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R J Dearman

Publications and source records attributed to R J Dearman.

At least 37 records · Page 2Linked to original sources
PubMed2002

Immunogenic properties of rapidly digested food proteins following gavage exposure of mice: a comparison of ovalbumin with a potato acid phosphatase preparation.

The ability of food proteins to resist digestion in simulated gastric fluid (SGF) correlates with allergenic potential. The purpose of the current investigations was to determine whether this association is due solely to the failure of unstable proteins to elicit an immune response when administered orally. We have examined immune responses induced in BALB/c mice by gavage administration of ovalbumin (OVA) and a crude potato protein extract (PPE) containing acid phosphatase activity. The stability of OVA and PPE in SGF was measured using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The ability of these proteins to stimulate specific IgG and IgE antibody production in mice following parenteral (intraperitoneal; ip) or oral (gavage) exposure was compared using enzyme-linked immunosorbent and homologous passive cutaneous anaphylaxis assays, respectively. Both OVA and PPE induced specific IgG antibody responses when administered either by gavage or by ip injection. Parenteral, but not gavage, exposure to OVA was associated with robust IgE antibody responses. Administration of PPE failed to stimulate strong IgE production via either route of exposure. Differential stability in SGF was observed, with PPE being digested extremely rapidly (within 1 min), whereas OVA was more resistant. The strong association reported by others between stability in SGF and allergenic potential is unlikely to be solely due to orally-ingested labile proteins failing to provoke immune responses due to degradation in the stomach.

Acid Phosphatase↗
PubMed2002

Examination of a vehicle for use with water soluble materials in the murine local lymph node assay.

The murine local lymph node assay (LLNA) is a validated method for identifying skin sensitization hazard. Vehicle choice can influence the sensitization potential of haptens in both the LLNA and in humans, therefore selection of an appropriate vehicle is important. Suggested vehicles for the LLNA include organic solvents and organic-aqueous mixtures. However, due to its high surface tension and poor wetting qualities, water is not recommended and therefore testing aqueous soluble materials can be problematic. The aims of this investigation were to identify a water-based vehicle that possesses better skin wetting properties than water alone, and to assess its performance relative to other solvents in the LLNA using aqueous soluble haptens. The selected wetting agent was the surfactant Pluronic(R) L92 (L92). Concentrations of L92 of up to 50% did not induce positive responses in the LLNA. 1% aqueous L92 was chosen for further examination. Dose-response analyses were performed with dinitrobenzene sulfonic acid (DNBS) and formaldehyde formulated either in water, 1% L92, dimethyl sulfoxide (DMSO) or dimethyl formamide (DMF). Potassium dichromate (PDC) and nickel sulfate were tested in 1% L92, DMSO or DMF. The highest concentration of potassium dichromate was retested in each vehicle and in water to assess the effect of the wetting agent. Estimates of the relative sensitizing potency in each vehicle were determined by calculation of EC3 values (the estimated concentration required to induce a threshold positive response). While DNBS and formaldehyde produced positive responses in all four vehicles, their relative potency varied among the vehicles. The rank ordering of potencies for both materials was, from highest to lowest, DMF > or = DMSO > 1% L92 > water. Compared with water, use of 1% L92 resulted in >2-fold increase in potency for DNBS and >3-fold increase for formaldehyde. PDC was positive in DMF, DMSO and 1% L92. The potency ranking was DMF > or = DMSO > 1% L92. Re-evaluation of 0.5% PDC confirmed that formulations of both DMSO and DMF induced strong proliferative responses, whereas somewhat less proliferation was recorded with the 1% L92 vehicle. PDC in water was without activity. The performance of 1% L92 as a vehicle for nickel sulfate was assessed relative to DMSO and DMF. In DMSO, nickel sulfate produced a stimulation index (SI) >3 at only the highest level. Testing in DMF induced low levels of proliferation, but failed to produce a SI of 3 at any concentration tested. When formulated in 1% L92, nickel sulfate caused a SI of 3 when tested at 2.5%. Based on the results of these experiments, for identification of sensitization hazard of aqueous soluble materials using the LLNA, DMF and DMSO are the preferred vehicles. However, if a test material is not soluble in DMF or DMSO, or if higher test concentrations can be achieved in an aqueous vehicle, then 1% L92 may provide a better alternative to water alone in terms of improved assay performance.

Allergens↗
PubMed2002

Cytokine fingerprinting of chemical allergens: species comparisons and statistical analyses.

The cellular and molecular mechanisms that result in the induction of chemical respiratory sensitization are unclear, although there is evidence for the development of T helper (Th) 2 type responses and, in some cases, the production of IgE. We have compared cytokine secretion patterns stimulated by topical exposure of BALB/c strain mice or Brown Norway (BN) strain rats to the reference respiratory allergen trimellitic anhydride (TMA), or to the reference contact allergen 2,4-dinitrochlorobenzene (DNCB). Under conditions where TMA and DNCB provoke similar levels of immune activation [increases in lymph node cell (LNC) cellularity and proliferation] divergent cytokine expression patterns are elicited. TMA-activated LNC isolated from BALB/c mice or BN rats elaborated high levels of the Th2-type cytokines interleukin (IL)-10 and IL-13, but relatively little of the Th1-type cytokines IL-12 or interferon gamma. For LNC derived from both species there was a requirement for restimulation in vitro with the mitogen concanavalin A for IL-4 production. Generally, DNCB-stimulated LNC displayed the converse type 1 cytokine phenotype. The cytokine secretion profiles of LNC isolated from BN rats were considerably more variable than those observed for LNC from BALB/c mice. Statistically significant differences (P<0.01) between DNCB- and TMA-activated LNC were recorded for all cytokines in BALB/c strain mice. For the BN rat, differences reached statistical significance (P<0.01) only for the expression of IL-4 and IL-13. These data demonstrate that the intrinsic ability of DNCB and TMA to promote preferential Th1- and Th2-type responses, respectively, is species-independent and provide further evidence that chemical respiratory allergens are associated with polarized Th2-type responses. For the prospective assessment of chemical respiratory allergens as a function of induced cytokine secretion profiles, however, these data suggest that the use of the BALB/c strain mouse will provide the more robust method.

Allergens↗
PubMed2002

The local lymph node assay: past, present and future.

The local lymph node assay (LLNA) was developed originally as a method for the identification of chemicals that have the potential to cause skin sensitization and allergic contact dermatitis. The assay is based on an understanding that the acquisition of contact sensitization is associated with, and dependent upon, the stimulation by chemical allergens of lymphocyte proliferative responses in skin-draining lymph nodes. Those chemicals that provoke a defined level of lymph node cell (LNC) proliferation (a 3-fold or greater increase compared with concurrent vehicle controls) are classified as skin sensitizers. Following its original inception and development, the LLNA was the subject of both national and international interlaboratory collaborative trials, and of very detailed comparisons with other test methods and with human skin sensitization data. The assay has now been validated fully as a stand-alone test for the purposes of hazard identification. In recent years, there has been a growing interest also in the use of the LLNA to assess the potency of contact allergens and in risk assessment. There is reason to believe that the extent of skin sensitization achieved is associated with the vigour of LNC proliferation induced in draining nodes. Given this relationship, the relative potency of skin sensitizing chemicals is measured in the LLNA by derivation of an EC3 value, this being the concentration of chemical required to provoke a 3-fold increase in the proliferation of LNC compared with controls. Experience to date indicates that relative potency as determined using this approach correlates closely with what is known of the activity of skin sensitizing chemicals in humans. In this article, we review the development, evaluation and validation of the LLNA for the purposes of hazard identification, and the more recent application of the method for evaluation of potency in the context of risk assessment. In addition, we consider what new applications and modifications are currently being investigated.

Allergens↗
PubMed2002

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.

Adolescent↗
PubMed2002

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.

Administration, Topical↗
PubMed2001

Characterization of antibody responses induced in rodents by exposure to food proteins: influence of route of exposure.

There is a growing interest in the development of methods to characterize the allergenic properties of novel proteins, particularly those expressed by transgenic crop plants. Approaches to the direct evaluation of allergenic potential have focused generally on the ability of proteins to induce antibody (particularly IgE antibody) after systemic (intraperitoneal; i.p.) or gavage administration to high IgE responder strain rodents. To date there has been no systematic comparison of the reliability, sensitivity or selectivity of these approaches. We have, therefore, compared antibody (IgG and IgE) responses induced in Brown Norway (BN) rats by daily gavage administration and in BALB/c strain mice following intraperitoneal or gavage exposure to food proteins of varying allergenic potential. Animals were exposed to the allergens peanut agglutinin and ovalbumin (OVA) or to a crude potato protein extract (PPE) containing acid phosphatase activity, a common foodstuff which appears to be of low allergenicity. All test proteins were clearly immunogenic when administered by gavage to BN rats, with measurable, and in some cases very vigorous, IgG antibody responses recorded for all animals. Identical exposure of BALB/c strain mice also stimulated detectable IgG antibody responses, with particularly high titers recorded following treatment with peanut agglutinin and somewhat less vigorous responses induced by OVA and PPE. Despite these high titer IgG antibody responses, however, none of the proteins provoked detectable IgE antibody following gavage administration to BN rats. In contrast, in BALB/c mice oral exposure to peanut agglutinin elicited high titer IgE antibody, although IgE antibody responses to both OVA and PPE were much weaker. Parenteral (i.p.) treatment of BALB/c strain mice with each of the test materials induced relatively high titer IgG antibody and a differential potential to stimulate IgE antibody was observed. High titer IgE responses were provoked by i.p. administration of peanut agglutinin and OVA, whereas PPE stimulated little or no detectable IgE antibody. It would appear, therefore, that while it is possible to elicit robust IgE responses by gavage exposure of BALB/c strain mice to some protein allergens, such as peanut agglutinin, such responses are generally weaker and less consistent than those provoked by i.p. administration. Furthermore, gavage treatment failed to induce detectable IgE responses in the BN rat, suggesting that the ability these animals to mount IgE responses is somewhat variable. Following i.p. administration to BALB/c strain mice, these proteins displayed immunological properties consistent with what is known of their allergenic potential in humans, suggesting that, following further evaluation with a wider range of proteins, this method may provide one approach to the identification of potential protein allergens.

Administration, Oral↗
PubMed2001

Preliminary assessment of the skin sensitizing activity of selected rodent carcinogens using the local lymph node assay.

It has been demonstrated previously that there exists an incomplete correlation between the skin sensitizing potential of chemicals and their mutagenic properties as judged by activity in the Salmonella mutation assay. More recently, it has been proposed that there may exist a broader association between carcinogenicity in rodents (including non-genotoxic carcinogenesis) and skin sensitizing activity. To explore further these putative relationships we have here examined the skin sensitizing potential of two non-genotoxic rodent carcinogens which are generally considered not to represent a carcinogenic hazard in humans (limonene and saccharin) and of three genotoxic rodent carcinogens (vinylidene dichloride, ethyl acrylate and bisphenol A diglycidyl ether). For this purpose we have used the local lymph node assay (LLNA), a method for the identification and characterization of skin sensitizing chemicals that has recently been recognized as a stand-alone method for hazard identification purposes. Activity in the LLNA was compared with the results of Salmonella tests conducted previously. This small series of investigations reveals that there exists no general relationship between skin sensitizing potential and rodent carcinogenicity. Furthermore, although a general correlation does exist between mutagenic activity and skin sensitization, this association is not universal and activity in the Salmonella mutation assay does not necessarily imply skin sensitizing potential. Collectively these data suggest that it is inappropriate currently to recommend the use of skin sensitization tests as an adjunct to conventional approaches to the evaluation of potential carcinogenicity.

Acetates↗
PubMed2001

Food allergy: what are the issues?

With a growing interest in the development of genetically modified crop plants there is a need for appropriate approaches to safety assessment. Among the issues that have to be addressed is consideration of whether the products of novel genes have the potential to cause allergic sensitization. Resulting from a collaboration between the International Food Biotechnology Council and the International Life Sciences Institute recommendations have been made for a step-wise approach to the assessment of allergenic potential based upon considerations of serological identity, and sequence or structural homology, with known allergens and examination of the stability of the test protein in a simulated gastric fluid. In parallel there has been interest in the development of animal models, which would permit a more direct evaluation of potential allergenic activity. Progress in these areas is reviewed briefly in the context of what is known of food allergy and some of the important issues, which must be addressed in designing safety assessment strategies identified.

Allergens↗
PubMed2001

Determination of protein allergenicity: studies in mice.

There is a need to identify and characterize the allergenic potential of novel proteins introduced into genetically-modified crop plants. Although several approaches have already been described, none of these measures directly the ability of proteins to cause allergic sensitization. For this reason there has been a growing interest in the development of suitable animal models. This article describes experience to date with a method based upon assessment of serological (IgG and IgE antibody) responses induced in BALB/c strain mice by proteins. Comparisons have been made between intraperitoneal (i.p.) administration and exposure by gavage using both allergenic and non-allergenic proteins. The available data indicate that responses provoked by i.p. exposure permit the identification of proteins that have the inherent potential to induce IgE antibody production and allergic sensitization. Moreover, this approach also provides a rank order of proteins with respect to allergenic potency that apparently reflects what is known of their relative sensitizing activity in humans. By comparison, oral exposure of mice by gavage is somewhat less sensitive. On this basis it is proposed that the inherent sensitizing potential of novel proteins can be evaluated as a function of IgE antibody responses stimulated by parenteral (i.p.) exposure of BALB/c mice.

Acid Phosphatase↗
PubMed2001

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.

Administration, Cutaneous↗
PubMed2001

Differential effect of thalidomide and dexamethasone on the transcription factor NF-kappa B.

Thalidomide was initially used as a sedative during pregnancy but was withdrawn from the market due to its teratogenic effects. In vitro studies have shown that thalidomide inhibits tumour necrosis factor alpha (TNF-alpha) mRNA expression and protein production by mitogen-stimulated macrophages and activated T cells. Even at the highest concentration (10-1 mM) tested, however, TNF-alpha levels are inhibited only partially and the mechanism of action is unknown. In the present investigations, we have examined the influence of thalidomide on nuclear levels of NF-kappa B in human peripheral blood mononuclear cells (PBMC) following activation with mitogen or phorbol myristate acetate (PMA)/ionophore. Dexamethasone was used as a positive control due to its well-characterised mechanism of action and NF-kappa B-mediated effects on TNF-alpha expression. PBMC from healthy human volunteers were stimulated optimally with phytohemagglutinin (PHA) or PMA/ionophore in the presence of 10(-1)-10(-5) mM thalidomide or dexamethasone, concentrations that displayed a range of inhibitory effects on TNF-alpha production. Cells were harvested at varying time points and nuclear extracts prepared. Nuclear levels of NF-kappa B were measured using electrophoretic mobility shift assays (EMSA) with a radiolabelled DNA probe specific for NF-kappa B. Results were analysed using optical densitometry. Nuclear levels of NF-kappa B were found to be unaffected by thalidomide at all concentrations tested, including concentrations (10(-1)-10(-3) mM) that exhibited significant inhibition of TNF-alpha protein and mRNA expression. In concurrent experiments, dexamethasone was found to reduce NF-kappa B expression in a dose-dependent manner with maximal inhibition at the highest dose tested (10(-1) mM). TNF-alpha gene expression is controlled by at least three separate transcription factors that are involved in binding to the promoter region. These observations suggest that thalidomide does not act directly on NF-kappa B and therefore inhibits TNF-alpha production through another independent mechanism.

Adult↗
PubMed2001

The suitability of hexyl cinnamic aldehyde as a calibrant for the murine local lymph node assay.

The murine local lymph node assay (LLNA) for the prospective identification of contact allergens assesses skin sensitization potential as a function of proliferative activity induced in lymph nodes draining the site of topical exposure to test chemical. This method has been endorsed recently as a stand alone test for the identification of contact allergens. We have now examined the suitability of hexyl cinnamic aldehyde (HCA), a recommended positive control for skin sensitization testing, as a calibrant for comparing the consistency of LLNA responses with time, and between laboratories, and thus for the routine assessment of assay reliability. Standard LLNAs were performed with CBA strain mice in 3 independent laboratories over a period of 8 years. Dose-response curves were used to derive mathematically the EC3 value (the estimated concentration of chemical necessary to cause a stimulation index (SI) of 3 compared with proliferation induced by concurrent vehicle controls). In each laboratory, 6 separate experiments were conducted using a single concentration of HCA (25%). Very similar stimulation indices were achieved, with mean values of 9.0, 6.5 and 6.6 recorded. A total of 10 dose-response experiments were performed independently in the 3 laboratories and these revealed that there was very little inter-laboratory, or temporal, variation in EC3 values. These data confirm that HCA responses in the LLNA are very stable and demonstrate that HCA provides a suitable calibrant for determining assay sensitivity and performance.

Acrolein↗
PubMed2001

Human potency predictions for aldehydes using the local lymph node assay.

The murine local lymph node assay (LLNA) assesses skin sensitization potential as a function of proliferative responses induced in lymph nodes draining the site of topical exposure to test chemical. It has been shown that interpolation of LLNA dose-response data to define the concentration of test chemical required to induce a 3-fold stimulation of proliferation (EC3) offers the prospect of a quantitative index of the relative potency of a contact allergen. Initial studies have demonstrated that there exists a strong (inverse) correlation between EC3 values and contact allergenic potency in humans. Thus, materials with a low EC3 value were more potent contact allergens in humans. However, it is necessary to examine a wide range of allergens to demonstrate that such correlations are generally true. Thus, in the present study, 10 aldehydes of varying degrees of allergenicity in man were evaluated in the LLNA and their EC3 values derived. Formaldehyde was regarded as the strongest allergen in man and also had the lowest EC3 value, 0.35% (equivalent to 0.93% formalin). In contrast, the extremely weak allergen vanillin and the non-sensitizer ethyl vanillin both had EC3 values of >50%. For the remaining 7 aldehydes, there was a close similarity between what is judged to be their rank order of allergenicity in humans and EC3 values derived from analysis of LLNA data. These results support further the utility of EC3 determinations in the LLNA as a measure of the relative potency of a contact allergen.

Aldehydes↗
PubMed2001

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.

Adult↗
PubMed2001

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.

Allergens↗
PubMed2001

Contact allergenic potency: correlation of human and local lymph node assay data.

BACKGROUND: Effective toxicologic evaluation of skin sensitization requires that potential contact allergens are identified and that the likely risks of sensitization among exposed populations are assessed. By definition, chemicals that are classified as contact sensitizers have the capacity to cause allergic contact dermatitis (ACD) in humans. However, this hazard is not an all-or-nothing phenomenon; clear dose-response relationships can be discerned and thresholds identified for both the induction of sensitization and the elicitation of ACD. Commonly, these parameters are grouped under the heading of potency, the determination of which is vital for risk assessment. Preclinical testing for sensitization potential is critically important for hazard assessment before human exposure. The murine local lymph node assay (LLNA) is the most recently accepted test method for sensitization hazard assessment. OBJECTIVE: The aim was to compare potency estimations derived from LLNA data with clinical determinations of relative potency based on human data. METHODS: No-effect levels (NOELs) for a range of 21 chemicals were determined from nondiagnostic human repeat patch test studies as reported in the literature. These levels were compared with LLNA EC(3) values, the estimated concentration required to produce a 3-fold increase (positive response) in draining lymph node cell (LNC) proliferative activity. RESULTS: Using available human repeat patch test data, together with expert judgment, the compounds were classified as strong, moderate, weak, extremely weak, or nonsensitizing. Additionally, the potency of each chemical was classified independently based on its LLNA EC(3) value. The results show clearly that LLNA EC(3) values are very comparable with the NOELs calculated from the literature. Moreover, the potency rankings based upon LLNA EC(3) data support their human classification. CONCLUSION: The present investigations show that the LLNA can be used to provide quantitative estimates of relative skin sensitizing potency EC(3) values that correlate closely with NOELs established from human repeat patch testing and from our clinical experience.

Allergens↗