Wound healing and T-lymphocytes

Osteoimmune Interaction and TH-1/TH-2 Ratio in Jawbone Marrow Defects: An Underestimated Association - Original Research

Introduction

Osteoimmunology recognizes the relationship between bone cells and immune cells. Chronic osteoimmune dysregulation is present in bone marrow defects of the jaw (BMDJ) as fatty-degenerative osteonecrosis (FDOJ). In comparison to samples from healthy jaw bone, the cytokine analysis of samples of BMDJ/FDOJ from 128 patients showed downregulated TNF-α and IL-6 expression and the singular overexpression of the chemokine RANTES/CCL5.

Aim and Objectives

This paper raises the question of whether the osteoimmune defects due to incomplete wound healing in BMDJ/FDOJ in 128 patients are related to dysregulation of the Th1/Th2 ratio and regulatory T cell (T-reg) expression in a control group of 197 BMDJ/FDOJ patients, each presenting with BMDJ/FJOD and one of seven different immune disorders.

Material and Methods

In the control group, serum concentrations of the cytokines IFN-y and IL-4 were determined after stimulated cytokine release and displayed as Th1/Th2 ratios.

Results

Data show a shift in Th2 in more than 80% (n = 167) of the control cohort of 197 chronically ill patients with concomitant BMDJ/FDOJ. In these 167 subjects, the Th1/Th2 ratio was <6.1 demonstrating impaired immune regulation. Forty-seven subjects or 30% showed not only a shift in Th2 but also excessive T-reg overactivation with levels of >1.900 pg/mL, indicating strongly downregulated immune activity.

Discussion

BMDJ/FDOJ is characterized by a lack of Th1 cytokines and an excessive expression of RANTES/CCL5 and IL-1ra and, thus, the inversion of an acute inflammatory cytokine pattern. In contrast, abdominal fat contains a very high proportion of regulatory Th1 cells and produces an inflammatory immune response through the high overexpression of TNF-α and IL-6. The lack of Th1 activation in BMDJ/FDOJ areas inhibits normal wound healing and supports the persistence of BMDJ/FDOJ.

Conclusion

The Th1/Th2 ratio requires greater consideration, especially with respect to wound healing following dental surgical interventions, such as jaw surgery, implantation and augmentation, to avoid the emergence of the osteoimmune situation that is characteristic of BMDJ/FDOJ.

Complex Spatio-Temporal Interplay of Distinct Immune and Bone Cell Subsets during Bone Fracture Healing

BACKGROUND

The healing of a bone injury is a highly complex process involving a multitude of different tissue and cell types, including immune cells, which play a major role in the initiation and progression of bone regeneration.

METHODS

We histologically analyzed the spatio-temporal occurrence of cells of the innate immune system (macrophages), the adaptive immune system (B and T lymphocytes), and bone cells (osteoblasts and osteoclasts) in the fracture area of a femoral osteotomy over the healing time. This study was performed in a bone osteotomy gap mouse model. We also investigated two key challenges of successful bone regeneration: hypoxia and revascularization.

RESULTS

Macrophages were present in and around the fracture gap throughout the entire healing period. The switch from initially pro-inflammatory M1 macrophages to the anti-inflammatory M2 phenotype coincided with the revascularization as well as the appearance of osteoblasts in the fracture area. This indicates that M2 macrophages are necessary for the restoration of vessels and that they also play an orchestrating role in osteoblastogenesis during bone healing. The presence of adaptive immune cells throughout the healing process emphasizes their essential role for regenerative processes that exceeds a mere pathogen defense. B and T cells co-localize consistently with bone cells throughout the healing process, consolidating their crucial role in guiding bone formation. These histological data provide, for the first time, comprehensive information about the complex interrelationships of the cellular network during the entire bone healing process in one standardized set up. With this, an overall picture of the spatio-temporal interplay of cellular key players in a bone healing scenario has been created.

CONCLUSIONS

A spatio-temporal distribution of immune cells, bone cells, and factors driving bone healing at time points that are decisive for this process-especially during the initial steps of inflammation and revascularization, as well as the soft and hard callus phases-has been visualized. The results show that the bone healing cascade does not consist of five distinct, consecutive phases but is a rather complex interrelated and continuous process of events, especially at the onset of healing.

The contribution of the immune system to genitourinary fibrosis

Fibrotic diseases of the genitourinary tract are devastating and incompletely understood pathologies. These diseases include urethral and ureteral strictures, retroperitoneal fibrosis, and Peyronie's disease. They can contribute to obstructive uropathy and sexual dysfunction. Poor understanding of the pathophysiology of these diseases severely limits our ability to prevent and treat them. Genitourinary fibrotic diseases likely represent related pathologies that share common underlying mechanisms involving wound healing in response to injury. These diseases share the common feature of extracellular matrix abnormalities-such as collagen deposition, transforming growth factor-β accumulation, and dysregulation of collagen maturation-leading to abnormal tissue stiffness. Given the association of many of these diseases with autoimmunity, a systemic pro-inflammatory state likely contributes to their associated fibrogenesis. Herein, we explore the immunologic contribution to fibrogenesis in several fibrotic diseases of the genitourinary system. Better understanding how the immune system contributes to fibrosis in these diseases may improve prevention and therapeutic strategies and elucidate the functions of immunologic contributors to fibrosis in general.

Immune Cells in Cutaneous Wound Healing: A Review of Functional Data from Animal Models

The healing of skin wounds involves the activation and recruitment of various immune cell types, many of which are believed to contribute significantly to different aspects of the repair process. Roles for immune cells have been described in practically all stages of wound healing, including hemostasis, inflammation, proliferation and scar formation/remodeling. Over the last decade, tools to deplete immune cell populations in animal models have become more advanced, leading to a surge in the number of studies examining the function of specific immune cell types in skin repair. In this review, we will summarize what is known about distinct immune cell types in cutaneous wound healing, with an emphasis on data from animal studies in which specific cell types have been targeted.

Assessment of Acute Wound Healing using the Dorsal Subcutaneous Polyvinyl Alcohol Sponge Implantation and Excisional Tail Skin Wound Models

Wound healing is a complex process that requires the orderly progression of inflammation, granulation tissue formation, fibrosis, and resolution. Murine models provide valuable mechanistic insight into these processes; however, no single model fully addresses all aspects of the wound healing response. Instead, it is ideal to use multiple models to address the different aspects of wound healing. Here, two different methods that address diverse aspects of the wound healing response are described. In the first model, polyvinyl alcohol sponges are subcutaneously implanted along the mouse dorsum. Following sponge retrieval, cells can be isolated by mechanical disruption, and fluids can be extracted by centrifugation, thus allowing for a detailed characterization of cellular and cytokine responses in the acute wound environment. A limitation of this model is the inability to assess the rate of wound closure. For this, a tail skin excision model is utilized. In this model, a 10 mm x 3 mm rectangular piece of tail skin is excised along the dorsal surface, near the base of the tail. This model can be easily photographed for planimetric analysis to determine healing rates and can be excised for histological analysis. Both described methods can be utilized in genetically altered mouse strains, or in conjunction with models of comorbid conditions, such as diabetes, aging, or secondary infection, in order to elucidate wound healing mechanisms.

Individual Effector/Regulator T Cell Ratios Impact Bone Regeneration

There is increasing evidence that T lymphocytes play a key role in controlling endogenous regeneration. Regeneration appears to be impaired in case of local accumulation of CD8+ effector T cells (T_EFF), impairing endogenous regeneration by increasing a primary “useful” inflammation toward a damaging level. Thus, rescuing regeneration by regulating the heightened pro-inflammatory reaction employing regulatory CD4+ T (T_Reg) cells could represent an immunomodulatory option to enhance healing. Hypothesis was that CD4+ T_Reg might counteract undesired effects of CD8+ T_EFF. Using adoptive T_Reg transfer, bone healing was consistently improved in mice possessing an inexperienced immune system with low amounts of CD8+ T_EFF. In contrast, mice with an experienced immune system (high amounts of CD8+ T_EFF) showed heterogeneous bone repair with regeneration being dependent upon the individual T_EFF/T_Reg ratio. Thus, the healing outcome can only be improved by an adoptive T_Reg therapy, if an unfavorable T_EFF/T_Reg ratio can be reshaped; if the individual CD8+ T_EFF percentage, which is dependent on the individual immune experience can be changed toward a favorable ratio by the T_Reg transfer. Remarkably, also in patients with impaired fracture healing the T_EFF/T_Reg ratio was higher compared to uneventful healers, validating our finding in the mouse osteotomy model. Our data demonstrate for the first time the key-role of a balanced T_EFF/T_Reg response following injury needed to reach successful regeneration using bone as a model system. Considering this strategy, novel opportunities for immunotherapy in patients, which are at risk for impaired healing by targeting T_EFF cells and supporting T_Reg cells to enhance healing are possible.

Sphingosine-1-Phosphate Facilitates Skin Wound Healing by Increasing Angiogenesis and Inflammatory Cell Recruitment with Less Scar Formation

Wound healing starts with the recruitment of inflammatory cells that secrete wound-related factors. This step is followed by fibroblast activation and tissue construction. Sphingosine-1-phosphate (S1P) is a lipid mediator that promotes angiogenesis, cell proliferation, and attracts immune cells. We investigated the roles of S1P in skin wound healing by altering the expression of its biogenic enzyme, sphingosine kinase-1 (SphK1). The murine excisional wound splinting model was used. Sphingosine kinase-1 (SphK1) was highly expressed in murine wounds and that SphK1^−/− mice exhibit delayed wound closure along with less angiogenesis and inflammatory cell recruitment. Nanoparticle-mediated topical SphK1 overexpression accelerated wound closure, which associated with increased angiogenesis, inflammatory cell recruitment, and various wound-related factors. The SphK1 overexpression also led to less scarring, and the interaction between transforming growth factor (TGF)-β1 and S1P receptor-2 (S1PR2) signaling is likely to play a key role. In summary, SphK1 play important roles to strengthen immunity, and contributes early wound healing with suppressed scarring. S1P can be a novel therapeutic molecule with anti-scarring effect in surgical, trauma, and chronic wound management.

Wound healing in post-smolt Atlantic salmon (Salmo salar L.)

Skin biopsies (5 mm) taken from behind the dorsal fin on Atlantic salmon post-smolts were followed over a 2 month period. The healing process was dominated by hemostasis, acute inflammation, and epidermal repair the first 14 days post wounding (dpw), as shown through imaging, histological evaluation, and transcriptomics. Most of the immune genes showed decreased expression after two weeks, approaching the levels of intact skin, as also reflected in sections where reduced inflammation in the wound bed was observed. Transcriptional events suggest recruitment of lymphocytes to the wound site during the acute phase, with activation of humoral responses from 14 dpw and onward. From the histology, a more adherent mucus was observed that correlated with altered transcription of glycosyltransferases. This may indicate different properties and functions of the mucus during the wound healing process. Wound contraction started between 14 and 36 dpw. The occurrence of these events was concurrent with granulation tissue formation, melanocyte migration and up-regulation of genes involved in extracellular matrix formation. The presented description of the wound healing processes in Atlantic salmon gives insight into comparative ulcerative biology in mammals and fish and provides both novel and updated knowledge that can be applied for improved best operational practices for fish welfare in aquaculture.

Adaptive Immunity and Skin Wound Healing in Amphibian Adults

Regeneration and repair with scarring of the skin are two different responses to tissue injury that proceed depending on the animal species. Several studies in multiple organisms have shown that the effectiveness of tissue repair gradually decreases with age in most vertebrates, while the molecular and cellular mechanisms underlying the diverse potentials remain incompletely understood. It is clear, however, that immune system actively participates in the whole process and immune-related activities can mediate both negative and positive roles to influence the quality and diversity of tissue response to damage. Compared with innate immunity, our understanding of the significance of adaptive immune cells in normal repair outcome is limited and deserves further investigation. Here, experimental evidence supporting the contribution of lymphocytes and the involvement of lymphoid organs in skin wound healing are discussed, focusing on the findings emerged in adult amphibians, key animal models for tissue repair and regeneration research.

Enhanced healing and anti-inflammatory effects of a carbohydrate polymer with zinc oxide in patients with chronic venous leg ulcers: preliminary results

INTRODUCTION

Insufficient wound healing related to chronic inflammation of chronic venous leg ulcers (CVUs) represents an important public health problem. The aim of this study was to evaluate the effects of a carbohydrate polymer with zinc oxide therapy on CVUs.

MATERIAL AND METHODS

Forty patients with CVUs were recruited for this study and were divided into a study group and control group. Patients In the study group were instructed to use venous compression treatment andtopical carbohydrate polymer with zinc oxide twice daily, while patients In the control group were treated with only venous compression treatment. All patients were followed up for 8 weeks. Peripheral blood samples and biosy tissue specimens were obtained at the initiation of treatment and after 8 weeks to assess serum levels of inflammatory cytokines as well as the percentage of leukocytes, T-helper cells, cytotoxic-T cells, macrophages and endothelial cells in the biopsy tissue using flow cytometry.

RESULTS

A significantly greater reduction in the mean percentage ulcer area from baseline to eight weeks was observed in the study group (up to 40% for large ulcers). Furthermore, the patients in the study group had reduced systemic levels of the pro-inflammatory cytokines IL-8 (p = 0.0028) and IL-6 (p = 0.0302), fewer total CD45+ cells (p = 0.0038) and more CD31+ cells (p = 0.045) present in ulcer biopsies compared to the control group.

CONCLUSIONS

The carbohydrate polymer with zinc oxide treatment with venous compression enhances healing of CVUs and improves quality of life due, in part, to its anti-inflammatory properties.

Exogenous peripheral blood mononuclear cells affect the healing process of deep‑degree burns

The regenerative repair of deep-degree (second degree) burned skin remains a notable challenge in the treatment of burn injury, despite improvements being made with regards to treatment modality and the emergence of novel therapies. Fetal skin constitutes an attractive target for investigating scarless healing of burned skin. To investigate the inflammatory response during scarless healing of burned fetal skin, the present study developed a nude mouse model, which was implanted with normal human fetal skin and burned fetal skin. Subsequently, human peripheral blood mononuclear cells (PBMCs) were used to treat the nude mouse model carrying the burned fetal skin. The expression levels of matrix metalloproteinase (MMP)-9 and tissue inhibitor of metalloproteinases (TIMP)-1 were investigated during this process. In the present study, fetal skin was subcutaneously implanted into the nude mice to establish the murine model. Hematoxylin and eosin staining was used to detect alterations in the skin during the development of fetal skin and during the healing process of deep-degree burned fetal skin. The expression levels of MMP-9 and TIMP-1 were determined using immunochemical staining, and their staining intensity was evaluated by mean optical density. The results demonstrated that fetal skin subcutaneously implanted into the dorsal skin flap of nude mice developed similarly to the normal growth process in the womb. In addition, the scarless healing process was clearly observed in the mice carrying the burned fetal skin. A total of 2 weeks was required to complete scarless healing. Following treatment with PBMCs, the burned fetal skin generated inflammatory factors and enhanced the inflammatory response, which consequently resulted in a reduction in the speed of healing and in the formation of scars. Therefore, exogenous PBMCs may alter the lowered immune response environment, which is required for scarless healing, resulting in scar formation. In conclusion, the present study indicated that the involvement of inflammatory cells is important during the healing process of deep-degree burned skin, and MMP-9 and TIMP-1 may serve important roles in the process of scar formation.

A mathematical model for the simulation of the formation and the subsequent regression of hypertrophic scar tissue after dermal wounding

A continuum hypothesis-based model is presented for the simulation of the formation and the subsequent regression of hypertrophic scar tissue after dermal wounding. Solely the dermal layer of the skin is modeled explicitly and it is modeled as a heterogeneous, isotropic and compressible neo-Hookean solid. With respect to the constituents of the dermal layer, the following components are selected as primary model components: fibroblasts, myofibroblasts, a generic signaling molecule and collagen molecules. A good match with respect to the evolution of the thickness of the dermal layer of scars between the outcomes of simulations and clinical measurements on hypertrophic scars at different time points after injury in human subjects is demonstrated. Interestingly, the comparison between the outcomes of the simulations and the clinical measurements demonstrates that a relatively high apoptosis rate of myofibroblasts results in scar tissue that behaves more like normal scar tissue with respect to the evolution of the thickness of the tissue over time, while a relatively low apoptosis rate results in scar tissue that behaves like hypertrophic scar tissue with respect to the evolution of the thickness of the tissue over time. Our ultimate goal is to construct models with which the properties of newly generated tissues that form during wound healing can be predicted with a high degree of certainty. The development of the presented model is considered by us as a step toward their construction.

This paper is the winner of an SFB Award in the Hospital Intern, Residency category: Peptide biomaterials raising adaptive immune responses in wound healing contexts

Biomaterials used in the context of tissue engineering or wound repair are commonly designed to be "nonimmunogenic." However, previously it has been observed that self-assembled peptide nanofiber materials are noninflammatory despite their immunogenicity, suggesting that they may be appropriate for use in wound-healing contexts. To test this hypothesis, mice were immunized with epitope-containing peptide self-assemblies until they maintained high antibody titers against the material, then gels of the same peptide assemblies were applied within full-thickness dermal wounds. In three different murine dermal-wounding models with different baseline healing rates, even significantly immunogenic peptide assemblies did not delay healing. Conversely, adjuvanted peptide assemblies, while raising similar antibody titers to unadjuvanted assemblies, did delay wound healing. Analysis of the healing wounds indicated that compared to adjuvanted peptide assemblies, the unadjuvanted assemblies exhibited a progression of the dominant T-cell subset from CD4(+) to CD8(+) cells in the wound, and CD4(+) cell populations displayed a more Th2-slanted response. These findings illustrate an example of a significant antibiomaterial adaptive immune response that does not adversely affect wound healing despite ongoing antibody production. This material would thus be considered "immunologically compatible" in this specific context rather than "nonimmunogenic," a designation that is expected to apply to a range of other protein- and peptide-based biomaterials in wound-healing and tissue-engineering applications. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1853-1862, 2016.

Contribution of Invariant Natural Killer T Cells to Skin Wound Healing

In the present study, we determined the contribution of invariant natural killer T (iNKT) cells to the skin wound healing process. In iNKT cell-deficient (Jα18KO) mice lacking iNKT cells, wound closure was significantly delayed compared with wild-type mice. Collagen deposition, expression of α-smooth muscle actin and CD31, and wound breaking strength were significantly attenuated in Jα18KO mice. The adoptive transfer of liver mononuclear cells from wild-type but not from Jα18KO or interferon (IFN)-γ gene-disrupted (IFN-γKO) mice resulted in the reversal of this impaired wound healing in Jα18KO mice. IFN-γ expression was induced in the wounded tissues, which was significantly decreased at 6, 12, and 24 hours, but increased on day 3 after wounding in Jα18KO mice. The main source of the late-phase IFN-γ production in Jα18KO mice were neutrophils rather than NK cells and T cells. Administration of α-galactosylceramide, an activator of iNKT cells, resulted in the acceleration of wound healing on day 3 in wild-type mice. This effect was not observed in IFN-γKO mice. These results indicate that iNKT cells play important roles in wound healing. The iNKT cell-induced IFN-γ production may regulate the wound healing process in the early phase.

Impaired T-cell differentiation in diabetic foot ulceration

Foot ulceration is one of the most debilitating complications associated with diabetes, but its cause remains poorly understood. Several studies have been undertaken to understand healing kinetics or find possible therapies to enhance healing. However, few studies have been directed at understanding the immunological alterations that could influence wound healing in diabetes. In this study, we analysed the T-cell receptor (TCR) repertoire diversity in TCR-αβ⁺ T cells. We also analysed the distribution and phenotype of T cells obtained from the peripheral blood of healthy controls and diabetic individuals with or without foot ulcers. Our results showed that diabetic individuals, especially those with foot ulcers, have a significantly lower naive T-cell number and a poorer TCR-Vβ repertoire diversity. We also showed that the reduced TCR-Vβ repertoire diversity in diabetic individuals was mainly owing to the accumulation of effector T cells, the major source of tumour necrosis factor-α production, which was even more pronounced in patients with acute foot ulceration. Moreover, the expression of several inflammatory chemokine receptors was significantly reduced in diabetic patients. In conclusion, effector T-cell accumulation and TCR repertoire diversity reduction appear to precede the development of foot ulcers. This finding may open new immunological therapeutic possibilities and provide a new prognostic tool in diabetic wound care.

Systemic effects of oral tolerance reduce the cutaneous scarring

BACKGROUND

Immunological tolerance refer to the inhibition of specific immune responsiveness and the ingestion of proteins previous to immunization is a reliable method to induce (oral) tolerance. Parenteral exposure to tolerated antigens, in adjuvant, trigger indirect and systemic effects that inhibits concomitant immune responses to other unrelated antigens and also decrease unrelated inflammatory responses. Interesting, intraperitoneal (i.p.) exposure to orally-tolerated proteins soon before an incisional linear skin wound improves the healing by primary intention in mice. An important clinical and surgical objective is to identify strategies to improve wound healing and reduce scarring.

OBJECTIVE

To evaluate whether i.p. injection of an orally-tolerated protein improves wound healing by secondary intention and reduce scarring of full-thickness excisional skin injury.

METHODS

C57Bl/6 mice were turned tolerant to ovalbumin (OVA) by drinking a solution containing OVA; seven days later, they received an i.p. injection of OVA plus Al(OH)3 adjuvant immediately before two full-thickness excisional skin wounds, under anesthesia. The wound healing process was evaluated macro and microscopically after H&E, toluidine blue and Gomori's Trichrome staining. The presence of granulocytes, macrophages, miofibroblasts, fibronectin, collagen I and collagen III was investigated by immunofluorescence and the levels of cytokines by flow cytometry or ELISA. Mice not tolerant to OVA were included as controls.

RESULTS

The i.p. injection of OVA+Al(OH)3 in mice orally tolerant to OVA reduced the subsequent inflammatory response in the wound bed and the cutaneous scarring. There was a change in the pattern of collagen deposition making it more similar to the pattern observed in intact skin. In tolerant mice, mast cells and granulocytes (Ly-6C/G+), were reduced, while lymphocytes (CD3+) were increased in the wound bed. Time course analysis of Th1/Th2/Th17 cytokines and growth factors showed slightly differences between tolerant and control groups.

CONCLUSION

Parenteral injection of an orally-tolerated protein has systemic consequences that impair the inflammatory response triggered by skin injury and reduce the cutaneous scarring.

Boon and Bane of Inflammation in Bone Tissue Regeneration and Its Link with Angiogenesis

Delayed healing or nonhealing of bone is an important clinical concern. Although bone, one of the two tissues with scar-free healing capacity, heals in most cases, healing is delayed in more than 10% of clinical cases. Treatment of such delayed healing condition is often painful, risky, time consuming, and expensive. Tissue healing is a multistage regenerative process involving complex and well-orchestrated steps, which are initiated in response to injury. At best, these steps lead to scar-free tissue formation. At the onset of healing, during the inflammatory phase, stationary and attracted macrophages and other immune cells at the fracture site release cytokines in response to injury. This initial reaction to injury is followed by the recruitment, proliferation, and differentiation of mesenchymal stromal cells, synthesis of extracellular matrix proteins, angiogenesis, and finally tissue remodeling. Failure to heal is often associated with poor revascularization. Since blood vessels mediate the transport of circulating cells, oxygen, nutrients, and waste products, they appear essential for successful healing. The strategy of endogenous regeneration in a tissue such as bone is interesting to analyze since it may represent a blueprint of successful tissue formation. This review highlights the interdependency of the time cascades of inflammation, angiogenesis, and tissue regeneration. A better understanding of these inter-relations is mandatory to early identify patients at risk as well as to overcome critical clinical conditions that limit healing. Instead of purely tolerating the inflammatory phase, modulations of inflammation (immunomodulation) might represent a valid therapeutic strategy to enhance angiogenesis and foster later phases of tissue regeneration.

Characterisation and comparison of the host response of 6 tissue-based surgical implants in a subcutaneous in vivo rat model

BACKGROUND

Hernia repair often involves fascial augmentation using biologic prostheses. Small processing changes during preparation modulate host tissue response, which influence material efficacy and longevity. In this pilot study, a rat model was used to determine the specific influence of tissue origin, decellularisation treatment and 1,6-hexamethylene diisocyanate (HMDI) cross-linking.

METHODS

Materials (1 cm2) were implanted subcutaneously into 6-week-old Wistar rats (4 materials per animal, n=6/material per time point) for 2, 5, 7, 14 and 28 days. Histologic processing was carried out after resin infiltration, observing classical histopathology and pathologic indexing. Materials comprised 6 tissue-based grafts covering both experimental and commercial porcine decellularised dermal and small intestinal submucosal materials.

RESULTS

Subcutaneous delivery of biologics demonstrated material-specific inflammatory/host responses. Controlled variations of the PermacolTM manufacturing process showed sodium dodecyl sulfate (SDS) was the most proinflammatory decellularisation reagent, and HMDI cross-linking had no effect on host response. All materials remained recoverable after 28 days, although SurgisisTM had partially resorbed.

CONCLUSION

Differences in host responses exist between biologic implants for hernia repair in this rat model. It is postulated that these modifications are induced during processing and may have an effect on the clinical outcome of hernia repair.

A primer on wound healing in colorectal surgery in the age of bioprosthetic materials

Wound healing is a complex, dynamic process that is vital for closure of cutaneous injuries, restoration of abdominal wall integrity after laparotomy closure, and to prevent anastomotic dehiscence after bowel surgery. Derangements in healing have been described in multiple processes including diabetes mellitus, corticosteroid use, irradiation for malignancy, and inflammatory bowel disease. A thorough understanding of the process of healing is necessary for clinical decision making and knowledge of the current state of the science may lead future researchers in developing methods to enable our ability to modulate healing, ultimately improving outcomes. An exciting example of this ability is the use of bioprosthetic materials used for abdominal wall surgery (hernia repair/reconstruction). These bioprosthetic meshes are able to regenerate and remodel from an allograft or xenograft collagen matrix into site-specific tissue; ultimately being degraded and minimizing the risk of long-term complications seen with synthetic materials. The purpose of this article is to review healing as it relates to cutaneous and intestinal trauma and surgery, factors that impact wound healing, and wound healing as it pertains to bioprosthetic materials.

Absence of CD4 or CD8 lymphocytes changes infiltration of inflammatory cells and profiles of cytokine expression in skin wounds, but does not impair healing

The involvement of lymphocytes in skin wound healing has not been studied extensively. This study shows that CD4 and CD8 cells are present in significant numbers in skin wounds with peak levels at days 5-10 and 7-10, respectively. Both subsets expressed inflammatory and/or regulatory cytokines. To examine the function of CD4 and CD8 lymphocytes in tissue repair, wound healing was examined in mice deficient for either CD4 or CD8 cells. Wounds in CD4 deficient mice exhibited an initial delayed infiltration of CD8 cells followed by a relative increase in CD8 cells at day 10 and thereafter. Wounds in CD4 deficient mice also displayed up-regulated expression of IL1β, IL-6, IL-17, IFN-γ, CXCL-1 and down-regulated expression of IL-4 as compared to wild-type mice. In contrast, wounds in CD8 deficient mice showed significantly decreased infiltration of CD4+ cells, neutrophils, and macrophages along with down-regulated expression of IL1β, IL-6, TNF-α, CXCL-1, CCL-2 and up-regulated expression of IL-4 as compared to wild-type mice. Despite these significant changes in cytokine expression and inflammatory cell infiltrate, the rate of wound closure, wound breaking strength, collagen content and angiogenesis in either CD4 or CD8 deficiency showed no significant difference from that of wild-type mice. The results suggest that, despite being present and involved in wound inflammation, neither CD4+ nor CD8+ cells play critical roles in the healing process of skin wounds. Further studies are needed to investigate whether these cells might play critical roles in wounds that experience stress such as ischemia or infection.

Initiation and early control of tissue regeneration - bone healing as a model system for tissue regeneration

INTRODUCTION

Tissue regeneration in itself is a fascinating process that promises repeated renewal of tissue and organs.

AREAS COVERED

This article aims to illustrate the different strategies available to control tissue regeneration at a very early stage, using bone as an exemplary tissue. The aspects of a controlled inflammatory cascade to achieve a balanced immune response, cell therapeutic approaches for improved tissue formation and angiogenesis, guiding the organization of newly formed extracellular matrix by biomaterials, the relevance of mechanical signals for tissue regeneration processes, and the chances and limitations of growth factor treatments are discussed.

EXPERT OPINION

The currently available knowledge is reviewed and perspectives for potential new targets are given. This is done under the assumption that early identification of risk patients as well as the application of early intervention strategies is possible.

The thymus and skin wound healing in Xenopus laevis adults

The capacity to heal wounds without scars is generally lost during the development in vertebrates. To explore the involvement of cells of the adaptive immune system in a scar-like tissue based repair, we studied the thymus in 15-month-old Xenopus after skin incisional wounding. After injury, the organ size significantly increased and marked changes in structure and TNF-α immunoreactivity were detected in the medullary microenvironment when the granulation tissue was present in the repair area. Most of the lymphocytes present in this wound connective tissue were found to be immunoreactive to specific T cell markers. Thymic mucocyte-like cells and epithelial cysts increased in number, the myoid cells acquired a faster turnover and associated in large clusters, blood vessels were dilated and corpuscles similar to mammalian Hassall's bodies were formed in medulla. A higher number of stronger medullary TNF-α immunoreactive cells, i.e., dendritic, epithelial, granular basophilic and myoid cells were also induced after wounding. With progression of healing the thymus gradually returned to histochemical patterns of controls. Our results suggest that during the scar-based skin repair of Xenopus adults the activity of the thymus may be stimulated and associated with the T lymphocyte infiltration observed into injured granulation tissue.

T and B cells participate in bone repair by infiltrating the fracture callus in a two-wave fashion

Fracture healing is a regenerative process in which bone is restored without scar tissue formation. The healing cascade initiates with a cycle of inflammation, cell migration, proliferation and differentiation. Immune cells invade the fracture site immediately upon bone damage and contribute to the initial phase of the healing process by recruiting accessory cells to the injury site. However, little is known about the role of the immune system in the later stages of fracture repair, in particular, whether lymphocytes participate in soft and hard callus formation. In order to answer this question, we analyzed femoral fracture healing in mice by confocal microscopy. Surprisingly, after the initial inflammatory phase, when soft callus developed, T and B cells withdrew from the fracture site and were detectable predominantly at the femoral neck and knee. Thereafter lymphocytes massively infiltrated the callus region (around day 14 after injury), during callus mineralization. Interestingly, lymphocytes were not found within cartilaginous areas of the callus but only nearby the newly forming bone. During healing B cell numbers seemed to exceed those of T cells and B cells progressively underwent effector maturation. Both, osteoblasts and osteoclasts were found to have direct cell-cell contact with lymphocytes, strongly suggesting a regulatory role of the immune cells specifically in the later stages of fracture healing.

Immunonutrition: Role in Wound Healing and Tissue Regeneration

Significance: The role of immunonutrition in wound healing has been an area of both interest and controversy for many years. Although deficiencies in certain nutrients have long been known to impair healing, supplementation of specific immune modulating nutrients has not consistently yielded improvements in wound healing. Still, the prospect of optimizing nutrition to assist the immune system in wound repair bears great significance in both medical and surgical fields, as the costs of wound care and repair cannot be ignored. Recent Advances: Recent studies have rekindled efforts to elucidate the roles of specific immunonutrients, and we now have a better understanding of the conditionally essential role of various nutrients such as arginine, which becomes essential in certain clinical situations such as for the trauma patient or patients at high risk for malnutrition. Immunonutrition in its current formulation usually includes supplementation with arginine, glutamine, omega-3 fatty acids, vitamins, and trace minerals, and its use has often been associated with decreased infectious complications and sometimes with improvements in wound healing. Critical Issues: A key to understanding the role of immunonutrition in wound healing is recognizing the distinct contributions and importance of the various elements utilized. Future Directions: Critical areas for future study include identifying the specific populations, timing, and ideal composition of immunomodulating diets in order to optimize the wound healing process.

Human immune cells' behavior and survival under bioenergetically restricted conditions in an in vitro fracture hematoma model

The initial inflammatory phase of bone fracture healing represents a critical step for the outcome of the healing process. However, both the mechanisms initiating this inflammatory phase and the function of immune cells present at the fracture site are poorly understood. In order to study the early events within a fracture hematoma, we established an in vitro fracture hematoma model: we cultured hematomas forming during an osteotomy (artificial bone fracture) of the femur during total hip arthroplasty (THA) in vitro under bioenergetically controlled conditions. This model allowed us to monitor immune cell populations, cell survival and cytokine expression during the early phase following a fracture. Moreover, this model enabled us to change the bioenergetical conditions in order to mimic the in vivo situation, which is assumed to be characterized by hypoxia and restricted amounts of nutrients. Using this model, we found that immune cells adapt to hypoxia via the expression of angiogenic factors, chemoattractants and pro-inflammatory molecules. In addition, combined restriction of oxygen and nutrient supply enhanced the selective survival of lymphocytes in comparison with that of myeloid derived cells (i.e., neutrophils). Of note, non-restricted bioenergetical conditions did not show any similar effects regarding cytokine expression and/or different survival rates of immune cell subsets. In conclusion, we found that the bioenergetical conditions are among the crucial factors inducing the initial inflammatory phase of fracture healing and are thus a critical step for influencing survival and function of immune cells in the early fracture hematoma.

Initial immune reaction and angiogenesis in bone healing

During hematoma formation following injury, an inflammatory reaction ensues as an initial step in the healing process. As granulation tissue matures, revascularization is a prerequisite for successful healing. The hypothesis of this study was that scarless tissue reconstitution in the regenerative bone healing process is dependent on a balanced immune reaction that initiates revasculatory steps. To test this hypothesis, cellular composition and expression profiles of a bone hematoma (regenerative, scarless) was compared with a muscle soft tissue hematoma (healing with a scar) in a sheep model. Upregulation of regulatory T helper cells and anti-inflammatory cytokine expression (IL-10) coincided with an upregulation of angiogenic factors (HIF1α and HIF1α regulated genes) in the regenerative bone hematoma but not in the soft tissue hematoma. These results indicate that the timely termination of inflammation and early onset of revascularization are interdependent and essential for a regenerative healing process. Prolonged pro-inflammatory signaling occurring in a delayed bone-healing model supports the finding that timely termination of inflammation furthers the regenerative process. Differing cellular compositions are due to different cell sources invading the hematoma, determining the ensuing cytokine expression profile and thus paving the path for regenerative healing in bone or the formation of scar tissue in muscle injury.

Inducible costimulator (ICOS) and ICOS ligand signaling has pivotal roles in skin wound healing via cytokine production

Skin wound healing is mediated by inflammatory cell infiltration of the wound site. Inducible costimulator (ICOS), expressed on activated T cells, and its ligand, ICOS ligand (ICOSL), expressed on antigen-presenting cells, have been considered a single receptor-ligand pair. Although the ICOS-ICOSL pathway participates in adaptive immunity, its roles in skin wound healing, which is mediated by innate immune responses, remain unknown. To clarify these roles, repair of excisional wounds was examined in ICOS(-/-) mice, ICOSL(-/-) mice, and ICOS(-/-)ICOSL(-/-) mice. Each mutant strain showed similar, dramatic delays in wound healing, especially at early times. Knockout mice showed suppressed keratinocyte migration, angiogenesis, and granulation tissue formation, and diminished T-cell, macrophage, and neutrophil infiltration. The loss of ICOS and/or ICOSL resulted in marked suppression of cytokine expression in wounds, especially the Th2 cytokines interleukin (IL)-4, IL-6, and IL-10. T-cell transfer experiments and T-cell depletion therapy further clarified the important roles of ICOS expressed on T cells and its interaction with ICOSL. Application of IL-6, but not IL-4, to the wounds significantly increased the onset of early wound healing in mutant mice. Thus, our results indicate that ICOS-ICOSL costimulatory signaling has critical roles during wound healing, most likely by inducing IL-6 production.

The early fracture hematoma and its potential role in fracture healing

Research regarding the potency and potential of the fracture hematoma has begun to receive increasing attention. However, currently there is a paucity of relevant literature on the capability and composition of the fracture hematoma. This review briefly summarizes the regenerative fracture healing process and the close interplay between the skeletal and immune systems. The role of immune cells in wound healing is also discussed to clarify their involvement in immunological processes during regeneration. We attempt to describe the current state of knowledge regarding the fracture hematoma as the initial stage of the regenerative process of fracture healing. The review discusses how a better understanding of immune reactions in the hematoma may have implications for bone tissue engineering strategies. We conclude the review by emphasizing how additional investigations of the initial phase of healing will allow us to better differentiate between deleterious and beneficial aspects of inflammation, thereby facilitating improved fracture treatment strategies.

Antibodies to wounded tissue enhance cutaneous wound healing

The wound repair process is a highly ordered sequence of events that encompasses haemostasis, inflammatory cell infiltration, tissue regrowth and remodelling. Wound healing follows tissue destruction so we hypothesized that antibodies might bind to wounded tissues, which would facilitate the engulfment of damaged tissues by macrophages. Here, we show that B cells, which produce antibodies to damaged tissues, are engaged in the process of wound healing. Splenectomy delayed wound healing, and transfer of spleen cells into splenectomized mice recovered the delay in wound healing. Furthermore, wound healing in splenectomized nude mice was also delayed. Transfer of enriched B220(+) cells by magnetic beads accelerated wound healing in splenectomized mice. We detected immunoglobulin G1 (IgG1) binding to wounded tissues by using fluorescein isothiocyanate-labelled anti-IgG1 6-24 hr after wounding. Splenectomy reduced the amount of IgG1 binding to wounded tissues. Immunoblotting studies revealed several bands, which were reduced by splenectomy. Using immunoprecipitation with anti-IgG bound to protein G we found that the intensity of several bands was lower in the serum from splenectomized mice than in that from sham-operated mice. These bands were matched to myosin IIA, carbamoyl-phosphate synthase, argininosuccinate synthase, actin and alpha-actinin-4 by liquid chromatography tandem mass spectrometry analysis.

Surgical stress-induced immune cell redistribution profiles predict short-term and long-term postsurgical recovery. A prospective study

BACKGROUND

The experience of undergoing surgery is known to induce a short-term, fight-or-flight physiological stress response. As an optimum immune response at the site of surgery would enhance tissue repair, we examined surgical stress-induced immune cell redistribution profiles as predictors, and potential mediators, of short and long-term postoperative recovery. We tested the a priori hypothesis that predefined adaptive immune cell redistribution profiles observed during surgery will predict enhanced postoperative recovery.

METHODS

This prospective longitudinal study involved fifty-seven patients undergoing meniscectomy. Knee function was assessed preoperatively and at one, three, eight, sixteen, twenty-four, and forty-eight weeks postoperatively with use of the clinically validated Lysholm scale, which assesses mechanical function, pain, mobility, and the ability to perform daily activities. Surgery-induced immune cell redistribution was measured in the blood at baseline, before surgery, and after surgery.

RESULTS

Mixed-model repeated-measures analyses revealed a main effect of immune cell redistribution: patients who showed the predefined "adaptive" lymphocyte and monocyte redistribution profiles during surgery showed enhanced recovery. Interesting differences were also observed between the sexes: women as a group showed less adaptive redistribution and correspondingly showed significantly delayed maximum recovery, requiring forty-eight weeks, compared with men, who required only sixteen weeks. Inter-individual differences in leukocyte redistribution predicted the rate of recovery across both sexes.

CONCLUSIONS

Immune cell redistribution that is induced by the stress of undergoing surgery can predict (and may partially mediate) postoperative healing and recovery. These findings may provide the basis for identifying patients (either prospectively or during surgery) who are likely to show good as opposed to poor recovery following surgery and for designing interventions that would maximize protective immune responses and enhance the rate and extent of recovery.

The spatio-temporal dynamics of ligament healing

Ligament injury commonly occurs with no effective treatment to restore its original state. Numerous studies have examined wound healing after injury, reporting a provisional matrix and scar formation within the wound. Few studies however report the inflammatory, proliferative, and remodeling process during ligament healing in a spatio-temporal manner. Our goal was then to more completely elucidate this process in a rat medial collateral ligament (MCL) healing model. In this study, medial collateral ligaments were surgically transected and allowed to heal. At 1, 3, 5, 7, 9, 11, 14, and 28 days postinjury ligaments were collected and examined with microangiography or immunohistochemistry. We demonstrate that neutrophils and mitotic cells peak between 1 and 5 days postinjury. The majority of factors crest between 5 and 9 days postinjury, including circulating macrophages, resident macrophages, T lymphocytes, hematopoietic cells, vascular endothelial growth factor, and blood vessels. The apoptotic cells predominate from day 9 to the end of the study (day 28). Initially, most assayed markers localize to the epiligament and to granulation tissue at the site of damage. Later, the healing region with its granulation tissue and cells continues to expand into the uninjured tissue. From these results, we have expanded current descriptions of ligament healing and offer a more complete representation of the healing process.

T cells contribute to lysophosphatidylcholine-induced macrophage activation and demyelination in the CNS

We have previously shown that intraspinal microinjection of lysophosphatidylcholine (LPC), a potent demyelinating agent, results in a rapid but brief influx of T cells (between 6 and 12 h). This is accompanied by a robust activation of macrophages/microglia that leads to demyelination by 48 h. In the present study, we examined whether this brief influx of T cells contributes to the activation of macrophages/microglia and demyelination by injecting LPC into the dorsal column white matter of athymic Nude mice that lack T cells. We show that there is a significant reduction in macrophage/microglial activation and myelin clearance after LPC injection in Nude mice as compared with wildtype controls. We also show that there is no difference in the recruitment of hematogenous macrophages into the spinal cord after LPC injection in the two mouse strains. Of the T cell cytokines assessed, there was a marked reduction in the mRNA expression of interleukin-2 (IL-2) in Nude mice compared with wildtype animals. Neutralizing IL-2 with function-blocking antibodies in wildtype animals resulted in a significant decrease in the number of phagocytic macrophages/microglia and a reduction in demyelination induced by LPC. While there may be other defects in Nude mice that might contribute to the effects shown here, these data suggest that the brief influx of T cells in this model of chemically-induced demyelination could play a role in macrophage/microglial activation and demyelination. These results may also have implications for remyelination in this and other types of CNS damage.

Molecular control of physiological and pathological T-cell recruitment after mouse spinal cord injury

The intraspinal cues that orchestrate T-cell migration and activation after spinal contusion injury were characterized using B10.PL (wild-type) and transgenic (Tg) mice with a T-cell repertoire biased toward recognition of myelin basic protein (MBP). Previously, we showed that these strains exhibit distinct anatomical and behavioral phenotypes. In Tg mice, MBP-reactive T-cells are activated by spinal cord injury (SCI), causing more severe axonal injury, demyelination, and functional impairment than is found in non-Tg wild-type mice (B10.PL). Conversely, despite a robust SCI-induced T-cell response in B10.PL mice, no overt T-cell-mediated pathology was evident. Here, we show that chronic intraspinal T-cell accumulation in B10.PL and Tg mice is associated with a dramatic and sustained increase in CXCL10/IP-10 and CCL5/RANTES mRNA expression. However, in Tg mice, chemokine mRNA were enhanced 2- to 17-fold higher than in B10.PL mice and were associated with accelerated intraspinal T-cell influx and enhanced CNS macrophage activation throughout the spinal cord. These data suggest common molecular pathways for initiating T-cell responses after SCI in mice; however, if T-cell reactions are biased against MBP, molecular and cellular determinants of neuroinflammation are magnified in parallel with exacerbation of neuropathology and functional impairment.

The effects of ZD6474, an inhibitor of VEGF signaling, on cutaneous wound healing in mice

BACKGROUND

ZD6474 is an inhibitor of the VEGFR-2 receptor tyrosine kinase with additional activity against EGFR-1 receptor tyrosine kinases that has been shown to inhibit tumor growth and wound-induced neovascularization in pre-clinical studies and phase I clinical trials. The purpose of this study was to determine the effects of ZD6474 on breaking strength in a murine model of cutaneous wound healing.

MATERIALS AND METHODS

Balb/C mice were given ZD6474 (50 or 100 mg/kg p.o.) or vehicle starting 7 days before wounding. Two full-thickness incisions were made in each mouse and closed using suture. On post-wounding day 7 or 28, laser Doppler blood flow measurements were made, and the breaking strength of the wounded skin was determined. Microvessel density measurements were performed using computer image analysis of CD31-stained sections.

RESULTS

Compared with controls, mice treated with ZD6474 showed a significantly reduced dose-dependent decline in breaking strength, both at POD 7 (P < 0.001) and at POD 28 (P < 0.005). Histologically, the ZD6474-treated mice showed a qualitative reduction in the degree of fibrosis and epithelial proliferation at the wound site, but no significant difference was noted between the 50 mg/kg and 100 mg/kg ZD6474-treated groups. Also, microvessel density measurements demonstrated no significant difference between groups.

CONCLUSION

In a murine model of wound healing, ZD6474 treatment did not prevent wound healing, but was associated with a reduced skin breaking strength compared with vehicle-treated controls at both 7 and 28 days post-wounding. These observations may have clinical relevance for the perioperative management of patients treated with inhibitors of angiogenesis.

Normal cutaneous wound healing: clinical correlation with cellular and molecular events

BACKGROUND

Cutaneous wound healing is a normal physiologic function, observed and described for centuries by those afflicted with wounds and by those caring for them. Recently, tremendous progress has been made in discovering the cellular and molecular mechanisms responsible for wound healing. Counseling patients appropriately and planning future therapeutic interventions in delayed or abnormal wound healing may be improved by a thorough understanding of the relationship between clinical, cellular, and subcellular events occurring during the normal healing process.

MATERIALS AND METHODS

A review of the wound healing literature from the past several decades, with a focus on the past 5 to 10 years in particular, along with illustrative case examples from our clinical practice over the past decade.

RESULTS

Traditional clinical stages of wounding healing are still relevant, but more overlap between stages is likely a more accurate depiction of events. The role of cells such as platelets, macrophages, leukocytes, fibroblasts, endothelial cells, and keratinocytes is much better known, particularly during the inflammatory and proliferation stages of healing. Molecules such as interferon, integrins, proteoglycans and glycosaminoglycans, matrix metalloproteinases, and other regulatory cytokines play a critical role in the regulation of healing mechanisms.

CONCLUSION

Cutaneous wound healing in normal hosts follows an orderly clinical process. The scientific underpinnings for healing are better understood than ever, although much remains to be discovered. Eventually, such improved understanding of cellular and subcellular physiology may lead to new or better forms of therapy for patients with acute, chronic, and surgical skin wounds.

Effects of T-lymphocyte depletion on muscle fibrosis in the mdx mouse

Duchenne muscular dystrophy was initially described as a myosclerosis because of the conspicuous progression of interstitial fibrosis. Using the mdx mouse homologue, we have shown previously that the accumulation of intramuscular collagen is profoundly influenced by the presence or absence of T lymphocytes. Here we have used thymectomy and antibody depletion to examine the effect of ablating CD4 or CD8 or both subsets of T lymphocytes on skeletal muscle fibrosis in mdx and C57BL10 (wild-type) mice. Depletion of either or both subsets at 4 weeks of age did not influence fibrosis in mdx mice, as determined by measuring hydroxyproline levels and collagen deposition in diaphragm. Additionally, expression of transforming growth factor-beta1, which is implicated in collagen deposition, either decreased (mdx mice) or increased (C57BL/10 mice) after double CD4/8 depletion. Our data suggest that depletion of lymphoid cells may affect the tight regulatory control of transforming growth factor-beta1, with possible pleiotropic effects, and more importantly, that the fibrotic process is self-sustaining from a very early stage.

The management of lower extremity wounds using topical negative pressure

The delivery of topical pressures at subatmospheric levels to heal acute and chronic wounds has been widely reported. This article reviews the role of this therapeutic modality to treat wounds of the lower extremity. Recent literature is re-viewed, and mechanisms of action of this process are also discussed.

Models to study ischemia in chronic wounds

Wound healing is a complex immune response designed to achieve tissue repair following injury. Imbalance of stimulating and inhibiting factors cause failure of healing. Ischemia is a major cause of wound repair dysregulation and may be limb and life threatening. Investigating ischemic wound healing using animal models minimizes the complex accompanying factors that are usually present in humans, such as age or diabetes. This paper presents a limited review on normal physiological healing and on models that are used to study compromised healing under ischemic conditions.

What do we mean by the term "inflammation"? A contemporary basic science update for sports medicine

Most practicing sports medicine clinicians refer to the concept of "inflammation" many times a day when diagnosing and treating acute and overuse injuries. What is meant by this term? Is it a "good" or a "bad" process? The major advances in the understanding of inflammation in recent years are summarised, and some clinical implications of the contemporary model of inflammation are highlighted.

Hindlimb unloading depresses corneal epithelial wound healing in mice

C57BL/6 mice were subjected to hindlimb unloading (HU) for a period of 3 wk to determine the possible effects on epithelial wound healing. A standardized corneal epithelial wound was performed, and parameters of the inflammatory response and reepithelialization were analyzed over an observation period of 96 h. Wound closure was significantly retarded in mice during HU with reepithelialization being delayed by ∼12 h. Both epithelial migration and cell division were significantly depressed and delayed. The inflammatory response to epithelial wounding was also significantly altered during HU. Neutrophils, as detected by the Gr-1 marker, were initially elevated above normal levels before wounding and during the first few hours afterward, but there was a significant reduction in neutrophil response to wounding at times where neutrophil influx and migration in controls were vigorous. A similar pattern was seen with CD11b+CD11c+ cells (monocyte lineage). Langerhans cells are normally resident within the peripheral corneal epithelium. They respond to injury by initially leaving the epithelial site within 6 h and returning to normal levels by 96 h, 2 days after reepithelialization is complete. During HU, this pattern is distinctly different, with Langerhans cell numbers slowly diminishing, reaching a nadir at 96 h, which is significantly below normal. Evidence for systemic effects of HU is provided by findings that collagen deposition within subcutaneous sponges was significantly reduced during HU. In conclusion, HU, a ground-based model simulating some physiological aspects of spaceflight, impairs wound repair of corneas. Multiple factors, both local and systemic, likely contribute to this delayed wound healing.

Effects of post-operative pain treatment using non-steroidal anti-inflammatory analgesics, opioids or epidural blockade on systemic and local immune responses in children

BACKGROUND

Many studies have been carried out on the effects of anaesthetic drugs and methods on the immune response, but pain and its relief also affect the immune response. We measured systemic immune responses in the blood circulation and local responses in the surgical wound when non-steroidal anti-inflammatory analgesics (NSAIDs), opioids or epidural blockade was used in the peri-operative treatment of pain.

METHODS

Responses were measured in 51 children, aged from 2 to 12 years and undergoing major surgery under balanced anaesthesia. Bolus doses of diclofenac intravenously (i.v.) and rectally (NSAID group), continuous i.v. infusion of oxycodone (opioid group) or continuous epidural infusion of bupivacaine + fentanyl (epidural group) were used peri-operatively for pain relief.

RESULTS

The only difference related to the analgesic method was shorter duration of post-operative leucocytosis and lower phytohaemagglutinin (PHA)-induced lymphocyte proliferative responses in peripheral blood in the opioid group than in the NSAID or epidural groups. By contrast, time-related alterations were seen overall in leucocyte and differential counts, lymphocyte and their subset counts, lymphocyte proliferative responses, and in serum cortisol, C-reactive protein, plasma interleukin-6 and group II phospholipase A2 concentrations and in the appearance of different cell types in the wound.

CONCLUSIONS

Post-operative pain treatments using diclofenac (NSAID), oxycodone (opioid) and epidural blockade have basically similar effects on systemic and local immune responses with only slight, probably clinically unimportant differences in children undergoing surgery under general anaesthesia.

Understanding the role of immune regulation in wound healing

The immune system plays an integral role in successful wound healing. In addition to contributing to host defenses and inflammation, immune cells are critical regulators of wound healing through the secretion of cytokines, lymphokines, and growth factors. We review the mechanisms by which the immune system regulates wound healing.

Rats and mice exhibit distinct inflammatory reactions after spinal cord injury

Spinal contusion pathology in rats and mice is distinct. Cystic cavities form at the impact site in rats while a dense connective tissue matrix occupies the injury site in mice. Because inflammatory cells coordinate mechanisms of tissue injury and repair, we evaluated whether the unique anatomical presentation in spinally injured rats and mice is associated with a species-specific inflammatory response. Immunohistochemistry was used to compare the leukocytic infiltrate between rats and mice. Microglia/macrophage reactions were similar between species; however, the onset and magnitude of lymphocyte and dendritic cell (DC) infiltration were markedly different. In rats, T-cell numbers were highest between 3 and 7 days postinjury and declined by 50% over the next 3 weeks. In mice, significant T-cell entry was not evident until 14 days postinjury, with T-cell numbers doubling between 2 and 6 weeks. Dendritic cell influx paralleled T-cell infiltration in rats but was absent in mouse spinal cord. De novo expression of major histocompatability class II molecules was increased in both species but to a greater extent in mice. Unique to mice were cells that resembled lymphocytes but did not express lymphocyte-specific markers. These cells extended from blood vessels within the fibrotic tissue matrix and expressed fibronectin, collagen I, CD11b, CD34, CD13, and CD45. This phenotype is characteristic of fibrocytes, specialized blood-borne cells involved in wound healing and immunity. Thus, species-specific neuroinflammation may contribute to the formation of distinct tissue environments at the site of spinal cord injury in mice and rats.

Autoreactive T cells promote post-traumatic healing in the central nervous system

In general, autoimmune responses are considered harmful to the host. In the best-defined model of autoimmune disease, murine experimental allergic encephalomyelitis (EAE), for example, brain-protein-specific autoimmune responses of both major classes, type-1 and type-2, have been implicated in causing brain pathology. We induced type-1 and type-2 autoimmunity to myelin oligodendrocyte protein (MOG) in C57.BL/6 mice. Instead of using pertussis toxin (PTX) to open the blood-brain barrier (BBB), which is the classic procedure, we set an aseptic cerebral injury (ACI) to see what the consequences of pre-primed, autoreactive type-1 and type-2 memory T cells gaining access to the brain in the course of sterile tissue injury would be. Neither of these autoimmune response types induced pathology; on the contrary, both accelerated re-vascularization and post-traumatic healing. The data suggest that induction of either type-1 or type-2 autoimmune responses is not inherently noxious to the host, but can have beneficial effects on tissue repair. Autoimmune pathology may develop only if molecules of microbial origin such as pertussis toxin additionally induce the "infectious nonself/danger" reaction in the antigen-presenting cells (APC) of the target organ itself.

Functional T lymphocytes infiltrate implanted polyvinyl alcohol foams during surgical wound closure therapy

Vacuum-assisted closure involving the implantation of polyvinyl alcohol foam is a technique recently developed for the treatment of patients suffering from either wound infection or chronic wounds. This method has been shown to improve and accelerate wound healing. However, little is known about the cell populations that infiltrate the foam, and their potential role in resolving the infection and promoting granulation tissue formation. Our study demonstrates that wound-implanted foams are mainly infiltrated with granulocytes, but that mononuclear cells, including macrophages and minor populations of T, B and natural killer lymphocytes, are also present. We show that foam-infiltrating T cells, especially CD4(+) T cells, constitute a phenotypically and functionally heterogeneous population influenced by wound-infecting bacteria. Thus, T lymphocytes could play a role in wound cleansing. In addition, our data indicate that implanted polyvinyl alcohol foams might be suitable microenvironments for manipulating T cell-mediated immune responses in patients.

Effect of CD4(+) and CD8(+) cell depletion on wound healing

BACKGROUND

Depression of the immune system can result in poor or delayed wound healing.

METHODS

Thymectomized rats were depleted of CD4(+) and CD8(+) lymphocytes by intraperitoneal injection of Medical Research Council Oxford (MRC OX)38 antibodies and MRC OX8. Significant depletion was demonstrated throughout the wound healing process by immunofluorescence studies of peripheral blood. Following depletion the rats underwent laparotomy incisions which were allowed to heal for 10 weeks. Differences in healing were demonstrated by analysing the wounds biomechanically by tensiometry to obtain values of ultimate strength, resilience, toughness, maximum extension and elastic constant.

RESULTS

Wounds of animals depleted of CD4+ lymphocytes showed a significant decrease in ultimate strength, resilience and toughness. Wounds of animals depleted of CD8(+) lymphocytes showed a significant increase in ultimate strength, resilience and toughness.

CONCLUSION

Wounds healed in the absence of T lymphocytes. However, the subsets have an opposing regulatory role, with CD4(+) lymphocytes upregulating and CD8(+) lymphocytes downregulating wound healing. Presented to the Surgical Research Society in Nottingham, UK, 11 July 1997 and published in abstract form as Br J Surg 1997; 84: 1618