Changes in the distribution of laminin alpha1 chain in psoriatic skin: immunohistochemical study using confocal laser scanning microscopy

Abnormal basement membrane results in increased keratinocyte-derived periostin expression in psoriasis similar to wound healing

The psoriatic skin resembles wound healing, and it shows abnormalities at the basement membrane (BM), also in the non-lesional skin. Fibroblast-derived dermal periostin has well-known functions in wound healing and Th2-mediated diseases, such as atopic dermatitis. Here we show that serum periostin level was elevated in psoriatic patients, remarkably in the systemically treated ones. Obvious periostin positivity was detected in basal keratinocytes of the non-lesional, lesional, and previously-lesional psoriatic vs. healthy skin. Ex vivo skin models were generated to examine how different skin injuries affect periostin expression during wound healing. Our newly developed cultured salt-split model demonstrated that BM-injury induced periostin expression in basal keratinocytes, and periostin levels in the supernatant were also increased upon healing. In wound healing models, β1-integrin expression was similarly induced. β1-integrin blocking caused reduced periostin expression in in vitro scratch assay, indicating that β1-integrin can mediate periostin production. In contrast to atopic dermatitis, psoriatic basal keratinocytes are in an activated state and show a stable wound healing-like phenotype with the overexpression of periostin. This abnormal BM-induced wound healing as a potential compensatory mechanism can be initiated already in the non-lesional skin present in the lesion and keratinocytes can remain activated in the healed skin.

Altered Distribution and Expression of Syndecan-1 and -4 as an Additional Hallmark in Psoriasis

Syndecans act as independent co-receptors to exert biological activities and their altered function is associated with many pathophysiological conditions. Here, syndecan-1 and -4 were examined in lesional skin of patients with psoriasis. Immunohistochemical staining confirmed altered syndecan-1 distribution and revealed absence of syndecan-4 expression in the epidermis. Fibronectin (FN)—known to influence inflammation and keratinocyte hyperproliferation via α5β1 integrin in psoriasis—was also decreased. Syndecan-1 and -4 expression was analyzed in freshly isolated lesional psoriatic human keratinocytes (PHK) characterized based on their proliferation and differentiation properties. mRNA levels of syndecan-1 were similar between healthy and PHK, while syndecan-4 was significantly decreased. Cell growth and release of the pro-inflammatory Tumor Necrosis Factor-alpha (TNFα) were selectively and significantly induced in PHKs plated on FN. Results from co-culture of healthy keratinocytes and psoriatic fibroblasts led to the speculation that at least one factor released by fibroblasts down-regulate syndecan-1 expression in PHK plated on FN. To assay if biological treatments for psoriasis target keratinocyte proliferation, gelatin-based patches enriched with inteleukin (IL)-17α or TNFα blockers were prepared and tested using a full-thickness healthy epidermal model (Phenion^®). Immunohistochemistry analysis showed that both blockers impacted the localisation of syndecan-1 within the refined epidermis. These results provide evidence that syndecans expression are modified in psoriasis, suggesting that they may represent markers of interest in this pathology.

Remodeling of the Dermal Extracellular Matrix in a Tissue-Engineered Psoriatic Skin Model by n-3 Polyunsaturated Fatty Acids

Psoriasis is an inflammatory skin disease mainly associated with an epidermal disorder. However, the involvement of the dermal extracellular matrix (ECM) composition in psoriasis is still poorly understood. This study aimed to investigate the expression of ECM components in psoriatic skin substitutes (PS⁻) compared with healthy skin substitutes (HS⁻), as well as the effect of an n-3 polyunsaturated fatty acid, namely α-linolenic acid (ALA), on the psoriatic dermal compartment (PS^ALA+). Liquid chromatography tandem mass spectrometry analyses revealed that the lipidome of PS⁻ contained higher amounts of n-6 derived prostaglandins (PGE₂) and lipoxygenase products (9-HODE and 15-HETE). ALA supplementation increased the levels of PGE₃, 13-HOTrE, 15-HEPE, and 18-HEPE, and decreased the levels of PGE₂, 15-HETE, and 9-HOPE compared with PS⁻, indicating that ALA modulates the dermal lipidome of psoriatic skin substitutes. Gene expression profiling showed that several genes encoding for different ECM proteins were overexpressed in PS⁻ compared with HS⁻, namely COL1A1 (4.2-fold), COL1A2 (3-fold), COL3A1 (4.4-fold), COL4A1 (2.3-fold), COL4A2 (6.3-fold), COL5A1 (3.3-fold), COL5A2 (5.2-fold), and COL5A3 (4.6-fold). Moreover, the expression of collagen IV (Col IV), collagen VII (Col VII), and laminin was found to be increased in PS⁻ compared with HS⁻, and to be restored with ALA (PS^ALA+) according to immunofluorescence staining, while only the collagen I to collagen III ratio was altered according to dot blot analyses. Linear regression analysis revealed several positive correlations, including Col III with 14-HDHA levels, fibronectin with 12-HETE and 15-HETE levels, the dermo-epidermal junction Col IV with PGF_2α, 9-HODE, and 13-HODE levels, and laminin with levels of PGF_2α, 9-HODE, 13-HODE, 5-HETE, 12-HETE, and 15-HETE. These results suggest that the ECM plays an underestimated role in the pathogenesis of psoriasis and that ALA supplementation can regulate the ECM composition.

The Psoriatic Nonlesional Skin: A Battlefield between Susceptibility and Protective Factors

In the last two decades, large-scale gene-expression studies on psoriatic skin samples revealed that even though nonlesional skin is macroscopically identical to healthy skin, it harbors several molecular differences. Originally, these molecular differences were thought to represent susceptibility factors for plaque formation. However, we review in this paper the several factors of immune regulation and structural alteration that are specific for the nonlesional skin and serve as protective factors by counteracting plaque formation and contributing to the maintenance of the nonlesional phenotype.

Stress-Related Regulation Is Abnormal in the Psoriatic Uninvolved Skin

Keratinocyte stress-response of the uninvolved psoriatic epidermis is known to be altered compared to healthy cells. Therefore, we aimed to reveal potential mechanisms underlying this alteration. We compared the expression of annotated cell-stress-related proteins between uninvolved psoriatic and healthy skin using the protein array method. Data were analyzed by the Reactome over-representation test. We found that p27/CDKN1B and cytochrome C showed at least a two-fold increase, while cyclooxygenase-2, indolamine-2,3-dioxygenase-1, serum paraoxonase 1, serum paraoxonase 3, serine-46-phosphorylated tumor protein p53, and superoxide-dismutase-2 showed a two-fold decrease in expression in the uninvolved skin. Over-representation analysis suggested the Forkhead-box protein O (FOXO)-mediated transcription as the most significant pathway affected by the differently expressed cell-stress-related proteins (DECSRPs). DECSRPs indicate increased FOXO-mediated transcription of cell-cycle genes and reduced interleukin-signaling in the psoriatic uninvolved skin. Nuclear positivity of the FOXO-signaling-related p27/CDKN1B and FOXO1 are negatively correlated with the disease severity and showed increased expression in the uninvolved epidermis and also in healthy primary keratinocytes, which were grown on cartilage oligomeric matrix protein-coated surfaces. Our results indicate a cell-cycle inhibitory process, as a stress-related compensatory mechanism in the uninvolved epidermis, that could be responsible for blocking keratinocyte hyperproliferation in the psoriatic uninvolved skin, thus maintaining the symptomless skin phenotype.

Could basement membrane alterations, resembling micro-wounds at the dermo-epidermal junction in psoriatic non-lesional skin, make the skin susceptible to lesion formation?

Current data suggest that tissue microenvironment control immune functions. Therefore, understanding the tissue environment in which immune activation occurs will enhance our capability to interfere with abnormal immune pathology. Here, we argue that studying the constitutively abnormal functions of clinically uninvolved psoriatic skin in patients with plaque type psoriasis is very important to better understand psoriasis pathobiology, because non-lesional skin provides the tissue environment in which the psoriatic lesion develops. A key question in psoriasis is what initiates the abnormal, uncontrolled immune activation in the first place and the answer may lie in the skin. In light of this concept, we summarize abnormalities at the dermal-epidermal junction region which shows a special "non-healing-like" micro-wound phenotype in the psoriatic non-lesional skin that may act as a crucial susceptibility factor in the development of the disease.

Patients with bullous pemphigoid and comorbid psoriasis present with less blisters and lower serum levels of anti-BP180 autoantibodies

BACKGROUND

Although the association of bullous pemphigoid (BP) and psoriasis is well-established, the clinical and immunological features of patients with coexisting BP and psoriasis are yet to be investigated.

OBJECTIVE

We aimed to estimate the prevalence of psoriasis amongst patients with BP and to elucidate the clinical and immunological characteristics of BP patients with comorbid psoriasis.

METHODS

A retrospective cohort study including all consecutive patients diagnosed with BP throughout the years 2009-2019 in a tertiary referral centre.

RESULTS

The study encompassed 273 patients with BP, of whom 11 (4.0%; 95% CI, 2.3-7.1%) had comorbid psoriasis. The onset of psoriasis preceded that of BP in 81.8% of patients by a median (range) latency of 26.5 (5.0-34.0) years. Compared to BP patients without psoriasis, those with BP and comorbid psoriasis were significantly younger at the onset of BP [71.8 (9.3) vs. 79.4 (9.8) years; P = 0.023], had a milder erosive phenotype [erosion/blister BPDAI mean (SD)score; 5 (4.1) vs. 22.3 (15.2); P = 0.025], lower levels of anti-BP180 NC16A serum autoantibodies [236.6 (266.3) vs. 556.2 (1323.6) U/mL; P = 0.008] and a higher prevalence of isolated linear C3 deposits (36.4% vs. 14.1%; P = 0.043) and a lower prevalence of linear immunoglobulin G deposits (36.4% vs. 68.7%; P = 0.025) along the dermal-epidermal junction by direct immunofluorescence microscopy.

CONCLUSIONS

Patients with BP and comorbid psoriasis present at a younger age with milder erosive phenotype and lower levels of pathogenic autoantibodies.

The Risk of Systemic Diseases in Those with Psoriasis and Psoriatic Arthritis: From Mechanisms to Clinic

Psoriasis and psoriatic arthritis (PsA) have been recently considered as chronic systemic inflammatory disorders. Over the past decades, enormous evidence indicates that patients with psoriasis and PsA have a higher risk of developing various comorbidities including cardiovascular disease, metabolic disease, cancers, infections, autoimmune disease, and psychiatric diseases. However, reported risks of some comorbidities in those with psoriasis and PsA are somewhat different according to the research design. Moreover, pathomechanisms underlying comorbidities of those with psoriasis and PsA remain poorly elucidated. The purpose of this review is to provide the most updated comprehensive view of the risk of systemic comorbidities in those with psoriasis and PsA. Molecular mechanisms associated with the development of various comorbidities in those with psoriasis and PsA are also reviewed based on recent laboratory and clinical investigations. Identifying the risk of systemic comorbidities and its associated pathomechanisms in those with psoriasis and PsA could provide a sufficient basis to use a multi-disciplinary approach for treating patients with psoriasis and PsA.

The Bidirectional Association Between Bullous Pemphigoid and Psoriasis: A Population-Based Cohort Study

The risk of developing psoriasis during the course of bullous pemphigoid (BP) is yet to be investigated. We aimed to assess the risk of psoriasis among patients with BP and the risk of BP in individuals with a history of psoriasis. A population-based retrospective cohort study was conducted comparing BP patients (n = 3,924) with age-, sex-, and ethnicity-matched control subjects (n = 19,280) with regard to incident cases of psoriasis. A case-control design was additionally followed to estimate the risk of BP in those with a preceding diagnosis of psoriasis. Adjusted hazard ratios (HRs) and adjusted odds ratios (ORs) were estimated by Cox regression and logistic regression, respectively. The incidence of psoriasis was 1.78 (95% CI, 1.25–2.48) and 0.67 (95%CI, 0.53–0.83) per 1,000 person-years among patients with BP and controls, respectively. Patients with BP were 2.6-fold more likely to develop psoriasis (HR, 2.60; 95%CI, 1.59–4.27) compared to controls. Furthermore, the prevalence of preexisting psoriasis was higher in patients with BP than in control subjects (1.7 vs. 1.1%, respectively; P < 0.001). A history of psoriasis was associated with a 50% increase in the risk of BP (OR, 1.53; 95%CI, 1.17–2.02). Patients with a dual diagnosis of BP and psoriasis were younger, had higher prevalence of smoking and hypertension, and were treated more frequently with prolonged systemic and topical corticosteroids when compared to the remaining patients with BP. To conclude, a bidirectional association exists between BP and psoriasis. Awareness of this association may be of great importance for physicians managing patients with BP and psoriasis.

Cartilage Oligomeric Matrix Protein Negatively Influences Keratinocyte Proliferation via α5β1-Integrin: Potential Relevance of Altered Cartilage Oligomeric Matrix Protein Expression in Psoriasis

In psoriasis, nonlesional skin shows alterations at the dermal-epidermal junction compared with healthy skin. Cartilage oligomeric matrix protein (COMP) is part of the papillary dermis of healthy skin, and its expression has not yet been studied in psoriatic skin. In this study, we found that COMP localization extended deeper into the dermis and formed a more continuous layer in psoriatic nonlesional skin compared with healthy skin, whereas in psoriatic lesions, COMP showed a partially discontinuous deposition at the dermal-epidermal junction. COMP and β1-integrin showed strong colocalization in nonlesional skin, where the laminin layer within the basement membrane is discontinuous. In in vitro models, the presence of exogenous COMP decreased the proliferation rate of keratinocytes, and this proliferation-suppressing effect was diminished by blocking α5β1-integrin. Our results suggest that COMP can interact with α5β1-integrin of basal keratinocytes through the disrupted basement membrane, and this interaction might stabilize the epidermis in the nonlesional state by contributing to the suppression of keratinocyte proliferation. The antiproliferative effect of COMP is likely to be relevant to other skin diseases in which chronic nonhealing wounds are coupled with massive COMP accumulation.

Biomechanical Factors in Psoriatic Disease: Defective Repair Exertion as a Potential Cause. Hypothesis Presentation and Literature Review

Joining main clinical manifestations of psoriatic skin disorder are inflammatory arthritis and nail lesions. Repetitive microdamage has been postulated as a main triggering factor in lesions of psoriatic arthritis. This concept of psoriatic disease might also be admissible for triggering nail lesions because the nail is a frequently traumatized structure. Here, we aimed to describe the conjectural injury mechanisms of nail complex with regard to acting biomechanical factors. Tissue repair response to physical microdamage may be altered in psoriatic disease. It is plausible to consider that a defective repair process in the dysregulated prepsoriatic tissue may lead to innate immune activation and further development of autoinflammatory lesions, although excessive inflammation is known to impair wound healing. Recently published data have revealed the importance of mechanosensitive Wingless-type (Wnt) signaling in the pathophysiology of psoriasis and ankylosing spondylitis. The Wnt signaling system is involved in morphogenesis, repair, and regeneration as a biologic process main regulator. Wnt5a seems to be a dominating mediator in both psoriatic plaques and during the spondylitis process that might also be a linking molecule of psoriatic response to mechanical stress. Future studies should focus on complex responsive interactions of tissue repair regulators regarded in psoriatic disease.

Unraveling the ECM-Immune Cell Crosstalk in Skin Diseases

The extracellular matrix (ECM) is a complex network of proteins and proteoglycans secreted by keratinocytes, fibroblasts and immune cells. The function of the skin ECM has expanded from being a scaffold that provides structural integrity, to a more dynamic entity that is constantly remodeled to maintain tissue homeostasis. The ECM functions as ligands for cell surface receptors such as integrins, dystroglycans, and toll-like receptors (TLRs) and regulate cellular signaling and immune cell dynamics. The ECM also acts as a sink for growth factors and cytokines, providing critical cues during epithelial morphogenesis. Dysregulation in the organization and deposition of ECMs lead to a plethora of pathophysiological conditions that are exacerbated by aberrant ECM-immune cell interactions. In this review, we focus on the interplay between ECM and immune cells in the context of skin diseases and also discuss state of the art therapies that target the key molecular players involved.

Re-investigating the Basement Membrane Zone of Psoriatic Epidermal Lesions: Is Laminin-511 a New Player in Psoriasis Pathogenesis?

Psoriasis is a complex chronic inflammatory skin disease characterized by epidermal thickening on the basis of increased keratinocyte proliferation and insufficient apoptosis. Laminins are important components of the basement membrane (BM) and impact on epidermal keratinocyte growth/apoptosis. Although several laminins are involved in the pathogenesis of psoriasis, it is still controversial about the expression patterns of laminin isoforms and which laminins are important in the development of psoriasis. Because laminin-511 and -332 are key BM components in human skin, and laminin-511 stimulates human hair follicle growth, we asked whether the BM zone in psoriasis shows any laminin-related abnormalities. This showed that the BM expression of laminin-511 and -332 was significantly increased within the skin lesion of psoriasis. Immunofluorescence microscopy revealed that laminin-511, -332, and collagen type IV proteins were also significantly increased in psoriasis-like skin lesions of Imiquimod-treated mice. Transmission electron microscopy showed a few gaps of lamina densa, and its thickness was significantly increased. Finally, laminin-511 treatment significantly stimulated the proliferation and inhibited apoptosis of HaCaT cells, while laminin-α5 chain gene knockdown decreased proliferation and induced apoptosis. These phenomenological observations raise the question of whether laminin-511-controlled keratinocyte growth/death may be a previously overlooked player in the pathogenesis of psoriatic epidermal lesions.

Humoral Epitope Spreading in Autoimmune Bullous Diseases

Autoimmune blistering diseases are characterized by autoantibodies against structural adhesion proteins of the skin and mucous membranes. Extensive characterization of their autoantibody targets has improved understanding of pathogenesis and laid the basis for the study of antigens/epitopes diversification, a process termed epitope spreading (ES). In this review, we have reported and discussed ES phenomena in autoimmune bullous diseases and underlined their functional role in disease pathogenesis. A functional ES has been proposed: (1) in bullous pemphigoid patients and correlates with the initial phase of the disease, (2) in pemphigus vulgaris patients with mucosal involvement during the clinical transition to a mucocutaneous form, (3) in endemic pemphigus foliaceus, underlining its role in disease pathogenesis, and (4) in numerous cases of disease transition associated with an intermolecular diversification of immune response. All these findings could give useful information to better understand autoimmune disease pathogenesis and to design antigen/epitope specific therapeutic approaches.

Differential Expression of Nitric Oxide Synthase Isoforms nNOS and iNOS in Patients with Non-Segmental Generalized Vitiligo

Nitric oxide (NO) is involved in several biological processes, but its role in human melanogenesis is still not well understood. Exposure to UVA and UVB induces nitric oxide production in keratinocytes and melanocytes through the activation of constitutive nitric oxide synthase, increasing tyrosinase activity and melanin synthesis, whereas inducible nitric oxide synthase over expression might be involved in hypopigmentary disorders. The aim of this study was to evaluate whether inducible nitric oxide synthase and neuronal nitric oxide synthase expression were modified in vitiligo skin compared to healthy controls. Skin biopsies were obtained from inflammatory/lesional and white/lesional skin in 12 patients with active, non-segmental vitiligo; site-matched biopsies of normal skin from eight patients were used as controls. Nitric oxide synthase isoforms expression was evaluated by confocal laser scanning microscopy and Western Blot analysis. Inducible nitric oxide synthase expression was significantly increased in inflammatory/lesional skin compared to healthy skin; melanocytes showed a moderate neuronal nitric oxide synthase expression in white/lesional skin, demonstrating that metabolic function still goes on. The obtained data demonstrated that vitiligo lesions were characterized by modifications of nitric oxide synthase isoforms, thus confirming the hypothesis that nitric oxide imbalance is involved in vitiligo and supporting the idea that nitric oxide synthase inhibitors might be used as a possible therapeutic approach for the management of vitiligo.

BAY 11-7082 inhibits the NF-κB and NLRP3 inflammasome pathways and protects against IMQ-induced psoriasis

BAY 11-7082 antagonizes I-κB kinase-β preventing nuclear translocation of nuclear factor-κB (NF-κB); it also inhibits NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome activation. NF-κB is involved in psoriasis, whereas the role of NLRP3 is controversial. We investigated BAY 11-7082 effects in an experimental model of psoriasis-like dermatitis. Psoriasis-like lesions were induced by a topical application of imiquimod (IMQ) cream (62.5 mg/day) on the shaved back skin of C57BL/6 and NLRP3 knockout (KO) mice for 7 consecutive days. Sham psoriasis animals were challenged with Vaseline cream. Sham and IMQ animals were randomized to receive BAY 11-7082 (20 mg/kg/i.p.) or its vehicle (100 μl/i.p of 0.9% NaCl). Skin of IMQ animals developed erythema, scales, thickening and epidermal acanthosis. IMQ skin samples showed increased expression of pNF-κB and NLRP3 activation. BAY 11-7082 blunted epidermal thickness, acanthosis and inflammatory infiltrate. BAY 11-7082 reduced pNF-κB, NLRP3, tumour necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β expression, blunted the phosphorylation of signal transducer and activators of transcription 3 (STAT3) and decreased IL-23 levels. In addition, BAY 11-7082 reawakened the apoptotic machinery. NLRP3 KO animals showed a reduced total histological score but persistent mild acanthosis, dermal thickness and expression of pNF-κB and pSTAT3, following IMQ application. Our data suggest that BAY 11-7082 might represent an interesting approach for the management of psoriasis-like dermatitis depending on the dual inhibition of NF-κB and NLRP3.

Application of Confocal Laser Scanning Microscopy in Biology and Medicine

Fluorescence confocal laser scanning microscopy and reflectance confocal laser scanning microscopy are up-to-date highend study methods. Confocal microscopy is used in cell biology and medicine. By using confocal microscopy, it is possible to study bioplasts and localization of protein molecules and other compounds relative to cell or tissue structures, and to monitor dynamic cell processes. Confocal microscopes enable layer-by-layer scanning of test items to create demonstrable 3D models. As compared to usual fluorescent microscopes, confocal microscopes are characterized by a higher contrast ratio and image definition.

Skin basement membrane zone: a depository for circulating microbial antigen evoking psoriasis and autoimmunity

BACKGROUND

Elevated levels of antibody to streptococcal exoenzymes have been found in patients with psoriasis or psoriatic arthritis. Research on the role of streptococcal antigen in psoriasis has been hampered by a potential molecular mimicry between streptococcal epitopes and human epidermal keratin.

OBJECTIVE AND METHODS

Evidence of microbial product was sought in skin biopsies of psoriasis patients thought clinically to have either streptococcal carrier state or gastrointestinal candidal colonization. A polyclonal antibody to streptococcal-derived exoenzymes unlikely to share antigenic structures with normal human skin, and an anticandidal antibody, were used with linked streptavidin biotin amplification stain.

RESULTS

The predicted microbial product appeared heavily in lesional epidermis, but unexpectedly also as a thin deposit along the skin basement membrane zone (SBMZ) of apparently unaffected skin. Staining was negative for nonpsoriatic subjects.

CONCLUSIONS

The findings support a direct effect of microbial antigen in psoriasis. They also suggest an important role for SBMZ as a very large adhesive surface in the first step of a process of percutaneous epidermal elimination of foreign antigens and microbial toxins. The many autoimmune phenomena seen so often at the SBMZ are probably a physiologic part of this important immune function. Efforts to enhance the adhesive properties of SBMZ should be exploitable for both diagnostic and therapeutic benefit.

Proliferating keratinocytes are putative sources of the psoriasis susceptibility-related EDA+ (extra domain A of fibronectin) oncofetal fibronectin

The extra domain A of fibronectin (EDA+ oncofetal isoform of fibronectin was recently reported to be overexpressed in psoriatic uninvolved epidermis. It has been proposed that the abnormal presence of EDA+ oncofetal protein at the dermal-epidermal junction in the uninvolved skin may provide the "psoriatic" environment in which keratinocytes are in a preactivated state with regard to mitogenic signals (e.g., T cell lymphokines). To determine the possible sources of cellular fibronectin in the non-lesional psoriatic skin, we aimed to investigate whether keratinocytes could produce the EDA+ oncofetal form of fibronectin. RT-PCR studies revealed that both cultured normal keratinocytes and HaCaT cells express the EDA+ splice variant of fibronectin mRNA, and in HaCaT cells the EDA+/EDA- transcript ratio was elevated compared with normal keratinocytes. Cultured keratinocytes and HaCaT cells showed intracytoplasmic staining with an EDA+ fibronectin-specific antibody and among the positively stained cells many showed mitosis. Using RT-PCR, western blot analysis, and flow cytometry, we showed that in synchronized HaCaT cells the amount of both total fibronectin and its EDA+ isoform change with the proliferation/differentiation state of HaCaT cells and peak in highly proliferating cells. We show that in short-term ex vivo cultures, a small population of EDA+ fibronectin containing cell population appear among psoriatic uninvolved, but not normal epidermal cells. We also demonstrate that cell attachment has a strong influence on the expression of both total and EDA+ fibronectin. Our results suggest that proliferating keratinocytes could be the sources of the psoriasis susceptibility-related EDA+ oncofetal fibronectin in the epidermis.