Adhesion molecule expression in polymorphic light eruption

Endothelial leukocyte adhesion molecule-1 (ELAM-1), vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) are cytokine-regulated cell-surface leukocyte adhesion molecules. We have investigated the in vivo kinetics and pattern of expression of these adhesion molecules in relation to tissue accumulation of leukocytes in the photodermatosis, polymorphic light eruption (PMLE), which is characterized by dense perivascular leukocytic infiltration. Immunohistology was performed on biopsies taken at varying time points from PMLE lesions induced in 11 subjects by suberythemal solar simulated irradiation. Vascular endothelial ELAM-1 expression was first observed at 5 h, maximal at 24 to 72 h, and remained elevated at 6 d. VCAM-1, minimally expressed in control skin, was induced above background levels on endothelium and some perivascular cells after 24 h and maintained at 6 d. Endothelial cell ICAM-1 expression was increased above control levels at 72 h and 6 d. Keratinocyte ICAM-1 expression, most marked overlying areas of dermal leukocytic infiltration, began at 5 h and was strong at 72 h and 6 d. In addition to lymphocytes, significant numbers of neutrophils but not eosinophils were detected in the dermal leukocytic infiltrate that appeared at 5 h and persisted at 6 d. The pattern of adhesion molecule expression that we have observed is similar to that seen in normal skin during a delayed hypersensitivity reaction. These observations support an immunologic basis for PMLE.

Preferential adherence of T lymphocytes and neutrophils to psoriatic epidermis

T lymphocytes and neutrophils accumulate in psoriatic epidermis. To determine whether the epidermis plays an active role in this process through the production of cellular adhesion factors, leucocyte adherence to lesional psoriasis was compared with normal skin in a modified frozen-section adhesion assay. Lymphocyte and neutrophil suspensions were prepared by standard Ficoll-Hypaque techniques from peripheral blood of normal volunteers and overlaid on to glutaraldehyde-fixed 8-microns cryostat sections of skin. Adhesion of phorbol ester-activated T lymphocytes to the epidermis was significantly greater in psoriasis compared with normal skin (P < 0.01). Adhesion was absent (a) at 7 degrees C, (b) in the presence of EDTA and (c) in the absence of lymphocyte activation. Immunostaining demonstrated that all adherent lymphocytes were CD3+ve (i.e. T cells). Likewise, neutrophils adhered more prominently to psoriatic epidermis. Adhesion was most prominent at the tips of dermal papillae, corresponding to areas of maximal intercellular adhesion molecule-1 (ICAM-1) expression. Both neutrophils and lymphocytes adhered to dermal papillary vascular endothelium. These studies provide functional data that psoriatic epidermal cells are actively involved in leucocyte adherence. The distribution of adhesion suggests that both ICAM-1-dependent and independent mechanisms are involved.

Epidermal dendritic cells in psoriasis possess a phenotype associated with antigen presentation: in situ expression of beta 2-integrins

BACKGROUND

Epidermal dendritic cells (DCs) isolated from psoriasis possess greatly enhanced T lymphocyte-activating properties compared with DCs from normal skin, suggesting that DCs in psoriasis express surface antigens crucial for antigen presentation. These include beta 2-integrins and intercellular adhesion molecule (ICAM)-1.

OBJECTIVE

Our purpose was to determine DC phenotype in psoriatic compared with normal epidermis with respect to these molecules.

METHODS

Tissue sections were single labeled with a peroxidase antiperoxidase (PAP) immunohistochemical technique and double labeled where necessary with a combination of a PAP and an alkaline phosphatase-anti-alkaline phosphatase technique.

RESULTS

In psoriatic compared with normal skin, decreased numbers of DCs expressed CD1a (p less than 0.05), whereas increased numbers of DCs expressed class II major histocompatibility antigens (p less than 0.05). In normal skin positive staining for CD18 was not observed, whereas in psoriasis both CD1a+ and CD1a- DCs expressed beta 2-integrins, LFA-1 (CD11a/CD18), and gp 150/95 (CD11c/CD18). DCs in atopic dermatitis and lichen planus were also found to express beta 2-integrins. Neither MAC 1 (CD11b/CD18) nor ICAM-1 was observed on DCs.

CONCLUSION

These data are consistent with either migration of dendritic antigen-presenting cells into the epidermis or in situ cytokine modulation of Langerhans cell phenotype in inflamed skin. Furthermore, they indicate that epidermal DCs in psoriasis and other cutaneous inflammatory diseases express molecules that are known to be crucial for Langerhans cell-driven T-cell activation in vitro.

HUT 78 T cells bind to noncytokine-stimulated keratinocytes using a non-CD18-dependent adhesion pathway

The initial in vitro observation that cultured keratinocytes, when treated with cytokines such as gamma interferon, increased the binding of T lymphocytes, opened up a whole new avenue of research to understand epidermal trafficking patterns in inflammatory skin diseases. A growing body of data strongly supports the in vivo role of lymphocyte-function-associated antigen-1 (CD18) expression by T cells in the binding to intercellular adhesion molecule-1 (CD54) expressing keratinocytes. To further explore the molecular basis for other possible adhesive interactions involving T cells and skin-derived cellular constituents, the authors used 2 cell lines (HUT 78 cells and Jurkat cells) and added them to multipassaged human keratinocytes, fibroblasts, and melanocytes. The skin-derived cells were treated with cytokines alone, or in combination, with a phorbol ester. HUT cells were capable of binding to keratinocytes in the absence of pretreatment with cytokines at 25 degrees C, which was not inhibited by anti-CD18 antibodies, or sensitive to reducing the temperature of the adhesion assay to 7 degrees C. Fibroblasts and melanocytes also constitutively bound HUT cells, but the binding to fibroblasts was highly temperature-sensitive. When keratinocytes were pretreated for 48 hours with gamma interferon plus phorbol ester, a "superadhesive" state was induced, resulting in a synergistically increased binding ability of both HUT cells and Jurkat cells. This effect was related to quantitative increases in keratinocyte intercellular adhesion molecule-1 expression. Several other clear-cut qualitative and quantitative differences were detectable in the ability of HUT cells and JS cells to bind to nontreated and cytokine/phorbol ester-treated keratinocytes, fibroblasts, and melanocytes. These results emphasize the complexity of molecular associations underlying T-cell trafficking patterns, potentially operative in the dermal and epidermal compartments of the skin.

Effect of In Vivo Interleukin-1 on Adhesion Molecule Expression in Normal Human Skin

We have examined the expression of three endothelial adhesion molecules (intercellular adhesion molecule-1 [ICAM-1], endothelial leukocyte adhesion molecule-1 [ELAM-1], and vascular cell adhesion molecule-1 [VCAM-1]) in normal human skin following intradermal injection of stratum corneum-derived interleukin-1 alpha (SCIL-1 alpha). In control skin, constitutive expression of ICAM-1 was found on endothelial cells and at low levels on dermal dendritic cells but not on keratinocytes. ELAM-1 and VCAM-1 were present in low levels on endothelium and perivascular dendritic cells, respectively. SCIL-1 alpha injection produced marked endothelial ELAM-1 upregulation. Double staining with neutrophil elastase demonstrated that many ELAM-1-positive vessels contained marginating neutrophils and that interstitial neutrophils were clustered around ELAM-1-positive vessels. An increase in dermal dendritic cell ICAM-1 expression occurred and in two of three biopsies there was keratinocyte expression of ICAM-1 in the SCIL-1 alpha-injected tissue. Also, there was upregulation of VCAM-1 on vascular endothelium and an increase in the dermal dendritic cell expression of this molecule. These results give in vivo confirmation that SCIL-1 alpha modulated endothelial and dermal dendritic cell adhesion molecule expression, and show that endothelial VCAM-1 is regulated in vivo by SCIL-1 alpha, thus providing a regulatable ICAM-1-independent means of mononuclear cell recruitment.

Role of keratinocytes in allergic contact dermatitis

Although once thought to play a purely structural role, there is increasing evidence that keratinocytes are actively involved in epidermal immune responses, including allergic contact dermatitis (ACD). In vitro studies demonstrate that both urushiol and nickel sulphate induce cytokine production in cultured keratinocytes including molecules responsible for endothelial cell activation and lymphocyte chemotaxis and adhesion. In vivo, these same molecules are expressed in experimentally induced patch test reactions to a variety of allergens. Furthermore, such expression precedes the onset of the inflammatory phase of ACD. Taken together, these studies suggest a role complementary to that of Langerhans cells for keratinocytes in the initiation and propagation of ACD.

Antigenic profile of human acrosyringium

The demonstration of HLA-DR on human acrosyringium has led to the suggestion that eccrine epithelium, through its interaction with certain molecules, might play an active role in epidermal immune responses. An immunohistochemical study was undertaken to identify the antigenic profile of acrosyringium in normal skin and following the intradermal administration of a T-lymphocyte-derived cytokine, interferon gamma (IFN-gamma). Acrosyringium in normal skin, in contrast to interappendageal epidermis, was found to lack CD1a+ Langerhans cells. However, antigens CD36 (OKM5) and L1 (MAC387) were uniquely expressed by keratinocytes immediately adjacent to the distal portion of acrosyringium. Constitutive expression of each class II MHC antigen, namely HLA-DR, DP and DQ was observed on luminal acrosyringial cells. EMB11 antigen (CD68), a mononuclear cell determinant, was similarly expressed on acrosyringial epithelium in normal skin. Following intradermal administration of IFN-gamma, intercellular adhesion molecule-1 (ICAM-1) (CD54) was induced on acrosyringial epithelium and the expression of HLA-DR was intensified. A range of other markers including CD3, CD4, CD8, CD11a, CD11b and CD15 were not expressed by acrosyringium either in normal skin or after administration of IFN-gamma. Expression of antigens associated with cell-mediated immune mechanisms on acrosyringium is consistent with the hypothesis that it may have an immunological role in epidermal immune responses.

Pulmonary capillary leak syndrome complicating generalized pustular psoriasis: possible role of cytokines

Two cases are reported of generalized pustular psoriasis complicated by profound alterations in pulmonary capillary permeability. Several features suggest the involvement of cytokines in the pathogenesis of this condition.

Modulation of keratinocyte-derived interleukin-8 which is chemotactic for neutrophils and T lymphocytes

Interactions between T lymphocytes, neutrophils, and epidermal cells are believed to play a central role in the pathophysiology of psoriasis and other inflammatory cutaneous disorders. Although there is strong evidence that lymphocyte-function-associated antigen-1 (LFA-1) positive T cells are retained in the epidermis via intercellular adhesion molecule-1 (ICAM-1) expression induced on keratinocytes, the molecular basis for the directed migration of T cells or neutrophils towards the epidermis is not known. To investigate whether epidermal keratinocyte-derived products may be important in the migration of T cells and neutrophils into the epidermis, human keratinocytes were cultured in the presence of various cytokines and chemotactic activity of the supernatants were assessed. TNF-alpha stimulation produced directed migrational responses for both neutrophils and T-lymphocytes (both CD4 and CD8), but not B lymphocytes; 69% of T-cell movement and 80% of neutrophil migration induced by the TNF-alpha treated keratinocyte cell supernatants could be inhibited by anti-interleukin-8 (IL-8) serum. Using the same antibody, IL-8 was immunoprecipitated from the supernatants of TNF-stimulated 35S-labelled keratinocytes, and a single 7-kd band product detected by SDS-PAGE. In keeping with these biological activities and protein data, Northern blot analysis of total cellular RNA extracted from keratinocyte monolayers hybridized with a 32P-labelled 1-kb cDNA to IL-8 mRNA, revealed induction of the IL-8 gene in the presence of TNF-alpha and IL-1 beta, but not IFN-gamma. The protein kinase C agonist, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), a known stimulator of psoriasiform cutaneous inflammation when applied directly to murine epidermis, strongly induced keratinocyte elaboration of IL-8 mRNA. These studies demonstrate that activated human keratinocytes are capable of producing biologically active IL-8, and provide evidence that keratinocytes can play a key role in mediating the influx of T cells and neutrophils into the epidermis.

Modulation of leucocyte adhesion molecules, a T-cell chemotaxin (IL-8) and a regulatory cytokine (TNF-alpha) in allergic contact dermatitis (rhus dermatitis)

To understand the molecular events which are important in leucocyte trafficking in cutaneous inflammation, poison ivy/oak extract was applied topically to the skin, and the simultaneous assessment of a variety of clinical and immunopathological parameters performed. The clinical response of subjects was divided into three main groups: I, 2-24h after application, before the onset of erythema; II, 48 h-1 week after application during maximal clinical changes; III, 2-3 weeks after application when the inflammation had subsided. Six different biopsies per subject were evaluated over the study period and the density of dermal cellular infiltrate, and the distribution of intercellular adhesion molecule-1, (ICAM-1), endothelial leucocyte adhesion molecule-1, (ELAM-1), vascular cell adhesion molecule-1, (VCAM-1), interleukin 8 (IL-8) and tumour necrosis factor-alpha (TNF-alpha), determined. Eight hours after exposure, before lymphocytes and monocytes had entered the dermal interstitium or epidermis, the keratinocytes expressed TNF-alpha and ICAM-1, whilst the endothelial cells expressed ELAM-1, VCAM-1 and ICAM-1. Group II biopsies revealed increasing keratinocyte expression of TNF-alpha and ICAM-1 with the appearance of IL-8, which correlated with the onset of epidermal T-cell trafficking. The endothelium was strongly positive for ELAM-1 and VCAM-1, but there was no influx of neutrophils. Group III biopsies showed a decrease in the expression of ICAM-1, VCAM-1 and ELAM-1 by both keratinocytes and endothelium with a reduction in epidermal/dermal inflammation, although the endothelial cell staining of VCAM-1 and ELAM-1 did not completely disappear. These results suggest that on exposure to poison ivy/oak, keratinocytes rapidly produce TNF-alpha which leads to an early autoinduction of ICAM-1, and later IL-8. There is also a paracrinemediated induction and augmentation of underlying endothelial cell ELAM-1, VCAM-1 and ICAM-1.

Keratinocyte expression of CD36 antigen in benign and malignant epidermal cell-derived tumours

Keratinocytes express the macrophage/monocyte antigen CD36 in a variety of inflammatory cutaneous diseases characterised by a T lymphocyte rich infiltrate. Since cell-mediated immune mechanisms also play a role in host responses to skin tumours, we investigated the presence of CD36 antigen on keratinocytes in a range of epidermal cell-derived benign and malignant tumours characterised by a peritumoural, dermal lymphocytic infiltrate. Frozen tissue sections of lesional tissue from a range of epidermally derived tumours were labelled with antibodies to CD1a, CD11b, CD36, and HLA-DR antigens. Benign and malignant squamoproliferative tumour cells exhibited a spectrum of CD36 expression, whereas those of basal cell origin were consistently CD36-. Suprabasal expression of CD36 was present in the normal perilesional epidermis of all tumours studied including basal cell carcinoma. Keratinocyte CD11b expression was not observed. The widespread presence of keratinocyte CD36 positivity in squamoproliferative, but not basal epidermal, tumours suggests its expression may be linked to the degree of keratinocyte differentiation. The stimulus for expression is unknown, but the fact that suprabasal perilesional epidermis expressed CD36 strongly in the absence of infiltrate suggests it may represent a non-specific response by keratinocytes to various stimuli.

Detection of interferon-gamma mRNA in psoriatic epidermis by polymerase chain reaction

Psoriatic skin lesions contain HLA-DR positive T lymphocytes, and other activation antigens, which suggest that the T cells may be producing lymphokines. Gamma interferon is produced by activated T cells, and its presence in psoriasis has been inferred by the lesional keratinocyte expression of 3 gamma interferon-inducible proteins i.e. HLA-DR, intercellular adhesion molecule-1, and gamma-IP-10. To determine whether gamma interferon is being produced directly in psoriatic lesions, punch biopsies of normal and diseased skin were separated into epidermal sheets and dermal fragments. Total cellular RNA was isolated from each epidermal and dermal compartment, and reverse transcribed followed by amplification of the resultant DNA by polymerase chain reaction. The amplification process involved the use of 5' and 3' primers for gamma interferon, and tumor necrosis factor-alpha, with beta-actin serving as a control. Gamma interferon mRNA, but not tumor necrosis factor alpha mRNA, was detectable in 4 of 5 psoriatic epidermal specimens. Neither mRNA was detectable in any normal skin dermal/epidermal specimens. Gamma interferon mRNA was also detectable in a single psoriatic dermal specimen. If reverse transcriptase was omitted, no polymerase chain reaction products were detected, indicating that the fragments detected were not derived from contaminating genomic DNA. These results indicate that gamma interferon mRNA can be extracted and successfully detected from human psoriatic lesional skin biopsies, using polymerase chain reaction technology. This molecular approach can easily be expanded to measure many other cytokines in both epidermal and dermal locations. The detection of gamma interferon in this clinical setting may be of particular pathophysiological significance because injection of gamma interferon has been reported to induce psoriatic lesions.

The development of excess numbers of melanocytic naevi in an immunosuppressed identical twin

The development of cutaneous proliferative lesions following renal transplantation has been well documented in the literature. Those lesions most commonly seen include viral warts, actinic keratoses and basal-cell and squamous-cell carcinomata. More recently it has been suggested that melanocyte proliferation, both benign and malignant, may follow renal transplantation, probably as a result of immunosuppression. We report the case of an identical twin who developed numerous benign melanocytic naevi following renal transplantation; no such proliferation of naevi occurred in his identical sibling.

Monocyte chemotaxis and activating factor production by keratinocytes in response to IFN-gamma

Monocytes accumulate in the epidermis and along the dermo-epidermal junction in several different inflammatory skin diseases. To determine whether human epidermal keratinocytes elaborate a specific chemotaxin responsible for the accumulation of monocytes at these anatomic sites, monocyte chemotactic activity in conditioned 16-h cultured keratinocyte supernatants were assayed using human peripheral blood monocytes as the target cell. Dilutional analysis revealed directed monocyte migration in IFN-gamma-treated (100 U/ml) keratinocyte supernatants (80% maximal FMLP response) which was 10-fold more than IFN-gamma itself or untreated keratinocyte activity alone. Gel filtration chromatography revealed that this activity eluted just ahead of a 12.5-kDa molecular mass marker. Blocking studies demonstrated that a rabbit polyclonal antibody to monocyte chemotaxis and activating factor (MCAF) inhibited all monocyte chemotaxis by greater than 80%. Keratinocytes were metabolically labeled with 35S-cysteine/methionine, and after 16 h incubation the supernatants immunoprecipitated with the same anti-MCAF antibody. MCAF was detected as a protein doublet of 12 and 9 kDa only in IFN-gamma-treated (100 U/ml) keratinocyte supernatants. Incubation with IFN-gamma and TNF-alpha (250 U/ml) in combination resulted in increased production of MCAF protein. By Northern blot analysis, MCAF mRNA was constitutively expressed in keratinocytes and upregulated only in the presence of IFN-gamma. TNF-alpha, IL-1 beta, transforming growth factor-beta and phorbol esters had no positive or negative influence on MCAF mRNA. These studies demonstrate that biologically active MCAF is elaborated by human epidermal keratinocytes upon activation by IFN-gamma, a cytokine also required for the induction of adherence between monocytes and keratinocytes. Keratinocyte-derived MCAF is likely to be important in the regulation of cutaneous monocyte trafficking and may also be responsible for the recruitment of Langerhans cells and dermal dendrocytes, which share many phenotypic features with monocytes/macrophages, to their anatomic locations in skin.

Monocyte chemotaxis and activating factor production by keratinocytes in response to IFN-gamma

Monocytes accumulate in the epidermis and along the dermo-epidermal junction in several different inflammatory skin diseases. To determine whether human epidermal keratinocytes elaborate a specific chemotaxin responsible for the accumulation of monocytes at these anatomic sites, monocyte chemotactic activity in conditioned 16-h cultured keratinocyte supernatants were assayed using human peripheral blood monocytes as the target cell. Dilutional analysis revealed directed monocyte migration in IFN-gamma-treated (100 U/ml) keratinocyte supernatants (80% maximal FMLP response) which was 10-fold more than IFN-gamma itself or untreated keratinocyte activity alone. Gel filtration chromatography revealed that this activity eluted just ahead of a 12.5-kDa molecular mass marker. Blocking studies demonstrated that a rabbit polyclonal antibody to monocyte chemotaxis and activating factor (MCAF) inhibited all monocyte chemotaxis by greater than 80%. Keratinocytes were metabolically labeled with 35S-cysteine/methionine, and after 16 h incubation the supernatants immunoprecipitated with the same anti-MCAF antibody. MCAF was detected as a protein doublet of 12 and 9 kDa only in IFN-gamma-treated (100 U/ml) keratinocyte supernatants. Incubation with IFN-gamma and TNF-alpha (250 U/ml) in combination resulted in increased production of MCAF protein. By Northern blot analysis, MCAF mRNA was constitutively expressed in keratinocytes and upregulated only in the presence of IFN-gamma. TNF-alpha, IL-1 beta, transforming growth factor-beta and phorbol esters had no positive or negative influence on MCAF mRNA. These studies demonstrate that biologically active MCAF is elaborated by human epidermal keratinocytes upon activation by IFN-gamma, a cytokine also required for the induction of adherence between monocytes and keratinocytes. Keratinocyte-derived MCAF is likely to be important in the regulation of cutaneous monocyte trafficking and may also be responsible for the recruitment of Langerhans cells and dermal dendrocytes, which share many phenotypic features with monocytes/macrophages, to their anatomic locations in skin.

Endothelial leucocyte adhesion molecule-1 (ELAM-1) expression in cutaneous inflammation

Endothelial leucocyte adhesion molecule-1 (ELAM-1) is a recently described endothelial surface glycoprotein which is inducible by interleukin 1 (IL-1), tumour necrosis factor-alpha (TNF-alpha) or bacterial lipopolysaccharide (LPS). Using an immunohistochemical technique and a monoclonal antibody (1.2B6) specific for ELAM-1 we have found marked vascular endothelial expression of ELAM-1 in many cutaneous inflammatory disorders, including allergic contact dermatitis, atopic dermatitis and psoriasis, and in dermal infiltrates associated with benign, premalignant and malignant keratinocyte proliferation. In normal skin, minimal levels of ELAM-1 expression were detected. In psoriasis, double-immunoenzyme staining studies revealed a close spatial relationship between ELAM-1 expression and neutrophil margination, suggesting a functional link. Recombinant human interferon-gamma (30 micrograms) injected intradermally in normal adult human volunteers did not substantially upregulate ELAM-1 in contrast to its marked effect on intercellular adhesion molecule-1 (ICAM-1) expression, indicating that this cytokine is probably not involved in ELAM-1 induction in vivo. These results indicate that ELAM-1 is widely induced in cutaneous inflammation with a time course of expression that is longer than that observed in vitro. As ELAM-1 acts as an adhesion ligand for neutrophils, and perhaps monocytes, the expression of this molecule in cutaneous lesions is likely to be an indication of the ability of vascular endothelium to recruit these cells from the circulation. Furthermore, the cytokine inducibility of ELAM-1 is indirect evidence for functional interactions between perivascular mononuclear cells, other resident cells and the blood vessel wall.

Keratinocytes as initiators of inflammation

Environmental stimuli responsible for inducing cutaneous inflammation include contact allergens and ultraviolet light. We postulate that these diverse stimuli trigger a cutaneous inflammatory response by directly inducing epidermal keratinocytes to elaborate specific pro-inflammatory cytokines and adhesion molecules. The consequences are activation of dermal microvascular endothelial cells and selective accumulation of specific mononuclear cells in the dermis and epidermis. Thus, keratinocytes may act as "signal transducers", capable of converting exogenous stimuli into the production of cytokines, adhesion molecules, and chemotactic factors (acting in an autocrine and paracrine fashion) responsible for initiation of "antigen-independent" cutaneous inflammation. The initiation phase may facilitate or promote an amplification phase with additional production of tumour-necrosis factor alpha and interferon gamma via an "antigen-dependent" pathway, and keratinocyte/T cell/antigen-presenting dendritic cellular associations. The direct activation of keratinocytes, with their ability to produce the complete repertoire of pro-inflammatory cytokines, can profoundly influence endogenous and recruited immunocompetent cells, thereby providing the critical trigger responsible for the swift and clinically dramatic alterations that occur following contact between the epidermis and a host of "noxious" agents.

Cellular localization of interleukin-8 and its inducer, tumor necrosis factor-alpha in psoriasis

The importance of immunologic mechanisms in psoriasis has been deduced from the ability of immunosuppressive therapies to ameliorate this common and chronic skin disease. Certainly the histology of psoriatic lesions suggests a dialogue between the hyperplastic keratinocytes and infiltrating T lymphocytes and macrophages. To begin dissecting the cytokine network involved in the pathophysiology of psoriasis, the location, in both epidermal and dermal compartments, of tumor necrosis factor-alpha, interleukin-8, intercellular adhesion molecule-1, and transforming growth factor-alpha at the protein and/or mRNA levels were identified. Tumor necrosis factor-alpha was selected as a potentially key regulatory cytokine, first because it induces cultured keratinocyte interleukin-8, intercellular adhesion molecule-1, and transforming growth factor-alpha production, and second because intercellular adhesion molecule-1 expression by keratinocytes in psoriatic epidermis had been identified previously. Using immunohistochemical localization, tumor necrosis factor-alpha was identified in 12 psoriatic lesions as intense and diffuse expression by dermal dendrocytes (macrophages) in the papillary dermis (without significant staining of endothelial cells, mast cells, or dermal Langerhans cells), and focally by keratinocytes and intraepidermal Langerhans cells. Functional interaction between the dermal dendrocytes and keratinocytes was suggested by the presence of interleukin-8 expression of suprabasal keratinocytes immediately above the tumor necrosis factor-alpha-positive dermal dendrocytes. Interleukin-8 mRNA and transforming growth factor-alpha mRNA were detectable in the epidermal roof of psoriatic lesions, but neither was detectable at the protein or mRNA levels in any normal skin specimens. Treatment of cultured human keratinocytes with phorbol ester (which experimentally produces psoriasiform changes on mouse skin) or tumor necrosis factor-alpha also increased interleukin-8 and transforming growth factor-alpha mRNAs. Further elucidation of the cellular and molecular basis for the genesis and evolution of psoriasis will provide the framework for a better evaluation of the cause and treatment of this skin disease.

Interferon-gamma activates co-ordinate transcription of HLA-DR, DQ, and DP genes in cultured keratinocytes and requires de novo protein synthesis

The purpose of this study was to determine the effect of interferon-gamma on keratinocyte major histocompatibility complex class II gene transcription. Transformed human foreskin keratinocytes (SVK14 cells) were incubated with recombinant IFN-gamma in the presence or absence of the protein synthesis inhibitor cycloheximide. Total cellular RNA was extracted from the cells and Northern blot analysis carried out using cDNA probes for all the functional class II genes. We report that 1) there is co-ordinate activation of all the class-II genes; 2) the rate of transcription varies between gene loci after activation; and 3) de novo protein synthesis is required for IFN-gamma activation of class II transcription.