No impairment of monocyte-derived Langerhans cell phenotype or function in early-onset psoriasis

Background

Migration of epidermal Langerhans cells (LCs) in response to the cytokines interleukin (IL)-1β and tumour necrosis factor (TNF)-α is impaired in uninvolved skin of patients with early-onset psoriasis.

Aim

To investigate whether this impairment is a reflection of a systemic defect in dendritic cells (DCs), using an established model of monocyte-derived LC-like cells (mLCs).

Methods

CD14+ monocytes isolated from both patients with psoriasis and healthy control volunteers were cultured in a cytokine cocktail for 5 days to promote their differentiation into mLCs, then stimulated for 24 h with TNF-α, IL-1β (both 100 ng/mL) or medium alone. Cellular surface protein expression was quantified by flow cytometry, and the ability of cells to migrate to media supplemented with C-C motif ligand (CCL)19 was assessed using a Transwell migration assay. The cytokine and chemokine content of supernatants was analysed by cytokine array.

Results

CD14+ cells acquired an LC-like phenotype with high expression of CD1a and major histocompatibility complex (MHC) class II. There were no differences in the expression of activation markers or in the secretion of cytokines by mLCs isolated from patients with psoriasis and those isolated from healthy controls. Moreover, mLCs isolated from both groups displayed comparable ability to migrate in vitro.

Conclusions

These data suggest that the failure of LCs to migrate in response to stimulation in patients with psoriasis is not attributable to a systemic defect in DC function, but is rather a reflection of local changes in the epidermal microenvironment.

Proteomic analysis of suction blister fluid isolated from human skin

The regulation of cutaneous immune responses in health and disease is mediated locally by proteins such as cytokines and chemokines. We used a novel approach involving proteomic profiling of fluid drawn from suction blisters to compare and contrast protein expression in normal skin with that in nonlesional skin from a patient with plaque psoriasis. We also examined the impact of exogenous interleukin-1beta, a proinflammatory cytokine, on protein expression in these tissues. Described here are the results of proteomic profiling of 670 proteins from blister fluid, and the identification by differential expression of nine proteins between one volunteer with psoriasis and one normal volunteer. Although the apparent disease association of these nine proteins will require validation using additional volunteers, the identification of candidate protein biomarkers through proteomic analyses of blister fluid represents a promising approach for monitoring the disease activity and efficacy of therapeutic intervention in human skin diseases.

Cytokines and Langerhans cell mobilisation in mouse and man

A critical event during the development of cutaneous immune responses, including those provoked by contact allergens, is the mobilisation of epidermal Langerhans cells (LC). These cells act as sentinels of the immune system in the skin, responding to a variety of local insults with migration and delivery of potentially foreign signals to draining lymph nodes. Experimental studies have revealed that the regulation of mobilisation and migration of LC display striking similarities in man and mouse. In both species it has been found that the successful induction of migration requires that LC receive (at least) 2 independent cytokine signals; provided by tumour necrosis factor-alpha (TNF-alpha) and interleukin 1beta. In addition, a similar heterogeneity in man and mouse is apparent with regard to the fraction of LC responding rapidly to mobilisation signals, with the same proportion of cells (20%-30%) being stimulated to migrate in each case. Other similarities exist between mice and humans with respect to LC function, including an age-related decrement in both LC frequency and responsiveness to TNF-alpha. Collectively these studies demonstrate that the mouse provides a valuable experimental surrogate for the human skin immune system, particularly with respect to LC biology, and suggest that it is possible to perform extrapolations between species with some confidence.

Dendritic cells and skin sensitisation hazard assessment

Allergic contact dermatitis is an important occupational and environmental health disease. There is a need, therefore, to identify skin sensitisation hazard, and to assess accurately likely risks to human health. During the past 15 years very significant advances have been made in our understanding of the cellular and molecular mechanisms that serve to initiate and regulate cutaneous immune responses, including the acquisition of skin sensitisation. This has facilitated parallel advances in the identification and characterisation of skin sensitising chemicals and the development of more robust approaches to risk assessment. It is relevant to consider whether advances in immunobiology provide opportunities also for the design of alternative approaches to the toxicological evaluation of skin sensitisation, including the development of in vitro methods. Here we review the potential use of strategies based on analysis of responses induced in Langerhans cells and dendritic cells; professional antigen processing and presenting cells that are known to play pivotal roles during the induction phase of adaptive immune responses.

IL-1beta-induced Langerhans' cell migration and TNF-alpha production in human skin: regulation by lactoferrin

In mice, the roles of cytokines in the initiation of epidermal Langerhans' cell (LC) migration are well documented; however, the mechanism of this response in humans is less well defined. The purpose of the present investigation was to examine the contribution of interleukin (IL)-1beta to human epidermal LC migration and to define further the mechanisms of this response. We demonstrate here that homologous recombinant IL-1beta administered intradermally to healthy human volunteers provides a stimulus for LC migration, with significant (P < 0.01) reductions in LC densities being observed at both 2 h and 4 h following treatment. At the later time-point of 4 h, injection of IL-1beta was also accompanied by activation of those LC remaining in the epidermis. Analysis of fluid aspirated from suction blisters formed at injection sites revealed significant (P < 0.01) tumour necrosis factor (TNF)-alpha production (2.99 +/- 1.18 pg TNF-alpha/mg protein; mean +/- s.d. of n = 10) in response to IL-1beta treatment compared with saline control injections (0.90 +/- 1.05 pg TNF-alpha/mg protein). Prior topical application of human recombinant lactoferrin (LF), an iron-binding protein found in exocrine secretions and skin, inhibited IL-1beta-mediated LC migration and also compromised the production of TNF-alpha protein as measured in suction blister fluids derived from each of the treatment sites. Taken together, these data demonstrate that IL-1beta is associated with both the stimulation of human epidermal LC migration and local TNF-alpha production. Topical treatment with LF compromises both these responses. These data suggest that topical LF may potentially represent a novel therapeutic in the treatment of skin inflammation where TNF-alpha is an important mediator.

Lactoferrin: influences on Langerhans cells, epidermal cytokines, and cutaneous inflammation

It has been suggested previously that, in addition to other biological roles, lactoferrin (LF) may display antiinflammatory properties secondary to the regulation of cytokine expression. To explore this concept further, we have here examined in human volunteers the influence of recombinant homologous LF on the migration of epidermal Langerhans cells (LC), a process that is known to be dependent upon the local availability of certain proinflammatory cytokines including tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta). In common with previous studies in mice, it was found that topical administration of LF prior to exposure at the same site to the contact sensitizer diphenylcyclopropenone resulted in a significant reduction of allergen-induced LC migration from the epidermis (measured as a function of the frequency of CD1a+ or HLA-DR+ LC found in epidermal sheets prepared from punch biopsies of the treated skin sites). However, under the same conditions of exposure, LF was unable to influence migration of LC induced by the intradermal administration of TNF-alpha data consistent with the hypothesis that one action of LF in the skin is to regulate the local production of this cytokine. Further support for this hypothesis was derived from experiments conducted with IL-1beta. This cytokine is also able to induce the mobilization of LC following intradermal injection, although in this case, migration is known to be dependent upon the de novo production of TNF-alpha. We observed that prior exposure to LF resulted in a substantial inhibition of IL-1beta-induced LC migration, data again consistent with the regulation of TNF-alpha production by LF. Collectively, these results support the view that LF is able to influence cutaneous immune and inflammatory processes secondary to regulation of the production of TNF-alpha and possibly other cytokines.

Tumour necrosis factor-alpha-induced migration of human Langerhans cells: the influence of ageing

BACKGROUND

Langerhans cells (LCs) play essential roles in the initiation and regulation of cutaneous immune responses mediated through their successful migration from the epidermis to draining lymph nodes while carrying antigen. Tumour necrosis factor (TNF)-alpha, a keratinocyte-derived cytokine, has recently been shown to play an important role in the mobilization of LCs from human epidermis. Although it is known that with age the immune system changes, the influence of increasing age on the function of human LCs has not been defined clearly.

OBJECTIVES

To examine the influence of age on the ability of TNF-alpha to induce LC migration.

METHODS

Ten elderly (six men, four women; mean age 76 years, range 72-79) and 10 young (six men, four women; mean age 23 years, range 18-35) volunteers received intradermal injections of 200 U of human recombinant TNF-alpha diluted in sterile saline, and control injections of sterile saline alone, at each of two paired sites identified on photoprotected buttock skin. Two hours later, paired injection sites were excised by punch biopsy. One set of paired biopsies was processed for assessment of the frequency and morphology of epidermal LCs, following preparation of epidermal sheets and immunofluorescence staining for the LC marker CD1a. The remaining paired biopsies were processed in formalin and the inflammatory response to TNF-alpha was assessed by standard histological examination.

RESULTS

Mean +/- SEM baseline values for LC frequency within epidermal sheets were significantly different between young (1156.3 +/- 38.5 cells mm(-2)) and elderly subjects (835.7 +/- 48.2 cells mm(-2); P < 0.01). Intradermal injections of 200 U of TNF-alpha caused a significant reduction in the frequency of LCs in both elderly and young subjects (P < 0.01). However, the extent of TNF-alpha-induced LC migration was substantially different between the two groups, with a mean 9% reduction in LC frequency in elderly volunteers compared with a mean 23% decrease in young subjects. Exposure to TNF-alpha was associated with a perivascular polymorphonuclear infiltrate at 2 h in all young subjects; in contrast, only 50% of the elderly individuals showed evidence of such a response.

CONCLUSIONS

There are significant differences between young and old skin with respect to both resting LC numbers and their response to TNF-alpha. These age-related changes in LC frequency and function may contribute to the altered cutaneous immune function observed in the elderly.

Alternative approaches to the identification and characterization of chemical allergens

Chemical allergy can take a variety of forms, those of greatest importance in an occupational setting being skin sensitization resulting in allergic contact dermatitis and sensitization of the respiratory tract associated with asthma and other symptoms. In both cases there is a need for predictive test methods that allow the accurate identification of sensitizing chemicals. Well characterized methods are available for skin sensitization testing, and although to date no tests for respiratory sensitization have been formally validated, progress has been made in defining suitable animal models. In recent years there have been significant advances in our understanding of the cellular and molecular mechanisms through which allergic sensitization to chemicals is induced and regulated. Such progress provides us now with new opportunities to consider alternative approaches to sensitization testing, including the design of in vitro test methods. The greatest investment has been in exploring novel methods for the identification of contact sensitizers and it is upon this aspect of chemical allergy that this article is focused. Described here are some of the general requirements of in vitro test methods for skin sensitization, and progress that has been made in developing suitable approaches with particular emphasis on the utility of dendritic cell culture systems.

Exogenous topical lactoferrin inhibits allergen-induced Langerhans cell migration and cutaneous inflammation in humans

BACKGROUND

Lactoferrin (LF), an iron-binding protein found in exocrine secretions, is known to possess antibacterial properties. It has recently been proposed that LF may also influence inflammatory reactions.

OBJECTIVES

To characterize in humans the ability of recombinant homologous LF to inhibit the induced migration of epidermal Langerhans cells (LCs) from the skin, a process known to be dependent upon the proinflammatory cytokines tumour necrosis factor (TNF)-alpha and interleukin 1beta and to influence cutaneous inflammatory reactions.

METHODS

We investigated the anti-inflammatory properties of LF in human volunteers.

RESULTS

Topical exposure to LF 2 h prior to sensitization caused a significant reduction in contact allergen (diphenylcyclopropenone, DPC)-induced LC migration from the epidermis as judged by the altered frequency of cells expressing either HLA-DR or CD1a determinants. That this reduction was secondary to an inhibition of TNF-alpha production was indicated by the fact that LF failed to influence LC migration induced by intradermal injection of this cytokine. In approximately 50% of those volunteers who displayed local inflammation in response to DPC, LF was found to cause a discernible reduction in the clinical severity of the reaction, associated with reduced infiltration of inflammatory cells.

CONCLUSIONS

These data demonstrate that LF is able to influence cutaneous immune and inflammatory responses, possibly because of an impaired production of local proinflammatory cytokines.

Functional caspase-1 is required for Langerhans cell migration and optimal contact sensitization in mice

Langerhans cell (LC) migration from epidermis to draining lymph node is a critical first step in cutaneous immune responses. Both TNF-alpha and IL-1 beta are important signals governing this process, but the potential regulatory role of IL-1 alpha processing by caspase-1 is unknown. In wild-type (WT) mice, application of the contact allergens 2,4-dinitrofluorobenzine and oxazolone lead to a marked reduction in epidermal LC numbers, but in caspase-1-deficient mice this reduction was not observed. Moreover, although intradermal injection of TNF-alpha (50 ng) induced epidermal LC migration in WT mice, this cytokine failed to induce LC migration in caspase-1-deficient mice. Intradermal IL-1 beta (50 ng) caused a similar reduction in epidermal LC numbers in both WT and caspase-1-deficient mice, indicating that, given an appropriate signal, caspase-1-deficient epidermal LC are capable of migration. Contact hypersensitivity to both 2,4-dinitrofluorobenzine and oxazolone was inhibited in caspase-1-deficient mice, indicating a functional consequence of the LC migration defect. In organ culture the caspase-1 inhibitor Ac-YVAD-cmk, but not control peptide, potently inhibited the epidermal LC migration that occurs in this system, and reduced spontaneous migration of LC was observed in skin derived from caspase-1-deficient mice. Moreover, Ac-YVAD-cmk applied to BALB/c mouse skin before application of contact sensitizers inhibited LC migration and contact hypersensitivity in vivo. Taken together, these data indicate that caspase-1 may play a central role in the regulation of LC migration and suggest that the activity of this enzyme is amenable to control by specific inhibitors both in vivo and in vitro.

Interleukin (IL)-18 induces Langerhans cell migration by a tumour necrosis factor-alpha- and IL-1beta-dependent mechanism

Following skin sensitization a proportion of epidermal Langerhans cells (LC) are stimulated to leave the skin and to migrate, via afferent lymphatics, to draining lymph nodes where they accumulate as immunostimulatory dendritic cells (DC). It has been demonstrated previously that tumour necrosis factor-alpha (TNF-alpha), an inducible product of epidermal keratinocytes, and interleukin (IL)-1beta, produced exclusively by LC in murine epidermis, provide important signals for the initiation of this response. Recently, it has been demonstrated that IL-18, a cytokine produced by both LC and keratinocytes within the epidermis, may also participate in immune responses induced following skin sensitization. In the present investigations, the ability of IL-18 to contribute to the regulation of LC migration and the accumulation of DC in draining lymph nodes has been examined. It was found that, like IL-1beta, IL-18 administered intradermally to mice resulted in a significant reduction in epidermal major histocompatibility complex (MHC) class II+ LC densities and a marked increase in lymph node DC numbers. Using neutralizing anti-TNF-alpha and blocking anti-type I IL-1 receptor (IL-1RI) antibodies, it was shown also that the induction by IL-18 of both LC mobilization and DC accumulation in regional lymph nodes was dependent upon availability of TNF-alpha and the integrity of IL-1RI signalling. Furthermore, using IL-1beta converting enzyme (caspase-1) knockout mice, IL-18-induced LC migration was found to have a mandatory requirement for active IL-1beta. Importantly, not only was IL-18 able to contribute to the regulation of LC migration, it was found to be essential for the manifestation of these processes in response to topical sensitization with the contact allergen oxazolone.

Allergen-induced changes in interleukin 1 beta (IL-1 beta) mRNA expression by human blood-derived dendritic cells: inter-individual differences and relevance for sensitization testing

The development of in vitro methods for the identification of skin sensitizers based upon analysis of Langerhans cell (LC) function has been constrained by the fact that these cells represent only a minority population in the skin that, once isolated, alter their phenotype spontaneously and rapidly. Methods have been developed recently that allow the expansion in culture using appropriate cytokine conditions of LC-like dendritic cells (DCs) from certain tissues, including human peripheral blood. It has been demonstrated that culture of human blood-derived LC-like cells with selected potent contact allergens such as 2,4-dinitrofluorobenzene (DNFB) stimulates selective phenotypic changes, including the up-regulation of interleukin 1 beta (IL-1 beta) mRNA expression, under conditions where skin irritants are without effect. However, in our own previous investigations, we have observed that there appear to be differences between blood donors with respect to the responsiveness of DCs to DNFB-induced changes in IL-1 beta expression, differences that could compromise the utility of this approach as a screening method for contact allergens. We have therefore investigated donor variability in DC responsiveness to a panel of known human contact allergens (DNFB; paraphenylene diamine, PPD; methyl- chloroisothiazolinone/methylisothiazolinone, CMIT), to the skin irritant benzalkonium chloride and to the mitogen phorbol myristate acetate (PMA). Dendritic cells derived from all donors expressed IL-1 beta mRNA constitutively. Treatment of DCs isolated from donors with a responder phenotype to DNFB with PPD or CMIT resulted also in up-regulation of IL-1 beta mRNA expression, although such changes were always comparatively modest, generally resulting in a twofold induction compared with vehicle-treated controls. Dendritic cells derived from donors with a non-responder phenotype to DNFB failed also to respond to these additional contact allergens under conditions where the mitogen PMA caused similar increases in IL-1 beta expression to those observed for allergen-responsive donors. Benzalkonium chloride failed to provoke changes in the expression of this cytokine in any donor examined, irrespective of their responder phenotype. The temporal stability of the responder/non-responder DC phenotype was confirmed, with stable phenotypes with respect to DNFB-induced changes in IL-1 beta mRNA expression observed over a period of some 18 months. Fifty per cent (6/12) of donors tested over this period displayed a responder phenotype. These data demonstrate that chemical allergens do stimulate consistent changes in IL-1 beta mRNA expression in the proportion of donors who have a responsive phenotype, and that such responses are apparently selective for allergen using the relatively narrow range of materials assessed to date. However, the modest response to very strong contact allergens, coupled with the difficulties of responder/non-responder phenotypes, means that in its present form this approach does not lend itself to the routine assessment of skin sensitizing activity.

Investigation of induced changes in interleukin 1beta mRNA expression by cultured human dendritic cells as an in vitro approach to skin sensitization testing

It has been reported previously that in vitro treatment of human blood derived dendritic cells (DC) with contact allergens provokes the elevated expression of mRNA for interleukin (IL) 1beta, under conditions where similar treatment of cells with the non-sensitizing skin irritant sodium lauryl sulfate (SLS) did not alter IL-1beta mRNA levels (Reutter et al., 1997). The purpose of the present investigation was to evaluate further this phenomenon and to explore the potential utility of this approach for the purpose of skin sensitization testing. Human peripheral blood progenitor cells prepared from healthy adult volunteers were cultured in the presence of IL-4 and granulocyte/macrophage colony stimulating factor. After 5 days of culture, the majority of cells had a Langerhans cell-like phenotype, with characteristic dendritic morphology and cell surface expression of CD83, major histocompatibility complex class II and CD1a determinants. These blood-derived DC were cultured in the presence of the contact allergen 2,4-dinitrofluorobenzene (DNFB), SLS or vehicle alone and mRNA expression for IL-1beta, IL-6 and IL-18 was analysed by semiquantitative reverse transcriptase polymerase chain reaction. Constitutive expression of all three cytokines was observed for DC isolated from all donors examined. Exposure to DNFB resulted in upregulation of IL-1beta mRNA (two- to threefold) in cells derived from three out of eight donors whereas IL-6 and IL-18 were largely unaffected by allergen exposure. In contrast, SLS treatment did not induce IL-1beta mRNA expression in any of the donors investigated. Analysis of cytokine mRNA expression using the protocol described by Reutter et al. (1997), did not increase the sensitivity of measurement of induced cytokine expression. Although selected upregulation of IL-1beta by blood derived DC has been confirmed, a wider range of contact allergens and irritants need to be assessed before this approach could be considered for hazard identification.

Langerhans cell migration

Epidermal Langerhans cells (LC) play pivotal roles in the induction of cutaneous immune responses. Encounter with antigen in the skin, or other stimuli, cause the mobilization of LC and their migration, via afferent lymphatics, to draining lymph nodes where they localize within the paracortex. During their movement from the skin LC acquire the characteristics of immunostimulatory dendritic cells (DC) such that the antigen-bearing cells which accumulate in lymph nodes are able to provoke specific T-lymphocyte responses. Epidermal cytokines initiate and regulate LC migration (and maturation), of particular importance being interleukin-1beta and tumour necrosis factor-alpha. Collectively, these cytokines, together with relevant chemokine receptor-ligand interactions, effect the liberation of LC from the epidermis and their directed movement to, and localization within, peripheral lymph nodes. Described here are the phenotypic changes induced during the activation of LC and the mechanisms through which their migration is regulated.

Regulation of epidermal Langerhans cell migration by lactoferrin

Lactoferrin (LF) is a member of the transferrin family of iron-binding glycoproteins to which several anti-inflammatory functions have been ascribed. LF has been shown to down-regulate expression of the pro-inflammatory cytokine tumour necrosis factor-alpha (TNF-alpha), although the possibility has been raised that the activity of LF in this regard was indirect and secondary to its ability to bind to and inactivate the bacterial lipopolysaccharide (LPS) used to induce cytokine production. However, the identification of putative membrane receptors for LF raises the possibility that the interaction of LF with its receptor may be one important route through which this protein exerts anti-inflammatory activity. In the present investigations the biological properties of LF have been examined in a model of cutaneous immune function where the allergen-induced migration of epidermal Langerhans cells (LC) from the skin and their subsequent accumulation as dendritic cells (DC) in skin-draining lymph nodes are known to be dependent upon the de novo synthesis of TNF-alpha, but independent of exogenous LPS. Consistent with the protein having direct anti-inflammatory properties, it was found that the intradermal injection of recombinant murine LF (either iron-saturated or iron-depleted LF) inhibited significantly allergen (oxazolone) -induced LC migration and DC accumulation. That these inhibitory effects were secondary to the inhibition of local TNF-alpha synthesis was suggested by the findings that first, LF was unable to inhibit LC migration induced by intradermal injection of TNF-alpha itself, and second, that migration stimulated by local administration of another epidermal cytokine, interleukin 1beta, which is also dependent upon TNF-alpha production, was impaired significantly by prior treatment with LF. Finally, immunohistochemical analyses demonstrated the presence of LF in skin, associated primarily with keratinocytes. Collectively these data support the possession by LF of direct immunomodulatory and/or anti-inflammatory activity, probably associated in this case with inhibition of cytokine production. Furthermore, the results suggest that as a constituent of normal skin, LF may play a role in homeostatic regulation of cutaneous immune function.

Cytokines and chemokines in the initiation and regulation of epidermal Langerhans cell mobilization

Langerhans cells (LC) are members of the wider family of dendritic cells. LC reside in the epidermis where they serve as sentinels of the immune system, their responsibilities being to sample the external environment for changes and challenges and to deliver information (antigen) to responsive T lymphocytes within skin draining lymph nodes. The ability of LC to migrate from the epidermis to regional lymph nodes is therefore of pivotal importance to the induction of cutaneous immune responses. The journey that LC have to make from the skin has a number of requirements. Initially it is necessary that LC disassociate themselves from surrounding keratinocytes and are liberated from other influences that encourage their retention in the epidermis. Subsequently, migrating LC must successfully traverse the basement membrane of the dermal-epidermal junction and make their way, via afferent lymphatics, to draining lymph nodes. Effective entry into lymph nodes is necessary, as is correct positioning of cells within the paracortex. There is increasing evidence that both cytokines and chemokines, and their interaction with appropriate receptors expressed by LC, orchestrate the mobilization and movement of these cells. We here consider the parts played by these molecules, and how collectively they induce and direct LC migration.

The novel NK1 receptor antagonist MK-0869 (L-754,030) and its water soluble phosphoryl prodrug, L-758,298, inhibit acute and delayed cisplatin-induced emesis in ferrets

The anti-emetic profile of the novel brain penetrant tachykinin NK1 receptor antagonist MK-0869 (L-754,030) 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenylethoxy)-3-(S)-(4-fluor o)phenyl-4-(3-oxo-1,2,4-triazol-5-yl)methylmorpholine and its water soluble prodrug, L-758,298, has been examined against emesis induced by cisplatin in ferrets. In a 4 h observation period, MK-0869 and L-758,298 (3 mg/kg i.v. or p.o.) inhibited the emetic response to cisplatin (10 mg/kg i.v.). The anti-emetic protection afforded by MK-0869 (0.1 mg/kg i.v.) was enhanced by combined treatment with either dexamethasone (20 mg/kg i.v.) or the 5-HT3 receptor antagonist ondansetron (0.1 mg/kg i.v.). In a model of acute and delayed emesis, ferrets were dosed with cisplatin (5 mg/kg i.p.) and the retching and vomiting response recorded for 72 h. Pretreatment with MK-0869 (4-16 mg/kg p.o.) dose-dependently inhibited the emetic response to cisplatin. Once daily treatment with MK-0869 (2 and 4 mg/kg p.o.) completely prevented retching and vomiting in all ferrets tested. Further when daily dosing began at 24 h after cisplatin injection, when the acute phase of emesis had already become established, MK-0869 (4 mg/kg p.o. at 24 and 48 h after cisplatin) prevented retching and vomiting in three out of four ferrets. These data show that MK-0869 and its prodrug, L-758,298, have good activity against cisplatin-induced emesis in ferrets and provided a basis for the clinical testing of these agents for the treatment of emesis associated with cancer chemotherapy.

Possible antimigraine mechanisms of action of the 5HT1F receptor agonist LY334370

This study investigated whether the selective 5HT1F receptor agonist LY334370 has other possible antimigraine mechanisms in addition to the proposed inhibition of dural plasma extravasation. LY334370 (up to 10(-5) M) had no vasoconstrictor effects on human cerebral arteries in vitro. It had no effect (up to 10 mg kg-1, i.v.) on neurogenic vasodilation of dural blood vessels produced by electrical stimulation of the dura mater in anesthetized rats. Nor had it any effect (at 3 mg kg-1, i.v.) on the hyperalgesia produced by injection of carrageenan into the paw of conscious rats or on nociceptive reflex responses in the spinalized, decerebrate rabbit (up to 3 mg kg-1, i.v.), indicating that it has no general analgesic properties. However, it significantly inhibited activation of second-order neurons in the trigeminal nucleus caudalis produced by electrical stimulation of the dura mater in anesthetised rats at 3 mg kg-1, i.v. These results provide evidence to suggest that LY334370 has a central mechanism of action in blocking the transmission of nociceptive impulses within the trigeminal nucleus caudalis and that this may represent a mechanism through which it has its antimigraine effect.

Tumour necrosis factor-alpha induces Langerhans cell migration in humans

The role of tumour necrosis factor (TNF)-alpha in the mobilization and migration of human epidermal Langerhans cells (LC) has been investigated. Intradermal injection of normal human volunteers with homologous recombinant TNF-alpha was found to cause a dose-dependent reduction in the frequency of LC within epidermal sheets 2 h later. Equivalent results were obtained when epidermal LC were identified on the basis of either CD1a or HLA-DR expression. At the dose of TNF-alpha used routinely (500 U), treatment resulted in an average reduction in LC density of approximately 24%. Treatment with TNF-alpha was associated with a perivascular polymorphonuclear infiltration at 2 h, but the epidermis appeared normal with neither fibrinoid necrosis nor vasculitis, and LC morphology was not affected significantly. These results demonstrate that TNF-alpha provides an important signal for LC migration in humans and is likely therefore to play a crucial part in the induction of cutaneous immune responses.

Induction by tumour necrosis factor alpha of dose-related changes in Langerhans cell frequency in mice

It has been demonstrated previously that tumour necrosis factor alpha (TNF-alpha) provides an important signal for the migration of epidermal Langerhans cells (LC) from the skin. Intradermal administration to mice of homologous recombinant TNF-alpha induces both a rapid reduction in the frequency of LC local to the site of exposure and, somewhat later, an accumulation of dendritic cells in draining lymph nodes. It has been proposed recently, however, that the influence of TNF-alpha on LC function may be dose-dependent in nature with lower concentrations inducing migration, but higher concentrations immobilizing LC in the epidermis. To investigate this proposal we examined the kinetics and dose-response relationships of TNF-alpha-induced LC migration in mice. At all concentrations tested (50, 150 or 300 ng/ear), intradermal exposure to TNF-alpha caused within 30 min a significant reduction in the frequency of MHC class II (Ia)+ LC within epidermal sheets. With the lower concentrations of TNF-alpha this effect was still apparent when LC were enumerated in the epidermis up to 4 h following cytokine treatment. In contrast, however, exposure of mice to 300 ng of TNF-alpha was consistently associated with a considerably less marked, and statistically insignificant, reduction in LC frequency by 4 h. These data indicate that at all concentrations of the cytokine examined here, TNF-alpha was able to stimulate a rapid (within 30 min) reduction in epidermal LC numbers, but that the rapidity with which the epidermis was repopulated following the initiation of LC migration was influenced by the concentration of TNF-alpha administered. It is suggested that TNF-alpha may influence not only the tempo of LC migration, but also the kinetics of epidermal repopulation.

Inhibition by dexamethasone of Langerhans cell migration: influence of epidermal cytokine signals

The influence of dexamethasone (DEX), a synthetic glucocorticoid, on the induction in mice of Langerhans cell (LC) migration has been investigated. Systemic treatment of mice with DEX was found to inhibit significantly the ability of a topically applied contact allergen (oxazolone) to induce the migration of LC from the epidermis and their subsequent accumulation as dendritic cells (DC) in draining lymph nodes. The stimulation of LC migration during skin sensitization is dependent upon signals provided by the epidermal cytokines tumour necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta). It was found that treatment with DEX was unable to inhibit either LC migration or DC accumulation induced by the intradermal injection of TNF-alpha. In contrast, LC migration provoked by similar exposure of mice to IL-1beta (the action of which is dependent upon the de novo synthesis of TNF-alpha) was inhibited by DEX as was the arrival of DC in draining lymph nodes induced by this cytokine. Taken together, the data reported here indicate that DEX is able to inhibit very markedly the stimulation of LC migration during skin sensitization and it is proposed that such inhibition may represent an important aspect of the immunosuppressive properties of glucocorticoids and of their proven utility in the treatment of cutaneous inflammatory disorders. The results also indicate that DEX does not inhibit LC migration secondary to direct effects on cell motility. The proposal is that impaired LC migration results from the regulation by DEX of the de novo synthesis and/or release of TNF-alpha, an inducible epidermal cytokine that provides one important signal for LC to traffic from the skin.

Langerhans cells and chemical allergy

Epidermal Langerhans cells (LCs) play a pivotal role in the induction of cutaneous immune responses, including those provoked by chemical allergens. The delivery by LCs of allergen to draining lymph nodes requires cell migration from the skin, a process that is dependent upon the availability of epidermal cytokines -particularly TNF-alpha and IL-1beta. Here we consider the ways in which these cytokines interact with LCs to both induce and regulate their mobilization in response to skin sensitization. In addition, the effects of these cytokines on both the selectivity of LC migration from the skin and protection of LCs from cell death are considered. Finally, the possible counter-regulatory activity of other cutaneous cytokines and the influence of LCs on the development of selective T lymphocyte responses are explored.

Characteristics and regulation of the expression on interleukin 1 receptors by murine Langerhans cells and keratinocytes

There is increasing evidence that interleukin 1beta (IL-1beta), a product in murine epidermis of Langerhans cells (LC) exclusively, contributes to the initiation and regulation of LC migration in response to skin sensitization. The hypothesis is that IL-1beta induces the production by keratinocytes of tumour necrosis factor alpha (TNF-alpha) which acts in a paracrine fashion on LC to provide one signal for migration. In addition, it is believed that IL-1beta acts in an autocrine fashion on LC to provide a second, TNF-alpha-independent, signal for the initiation of this response. The viability of this hypothesis is dependent upon the availability of appropriate membrane receptors. We describe therefore experiments designed to investigate the IL-1 receptor (IL-1R) status of keratinocytes, LC and lymph node dendritic cells (DC). Flow cytometric analyses of epidermal cell suspensions revealed at least 60% of LC positive for the type I IL-1R (IL-1RI). In contrast, only a small proportion of keratinocytes displayed surface IL-1RI, although high intracellular expression of this receptor could be detected either by flow cytometric analysis of cells permeabilized with saponin or by immunofluorescence microscopy. Expression of the type II IL-1R (IL-1RII) was detected at relatively low levels on both LC and keratinocytes. Interestingly, DC isolated from the lymph nodes of sensitized mice displayed upregulated expression of IL-1RI and lower levels of IL-1RII compared to LC. The conclusion drawn is that the IL-1R phenotype of LC and keratinocytes under resting conditions is consistent with the proposed contribution of IL-1beta to LC migration. Furthermore, the regulation of IL-1R expression by epidermal cells and DC will undoubtedly influence the development of cutaneous immune responses.

Alpha 6 integrins are required for Langerhans cell migration from the epidermis

Topical exposure of mice to chemical allergens results in the migration of epidermal Langerhans cells (LCs) from the skin and their accumulation as immunostimulatory dendritic cells (DCs) in draining lymph nodes. Epidermal cell-derived cytokines have been implicated in the maturation and migration of LCs, but the adhesion molecules that regulate LC migration have not been studied. We hypothesized that integrin-mediated interactions with extracellular matrix components of the skin and lymph node may regulate LC/DC migration. We found that alpha 6 integrins and alpha 4 integrins were differentially expressed by epidermal LCs and lymph node DCs. A majority of LCs (70%) expressed the alpha 6 integrin subunit, whereas DCs did not express alpha 6 integrins. In contrast, the alpha 4 integrin subunit was expressed at high levels on DCs but at much lower levels on LCs. The anti-alpha 6 integrin antibody, GoH3, which blocks binding to laminin, completely prevented the spontaneous migration of LCs from skin explants in vitro and the rapid migration of LCs from mouse ear skin induced after intradermal administration of TNF-alpha in vivo. GoH3 also reduced the accumulation of DCs in draining lymph nodes by a maximum of 70% after topical administration of the chemical allergen oxazolone. LCs remaining in the epidermis in the presence of GoH3 adopted a rounded morphology, rather than the interdigitating appearance typical of LCs in naive skin, suggesting that the cells had detached from neighboring keratinocytes and withdrawn cellular processes in preparation for migration, but were unable to leave the epidermis. The anti-alpha 4 integrin antibody PS/2, which blocks binding to fibronectin, had no effect on LC migration from the epidermis either in vitro or in vivo, or on the accumulation of DCs in draining lymph nodes after oxazolone application. RGD-containing peptides were also without effect on LC migration from skin explants. These results identify an important role for alpha 6 integrins in the migration of LC from the epidermis to the draining lymph node by regulating access across the epidermal basement membrane. In contrast, alpha 4 integrins, or other integrin-dependent interactions with fibronectin that are mediated by the RGD recognition sequence, did not influence LC migration from the epidermis. In addition, alpha 4 integrins did not affect the accumulation of LCs as DCs in draining lymph nodes.

Langerhans cells require signals from both tumour necrosis factor-alpha and interleukin-1 beta for migration

The induction phase of contact sensitization is associated with the movement of epidermal Langerhans cells (LC) from the skin and their migration, via afferent lymphatics, to draining lymph nodes where they accumulate as immunostimulatory dendritic cells (DC). It has been demonstrated previously that tumour necrosis factor-alpha (TNF-alpha) provides an important signal for LC migration and that in the absence of this cytokine, movement of LC from the epidermis to regional lymph nodes is inhibited. Recent evidence indicates that interleukin-1 beta (IL-1 beta), a cytokine produced in murine epidermis exclusively by LC, may also play a role in LC migration. The purpose of the investigations described here was to clarify, using relevant neutralizing anti-cytokine antibodies, the contributions made by TNF-alpha and IL-1 beta to the migration of LC from the epidermis. It was found that like anti-TNF-alpha, anti-IL-1 beta administered systemically to mice (by intraperitoneal injection), prior to skin sensitization with the contact allergen oxazolone, resulted in a marked inhibition of DC accumulation in draining lymph nodes. It was shown also that anti-IL-1 beta inhibited TNF-alpha-induced LC migration and DC accumulation and that; in similar fashion, the stimulation of LC migration and DC accumulation induced by IL-1 beta was compromised by prior treatment with anti-TNF-alpha. Based upon these data it is proposed that the stimulation of LC migration in response to skin sensitization requires the receipt by LC of two independent signals, one provided by TNF-alpha and the other by IL-1 beta. Morphological analyses of LC in epidermal sheets prepared from animals exposed to these cytokines with or without prior systemic treatment with anti-cytokine antibody suggested that the changes induced in LC by TNF-alpha and IL-1 beta may include the altered expression of adhesion molecules and acquisition of the ability to interact with and pass through the basement membrane.

Interleukin 1 beta and the stimulation of Langerhans cell migration: comparisons with tumour necrosis factor alpha

Epidermal Langerhans cells (LC) and the cells into which they mature are believed to play a pivotal role in cutaneous immune function. The induction phase of contact sensitization is associated with the migration of LC from the skin and their accumulation as dendritic cells (DC) in lymph nodes draining the site of exposure. We have demonstrated previously that tumour necrosis factor alpha (TNF-alpha), an epidermal cytokine produced by keratinocytes, provides one signal for LC migration. We describe here experiments designed to evaluate the influence of interleukin 1 beta (IL-1 beta), a product exclusively of LC in murine epidermis, on LC migration, LC morphology and DC accumulation, and to compare the effects of this cytokine with those of TNF-alpha. Both cytokines induced a significant reduction in the frequency of epidermal LC and the arrival of DC in draining lymph nodes. Changes in both parameters were induced more rapidly following intradermal administration of TNF-alpha than were observed after treatment with IL-1 beta. However, the reduction in LC frequency was more persistent with IL-1 beta. Both cytokines caused the activation of LC, characterized by the acquisition of a more dendritic morphology and the increased expression of Ia molecules. These results demonstrate that IL-1 beta and TNF-alpha can each stimulate the migration of epidermal LC, but that the changes induced by these cytokines are not identical.

A re-appraisal of the skin-sensitizing activity of 2,4-dinitrothiocyanobenzene

A debate continues regarding the immunological properties of 2,4-dinitrothiocyanobenzene (DNTB). In some investigations this chemical was shown not to cause skin sensitization when applied topically but to induce instead hyporesponsiveness or immunological tolerance. In other studies DNTB was found to cause skin sensitization, but not tolerance. However, this chemical continues to be used to discriminate between the properties of skin sensitizing and non-sensitizing chemicals. This study demonstrates that topical exposure of mice to DNTB induces skin sensitization in mice and that this is associated with the accumulation of dendritic cells in draining lymph nodes and the stimulation of lymph node cell proliferation; the latter responses being of equivalent magnitude to those stimulated by 2,4-dinitrochlorobenzene (DNCB), a chemical known to cause contact sensitization. Moreover, exposure of mice to DNTB, as with exposure to DNCB, resulted in the development of a cytokine secretion pattern by draining lymph node cells (LNC) characteristic of contact allergens. Thus, DNTB and DNCB each induced the production by LNC of high levels of interferon-gamma, but little or no interleukin 4 or interleukin 10. Finally, DNTB was shown in the guinea pig maximization test to behave as an extreme skin sensitizer. These results confirm that DNTB should not be regarded as a universal tolerogen and that it possesses a significant potential to induce contact sensitization. The use of this chemical as a presumptive non-sensitizer and/or tolerogen for the evaluation of the selectivity of new predictive test methods for the identification of contact allergens is therefore considered to be inappropriate.

Adhesion molecule expression by epidermal Langerhans cells and lymph node dendritic cells: a comparison

The migration of epidermal Langerhans cells (LC) and their transport of antigen from the skin to draining lymph nodes are of considerable importance in the induction of cutaneous immune responses, including contact sensitization. While in transit to the lymph nodes, LC are subject to a number of phenotypic changes required for their movement from the skin and acquisition of the capacity for antigen presentation. Among these are alterations in the expression of adhesion molecules that regulate interactions with the surrounding tissue matrix and with T lymphocytes. In the study described here, we investigated, using a combination of immunocytochemistry and flow cytometry, the expression by LC, and the lymph node dendritic cells into which they mature, of the three adhesion molecules, E-cadherin, intercellular adhesion molecule-1 (ICAM-1) and the membrane glycoprotein CD44. The migration of LC was associated with a marked reduction in the expression of E-cadherin, but a parallel upregulation of ICAM-1. No change in the expression of CD44 was detectable. The significance of these changes and their relevance for the functional maturation of LC are discussed.

Influence of dibutyl phthalate on dermal sensitization to fluorescein isothiocyanate

What limited evidence there is indicates that the formulation in which a chemical allergen is encountered on the skin can have a marked impact upon the induction of cutaneous immune responses and the subsequent development of contact sensitization. The purpose of the present investigations was to examine further this phenomenon by analysis of the influence of dibutyl phthalate (DBP) on dermal sensitization to fluorescein isothiocyanate (FITC), a skin sensitizing fluorochrome. Addition of DBP augmented very substantially, in a dose-dependent fashion, the ability of topically applied FITC to stimulate proliferative responses in mice by draining lymph node cells (LNC), a correlate of skin sensitizing potential. Under these conditions, exposure of mice to DBP alone failed to elicit significant LNC responses. The influence of DBP on the accumulation of dendritic cells (DC) induced by FITC was examined also. Although 10% DBP had little effect on the numbers of DC found within draining nodes 18 hr following exposure of mice to FITC, the phthalate did result in a very substantial increase in the frequency of lymph node DC bearing detectable antigen (FITC+ DC). Furthermore, in the presence of DBP the median amount of FITC associated with antigen-bearing DC was higher. In vitro skin absorption studies indicated that DBP was associated with a small increase in percutaneous absorption of FITC. Collectively these data demonstrate that the vehicle formulation can exert a marked influence on dermal sensitization and that one mechanism which may be relevant is the increased acquisition of antigen by DC, associated possibly with altered penetration of the allergen into or through the skin.