Keloid Pathogenesis and Treatment

BACKGROUND

Keloid management can be difficult and frustrating, and the mechanisms underlying keloid formation are only partially understood.

METHODS

Using original and current literature in this field, this comprehensive review presents the major concepts of keloid pathogenesis and the treatment options stemming from them.

RESULTS

Mechanisms for keloid formation include alterations in growth factors, collagen turnover, tension alignment, and genetic and immunologic contributions. Treatment strategies for keloids include established (e.g., surgery, steroid, radiation) and experimental (e.g., interferon, 5-fluorouracil, retinoid) regimens.

CONCLUSION

The scientific basis and empiric evidence supporting the use of various agents is presented. Combination therapy, using surgical excision followed by intradermal steroid or other adjuvant therapy, currently appears to be the most efficacious and safe current regimen for keloid management.

Skin tissue regeneration for burn injury

The skin is the largest organ of the body, which meets the environment most directly. Thus, the skin is vulnerable to various damages, particularly burn injury. Skin wound healing is a serious interaction between cell types, cytokines, mediators, the neurovascular system, and matrix remodeling. Tissue regeneration technology remarkably enhances skin repair via re-epidermalization, epidermal-stromal cell interactions, angiogenesis, and inhabitation of hypertrophic scars and keloids. The success rates of skin healing for burn injuries have significantly increased with the use of various skin substitutes. In this review, we discuss skin replacement with cells, growth factors, scaffolds, or cell-seeded scaffolds for skin tissue reconstruction and also compare the high efficacy and cost-effectiveness of each therapy. We describe the essentials, achievements, and challenges of cell-based therapy in reducing scar formation and improving burn injury treatment.

Understanding Keloid Pathobiology From a Quasi-Neoplastic Perspective: Less of a Scar and More of a Chronic Inflammatory Disease With Cancer-Like Tendencies

Keloids are considered as benign fibroproliferative skin tumors growing beyond the site of the original dermal injury. Although traditionally viewed as a form of skin scarring, keloids display many cancer-like characteristics such as progressive uncontrolled growth, lack of spontaneous regression and extremely high rates of recurrence. Phenotypically, keloids are consistent with non-malignant dermal tumors that are due to the excessive overproduction of collagen which never metastasize. Within the remit of keloid pathobiology, there is increasing evidence for the various interplay of neoplastic-promoting and suppressing factors, which may explain its aggressive clinical behavior. Amongst the most compelling parallels between keloids and cancer are their shared cellular bioenergetics, epigenetic methylation profiles and epithelial-to-mesenchymal transition amongst other disease biological (genotypic and phenotypic) behaviors. This review explores the quasi-neoplastic or cancer-like properties of keloids and highlights areas for future study.

Altered cytokine production in black patients with keloids

The treatment of keloids in black patients remains a medical dilemma. Previous studies have focused on primary alterations in the metabolism of fibroblasts as the key in the etiology of this condition. Yet alterations in the production of various cytokines which may alter fibroblast responses secondarily have received little attention. Twelve black patients with clinical and histological diagnosis of keloids and eight black control volunteers were studied. Peripheral blood mononuclear-cell (PBMC) fractions from both groups were assayed for production of interleukin-1 (IL-1), interleukin-2 (IL-2), interleukin-6 (IL-6), alpha-interferon (IFN-alpha), beta-interferon (IFN-beta), gamma-interferon (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and tumor necrosis factor-beta (TNF-beta). The production of IFN-alpha, IFN-gamma, and TNF-beta were markedly depressed in keloid patients compared to normal controls. However, IL-1 and IL-2 production was not significantly different between the two groups. In contradistinction, keloid patients produce greater amounts of IL-6, TNF-alpha, and IFN-beta. Altered levels of immunoregulatory cytokines may play a significant role in the net increase in collagen which characterizes keloid formation.

Keloids and hypertrophic scars of Caucasians show distinctive morphologic and immunophenotypic profiles

The aim of this study was to identify possible morpho-phenotypic differences between keloids (K) and hypertrophic scars (HS) in a Caucasian population. Young HS (< or =1 year of age) presented a high number of diffusely distributed spindle-shaped cells (alpha-smooth-muscle actin+ and fibronectin+). Fully developed HS (> 1 year of age and <3 years of age) were characterized by the frequent presence of distinct collagenous cellular nodules (cells: alpha-smooth-muscle actin+ and fibronectin+). Old HS (> or =3 years of age) showed widespread collagenization phenomena. The histological profile of K was not related to the age of the lesion and was characterized by the almost constant presence of abnormally thick, hyalinized collagen fibers, the presence of collagenous cellular nodules, and variable--albeit lower than in HS-- expression of alpha-smooth-muscle actin and fibronectin. Ultrastructurally, myofibroblasts were the predominant cell type in young and fully developed HS and in K. The immune-cell infiltrate was composed of CD3+, CD45RO+, CD4+, human lymphocyte antigen (HLA)-DR+, and lymphocyte function associated antigen (LFA)-1+ T lymphocytes, strictly associated with CD1a+/ CD36+, HLA-DR+, and intercellular adhesion molecule (ICAM)-1+ dendritic cells, both in HS and K. However, different amounts of immune cells were observed in relation to the type and age of the lesion, and these findings support the hypothesis that cell-mediated, major histocompatibility complex (MHC)-class II-restricted immune responses play an important role in the development of HS and K.

Inverse correlation between CD34 expression and proline-4-hydroxylase immunoreactivity on spindle cells noted in hypertrophic scars and keloids

The CD34 positive (CD34+) spindle cells constitute a special population of spindle cells which shows a unique distribution in the skin. So far, however, the functional role of CD34+ spindle cells and the regulation of CD34 expression on dermal spindle cells are totally unknown. We examined immunohistologically the pattern of the expression of CD34 and proline-4-hydroxylase, a marker for the fibroblasts that participate in active collagen synthesis, on dermal spindle cells at various stages of scar and keloidal tissues. Dermal spindle cells in the lesions of hypertrophic scar and those at inflammatory expanding borders of keloids totally lost CD34 expression, but they strongly expressed proline-4-hydroxylase. On the other hand, they expressed CD34, together with decreased immunoreactivity to anti-proline-4-hydroxylase antibody, in non-inflammatory scars or in a non-inflammatory central portion of keloid. In two cases of scars, in which inflammation began to subside, double immunofluorescence demonstrated that both CD 34 and proline-4-hydroxylase were expressed on the same spindle cells. CD34 expression, once disappeared from the lesions of hypertrophic scar or keloid, seems to return on CD34-proline-4-hydroxylase+ cells, when the initial inflammatory changes begin to regress. There is a reverse correlation between CD34 expression on spindle cells and the synthesis of type I collagen in the skin.

Inflammatory-cell subpopulations in keloid scars

The aim of this study was to investigate the contribution of lymphocytes and macrophages to keloid scarring by morphologically characterising inflammatory cell subpopulations in keloid scars in comparison with normal skin. We took 3mm punch biopsies from the anterior forearms of eight normal healthy volunteers. Eight keloid scars were excised using an intralesional technique. All tissue was snap frozen in liquid nitrogen and serial sections were stained with a panel of anti-inflammatory cell monoclonal antibodies. The numbers of macrophages and lymphocytes and the proportions of the subpopulations were compared. Higher numbers of both macrophages and lymphocytes were found in keloid dermis (P=0.01 and P=0.02, respectively (Mann-Whitney U -test)). There was no significant increase in the expression of the lymphocyte-activation markers, CD25 and CD27. However, there was a significantly higher CD4(+):CD8(+)(Th:Ts) ratio (P= 0.046) in keloid tissue. This suggests that an imbalance in these inflammatory cell subpopulations may contribute to keloid scarring in man.

Upregulation of transforming growth factor-beta1 and vascular endothelial growth factor in cultured keloid fibroblasts: relevance to angiogenic activity

Keloids are tumor-like lesions that result from excessive scar formation during healing of wounds. Histologically, keloids show an increased blood vessel density compared with normal dermis or normal scars. However, the angiogenic activity of keloid fibroblasts remains unknown. In this study, we investigated angiogenic activity of keloid fibroblasts. Transforming growth factor-beta1 (TGF-beta1) and vascular endothelial growth factor (VEGF) were investigated as elements of the angiogenic factors. Expressions of TGF-beta1 and VEGF in conditioned medium were measured with enzyme-linked immunosorbent assay (EIA) and Northern blot analysis. Participation of TGF-beta1 in the production of VEGF was also investigated with addition of TGF-beta1 and a neutralizing anti-TGF-beta1 antibody. A modified Boyden chamber assay was performed to assess the chemotactic activity of vascular endothelial cells. Angiogenic activity in vivo was evaluated by neovascularization of nodules formed by implantation of fibroblasts into severe combined immunodeficiency (SCID) mice. EIA showed that the concentrations of TGF-beta1 and VEGF in conditioned medium were increased 2.5- and 6-fold, respectively, after the culture of keloid fibroblasts compared with normal fibroblasts. Northern blot analysis revealed that the expression of TGF-beta1 and VEGF mRNA was upregulated 3.6- and 6-fold, respectively, in keloid fibroblasts compared with normal fibroblasts. Addition of TGF-beta1 to keloid fibroblast cultures increased VEGF production by 3.5-fold, while there was a 6-fold in culture of normal fibroblasts. A neutralizing anti-TGF-beta1 antibody reduced VEGF secretion to control levels, suggesting that TGF-beta1 mediated the upregulation of VEGF expression. A modified Boyden chamber assay demonstrated that the chemotactic activity of vascular endothelial cells was more strongly (sevenfold) induced by keloid fibroblast-conditioned medium than by normal fibroblast-conditioned medium. Anti-VEGF antibody inhibited chemotaxis to basal levels. When SCID mice underwent implantation of fibroblasts into the back, the nodules formed by keloid fibroblasts were three times larger than those formed by normal fibroblasts. Although abundant neovascularization was observed in keloid fibroblast nodules, neovascularization was scarce in normal fibroblast nodules. Both in vitro and in vivo studies confirmed the significantly higher angiogenic activity of keloid fibroblasts compared with normal fibroblasts, and TGF-beta1 and VEGF were clearly shown to be involved. These results suggest that angiogenesis in keloids is promoted by endogenous TGF-beta1 and VEGF.

RNA Sequencing Keloid Transcriptome Associates Keloids With Th2, Th1, Th17/Th22, and JAK3-Skewing

Keloids are disfiguring, fibroproliferative growths and their pathogenesis remains unclear, inhibiting therapeutic development. Available treatment options have limited efficacy and harbor safety concerns. Thus, there is a great need to clarify keloid pathomechanisms that may lead to novel treatments. In this study, we aimed to elucidate the profile of lesional and non-lesional keloid skin compared to normal skin. We performed gene (RNAseq, qRT-PCR) and protein (immunohistochemistry) expression analyses on biopsy specimens obtained from lesional and non-lesional skin of African American (AA) keloid patients compared to healthy skin from AA controls. Fold-change≥2 and false-discovery rate (FDR)<0.05 was used to define significance. We found that lesional versus normal skin showed significant up-regulation of markers of T-cell activation/migration (ICOS, CCR7), Th2- (IL-4R, CCL11, TNFSF4/OX40L), Th1- (CXCL9/CXCL10/CXCL11), Th17/Th22- (CCL20, S100As) pathways, and JAK/STAT-signaling (JAK3) (false-discovery rate [FDR]<0.05). Non-lesional skin also exhibited similar trends. We observed increased cellular infiltrates in keloid tissues, including T-cells, dendritic cells, mast cells, as well as greater IL-4rα+, CCR9+, and periostin+ immunostaining. In sum, comprehensive molecular profiling demonstrated that both lesional and non-lesional skin show significant immune alternations, and particularly Th2 and JAK3 expression. This advocates for the investigation of novel treatments targeting the Th2 axis and/or JAK/STAT-signaling in keloid patients.

Immunoglobulin, complement, and histocompatibility antigen studies in keloid patients

The increased collagen synthesis and deposition, which is characteristic of keloids, may be related to an immune response initiated by wounding. Therefore, we examined various systemic and localized immune parameters in keloid patients to establish if such factors are related to keloid pathogenesis. To determine if there is a systemic immune response, we compared the serum levels of IgG and IgM in keloid patients to those in a closely matched population. In addition, we measured complement levels (Clq, C3, and C4) and receptors for sheep (E), mouse erythrocytes (MRBC), and complement (EAC) on blood lymphocytes. All of these were in the normal range in the keloid patients. However, the extractable IgG from keloid tissue was significantly increased (compared to normal skin and normal scar controls), suggesting a localized immune response. To determine whether keloid formation is associated with a specific histocompatibility locus, human lymphocyte antigen (HLA) profiles of 45 keloid patients were analyzed; no significant differences in the incidence of HLA-A and B antigens were found (compared to 200 controls). These studies suggest that there is a localized immune response involved in keloid pathogenesis, one which is not related to either the HLA-A or B histocompatibility loci.

Are keloids really "gli-loids"?: High-level expression of gli-1 oncogene in keloids

BACKGROUND

Keloids are a common lesion arising from sites of previous trauma and are a considerable source of morbidity because of continued growth of lesions, pruritus, and physical appearance. They consist of mesenchymal cells embedded in a stroma of disordered collagen matrix. Clinically, keloids are distinguished from scars in that keloids demonstrate continued growth over the borders of the original injury. Keloids appear with increased frequency in patients of African and Asian descent. Currently, no entirely satisfactory method of treatment exists for these lesions. Recently, a patient who was enrolled in a clinical trial of topical tacrolimus for atopic dermatitis applied this drug to a keloid and noted clearing.

OBJECTIVE

Based on this clinical observation and the observation that rapamycin, a chemically similar compound to tacrolimus, is known to inhibit signaling from the gli-1 oncogene, we examined keloids and scars for expression of Gli-1 protein.

METHODS

Skin sections from keloids and scars were examined by immunohistochemical staining for gli-1. To further confirm the presence of gli-1 expression in keloids, reverse transcriptase-polymerase chain reaction was carried out.

RESULTS

Expression of gli-1 was strongly elevated in keloids compared with scars.

CONCLUSION

These results provide a rationale for the treatment of keloids with topical rapamycin analogs, including tacrolimus. Clinical trials of topical tacrolimus are warranted.

The immunological aspects of keloid tumor formation

This study considered possible immunological alterations that may be associated with keloid tumor formation. Laser immunonephelometry was used to quantitate circulating immune complexes and complement C3 and C4 among keloid formers. IgG complex level was significantly higher, while C3 and C4 were lower, than in the control population. The raised IgG was positively correlated with C4 (r = 0.15). When considered with reports of earlier workers, keloid genesis could result from genetic predisposition, environmental trigger, or localized and systemic immune complex formations. The relationship of these factors to a disequilibrium between fibroblast synthesis of collagen and turnover degradation still remains unclear.

Site-specific gene expression profiling as a novel strategy for unravelling keloid disease pathobiology

Keloid disease (KD) is a fibroproliferative cutaneous tumour characterised by heterogeneity, excess collagen deposition and aggressive local invasion. Lack of a validated animal model and resistance to a multitude of current therapies has resulted in unsatisfactory clinical outcomes of KD management. In order to address KD from a new perspective, we applied for the first time a site-specific in situ microdissection and gene expression profiling approach, through combined laser capture microdissection and transcriptomic array. The aim here was to analyse the utility of this approach compared with established methods of investigation, including whole tissue biopsy and monolayer cell culture techniques. This study was designed to approach KD from a hypothesis-free and compartment-specific angle, using state-of-the-art microdissection and gene expression profiling technology. We sought to characterise expression differences between specific keloid lesional sites and elucidate potential contributions of significantly dysregulated genes to mechanisms underlying keloid pathobiology, thus informing future explorative research into KD. Here, we highlight the advantages of our in situ microdissection strategy in generating expression data with improved sensitivity and accuracy over traditional methods. This methodological approach supports an active role for the epidermis in the pathogenesis of KD through identification of genes and upstream regulators implicated in epithelial-mesenchymal transition, inflammation and immune modulation. We describe dermal expression patterns crucial to collagen deposition that are associated with TGFβ-mediated signalling, which have not previously been examined in KD. Additionally, this study supports the previously proposed presence of a cancer-like stem cell population in KD and explores the possible contribution of gene dysregulation to the resistance of KD to conventional therapy. Through this innovative in situ microdissection gene profiling approach, we provide better-defined gene signatures of distinct KD regions, thereby addressing KD heterogeneity, facilitating differential diagnosis with other cutaneous fibroses via transcriptional fingerprinting, and highlighting key areas for future KD research.

Immunoglobulins in hypertrophic scars and keloids

Immunoglobulins A, G, and M were localized in normal skin, hypertrophic scars, keloids, and mature scars by the direct immunofluorescent antibody method. All three immunoglobulins appeared increased in the lesions above levels observed in normal skin. Extractions of the immunoglobulins from the same type of tissues also suggested an increase above levels from normal skin. The data suggest attritional leakage of several plasma proteins from the microvasculature in the lesions. No one immunoglobulin appears significantly increased in the lesions compared with others.

Conditioned medium from keloid keratinocyte/keloid fibroblast coculture induces contraction of fibroblast-populated collagen lattices

BACKGROUND

Keloid scars represent a pathological response to cutaneous injury. Overproliferation of fibroblasts and overproduction of collagen characterize these abnormal scars. The pathology of these scars remains poorly understood. The role of epithelial-mesenchymal interactions in keloid pathogenesis and scar contracture has recently been explored.

OBJECTIVES

To test our hypothesis that epithelial-mesenchymal interactions play a major role in modulating keloid scar contracture.

METHODS

A coculture model was employed wherein keloid and normal keratinocytes were cocultured with keloid or normal fibroblasts, and the conditioned media from day 5 cocultures were collected to study the effect of the paracrine secretions on contraction of an in vitro fibroblast-populated collagen lattice (FPCL) model.

RESULTS

Keloid keratinocyte/keloid fibroblast coculture conditioned media brought about increased contraction of the collagen lattice compared with non-cocultured conditioned media. When keloid fibroblasts populated the collagen lattice, significantly increased lattice contraction was induced compared with lattices populated by normal fibroblasts. The addition of antitransforming growth factor (TGF)-beta neutralizing antibody to the conditioned media produced an attenuation of the contraction of the FPCLs. When keloid and normal fibroblasts were cultured on chamber slides and treated with conditioned media from coculture and non-coculture series, immunohistochemical analysis demonstrated an increased expression of alpha-smooth muscle actin (a marker for fibroblast differentiation into myofibroblasts) in fibroblasts exposed to conditioned media from coculture.

CONCLUSIONS

These data indicate that epithelial-mesenchymal interactions are likely to play a major role in scar contracture and scar pathogenesis, and underscore the role of TGF-beta1 as a key player in keloid pathogenesis.

Keloids - the sebum hypothesis revisited

The aetiology of the keloid scar has not been completely elucidated. Numerous hypotheses have been proposed in the past to explain the unusual characteristics of the keloid scar. While we do know that there is excessive and ongoing collagen-deposition, the exact triggering stimulus is a subject of conjecture. We present some of our photographic records of keloids and electron microscopic findings of keloid edges and reiterate the sebum hypothesis. We also attempt to explain the features of keloids in the light of the present knowledge of immunology and cell biology.

General immune reactivity in keloid patients

Serum immunoglobulin levels (IgM, IgG, IgA), complement levels (C3 and C4), and the response of peripheral blood lymphocytes to mitogens [phytohemagglutinin (PHA), concanavalin A (Con-A), and pokeweed mitogen (PWM)] were investigated in healthy patients clinically diagnosed as keloid formers and in nonkeloid volunteers in good health. Serum IgM and serum C3 were significantly higher in keloid patients than in nonkeloid patients both at P less than 0.001, while serum IgA and serum C4 levels were higher in nonkeloid patients than in keloid patients at P less than 0.01 and P less than 0.001, respectively. Serum IgG levels were essentially unchanged in the keloid and the control groups in this study. Mitogenic stimulation was significantly lower in the keloid population in this investigation at P less than 0.001 for both PHA and Con-A. However, major differences were not observed with PWM stimulation in both keloid and control groups.

Analysis of Characteristics Similar to Autoimmune Disease in Keloid Patients

BACKGROUND

Keloid is a fibrotic skin disease for which immune cell infiltration is a primary pathological hallmark. Meanwhile, in autoimmune diseases, triggering of the inflammation response can lead to tissue injury and subsequent organ fibrosis. When the skin is involved in autoimmune disease, skin fibrosis such as that seen in scleroderma can occur. In this study, we propose that keloid possesses features of autoimmune disease.

METHODS

To verify whether keloid possesses features of autoimmune disease, immune cell infiltration and immune complex deposits were detected with immunohistochemical staining and immunofluorescence, respectively, in keloid and normal skin tissues. A routine antinuclear antibody profile was tested in sera from 28 keloid patients and 28 healthy controls. Lastly, the anti-hnRNPA2B1 autoantibody in sera was evaluated by enzyme-linked immunosorbent assay.

RESULTS

The numbers of CD1α(+) Langerhans cells, CD3(+) T lymphocytes, CD68(+) macrophages, and CD20(+) B lymphocytes increased in keloid tissues compared to normal skin. IgA, IgM, C3, and C1q deposits were found in keloid tissues but not in normal skin, while anti-hnRNPA2B1 levels in sera from keloid patients were elevated.

CONCLUSION

The above findings suggest that keloids have some characteristics that are similar to autoimmune disease and might be mediated by autoimmune responses.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Studies on the immunologic aspects of keloids and hypertrophic scars

A significant difference between keloids and hypertrophic scars could be demonstrated by means of acid elution of lymphoid blood cells and immunofluorescence studies. A total of 20 patients (13 patients with keloids and seven with hypertrophic scars) were investigated. All the 13 patients with keloids revealed in the eluates antinuclear antibodies belonging to one or more of the five main classes and directed mainly against fibroblasts. On the other hand, there were no antinuclear antibodies detectable in the eluates of the seven patients with hypertrophic scars and in over 40 healthy controls.

Downregulated cytotoxic CD8+ T-cell identifies with the NKG2A-soluble HLA-E axis as a predictive biomarker and potential therapeutic target in keloids

Keloids are an abnormal fibroproliferative wound-healing disease with a poorly understood pathogenesis, making it difficult to predict and prevent this disease in clinical settings. Identifying disease-specific signatures at the molecular and cellular levels in both the blood circulation and primary lesions is urgently needed to develop novel biomarkers for risk assessment and therapeutic targets for recurrence-free treatment. There is mounting evidence of immune cell dysregulation in keloid scarring. In this study, we aimed to profile keloid scar tissues and blood cells and found that downregulation of cytotoxic CD8+ T cells is a keloid signature in the peripheral blood and keloid lesions. Single-cell RNA sequencing revealed that the NKG2A/CD94 complex was specifically upregulated, which might contribute to the significant reduction in CTLs within the scar tissue boundary. In addition, the NKG2A/CD94 complex was associated with high serum levels of soluble human leukocyte antigen-E (sHLA-E). We subsequently measured sHLA-E in our hospital-based study cohort, consisting of 104 keloid patients, 512 healthy donors, and 100 patients with an interfering disease. The sensitivity and specificity of sHLA-E were 83.69% (87/104) and 92.16% (564/612), respectively, and hypertrophic scars and other unrelated diseases exhibited minimal interference with the test results. Furthermore, intralesional therapy with triamcinolone combined with 5-fluorouracil drastically decreased the sHLA-E levels in keloid patients with better prognostic outcomes, while an incomplete reduction in the sHLA-E levels in patient serum was associated with higher recurrence. sHLA-E may effectively serve as a diagnostic marker for assessing the risk of keloid formation and a prognostic marker for the clinical outcomes of intralesional treatment.

Assessment of morphological and immunohistological alterations in long-term keloid skin explants

One of the major impediments in keloid research is the lack of a keloid animal model that can mimic human keloid. This imposes investigative constraints on studying cellular interactions and biochemical processes that normally occur in vivo. Our main objective is to establish an in vitro model for maintaining long-term viable keloid dermal explants as a tool for investigating the pathogenesis of keloid scar formation. Explants of adult keloid scars were cultured in vitro by embedding them in enriched collagen gel matrix and maintaining them for up to 6 weeks, whereupon changes in tissue morphology and cellular differentiation were examined. The effects of medium enrichment, air versus liquid submersion, and different substrates on the explants were examined. Our results indicated that keloid explants embedded in a collagen gel matrix were morphologically better preserved than explants placed on a plastic substrate. Explants with epidermis at the air-liquid interface had better morphology than collagen-submerged explants, and there were no differences between serum-free and serum-supplemented explant cultures. Immunohistochemical and apoptotic analyses were performed to assess cellular viability and differentiation. In situ hybridization confirmed that keloid fibroblasts had sustained collagen type I gene expression throughout the 6 weeks in culture, thus validating the integrity of a long-term keloid culture system. In conclusion, the collagen-embedded skin explant system demonstrates that keloid tissues could be maintained for up to 6 weeks for long-term in vitro studies.

Keloids and hypertrophic scars--immunological aspects

A significant difference between keloids and hypertrophic scars could be demonstrated by means of acid elution technique of lymphoid blood cells and immunofluorescence studies. Tests on 20 patients with keloids revealed in the eluates antinuclear antibodies belonging to one or more of the 5 main classes and directed mainly against fibroblasts. On the other hand, there were no antinuclear antibodies detectable in the eluates of the 7 patients with hypertrophic scars and in 40 healthy controls.