Epidermal cell production of thymocyte activating factor (ETAF)

Interleukin-1α released from HSV-1-infected keratinocytes acts as a functional alarmin in the skin

Herpes simplex virus-1 (HSV-1) is a human pathogen that utilizes several strategies to circumvent the host immune response. An immune evasion mechanism employed by HSV-1 is retention of interleukin-1β (IL-1β) in the intracellular space, which blocks the pro-inflammatory activity of IL-1β. Here, we report that HSV-1 infected keratinocytes actively release the also pro-inflammatory IL-1α, preserving the ability of infected cells to signal danger to the surrounding tissue. The extracellular release of IL-1α is independent of inflammatory caspases. In vivo recruitment of leukocytes to early HSV-1 micro-infection sites within the epidermis is dependent upon IL-1 signalling. Following cutaneous HSV-1 infection, mice unable to signal via extracellular IL-1α exhibit an increased mortality rate associated with viral dissemination. We conclude that IL-1α acts as an alarmin essential for leukocyte recruitment and protective immunity against HSV-1. This function may have evolved to counteract an immune evasion mechanism deployed by HSV-1.

The regulation of epithelial cell proliferation and growth by IL-1 receptor antagonist

We have performed clinical translation of epithelial cell sheets fabricated on temperature-responsive culture surfaces to treat cornea and esophagus. In the preclinical study using animal models, we found epithelial cell growth potential varied among species. Canine epithelial cell growth was prominent, while rat one was poor under 3T3 feeder layer-free condition. The aim of the present study was to identify growth-promoting factors for epithelial cells. Conditioned medium of canine cell culture harvested at different time points showed different growth promotive activity for rat epithelial cells. Time-dependent gene expression was quantitatively evaluated for forty growth factors, and compared with conditioned medium results. Statistically significant promotive activity was observed with IL-1RA, and significant inhibitory activity was observed with IL-1α. Furthermore, neutralizing anti-IL-1α antibody also showed significant promotive activity. Human epidermal keratinocytes were promoted to proliferate by IL-1RA and neutralizing anti-IL-1α antibody, and showed well differentiation to form transplantable, squamous stratified epithelial cell sheets. These findings would be useful to fabricate reproducible, transplantable epithelial cell sheets for regenerative medicine.

Mediators of increased blood flow in porcine skin

Nicotinates and benzalkonium chloride (B.Cl) cause inflammatory changes in human skin, thought to be dependent upon prostaglandin formation. This study has examined the effects of hexyl-nicotinate (HN) and B.Cl on blood flow in porcine skin. The role of prostaglandins and interleukin (IL)-1 in the blood flow response has been investigated. Blood flow was increased by both HN and B.Cl, the response to B.Cl being more protracted. Cyclooxygenase inhibitor pretreatment reduced these responses. IL-1-like biological activity was identified in normal porcine epidermis and the amounts recovered from inflamed skin were similar. Thus prostaglandin formation in HN or B.Cl-induced inflammation, if IL-1 dependent, is not associated with the loss of significant amounts of the cytokine from the epidermis.

The epidermis as an adjuvant

It is now clear that the epidermis has an active role in local immune responses in the skin. Keratinocytes are involved early in inflammation by providing first-line innate mechanisms and, in addition, can contribute to adaptive immune responses that may be associated with clinical disease. Moreover, keratinocytes are capable of enhancing and shaping the outcome of inflammation in response to stimuli and promoting particular types of immune bias. Through understanding the underlying mechanisms, the role of keratinocytes in disease pathogenesis will be further defined, which is likely to lead to the identification of potential targets for prophylactic or therapeutic intervention.

The use of cultured allogenic keratinocyte grafting in a patient with epidermolysis bullosa simplex

Epidermolysis bullosa (EB) is a rare genetic disease that is known for continuous skin blistering caused by minor trauma. The skin blisters and bullae that develop often cause skin defects. There is no definitive treatment for EB, only symptomatic relief. We report our experience with cultured allogenic keratinocyte grafting in a newborn patient with EB simplex who had unhealed raw surfaces and was not a skin grafting candidate. The skin lesions of the patient were covered with cultured allogenic keratinocyte grafts and re-epithelialized quickly with no scarring. Allogenic keratinocyte grafting reduced pain and produced noticeable improvements in the unhealed wounds. We think that allogenic keratinocyte grafting can play an important role in the management of patients with EB simplex.

Keratinocytes function as accessory cells for presentation of endogenous antigen expressed in the epidermis

The precise contribution(s) of skin dendritic cells (DCs) to immune responses in the skin has not been well delineated. We developed an intradermal (i.d.) injection model in which CD8+ T (OT-I) cells that express ovalbumin (OVA) peptide-specific TCRs (Valpha2/Vbeta5) are delivered directly to the dermis of transgenic (Tg) mice expressing OVA in the epidermis. After i.d. injection, these mice reliably develop skin graft-versus-host disease (GVHD) by day 7. To determine the relative contribution of Langerhans cells (LCs) to the ensuing GVHD-like reaction, we generated K14-OVA x Langerin-diphtheria-toxin-receptor (Langerin-DTR) Tg mice to allow conditional ablation of LCs in the epidermis. To delineate the role of dermal DCs (dDCs) in the reaction, we also generated K14-OVA Tg chimeras using beta(2)-microglobulin-deficient (beta(2)m) congenic donor bone marrow cells. Dermal DCs in these mice cannot present OVA to autoreactive T cells (OT-I cells), whereas the LCs are antigen presentation-competent. Unexpectedly, OT-I cell injection into diphtheria toxin (DT)-treated beta(2)m --> K14-OVA x Langerin-DTR Tg mice resulted in skin GVHD. Thus, in vivo, both LC and dDC appear to be dispensable for the induction of keratinocyte-directed, CD8-mediated effector immune responses. Furthermore and surprisingly, OVA-expressing epidermal cells depleted of LCs that could not initiate allogeneic epidermal lymphocyte reactions activated naive OT-I cells in vitro. These results indicate that keratinocytes may function as accessory cells competent to prime naive skin-reactive T cells.JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article, please go to http://network.nature.com/group/jidclub.

Neuronal nicotinic alpha7 receptors modulate inflammatory cytokine production in the skin following ultraviolet radiation

The anti-inflammatory effects of the neuronal nicotinic receptor alpha7 (nAChRalpha7) are proposed to require acetylcholine release from vagal efferents. The necessity for vagal innervation in this anti-inflammatory pathway was tested in the skin, which lacks parasympathetic innervation, using ultraviolet radiation (UVB) to induce a local pro-inflammatory response. Cytokine responses to UV in mice administered chronic oral nicotine, a nAChR agonist, were reduced. Conversely, nAChRalpha7 knock-out mice exposed to UVB elicit an enhanced pro-inflammatory cytokine response in the skin. Altered pro-inflammatory responses correlated with changes in SOCS3 protein. These results demonstrate that nAChRalpha7 can participate in modulating a local pro-inflammatory response in the absence of parasympathetic innervation.

Cytokine knockouts in contact hypersensitivity research

Contact hypersensitivity (CHS) is a Langerhans cell (LC)-dependent, T cell-mediated cutaneous immune response. CHS reflects a culmination of LC activities in vivo: uptake of epicutaneous antigens, migration into lymph nodes, and presentation of antigens to naïve T cells. Although studies have suggested involvement of the cytokine network in LC migration and CHS initiation, the in vivo function of individual cytokines remains largely unknown. Gene targeting technology has made it possible to study in vivo functions of cytokines through gene-targeted knockout (KO) mice deficient in a given cytokine or its receptor. A variety of cytokine knockouts have been used to assign biological functions to specific cytokines in CHS. These studies have contributed significantly to our understanding of molecular mechanisms underlying CHS.

Antioxidant balance and free radical generation in vitamin e-deficient mice after dermal exposure to cumene hydroperoxide

Organic peroxides are widely used in the chemical industry as initiators of oxidation for the production of polymers and fiber-reinforced plastics, in the manufacture of polyester resin coatings, and pharmaceuticals. Free radical production is considered to be one of the key factors contributing to skin tumor promotion by organic peroxides. In vitro experiments have demonstrated metal-catalyzed formation of alkoxyl, alkyl, and aryl radicals in keratinocytes incubated with cumene hydroperoxide. The present study investigated in vivo free radical generation in lipid extracts of mouse skin exposed to cumene hydroperoxide. The electron spin resonance (ESR) spin-trapping technique was used to detect the formation of alpha-phenyl-N-tert-butylnitrone (PBN) radical adducts, following intradermal injection of 180 mg/kg PBN. It was found that 30 min after topical exposure, cumene hydroperoxide (12 mmol/kg) induced free radical generation in the skin of female Balb/c mice kept for 10 weeks on vitamin E-deficient diets. In contrast, hardly discernible radical adducts were detected when cumene hydroperoxide was applied to the skin of mice fed a vitamin E-sufficient diet. Importantly, total antioxidant reserve and levels of GSH, ascorbate, and vitamin E decreased 34%, 46.5%. 27%, and 98%, respectively, after mice were kept for 10 weeks on vitamin E-deficient diet. PBN adducts detected by ESR in vitamin E-deficient mice provide direct evidence for in vivo free radical generation in the skin after exposure to cumene hydroperoxide.

Skin grafting

No longer an option of last resort, skin grafting has become a technique that is routinely and sometimes preferentially considered as skin replacement for burns, chronic ulcers, and skin defects after cutaneous surgical procedures. When selected as the best alternative for wound closure, autologous skin grafts are commonly considered the gold standard. Availability of autologous grafts is a major obstacle, however, and the search for a manufactured skin replacement has continued. In cases in which autologous grafts cannot be performed, skin substitutes have become an attractive alternative.

Interleukin-1 and cutaneous inflammation: a crucial link between innate and acquired immunity

As our primary interface with the environment, the skin is constantly subjected to injury and invasion by pathogens. The fundamental force driving the evolution of the immune system has been the need to protect the host against overwhelming infection. The ability of T and B cells to recombine antigen receptor genes during development provides an efficient, flexible, and powerful immune system with nearly unlimited specificity for antigen. The capacity to expand subsets of antigen-specific lymphocytes that become activated by environmental antigens (memory response) is termed "acquired" immunity. Immunologic memory, although a fundamental aspect of mammalian biology, is a relatively recent evolutionary event that permits organisms to live for years to decades. "Innate" immunity, mediated by genes that remain in germ line conformation and encode for proteins that recognize conserved structural patterns on microorganisms, is a much more ancient system of host defense. Defensins and other antimicrobial peptides, complement and opsonins, and endocytic receptors are all considered components of the innate immune system. None of these, however, are signal-transducing receptors. Most recently, a large family of cell surface receptors that mediate signaling through the NF-kappaB transcription factor has been identified. This family of proteins shares striking homology with plant and Drosophila genes that mediate innate immunity. In mammals, this family includes the type I interleukin-1 receptor, the interleukin-18 receptor, and a growing family of Toll-like receptors, two of which were recently identified as signal-transducing receptors for bacterial endotoxin. In this review, we discuss how interleukin-1 links the innate and acquired immune systems to provide synergistic host defense activities in skin.

Comparison of Nd:YAG laser versus scaling and root planing in periodontal therapy

BACKGROUND

The Nd:YAG laser has recently been used in the treatment of periodontal disease. However, although a clinical reduction of probing depth and gingival inflammation to this new approach has been reported, it has not been fully evaluated. Interleukin-1 beta (IL- 1beta), a potent stimulator of bone resorption, has been identified in gingival crevicular fluid (GCF), which is closely associated with periodontal destruction. The aim of this study was to compare the effects of Nd:YAG laser treatment versus scaling/root planing (SRP) treatment on crevicular IL-1beta levels in 52 sampled sites obtained from 8 periodontitis patients.

METHODS

One or 2 periodontitis-affected sites with a 4 to 6 mm probing depth and horizontal bone loss from 3 adjacent single-root teeth in each of 4 separate quadrants were selected from patients for clinical documentation and IL-1beta assay. Sampling site(s) from each diseased quadrant was randomly assigned to one of the following groups: 1) subgingival laser treatment (20 pps, 150 mJ) only; 2) SRP only; 3) laser treatment first, followed by SRP 6 weeks later; or 4) SRP first, followed by laser therapy 6 weeks later. The GCF was collected and the amount of IL-1beta was assayed by enzyme-linked immunosorbent assay (ELISA). Clinical parameters and GCF were measured at baseline and biweekly after therapy for 12 weeks.

RESULTS

An obvious clinical improvement (marked decrease in the number of diseased sites with gingival index > or =2) and reduction of crevicular IL- 1beta were found in all groups. The level of IL- 1beta was significantly lower in the SRP group (P = 0.035) than in the laser therapy group for the duration of the 12 weeks. The laser combined SRP therapy group showed a further reduction of IL- 1beta (6 to 12 weeks after treatment) than either laser therapy alone or SRP combined laser therapy.

CONCLUSIONS

Our data suggest that laser therapy appeared to be less effective than traditional SRP treatment. Of the 4 treatment modalities, inclusion of SRP was found to have a superior IL- 1beta response, when compared to other therapies without it. In addition, no additional benefit was found when laser treatment was used secondary to traditional SRP therapy.

Clinical application of cultured oral epithelium for palatal wounds after palatoplasty: a preliminary report

OBJECTIVE

Mucoperiosteal defects of the hard palate after palatoplasty scar causing scar contraction, leading to poor growth of the maxilla. The promotion of wound healing in these cases through cultured epithelial allografting has been reported. Cultured epithelial allografting was done using allogeneic cultured cells, in the hope of improving growth of maxilla.

SUBJECTS AND METHODS

Clefts of the soft and hard palate (seven patients), and a cleft of the soft palate (two patients) were present. Average patient age was 1 year 4 months. Palatoplasty was done by a conventional push-back operation. Oral epithelial cells from healthy adults were cultured using 3T3 cells as the feeder layer. After 3 weeks, cultured oral mucosal epithelium was grafted on a raw surface following palatoplasty.

RESULTS

The result was compared in two patients who had undergone push-back operation only. In all patients, the grafted areas underwent re-epithelialization after about 1 week and did not exhibit any clinical signs of graft rejection. Grafted areas healed completely after 2-3 weeks in all cases.

CONCLUSION

Cultured epithelial allografts serve as a temporary biological dressing, and accelerate epithelialization and wound healing. Allografting by cultured oral epithelium has proved to be a very useful therapeutic modality in palatoplasty, as well as effective augmentation materials in cases of oral mucosal defects.

Involvement of cyclooxygenase-2 in interleukin-1alpha-induced prostaglandin production by human periodontal ligament cells

BACKGROUND

Human periodontal ligament (PDL) cells produce prostaglandin (PG) E2 in response to proinflammatory cytokines. However, the mechanism of PGE2 production is not well understood. The purpose of the present study was to investigate the involvement of cyclooxygenase (COX)-1 and COX-2 in PGE2 production by PDL cells stimulated with a proinflammatory cytokine, interleukin-1alpha (IL-1alpha), and to examine the regulation of PGE2 production by cell-cell interaction of human gingival keratinocytes and PDL cells.

METHODS

The levels of PGE2 in the culture media of PDL cells stimulated with IL-1alpha or culture media of human gingival keratinocytes were determined by an enzyme-linked immunosorbent assay. Expression of COX-1 and -2 mRNA and protein was studied by Northern blot analysis and Western blot analysis, respectively.

RESULTS

IL-1alpha-stimulated PDL cells produced PGE2 in a time-dependent manner. Indomethacin, a non-selective COX-1/COX-2 inhibitor, and NS-398, a selective COX-2 inhibitor, completely inhibited PGE2 production by the IL-1alpha-stimulated cells. COX-2 mRNA was detected after IL-1alpha stimulation, although it was not detected in unstimulated cells. There was no difference in expression of COX-1 mRNA between unstimulated cells and IL-la-stimulated cells. Expression of COX-2 protein in IL-1alpha-stimulated cells was increased, compared with that in unstimulated cells, whereas COX-1 protein expression was almost the same in both the cells. Treatment of IL-1alpha-stimulated PDL cells with dexamethasone, known to inhibit COX-2 expression, prevented PGE2 production and COX-2 mRNA expression. Addition of the culture media of human gingival keratinocytes to PDL cells increased PGE2 production. The PGE2 production was depressed by treatment of the cells with IL-1 receptor antagonist and anti- IL-1alpha antibody, not with anti-IL-1beta antibody. The PGE2 production was also inhibited by treatment with NS-398 and dexamethasone.

CONCLUSIONS

We suggest that PDL cells stimulated with IL-1alpha produce PGE2 through de novo synthesis of COX-2 and that the cell interaction of gingival keratinocytes and PDL cells controls COX-2 expression and PGE2 production via IL-1alpha or 1alpha IL-la-like factor(s). Selective COX-2 inhibitors, which have the advantage of reduced gastric toxicity, may provide a useful approach to treatment of periodontal disease.

A partial catalog of proteins secreted by epidermal keratinocytes in culture

Proteins secreted by epidermal keratinocytes are known to engage in functions other than those directly associated with barrier formation. We have used a previously published culture model to collect proteins secreted by adult human epidermal keratinocytes. Electrophoresis and microsequencing allowed us to identify 20 proteins. The list of proteins includes those known to be produced by keratinocytes (beta-2 microglobulin, betaIG-H3, calgranulin A, cathepsin B and D, E-cadherin, gelatinase B, gelsolin, interstitial collagenase, laminin B2t, plasminogen activator inhibitor-1, protein 14-3-3epsilon, SCC antigen, stratifin, and translationally controlled tumor protein) as well as those not previously known to be secreted by keratinocytes (epididymis secretory protein, maspin, and anti-neoplastic urinary protein). In addition, two proteins were identified that are not known to be secreted (glutathione-S-transferase and heat shock protein 27/28 kDa). The varied nature of the proteins identified suggests that epidermal keratinocytes have physiologic functions that have yet to be identified.

Roxithromycin down-modulates antigen-presenting and interleukin-1 beta-producing abilities of murine Langerhans cells

The immunomodulatory effect of the macrolide antibiotic, roxithromycin (RXM) on Langerhans cells (LC) was studied in mice. RXM inhibited the ability of LC to present superantigen and hapten to T cells at 100 microM. The superantigen-presenting activity of LC was more profoundly abrogated by RXM than the hapten-presenting activity. This functional reduction was partly attributed to an RXM-induced decrease in promotion of the expression of major histocompatibility complex class II molecules on LC. On the other hand, RXM down-modulated the production of interleukin-1 beta by LC at a lower concentration of 10 microM than concentrations that inhibited antigen presentation. These results imply that RXM exerts therapeutic effectiveness via not only bacteriocidal action but also inhibitory effect on the LC ability in T-cell-mediated cutaneous diseases that can be exacerbated by skin-colonized Staphylococcus aureus.

Membranes of herpes simplex virus type-1-infected human corneal epithelial cells are not permeabilized to macromolecules and therefore do not release IL-1alpha

Nanogram amounts of the proinflammatory cytokine interleukin-1alpha (IL-1alpha) were detected in uninfected cultures of human corneal epithelial cells (HCEC). Although HSV-1 replicated >10(4)-fold in these cells and caused extensive cytopathic effects, virus infection was not accompanied by significant extracellular release of IL-1alpha. Additional studies showed that release of radiolabeled cytosolic proteins from virus-infected HCEC was no greater than that released by mock-infected cells. These findings indicate that HSV-1 infection of HCEC does not result in IL-1alpha release because newly formed virus progeny can escape infected cells without disrupting cell membranes.

Cross-Reactivity in Murine Fluoroquinolone Photoallergy: Exclusive Usage of TCR Vβ13 by Immune T Cells That Recognize Fluoroquinolone-Photomodified Cells

Fluoroquinolone antibacterial agents are well known to elicit photosensitivity as an adverse effect, and their cross-reactivity has been clinically documented. The photoallergenicity of fluoroquinolones is mainly derived from their photohaptenic moiety, and photomodification of skin epidermal cells with fluoroquinolones is thought to be an initial step for this photoallergy. Here we have explored, both in vivo and in vitro, T cell responses to fluoroquinolone-photomodified cells, focusing on their photoantigenic cross-reactivity. Cells were derivatized with fluoroquinolones under exposure to UV-A, and fluoroquinolone photoadducts were detected in photomodified cells by immunostaining, flow cytometry, and cell ELISA using fluoroquinolone-specific mAb. T cell-mediated hypersensitivity induced and elicited by s.c. injection of fluoroquinolone-photomodified epidermal cells was cross-reactive among six fluoroquinolones. In addition, lymph node cells from mice sensitized with fluoroquinolone-photomodified cells proliferated well in vitro not only to Langerhans cell-enriched epidermal cells photoderivatized with corresponding fluoroquinolone, but also to those photomodified with any of five other fluoroquinolones, supporting their cross-reactivity. In three fluoroquinolones tested, Th1 populations that expanded after in vitro photoantigenic stimulation of immune lymph node cells expressed the same Vβ13 of TCR. The sensitivity could be transferred by the i.v. administration of this Vβ13+ T cell line into naive recipients, in which a high percentage of Vβ13+ cells infiltrated at the challenge site. These findings suggest that these fluoroquinolones carry the same photoantigenic epitope, which is recognized by Vβ13+ T cells, leading to fluoroquinolone photosensitivity and cross-reactivity.

Altered permeability and disordered cutaneous immunoregulatory function in mice with acute barrier disruption

In vivo and in vitro T-cell-activating ability of murine epidermal cells (EC) was investigated in acutely barrier-disrupted skin by extraction of epidermal lipids with acetone or removal of corneocytes by tape stripping. Contact sensitivity (CS) to 2,4-dinitrofluorobenzene (DNFB) and picryl chloride (PCl) and contact photosensitivity (CPS) to tetrachlorosalicylanilide (TCSA) were significantly augmented when challenged or sensitized at sites treated with acetone 24 h before, compared with the intact skin. CS to DNFB was also enhanced by tape stripping, but not by water rubbing, suggesting that physical stress or a toxic effect of acetone was not responsible for the augmentation. Semi-quantification of TCSA-EC photoadducts showed markedly increased permeability of hapten in the epidermis 24 h after acetone treatment. Bioactive IL-1alpha was more pronounced in barrier-disrupted than in intact skin. Lymph node T cells from PCl-sensitized mice proliferated significantly more in a hapten-specific and co-stimulatory molecule-dependent manner in response to trinitrophenylated (TNP) EC from acetone-treated skin than to those from untreated skin. Immunofluorescence staining of epidermal sheets and flow cytometric analysis of dispersed EC showed that subpopulations of Langerhans cells (LC) in acetone-rubbed or tape-stripped skin expressed major histocompatibility complex class II CD54 and CD86 molecules at levels higher than the rest of LC and LC from water-treated or untreated epidermis. Therefore, not only increased permeability of hapten through the epidermis but also altered immune functions of EC potentiate T-cell activation in acute barrier disruption. Such augmentation of immune reactivity may be critical to elimination of environmental noxious agents that penetrate easily into the barrier-disrupted epidermis.

Spontaneous hair follicle cycling may influence the development of murine contact photosensitivity by modulating keratinocyte cytokine production

The development of murine contact hypersensitivity is influenced by hair follicle cycling. Here, we have examined hair cycle-associated fluctuations of murine contact photosensitivity (CPS) to tetrachlorosalicylanilide (TCSA) and its immunologic mechanism(s). When the CPS outcome was monitored in correlation with their spontaneous, synchronized hair cycling, mice aged 8 and 14 weeks, with most of their hair follicles in telogen, exhibited strong CPS responses, whereas 4-, 11-, and 16-week-old mice with a predominance of anagen follicles in a large area of their integument exhibited lower responses. This suggests that the development of CPS is inhibited in mice with anagen hair follicles. Antigen-specific, T-cell receptor V beta 7+ suppressor T cells, which are recognized to down-regulate the CPS response to TCSA, were not generated in sensitized anagen mice. Culture supernatants of epidermal cells derived from mice with anagen hair follicles contained factor(s) that suppress in vivo the development of CPS. It was found that levels of mRNA for tumor necrosis factor alpha (TNF alpha) were markedly decreased in epidermal cells from early anagen to telogen mice, whereas message for IL-1 receptor antagonist (IL-1ra) was transcribed increasingly during this hair cycling. These findings suggest that altered keratinocyte production of these cytokines is involved in mediating the anagen-associated depression of CPS.

UV-induced cutaneous photobiology

Ultraviolet radiation (UVR) present in sunlight is a major environmental factor capable of affecting human health and well being. The organ primarily affected by UVR is the skin, which is composed of a variety of different cell types. Here, UVR is needed for production of active vitamin D as well as producing undesirable effects such as sunburn, premature cutaneous photoaging, and promoting skin cancer development. Depending on the radiation dose, UVR influences virtually every cutaneous cell type investigated differently. Since the end of the nineteenth century, sun exposure has been known to induce skin cancer, which is now the human malignancy with the most rapidly increasing incidence. In several experimental models, mid-range UVR has been demonstrated to be the major cause of UV-induced cutaneous tumors. The stratospheric ozone layer protecting the terrestrial surface from higher quantum energy solar radiation is being damaged by industrial activities resulting in the possibility of increased UVR exposure in the future. Investigations in the field of experimental dermatology have shown that within the skin an immunosurveillance system exists that may be able to detect incipient neoplasms and to elicit a host responses against it. This article reviews the literature on studies designed to investigate the effects of UVR on cutaneous cellular components, with special focus on the immune system within the skin and the development of UV-induced cancer.

Differential regulation of IL-1 and IL-1 receptor antagonist in HaCaT keratinocytes by tumor necrosis factor-alpha and transforming growth factor-beta 1

Cytokines such as TNF alpha and TGF beta 1 have potent effects on keratinocyte differentiation and have been implicated in cutaneous injury, immunologic reactions, and wound healing. To determine whether such conditions might alter the balance of epidermal keratinocyte IL-1 and the IL-1 receptor antagonist (IL-1ra), TNF alpha and TGF beta 1 were added to HaCaT cells, a human adult keratinocyte cell line. mRNA levels of IL-1 alpha, IL-1 beta, and IL-1Ra were detected by polymerase chain reaction (PCR) on reverse transcribed RNA extracts, followed by Southern blot of the PCR products, 35S-labeled probe hybridization, and quantification against standard curves. TNF alpha (100 ng/ml) at the 3-h time point significantly induced increases in mRNA expression of II-1 alpha (9.2 +/- 2.9 fold increase) and IL-1 beta (2.5 +/- 0.7 fold increase) (n=7) which were concordant with increases in IL-1 alpha protein (7.1 +/- 1.3 fold increase) and Il-beta protein (4.4 +/- 1.0 fold increase) measured by ELISA 24 h after stimulation. By contrast, icIL-1Ra mRNA and protein levels were not affected by TNF alpha. TGF beta 1 induced a mild increase in IL-1 alpha mRNA (3.8 +/- 1.8 fold) and protein (3.5 +/- 1.2 fold). TGF beta 1 did not affect IL-1 beta mRNA levels but caused variable increases in IL-1 beta protein levels. TGF beta 1 did not alter icIL-1Ra mRNA or protein levels. Inhibition of RNA synthesis with actinomycin D demonstrated that the rate of degradation of IL-1 beta mRNA was reduced by treatment with TNF alpha. This stabilization of IL-1 beta mRNA was specific, because TGF beta 1 did not stabilize IL-1 beta mRNA, and TGF beta 1 and TNF alpha did not increase the stability of Il-1 alpha mRNA. icIL-1Ra mRNA was fairly stable over a 20 hour period and its slow degradation was not affected by treatment with either TNF alpha or TGF beta 1, indicating a higher steady state stability of icIL-1ra mRNA relative to IL-1 mRNA's. Given the high rate of degradation of IL-1 alpha and IL-1 beta mRNA, levels of these mRNAs may rapidly decrease while the icIL-1ra mRNA levels remain constant, thus allowing for rapid dampening of IL-1 activity soon after the stimuli provoking an inflammatory or reparative response have abated. In conclusion, TNF alpha and TGF beta 1, cytokines with potent effects on inflammation and differentiation, both induce keratinocyte IL-1 alpha mRNA and protein levels, but differentially regulate IL-1 beta mRNA. They both exert little effect on IL-1 Ra levels, which were constitutively highly stable. Such differential regulation provides mechanisms for separately controlling the relative activity of these cytokines under normal and disordered conditions.

Macrophage colony-stimulating factor (M-CSF) inhibits the decrease in the amount of rRNA and IA beta mRNA in cultured epidermal Langerhans cells of the mouse

Macrophage colony-stimulating factor (M-CSF) is a keratinocyte-derived cytokine whose function in skin is not completely clarified. We investigated its effects on Langerhans cells by examining the amount of IA beta mRNA, beta-actin mRNA and rRNA per cell, and compared them with the effects of other cytokines such as granulocyte/macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha). After culture for 24 h in the absence of exogenous cytokines, rRNA in Langerhans cells decreased steeply while beta-actin mRNA increased. IA beta mRNA also decreased sharply. These decreases in the amount of rRNA and IA beta mRNA were limited when cytokines were added to the culture medium (in order of efficiency M-CSF > GM-CSF > TNF-alpha), but M-CSF was less potent than GM-CSF in up-regulating beta-actin mRNA (GM-CSF > M-CSF, TNF-alpha). The effect of M-CSF, but not that of GM-CSF, was restricted by simultaneous treatment of cells with TNF-alpha. None of these effects engendered a change in the viability of the Langerhans cells in a 24-hr culture. Reverse-transcribed polymerase chain reaction analysis demonstrated that c-fms, the gene of the M-CSF receptor, was expressed in Langerhans cells, implying the physiological importance of M-CSF in vivo. A protein kinase C activator, TPA, up-regulated the amount of IA beta mRNA, while a protein kinase C inhibitor, H-7, suppressed the effects of all three cytokines. These results suggest that M-CSF, in conjugation with TNF-alpha and GM-CSF, plays an important role in controlling the physiological state of Langerhans cells, probably through the activation of protein kinase C.

Messenger RNAs for the multifunctional cytokines interleukin-1 alpha, interleukin-1 beta and tumor necrosis factor-alpha are present in adnexal tissues and in dermis of normal human skin

Interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) are 3 cytokines that play a key rôle in cutaneous homeostasis and in the immunopathogenesis of a number of dermatologic diseases. Most studies have focused on their production by keratinocytes and Langerhans cells. To determine whether there are non-epidermal sites of cytokine transcription, biopsy specimens of normal human skin were probed for IL-1 alpha, IL-1 beta and TNF-alpha messenger RNAs using the method of in situ hybridization. The results demonstrate that each cytokine mRNA is present at multiple sites within the skin, including epidermal appendages and adnexal structures (hair follicles, sebaceous glands), the dermal microvasculature, arrectores pilorum smooth muscle, and the dermal connective tissue. These data provide evidence that in vivo there are multiple sites other than the epidermis of constitutive IL-1 alpha, IL-1 beta, and TNF-alpha gene transcription in normal human skin.

Epidermal cytokines in allergic contact dermatitis

The understanding of cutaneous immunology has grown significantly during the past decade, particularly regarding the immune function of keratinocytes. Keratinocytes play a major role in immune and inflammatory reactions, mainly through synthesis and release of cytokines. The cytokine network in the skin is an important contributor to normal homeostasis and to the pathogenesis of cutaneous disease. Although cytokine dysregulation has been implicated in the pathogenesis of many cutaneous diseases, allergic contact dermatitis is one that has been the most extensively studied. The aim of this article is to provide a comprehensive current review of the mechanisms of allergic contact dermatitis with particular emphasis on the role of epidermal cytokines.

In vitro modulation of keratinocyte-derived interleukin-1 alpha (IL-1 alpha) and peripheral blood mononuclear cell-derived IL-1 beta release in response to cutaneous commensal microorganisms

The ability of a range of skin commensal microorganisms to modulate interleukin-1 (IL-1) release by cultured human keratinocytes and peripheral blood mononuclear cells (PBMCs) was investigated by a combination of enzyme-linked immunosorbent assays and bioassays. Three fractions (formaldehyde-treated whole cells, culture supernatants, and cellular fractions) were prepared from Propionibacterium acnes, Propionibacterium granulosum, Staphylococcus epidermidis, Staphylococcus capitis, Staphylococcus hominis, and Malassezia furfur serovar B. The levels of immunochemical IL-1 alpha released by cultured keratinocytes during coincubations with these microbial fractions ranged from 0 to 136 pg/ml and were maximal after 72 h. No microbial fraction consistently upregulated immunochemical IL-1 alpha release by freshly isolated keratinocytes from two donors and a transformed cell line, all of which produced the cytokine constitutively to various extents. Bioassays revealed that most of the IL-1 released was biologically inactive. In contrast, whole cells of formaldehyde-treated P. granulosum and S. epidermidis significantly stimulated release of IL-1 beta by PBMCs from three donors compared with the negative control (culture medium). Release was maximal at 24 h. Coincubation with intact cells of the yeast M. furfur significantly decreased levels of IL-1 beta below the values for the negative control by PBMCs from all three donors. There was good correlation between bioassay data and immunoassay data for IL-1 beta, and the depressive effect of M. furfur cells on cytokine production by all three cultures of PBMCs was mirrored in the levels of bioactive cytokine. This reduction in IL-1 beta release by PBMCs by M. furfur may provide an explanation why dermatoses thought to be caused by this yeast are essentially noninflammatory or only mildly inflammatory.

Crevicular interleukin-1 beta in moderate and severe periodontitis patients and the effect of phase I periodontal treatment

Interleukin-1 beta (IL-1 beta), a potent stimulator of bone resorption, has been implicated in the pathogenesis of periodontal destruction. However, the relationship between cytokines and periodontal disease has not been studied sufficiently to allow definitive conclusions. The aims of this study are to investigate crevicular IL-1 beta and the clinical status of patients with periodontitis and the effect of phase I periodontal therapy on levels of IL-1 beta. For this study, 130 gingival crevicular fluid (GCF) samples were harvested from non-inflamed (15) and diseased sites (115) in 11 patients with periodontitis. The gingival index (GI) and probing depth (PD) of each site was recorded initially and one month after treatment. The amount of IL-1 beta in the GCF was measured by enzyme-linked immunosorbent assay (ELISA) using an antibody specific for this cytokine. Before treatment, IL-1 beta was found in 12 of 15 non-inflamed gingival crevices and in 112 of 115 diseased pockets. The amount of IL-1 beta varied from 4.03 to 511.12 pg/site. The average amount of IL-1 beta from diseased sites was 3-fold greater than that from non-inflamed sites. Both total amount of IL-1 beta and the GCF volume, but not IL-1 beta concentration, were found to be correlated, positively, with GI score and PD. After therapy, 63 sites from 7 patients were re-examined, and the amount of IL-1 beta in 49 of 63 sites was found to have declined. These data suggest that the amount of crevicular IL-1 beta is closely associated with periodontal status. This relationship may be valuable in monitoring periodontal disease activity.

Prostaglandin E2 and interleukin-1 levels in smokeless tobacco-induced oral mucosal lesions

Inflammatory mediators released as a result of smokeless tobacco (ST)-induced irritation may play a role in the development of oral mucosal lesions at habitual tobacco placement sites in ST users. The present study examined levels of interleukin-1 (IL-1) and prostaglandin E2 (PGE2) in ST-induced mucosal lesions and compared these to mediator levels in clinically normal mucosa. Soft tissue biopsies were obtained from white mucosal lesions at habitual placement sites and normal alveolar mucosal tissue at non-placement sites in 18 ST users. Fifteen non-tobacco using subjects also provided normal alveolar mucosal biopsies. IL-1 and PGE2 were recovered from the specimens, and mediator levels were determined by enzyme immunoassay. Prostaglandin E2 levels (pg/mg) were lower in both regions in the ST subjects, but values did not vary significantly between the regions with 2.77 +/- 0.72 and 2.86 +/- 0.99 at placement and non-placement sites, respectively, in ST users and 7.31 +/- 3.84 in non-tobacco users. Both IL-1 alpha and IL-1 beta (pg/mg) were significantly (p < 0.01) elevated in ST lesions (IL-1 alpha = 25.56 +/- 4.00; IL-1 beta = 7.76 +/- 1.68) compared to either non-placement sites in ST users (IL-1 alpha = 14.64 +/- 2.65; IL-1 beta = 1.63 +/- 0.72) or non-tobacco users (IL-1 alpha = 12.84 +/- 2.60; IL-1 beta = 2.04 +/- 0.75). In view of IL-1's role in keratinocyte proliferation and its inflammatory effects, this cytokine may contribute to mucosal and gingival alterations observed in ST users.

Acute cutaneous eruptions after marrow ablation: roses by other names?

This review will cover acute cutaneous eruptions following marrow ablation in the treatment of various malignant neoplasms. The clinical and histopathological features of 1. the eruption of lymphocyte recovery, 2. acute allogeneic graft-vs-host reaction, 3. acute autologous (spontaneous) graft-vs-host reaction, 4. eruptions associated with the administration of cyclosporin A, and 5. eruptions associated with the administration of human recombinant cytokines in pharmacologic doses will be considered. The idea is put forth that the second, third, and fourth cutaneous eruptions listed above represent variations on the theme of the eruption of lymphocyte recovery. The final common pathway in the development of all these diffuse erythematous eruptions probably relates to the elaboration of cytokines by infiltrating lymphocytes or to the administration of cytokines in pharmacologic doses.

Cyclosporin A inhibits keratinocyte cytokine gene expression

The immunosuppressive peptide cyclosporin A (CyA) is an extremely effective therapy for severe recalcitrant psoriasis, although its mechanism of action is unknown. In this study, we examined the effect of CyA on keratinocyte growth and cytokine expression, and showed that CyA inhibits the growth of murine and human keratinocytes (KC) and KC cell lines. In addition, CyA inhibits the expression of cytokine genes in a dose-dependent fashion. After 2 days' incubation with 20 microM CyA, interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta), and interleukin 8 (IL-8) mRNA were decreased by 4-fold, 3.3-fold and 3.3-fold, respectively, in COLO-16, a keratinocyte cell line. IL-1 biological activity recovered from COLO-16 culture supernatants decreased to one-fifth of that of controls. In the murine KC cell line PAM 212, 10 microM CyA treatment for 2 days downregulated IL-1 alpha, tumour necrosis factor-alpha (TNF-alpha) and IL-1 receptor by 60%, but had no effect on the message for interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), ornithine decarboxylase and beta-actin. Cells cultured for 5 days in the presence of CyA required much lower concentrations (2 microM) to achieve the same degree of inhibition of IL-1 alpha. Similar tissue concentrations of CyA have been reported in psoriatics undergoing CyA therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Superantigenic staphylococcal exotoxins induce T-cell proliferation in the presence of Langerhans cells or class II-bearing keratinocytes and stimulate keratinocytes to produce T-cell-activating cytokines

Several staphylococcal toxins are among a growing number of immunostimulatory molecules called "superantigens" because of their ability, when presented by appropriate major histocompatibility complex class II+ accessory cells, to activate essentially all T cells bearing particular T-cell receptor V beta gene segments. We have examined the ability of murine epidermal Langerhans cells and/or keratinocytes to act as accessory cells in the T-cell response to the superantigens staphylococcal enterotoxin B and exfoliative toxin, also known as epidermolysin. Purified murine splenic T cells were stimulated with staphylococcal enterotoxin B or exfoliative toxin in the presence of Langerhans cells--enriched epidermal cells from normal mice or epidermal cells isolated from mice pretreated with recombinant interferon-gamma, a procedure that induces the expression of major histocompatibility complex class II molecules on keratinocytes. The data show that both Langerhans cells and class II-bearing keratinocytes can act as accessory cells in the T-cell response to staphylococcal enterotoxin B and exfoliative toxin. We also observed that both human and murine keratinocytes cultured in the presence of staphylococcal enterotoxin B or exfoliative toxin produce increased amounts of cytokine(s) capable of stimulating thymocytes and D10 cells, and that this toxin activity is independent of the level of expression of class II on keratinocytes. Studies by enzyme-linked immunosorbent assay showed that staphylococcal enterotoxin B stimulates keratinocytes to produce tumor necrosis factor-alpha but not interleukin-1, suggesting tumor necrosis factor-alpha and perhaps other cytokines are responsible for the T-cell proliferative activity. These results demonstrate that two distinct epidermal constituents (i.e. Langerhans cells and keratinocytes) can serve as accessory cells in the responses of T cells to superantigenic bacterial toxins. It is possible that such toxins contribute to the pathogenesis of a variety of skin diseases by either locally activating T cells bearing particular V beta genes and/or enhancing keratinocyte production of immunomodulatory cytokines.

IL-8 gene expression and production in human keratinocytes and their modulation by UVB

Interleukin (IL)-8 is a member of the supergene family of proinflammatory and chemotactic cytokines recently termed chemokines. IL-8 has been implicated in the pathogenesis of inflammatory skin diseases such as psoriasis. In this study, IL-8 mRNA expression and protein production were determined in normal cultured human epidermal keratinocytes after ultraviolet-B (UVB) irradiation. Messenger RNA levels were determined by the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Total RNA was extracted from cultured keratinocytes at various time points post-irradiation, reverse transcribed to cDNA, and amplified by PCR using a labeled specific primer for the target gene. Amplified products were sized by electrophoresis, visualized by autoradiography, and quantitated by densitometry. Autoradiographs were normalized relative to glyceraldehyde-3-phosphate-dehydrogenase (G3PDH) signals. Constitutive expression of IL-8 mRNA was seen in normal cultured keratinocytes. After 100 or 300 J/m2 UVB irradiation, a rapid increase in IL-8 mRNA level was observed within 1 h after irradiation. At 24 h after irradiation, the mRNA level was elevated 11-13 times compared with the control level. Production of IL-8 protein in culture supernatants was assayed by enzyme-linked immunosorbent assay (ELISA). Significant levels of IL-8 protein were observed at 24 h after irradiation. Cycloheximide treatment blocked this IL-8 protein induction. As IL-8 is known to be an inflammatory cell chemotactic factor, these results suggest a possible role for IL-8 in UVB-induced skin inflammation and diseases.

Profiles of cytokine mRNA expressed by dendritic epidermal T cells in mice

The epidermis of mice contains, in addition to Langerhans cells, a second dendritic population that is Thy-1+/CD3+/CD4-/CD8-/T-cell receptor-V gamma 3/V delta 1+. These dendritic epidermal T cells (DETC) are now thought to comprise one element in the family of epithelial tissue-resident gamma delta T cells. In the present study, DETCs were examined for their expression of mRNA for cytokines, using a reverse transcription-polymerase chain reaction. Freshly isolated Thy-1+ epidermal cells constitutively expressed mRNA for gamma-interferon, but not IL-2. Within 24 h after stimulation with Con A, these cells then expressed mRNA for gamma-interferon and IL-2, but not IL-4. The rapid onset of expression of mRNA for IL-2 occurred exclusively within the Thy-1+ population, and in a Con A-dependent fashion. When freshly isolated epidermal cells were first stimulated with Con A and then expanded in bulk with rIL-2 for 20-24 d, cells expressing IL-4 mRNA then emerged, upon secondary stimulation with Con A. These "short-term" DETC lines also expressed mRNA for IL-2, interferon-gamma, IL-1 alpha, IL-3, IL-6, IL-7, tumor necrosis factor alpha and beta, and granulocyte macrophage-colony stimulating factor. Interestingly, mRNA for IL-4 and IL-6 was no longer detected in long-term (> 1 year) DETC lines 7-17 and 12-12. In addition, one line (7-17) maintained IL-3 mRNA expression, whereas another (12-12) had lost this capacity. These results emphasize the concept that, as resident cells in epidermis, DETCs exhibit several different immunorelevant activities, and the heterogeneity in cytokine mRNA profiles suggests that DETCs may divide into functional subsets.

Reciprocal cytokine-mediated cellular interactions in mouse epidermis: promotion of gamma delta T-cell growth by IL-7 and TNF alpha and inhibition of keratinocyte growth by gamma IFN

A unique subset of gamma delta T cells, termed dendritic epidermal T cells (DETC), resides in symbiosis with keratinocytes in mouse epidermis. We have shown previously that interleukin 7 (IL-7) which is produced by keratinocytes, promotes growth and prevents apoptosis in DETC. To extend this observation, we examined 12 cytokines, each of which is expressed by epidermal cells at mRNA and/or protein levels, for their capacities to modulate the growth of DETC. Cytokines examined included IL-1 alpha, IL-2, IL-3, IL-4, IL-6, IL-7, IL-8, IL-10, tumor necrosis factor-alpha (TNF alpha), interferon-gamma (IFN gamma), granulocyte/macrophage-colony stimulating factor (GM-CSF), and macrophage inflammatory protein-1 alpha (MIP-1 alpha). When tested individually, IL-2 and IL-7 promoted maximal growth of the long-term cultured DETC line 7-17. When tested in combinations, synergistic growth-promoting effects were seen with IL-2 and IL-4 or IL-7, and with IL-7 and IL-4 or TNF alpha. Dose-response experiments demonstrated that TNF alpha, which is produced by keratinocytes, enhances IL-7-induced DETC proliferation, but inhibits IL-2-induced proliferation. The mouse keratinocyte-derived cell line Pam 212 was used to test these cytokines for their capacities to regulate keratinocyte growth. Only gamma IFN, which is produced by DETC, inhibited proliferation in a dose-dependent fashion. These results illustrate three reciprocal pathways by which epidermal cytokines regulate the growth of epidermal cells: 1) a paracrine mechanism by which keratinocyte-derived cytokines (e.g., IL-7 and TNF alpha) promote the growth of DETC, 2) an autocrine mechanism by which DETC-derived cytokines (e.g., IL-2 and IL-4) support their own growth, and 3) a reciprocal pathway in which a cytokine produced by resident epidermal leukocytes (e.g., gamma IFN) modulates the growth of keratinocytes.

Human keratinocytes activate primed major and minor histocompatibility antigen specific Th cells in vitro

Keratinocytes are activated to express MHC class II and ICAM-1 molecules during cutaneous inflammatory reactions. It is controversial how the interaction between these 'nonprofessional' antigen presenting cells (APC) and infiltrating T cells affects the local inflammatory response. To address this issue we analyzed whether IFN gamma-treated cultured human keratinocytes would activate established Th cell clones in vitro. Three allo DR specific T cell clones were induced to proliferate in a HLA-DR and LFA-1/ICAM-1 dependent fashion upon coculture with intact layers of IFN gamma stimulated keratinocytes. Likewise, keratinocytes also could activate two out of four minor histocompatibility (mH) antigen specific Th cell clones obtained from peripheral blood leukocytes (PBL) of graft versus host disease patients. The T cell activating potential of MHC class II+ keratinocytes was shown to be relatively low compared to specialized APC as PMNC and EBV-BLCL. Most strikingly, measurable allo MHC and mH antigen specific Th cell proliferation was only induced by using adherent keratinocytes at low cell densities, but not by keratinocytes in suspension. The results presented here indicate that in vitro conditions may crucially influence observations regarding the T cell activating potential of MHC class II expressing keratinocytes. Furthermore, our results indicate that, in addition to a tolerizing effect as suggested by previous reports, interaction of primed antigen specific T cells with activated keratinocytes may also result in enhancement of a cutaneous immune response in vivo.

Interleukin-1 alpha gene expression and localization of interleukin-1 alpha protein during tumor promotion

Treatment of the dorsal epidermis of SENCAR mice with 12-O-tetradecanoylphorbol-13-acetate (TPA) induced a time- and dose-dependent stimulation of interleukin-1 alpha (IL-1 alpha) gene expression. Levels of IL-1 alpha mRNA were elevated as early as 15 min and peaked at 3-4 h after a single application of TPA (2 micrograms or 10 micrograms). IL-1 alpha gene expression increased in epidermal tissue isolated from SENCAR mice at 1, 3, 6, 10, 16, and 22 wk after a single treatment with 10 nmol 7,12-dimethylbenz[a]anthracene (DMBA) and subsequent twice-weekly application of 2 micrograms TPA. IL-1 alpha-immunoreactive protein was specifically localized within suprabasal keratinocytes in cutaneous tissue isolated from mice treated with DMBA-TPA for 1-22 wk and in nonproliferating cells located within papilloma tissue isolated from SENCAR mice at 22 wk after initiation and promotion. Basal cells within hyperplastic epidermis did not produce IL-1 alpha-immunoreactive protein. DMBA treatment alone did not induce IL-1 alpha gene expression. Injection of IL-1 alpha-specific antibodies (50 micrograms) into SENCAR mice via the tail vein 2 h before treatment with TPA (2 micrograms or 10 micrograms) significantly (P < 0.05) inhibited the skin thickening usually observed 24 h after treatment with TPA. Autoradiography studies showed that injection of anti-IL-1 alpha antibodies inhibited incorporation of [methyl-3H]thymidine by keratinocytes within the epidermis and by cells within hair follicles. It also inhibited neutrophil infiltration into the dermis, which usually results from topical application of TPA. These data suggest that IL-1 alpha is a pivotal cytokine produced by specific subpopulations of epidermal keratinocytes and that IL-1 alpha primarily regulates the epidermal proliferative response of a distinctly separate population of keratinocytes after topical exposure of murine epidermis to TPA and secondarily modulates neutrophil migration into the dermis. Consequently, manipulation of IL-1 alpha may be a way to attenuate or abrogate the cutaneous response to TPA by altering keratinocyte proliferation, the resultant hyperplasia, and a portion of the inflammatory response characterized by dermal infiltration of neutrophils.

HLA class II+ human keratinocytes present Mycobacterium leprae antigens to CD4+ Th1-like cells

In a variety of inflammatory skin diseases like leprosy, keratinocytes (KC) are induced to express MHC class II molecules and may therefore serve as antigen-presenting cells (APC) for MHC class II restricted T cells infiltrating the lesions. However, KC have been thought to be improper APC for MHC class II restricted T cells and to drive T cells into an anergic rather than into an activation state. We evaluated this issue in relation to leprosy and tested whether HLA-DR+ KC could present M. leprae antigens to well-defined, CD4+, cytotoxic as well as proliferative, Th1-like cell clones. Using a recently developed sensitive assay system which employs intact layers of basal KC as APC we found that most T-cell clones (6/8) lysed HLA-DR+ KC pulsed with M. leprae antigens. KC were only recognized after induction of HLA-DR expression by IFN-gamma, in an antigen-specific and HLA class II restricted manner. All T-cell clones tested also showed significant proliferation and IFN-gamma production in response to M. leprae antigens presented by HLA-DR+ KC, arguing against a KC dependent anergizing effect on T cells. Thus, HLA class II+ KC can function as proper APC for HLA class II restricted CD4+ Th 1-like cells. It seems therefore possible that antigen presentation by KC contributes to the local cell-mediated immune responses in DTH lesions.

Dendritic cells and cutaneous immune responses to chemical allergens

This article reviews the role of epidermal Langerhans cells (LC) in the development of cutaneous immune responses to chemical allergens. Following topical exposure to sensitizing chemicals, LC, many of which bear allergen, are induced to migrate from the skin, via the afferent lymphatics, to the draining lymph nodes. The phenotypic and functional changes to which LC are subject during this process and their development into active immunostimulatory cells closely resembling lymphoid dendritic cells is discussed. The migration and maturation of LC following skin sensitization is of critical importance to the effective presentation of chemical allergens to T lymphocytes and the induction of allergic responses. Evidence is reviewed which suggests that these events are initiated and regulated by epidermal cytokines. The conclusion drawn is that an early event during the induction of skin sensitization is the production by keratinocytes of cytokines which stimulate the migration of LC from the skin and which also result in the functional maturation of LC into potent antigen-presenting cells.

Cytokine expression by epidermal cell subpopulations

Epidermal cells (EC) are a rich source of cytokines that can regulate the function of cells in skin and in other tissues. To organize the array of data pertaining to cytokine expression by EC subpopulations, we have tabulated such data according to cell source, state of cell activation, and type of assay employed. This information forms a background for our own studies, in which reverse transcriptase-polymerase chain reaction (RT-PCR) was used to show that Langerhans cells (LC) are the principal source of mRNA for interleukin 1 beta and macrophage inflammatory protein-1 alpha (MIP-1 alpha) among unstimulated mouse EC.

Distribution of interleukin 1 receptor antagonist protein (IRAP), interleukin 1 receptor, and interleukin 1 alpha in normal and psoriatic skin. Decreased expression of IRAP in psoriatic lesional epidermis

The distribution of interleukin 1 alpha (IL-1 alpha), type 1 interleukin 1 receptor (IL-1R), and the interleukin 1 receptor antagonist protein (IRAP), was investigated in biopsies of normal skin, and in uninvolved and lesional skin of patients with psoriasis, using specific monoclonal antibodies. We report the novel finding that IRAP is distributed throughout the living layers of the epidermis in normal skin, and is also associated with sebaceous glands and eccrine sweat glands. Our finding that the inhibitor protein IRAP is present in areas where the pro-inflammatory cytokine IL-1 alpha is distributed provides strong evidence in favour of a cytokine regulatory system in normal skin. We further document for the first time that IL-1R in normal skin is localized to the living layers of the epidermis, sebaceous and eccrine glands, as well as to a prominent network of dermal dendritic cells, and upper dermal blood vessels. There was a consistent reduction in the level of IRAP expression in lesional compared with uninvolved skin in biopsies from six out of seven psoriasis patients. Decreased IRAP expression in lesions of psoriasis indicates that alterations in the level of this inhibitor protein may be important in the pathogenesis of inflammatory skin conditions.

Transthyretin is an inhibitor of monocyte and endothelial cell interleukin-1 production

Human serum was found to contain an inhibitor of constitutive interleukin-1 (IL-1) production by human umbilical vein endothelial cells (ECs). Purification of the serum activity by anion exchange chromatography, molecular sieve HPLC, and hydroxyl apatite chromatography yielded material 82% pure with a molecular weight of 17 kDa by SDS-PAGE. Amino acid sequencing revealed the purified inhibitor to be transthyretin (TTR), a liver-derived protein. There was a 42.6% reduction in the production of spontaneous IL-1 activity in EC supernatants after coculture with 10 micrograms/ml TTR. TTR was subsequently found by ELISA to inhibit LPS-stimulated IL-1 production by cells of the human monocytic leukemia line THP-1 by 47.1 +/- 9.4%, whereas a less striking but still significant inhibition of monocyte-derived IL-1 beta production was also observed. Inhibition of IL-1 secretion correlated with increased IL-1 mRNA synthesis in both THP-1 cells and monocytes. Furthermore, TTR was associated with increased intracellular concentrations of IL-1 beta. These data suggest that TTR functions by inhibiting processing of newly synthesized peptide for secretion. This novel inhibitory effect of TTR on the production of IL-1 activity suggests a previously unrecognized endogenous antiinflammatory mediator.