate interplay between numerous cell types that orchestrate a series of regulated and overlapping events. Fibrocytes are a unique leukocyte subpopulation implicated in this process. One role proposed for these cells in wound healing is to synthesize extracellular matrix. Interestingly, using mass spectrometry to quantify hydroxyproline, we discovered that the capacity of fibrocytes from normal subjects or from burn patients to produce collagen is much less than that of dermal fibroblasts. Therefore, we investigated whether fibrocytes could play an indirect, regulatory, role in the healing of burn wounds by affecting the functions of dermal fibroblasts. Dermal fibroblasts treated with medium conditioned by burn patient fibrocytes, but not by those derived from normal subjects, showed an increase in cell proliferation and migration. Using confocal microscopy, flow cytometry, and immunoblotting, we found the level of alpha-smooth muscle actin (alpha-SMA) expression to be increased in these treated dermal fibroblasts, which also showed an enhanced ability to contract collagen lattices. To determine whether these effects could be attributed to transforming growth factor beta (TGF-beta1) or to connective tissue growth factor (CTGF), we measured total TGF-beta1 levels in the conditioned medium by an enzyme-linked immunosorbtion assay and assessed levels of CTGF mRNA and protein in fibroblasts and fibrocytes by reverse transcription-polymerase chain reaction and Western blotting. The results showed significantly higher levels of TGF-beta1 and CTGF produced by burn patient fibrocytes. In addition, the application of a TGF-beta1 neutralizing antibody significantly reduced the effect of burn patient fibrocyte medium on dermal fibroblast proliferation, migration, and collagen lattice contraction. Our results suggest that in healing burn wounds, fibrocytes could regulate the activities of local fibroblasts.