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R J Dearman

Publications and source records attributed to R J Dearman.

At least 109 records · Page 6Linked to original sources
PubMed1996

Selectivity of IgE responses, mast cell sensitization, and cytokine expression in the immune response of Brown Norway rats to chemical allergens.

Sensitizing chemicals can induce various types of allergic disease, including contact dermatitis and occupational asthma. In the present study we have examined the nature of the immune response induced in Brown Norway (BN) rats by oxazolone (OX), a potent contact allergen, and by trimellitic anhydride (TMA), a chemical known to cause sensitization of the respiratory tract and occupational asthma. BN rats were exposed topically to either OX or TMA at doses selected to achieve similar levels of proliferative activity by draining LNC. Both chemicals stimulated hapten-specific IgG antibody responses, but only TMA induced specific IgE antibody, an increase in total serum IgE and active sensitization of mast cells. Draining LNC from OX-treated rats expressed elevated IFN-gamma mRNA, whereas those from TMA-treated rats expressed elevated IL-5 mRNA compared to controls. Furthermore, Con A-activated draining LNC from rats exposed to TMA, but not OX, released significantly increased concentrations of IL-4. In conclusion, different chemical allergens can induce in the BN rat divergent patterns of IgE response and cytokine expression.

Allergens↗
PubMed1996

Sensitization to 2,4-dinitrochlorobenzene: influence of vehicle on absorption and lymph node activation.

Effective skin sensitization is dependent upon immune activation of lymph nodes draining the site of exposure. The influence of vehicle formulation on the vigour of lymph node cell proliferative responses to 2,4-dinitrochlorobenzene (DNCB) has been examined. Mice (BALB/c strain) were exposed topically to 0.5% DNCB dissolved in either acetone or propylene glycol (PG). A significantly greater lymph node cell proliferative response was induced by DNCB in acetone. The observed differences were not attributable to variations in the numbers of immunostimulatory dendritic cells accumulating in the draining nodes following sensitization. In parallel studies, the absorption and cutaneous disposition of DNCB dissolved in acetone or PG were measured in vitro using static diffusion cells and full thickness mouse skin. Although flux of DNCB through the skin was comparable with both vehicles over 24 h, the absorption of the allergen during the first 4 h of exposure was significantly faster when acetone was used as the vehicle. Localization of DNCB demonstrated that much less of the chemical allergen was present in the skin at 4 h when applied in PG vehicle. However, there were no measurable vehicle effects on skin disposition of DNCB at 24 h. These data indicate that the sensitization potential of DNCB is influenced significantly by the nature of the vehicle used, possibly due to consequential effects on chemical absorption and disposition. The studies described in this paper reveal that the application vehicle may have a significant influence on the ability of DNCB to induce immune activation of draining lymph nodes and hence skin sensitization and that this may in turn be associated with important changes in the absorption and/or disposition of the chemical within the skin.

Acetone↗
PubMed1996

Further evaluation of the local lymph node assay in the final phase of an international collaborative trial.

The local lymph node assay (LLNA) is a method used for the prospective identification in mice of chemicals that have the potential to cause skin sensitization. We report here the results of the second and final phase of an international trial in which the performance of the assay has been evaluated using seven test materials in five independent laboratories. The additional chemicals examined here included compounds which are considered less potent allergens than some of those tested in the first phase of the investigation, and includes hexylcinnamic aldehyde (HCA), a chemical recommended by the Organization for Economic Cooperation and Development (OECD) as a positive control for skin sensitization studies. In each laboratory all skin sensitizing chemicals examined (2,4-dinitrochlorobenzene {DNCB}, HCA, oxazolone, isoeugenal and eugenol) elicited positive responses of comparable magnitude as judged by the derived lowest concentration of test chemical required to elicit a 3-fold or greater increase in the proliferative activity of draining lymph node cells compared with vehicle-treated controls. We observed that sodium lauryl sulphate, considered to be a non-sensitizing skin irritant, also induced a positive response in the assay. Para-aminobenzoic acid (pABA), a nonsensitizing chemical, was negative at all test concentrations in each laboratory. Some laboratories incorporated minor modifications into the standard assay procedure, including the evaluation of lymph nodes pooled from individual mice rather than treatment groups and the use of statistical analyses. The use of statistics did not markedly change the determination of the lowest concentration yielding a positive response. These data confirm that the local lymph node assay is robust and yields equivalent results when performed independently.

Animals↗
PubMed1996

Stimulation by oxazolone of increased IL-6, but not IL-10, in the skin of mice.

Interleukin 6 (IL-6), a multi-functional cytokine, is expressed constitutively by epidermal Langerhans cells and can be produced also by keratinocytes following stimulation. We have investigated the production of cutaneous IL-6 following topical exposure of mice to oxazolone, a potent contact allergen. Homogenates of ear skin prepared from untreated BALB/c strain mice, or from mice exposed on the dorsum of both ears to vehicle alone, contained low levels of IL-6. Topical application of oxazolone to the ears of mice induced a rapid and dose-dependent increase in IL-6 expression that was maximal 4-8 h following application and remained elevated for up to 24 h. Under the same conditions of exposure the expression of a second epidermal cytokine, interleukin 10, a product of keratinocytes, was unaffected. It is concluded that topical exposure to the chemical allergen oxazolone results in the selective stimulation of cutaneous cytokine production. The experimental approach described herein provides a simple and reliable method for the investigation of induced changes in the expression of skin cytokines.

Administration, Topical↗
PubMed1996

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.

Administration, Topical↗
PubMed1996

Characterization of chemical allergens as a function of divergent cytokine secretion profiles induced in mice.

Allergic contact dermatitis (contact sensitivity) may be caused by a wide variety of chemicals. In addition, some chemical allergens may also induce respiratory sensitization. It has been demonstrated previously that topical exposure of mice to chemical contact and respiratory sensitizers stimulates divergent immune responses consistent with the selective activation of T helper 1 (Th1)- and Th2-type cells, respectively. Thus, exposure to trimellitic: anhydride (TMA) induces hapten-specific IgE antibody and a substantial increase in the total serum concentration of IgE. Conversely, oxazolone fails to provoke IgE production. In addition, lymph node cells (LNC) isolated following repeated topical exposure of mice to oxazolone or TMA display cytokine secretion profiles characteristic of Th1- and Th2-type cell stimulation. The purpose of the present investigations was to determine whether chemical allergens other than TMA and oxazolone, the respiratory allergen toluene diisocyanate (TDI) and the skin sensitizer dinitrofluorobenzene (DNFB), provoke differential cytokine expression. The production of the Th1-type product interferon gamma (IFN-gamma) and the Th2-type cytokines interleukins 4 and 10 (IL-4 and IL-10) by TDI- and DNFB-activated LNC has been measured. LNC derived from DNFB-exposed animals expressed substantial amounts of IFN-gamma, but only low levels of IL-10 and mitogen-inducible IL-4; exposure to TDI resulted in the converse profile of cytokine secretion. These data demonstrate that repeated topical administration of chemical allergen of different classes elicits in mice divergent cytokine secretion patterns consistent with the selective stimulation of distinct Th subsets. Analysis of such cytokine production profiles may permit in a single integrated assay the simultaneous identification and classification of chemical allergens.

Allergens↗
PubMed1996

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.

Animals↗
PubMed1996

Accessory cell requirements for T lymphocyte activation and interferon-gamma production in peripheral lymph nodes.

Allergen-activated draining lymph node cells (LNC) isolated from mice exposed topically to the contact allergen oxazolone mount vigorous proliferative responses and secrete substantial amounts of interferon-gamma (IFN-gamma) when cultured with the T lymphocyte mitogen concanavalin A (con A). In contrast, although naive LNC prepared from untreated mice display con A-driven proliferative responses of comparable magnitude, they produce only very low levels of IFN-gamma. Secretion of IFN-gamma by con A-stimulated naive LNC was augmented significantly by the addition to culture of a small number of syngeneic dendritic cells (DC), under conditions where there was no influence on the vigour of proliferative responses and where the exogenous DC themselves failed to produce IFN-gamma. Augmentation of IFN-gamma production was not observed when exogenous populations depleted of DC were added to culture. It is proposed that discrete aspects of the primary activation of naive T lymphocytes display differential requirements for accessory cells and that the development of IFN-gamma producing cells necessitates sufficient numbers of dendritic cells.

Animals↗
PubMed1996

Antigen-induced unresponsiveness in contact sensitivity: association of depressed T lymphocyte proliferative responses with decreased interleukin 6 secretion.

Topical exposure of mice to the contact allergen oxazolone induces both 4 persistent antigen-specific down-regulation of subsequent lymph node cell (LNC) proliferative responses stimulated by the same chemical and a more transient depression of LNC proliferative responses provoked by exposure to unrelated chemical sensitizers: the latter being associated with antigenic competition in contact sensitivity. In this paper a relationship between reduced LNC proliferative activity and the secretion of interleukin 6 (IL-6) is described. Pretreatment of mice with oxazolone caused a persistent, dose-dependent inhibition of LNC proliferative activity and a parallel reduction of IL-6 secretion when mice were re-exposed, at a different site, to the same chemical. Consistent with dendritic cells (DC) being the major source of IL-6 within allergen-activated lymph nodes, depletion of Thy-lt T lymphocytes did not compromise production of this cytokine. Although in mice pretreated with oxazolone IL-6 secretion by cultured LNC was impaired markedly, the initial IL-6 content of freshly isolated LNC was apparently normal. These data suggest that the down-regulation of lymphocyte proliferative responses induced by exposure of mice to oxazolone, and the consequential impaired responsiveness, is associated with, and possibly secondary to, the reduced secretion by lymph node DC of IL-6, a cytokine that is a costimulator of T lymphocyte activation and the production of which correlates closely with the vigour of LNC proliferative activity.

Adjuvants, Immunologic↗
PubMed1996

Experimental assessment of the sensitizing properties of formaldehyde.

Formaldehyde causes upper respiratory tract irritation and has been reported in some investigations to be a cause of occupational allergic asthma. The data are equivocal, however, and it has proved difficult to confirm that exposure to formaldehyde induces respiratory sensitization or provokes the production of specific immunoglobulin E (IgE) antibody. In this study the sensitizing properties of formaldehyde were examined experimentally. This chemical elicited strong positive responses in three independent methods for the prospective identification of contact sensitizing chemicals-the guinea pig maximization test, the occluded patch test of Buehler and the murine local lymph node assay. In contrast, in a novel predictive test method for assessment of respiratory sensitization potential-the mouse IgE test-formaldehyde at the same test concentrations was negative. Furthermore, formaldehyde induced in mice a pattern of cytokine secretion by draining lymph node cells inconsistent with the stimulation of IgE antibody responses or respiratory sensitization. These data indicate that, although formaldehyde is a potent contact allergen, it lacks a significant potential to cause sensitization of the respiratory tract.

Administration, Topical↗
PubMed1996

Predictive testing for respiratory sensitization in the mouse.

Attempts to develop predictive test methods for the identification of chemical respiratory allergens have to date focused almost exclusively on the guinea pig. In recent years there has, however, been a growing interest in the mouse as a model for examination of sensitization potential. In this article two alternative approaches to the toxicological investigation of respiratory sensitization are described. Both are based on an understanding of the nature of immune responses induced in mice by chemical allergens. The mouse IgE test seeks to identify chemicals capable of causing allergic sensitization of the respiratory tract as a function of induced increases in the serum concentration of IgE. The second approach, cytokine fingerprinting, makes use of the observation that chemical allergens of different types provoke in mice qualitatively divergent immune responses characterized by discrete cytokine secretion profiles.

Allergens↗
PubMed1996

Constitutive and inducible expression of interleukin-6 by Langerhans cells and lymph node dendritic cells.

During the induction phase of contact sensitization and other cutaneous immune responses a proportion of epidermal Langerhans cells (LC) is induced to leave the skin and migrate via afferent lymphatics to lymph nodes draining the site of exposure. The cells that accumulate in draining nodes have acquired the characteristics of immunostimulatory dendritic cells and effectively present antigen to responsive T lymphocytes. In the present study we have questioned whether LC in the epidermis and the lymph node dendritic cells into which they develop express interleukin-6 (IL-6), a cytokine that has been shown to serve as an important costimulator of T lymphocyte activation. In situ immunocytochemical analyses using a biotin-streptavidin staining technique revealed that dendritic cells resident in the epidermis of untreated mice constitutively express this cytokine. Keratinocytes expressed detectable IL-6 only following local exposure to the contact allergen oxazolone. Such treatment also appeared to enhance the expression by epidermal dendritic cells of this cytokine. Analyses of unfractionated and LC-enriched and -depleted populations of epidermal cells revealed a close correlation between major histocompatibility complex (MHC) class II (Ia) antigen expression and staining for IL-6, implicating LC as the sole or major source of this cytokine in unstimulated epidermis. Finally, compared with tissue isolated from mice treated with vehicle alone, draining lymph nodes prepared from animals 18 hr following sensitization with oxazolone displayed a substantial increase in both the frequency of dendritic cells and the number of IL-6+ cells within the paracortex. These data demonstrate that resident epidermal LC and the dendritic cells into which they develop are important sources of IL-6. Their constitutive and inducible expression of this cytokine will facilitate the induction of cutaneous immune responses.

Animals↗
PubMed1996

Contribution of CD4+ and CD8+ T lymphocyte subsets to the cytokine secretion patterns induced in mice during sensitization to contact and respiratory chemical allergens.

Chemical allergens of different types, those that cause in humans allergic contact dermatitis or occupational asthma induce in mice divergent immune responses characteristic, respectively, of T-helper 1 (Th1)- and Th2-type cell activation. Such responses are associated with the development of different cytokine secretion patterns by draining lymph node cells (LNC), such that contact allergens stimulate vigorous interferon-gamma (IFN-gamma) production, but little secretion of the Th2 cytokines interleukin-4 and interleukin-10 (IL-4 and IL-10), whereas the converse pattern is provoked by respiratory allergens. Using selective depletion with antibody and complement we have here examined the relative contribution of CD4+ and CD8+ T lymphocytes to the cytokine secretion patterns of draining LNC isolated from mice sensitized to chemical allergens. Mice received repeated topical applications of respiratory allergens, trimellitic anhydride (TMA) or diphenylmethane diisocyanate (MDI), or of contact allergens 2,4-dinitrochlorobenzene (DNCB) or formaldehyde. Thirteen days following the initiation of exposure the production by draining LNC of IL-10, IFN-gamma and mitogen (concanavalin A)-inducible IL-4 was measured by enzyme-linked immunosorbent assay (ELISA) after various periods of culture. It was found that the high levels of IL-4 and IL-10 secretion stimulated by TMA or MDI, and the lower levels of these cytokines induced by DNCB or formaldehyde, were in all cases dependent upon the presence of CD4- cells. In contrast, the comparatively high concentrations of IFN-gamma observed following exposure to contact allergens were found to be derived from CD4+ cells, and in the case of DNCB from CD8+ cells also. The low levels of IFN-gamma induced by treatment with TMA or MDI were associated largely or wholly with CD8+ cells. These data indicate that the type 2 cytokine responses induced to different extents by both contact and respiratory chemical allergens are almost exclusively a function of CD4+ cells, but that IFN-gamma is produced by either CD4+ cells in the case of contact allergens or largely by CD8+ cells in the case of chemical respiratory allergens.

Allergens↗
PubMed1996

Dichloronitrobenzene: a reappraisal of its skin sensitization potential.

Unlike the closely related chemical dinitrochlorobenzene (DNCB), which is a very strong contact allergen, dichloronitrobenzene (DCNB) has been widely regarded as a non-allergen and, as such, a useful control for its strongly sensitizing counterpart. Nevertheless, it is still an organic chemical species readily capable of penetrating skin and, rather than being regarded as completely inert, it has even been suggested to react with the immune system in such a way that it induces specific tolerance to its chemical structure. We investigated whether DCNB was in reality a non-allergen, or rather merely a weak contact sensitizer. In both a rigorously conducted guinea pig maximization test and in a modified murine local lymph node assay, DCNB was demonstrated to possess weak sensitizing activity. On this basis, DCNB cannot be regarded as inert with respect to contact allergic potential, and is therefore inappropriate as a negative control in studies of skin sensitization.

Animals↗
PubMed1996

Exposure of UVB-sensitive mice to immunosuppressive doses of UVB in vivo fails to affect the accessory function or the phenotype of draining lymph node dendritic cells.

Following the application of sensitizing chemicals to the skin, hapten-bearing Langerhans cells (LC) and possibly other cutaneous dendritic cells (DC) migrate to the draining lymph nodes (DLN) of mice and induce the proliferation of antigen specific effector T cells. This migration of DC to the DLN is required for the induction of primary immune responses. In certain strains of mice, irradiation with ultraviolet-B light (UVB) before sensitization results in the suppression of contact hypersensitivity responses. In vitro investigations have suggested that one influence of UVB is to modify the ability of Langerhans cells (LC) to present antigen. In the present investigation, putative UVB-induced alterations in lymph node DC in vivo were examined. Lymph node DC were analysed following exposure of C3H/HeN mice to an immunosuppressive dose of UVB (1440 J/m2) 48 and 24 h prior to skin painting with the sensitizers fluorescein isothiocyanate or oxazolone. In functional studies, DC prepared from the DLN of contact sensitized mice were examined for their ability to induce hapten-specific secondary T-lymphocyte proliferative responses or mixed lymphocyte reactions in vitro. In neither case was the activity of DC influenced by local exposure to an immunosuppressive dose of UVB. The migration of LC from the epidermis to the draining lymph node in response to contact sensitization is associated with increased expression of several membrane determinants necessary for effective antigen presentation, including intercellular adhesion molecule-1 (ICAM-1; CD54), B7-2 (CD86) and Ia antigen. The expression of these molecules was identical on DC isolated from the DLN of UVB-irradiated and from control, unirradiated mice. Thus, the immunosuppressive effect of UVB on the cutaneous immune system may not necessarily reflect changes in the antigen-presenting DC that accumulate in the DLN following skin sensitization.

Adjuvants, Immunologic↗
PubMed1995

An international evaluation of the murine local lymph node assay and comparison of modified procedures.

The murine local lymph node assay is a predictive test for the identification of skin-sensitizing chemicals. The method has been the subject both of national inter-laboratory studies and of extensive comparisons with guinea pig tests. In the investigations reported here, the local lymph node assay has been evaluated further in the context of an international study comprising five independent laboratories. In addition, the influence of minor modifications to the standard assay procedure on the performance of the test has been examined. The modified procedures investigated were exposure of mice for 4 rather than 3 consecutive days, excision of lymph nodes 4 rather than 5 days after the initiation of exposure and the use of an alternative isotope. All five laboratories, irrespective of whether the standard or a modified protocol was used, were able to identify accurately, and with comparable sensitivity, potassium dichromate and 2,4-dinitrochlorobenzene as skin sensitizers. Using standard criteria, none of the laboratories recorded positive responses with methyl salicylate, a non-sensitizer. In the standard protocol, lymph nodes are pooled for each experimental group and the vigor of responses measured as a stimulation index relative to vehicle controls. A stimulation index of 3 or greater is considered to indicate skin-sensitizing potential. One further modification adopted by three of the laboratories was to analyze nodes from individual animals and, thereby, permit statistical evaluation. This allowed a direct comparison of statistical significance with the conventional stimulation index as criteria for a positive response. The data indicate that, while statistical evaluation may provide, in some instances, for small increases in sensitivity, this may be at the expense of some loss of selectivity. There are, however, insufficient data presently to draw firm conclusions regarding the relative value of statistical analysis. These studies demonstrate that the local lymph node assay is sufficiently robust to accommodate minor procedural and technical modifications without material changes in test performance.

Analysis of Variance↗
PubMed1995

Cytokine regulation of chemical sensitization.

The skin is an immunologically active tissue. Epidermal cells, both keratinocytes and Langerhans cells (LC), produce constitutively or can be stimulated to produce a variety of cytokines, many of which play important roles in the induction and regulation of allergic responses to sensitizing chemicals. Tumor necrosis factor alpha (TNF-alpha) provides the signal for LC migration from the skin and granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin 1 (IL-1) and other cytokines effect the functional maturation of LC and their acquisition of immunostimulatory potential. The initial stimulus for induced or increased epidermal cytokine production derives from chemical exposure, or some other form of skin trauma. However, some epidermal cytokines are regulated in paracrine or autocrine fashion by other cytokines produced locally. The availability of epidermal cytokines has a major impact on the induction of sensitization and on the characteristics of immune responses to chemical allergens.

Animals↗