Biomedical subjects

R J Dearman

Publications and source records attributed to R J Dearman.

At least 127 records · Page 7Linked to original sources

PubMed1995

Streptozotocin: inherent but not expressed skin sensitizing activity.

We have shown previously that the alkylating agent streptozotocin (STZ) fails to induce responses in the murine local lymph node assay, a predictive test for contact sensitizing potential. In the present study, we demonstrate that this same compound when injected intradermally into the ears of mice provokes a dose-dependent induction of draining lymph node cell proliferation. These data indicate that the intrinsic immunogenicity of STZ is not displayed in the local lymph node assay under conditions of conventional topical exposure, secondary to a failure to cross the lipophilic stratum corneum in sufficient quantities. This finding has implications for the discernment of structure-activity relationships in contact sensitization.

Animals↗

PubMed1995

Identification of dendritic cells as a major source of interleukin-6 in draining lymph nodes following skin sensitization of mice.

Skin sensitization with chemical allergens is associated with the activation and proliferation of T lymphocytes within lymph nodes draining the site of exposure. These events are accompanied by the secretion of interleukin-6 (IL-6) by lymph node cells (LNC). We have investigated the cellular source of IL-6 seventy-two hours following primary exposure of mice to the contact allergen oxazolone. Immunocytochemical analyses of sections of activated lymph nodes have revealed that cells expressing IL-6 are located within the T-dependent lymph node paracortex, with none present in lymphoid follicles. Cells which expressed IL-6 cofractionated exclusively with LNC of low buoyant density, the majority of which also expressed membrane Ia and had a dendritic morphology. Depletion of dendritic cells from LNC culture was associated with a significant decrease in the secretion of IL-6 by the residual population. These data demonstrate that dendritic cells are a major source of IL-6 within lymph nodes during primary immune responses to cutaneous antigens.

Animals↗

PubMed1995

Differential cytokine production following chronic exposure of mice to chemical respiratory and contact allergens.

It has been demonstrated previously that a selective pattern of mitogen-inducible interleukin-4 (IL-4) production becomes apparent in mice after temporal evolution of the immune response to different classes of chemical allergen. Mitogen-stimulated draining lymph node cells (LNC) isolated after primary exposure to both the respiratory allergen trimellitic anhydride (TMA) and oxazolone, a contact allergen, secreted similar amounts of IL-4. Following secondary exposure, however, TMA, but not oxazolone, caused a marked increase in IL-4 production, consistent with the stimulation by TMA of a T-helper type-2 (Th2)-type response. In the present study, cytokine production characteristic of Th1 (interferon-gamma; IFN-gamma) and Th2 (IL-4 and IL-10) cell activation was examined following chronic exposure of mice to allergen over a 13-day period. In accord with previous studies, chronic exposure to TMA, but not to oxazolone, resulted in a substantial potentiation of mitogen-inducible IL-4 secretion. In addition, spontaneous IL-10 production by TMA-activated LNC was significantly higher than by cells prepared from oxazolone-exposed animals. The lower levels of Il-4 and IL-10 elaborated by oxazolone-activated LNC were not attributable to a reduced potential to secrete cytokine per se, as significantly more IFN-gamma was produced compared with TMA-activated LNC. It is proposed that these divergent cytokine production patterns reflect the selective stimulation of Th1- and Th2-type responses by contact and respiratory chemical allergens.

Allergens↗

PubMed1994

The local lymph node assay: developments and applications.

The murine local lymph node assay is a predictive test method for the identification of contact allergens in which sensitizing activity is measured as a function of induced proliferative responses in lymph nodes draining the site of application. In this article the development and validation of the assay are described and comparisons with guinea pig predictive test methods discussed. In addition we examine the advantages and limitations of the method and consider new opportunities and applications of the assay in the context of the toxicological evaluation of sensitizing potential.

Allergens↗

PubMed1994

Induction of respiratory hypersensitivity to diphenylmethane-4,4'-diisocyanate (MDI) in guinea pigs. Influence of route of exposure.

The induction of respiratory sensitization in guinea pigs to diphenylmethane-4,4'-diisocyanate (MDI), a known human respiratory allergen, has been investigated and different routes of exposure compared. Guinea pigs were exposed to MDI by i.d. injection, by topical application or by inhalation. Pulmonary hypersensitivity was measured subsequently as a function of changes in respiratory rate following challenge with atmospheres containing MDI. In addition, contact hypersensitivity was measured by topical challenge and antibody responses evaluated by enzyme-linked immunosorbent assay (ELISA) and passive cutaneous anaphylaxis (PCA). Attempts to sensitize guinea pigs by inhalation exposure to MDI were unsuccessful. Antibody responses and contact sensitization were both infrequent and low grade, and no animals exhibited pulmonary responses following challenge with atmospheric MDI. In contrast, sensitization by either i.d. injection or topical application of MDI induced antibody responses in the majority of animals. Moreover, a proportion of animals in each case exhibited pulmonary responses following subsequent inhalation challenge. These data indicate that the route of exposure influences markedly the effectiveness of sensitization to respiratory allergens such as MDI and that skin contact may be an important cause of occupational respiratory allergy.

Administration, Inhalation↗

PubMed1994

Cytokine-mast cell interactions: relevance to IgE-mediated chemical allergy.

Recent work has shown that certain cytokines (inducible secreted proteins) are potent regulators of mast cell development and secretory function. We know also that sensitization of mice to chemical allergens induces T cell-dependent immune responses in which cytokines play an important role. Combining these observations, we postulate that in vivo T cell responses might influence, via the production of cytokines, the behaviour of mast cells in situ. In support of this hypothesis we have found that mast cells isolated from chemical allergen-sensitized mice show enhanced responsiveness to IgE-dependent activation in vitro. This effect is seen with chemical allergens that are either contact or respiratory sensitizers in man. Although respiratory and contact allergens cannot be distinguished according to their ability to modulate mouse mast cell function in vivo, they can be separated on the basis of their differential ability to induce specific IgE-dependent mast cell sensitization. In conclusion, the mouse may offer a useful model for investigating and predicting the potential of chemicals to act as mast cell promoting agents and/or respiratory sensitizers.

Allergens↗

PubMed1994

Serological responses induced in mice by immunogenic proteins and by protein respiratory allergens.

It is known that a variety of materials, including both low molecular weight chemicals and proteins, is able to induce occupational respiratory allergy. We have shown previously that exposure of mice to chemical respiratory sensitizers results in both a marked increase in the serum concentration of IgE and the appearance of specific IgE antibody. In the present study we have examined the characteristics of immune responses induced in mice following intraperitoneal exposure to 3 protein respiratory allergens, ovalbumin (OVA), a lipase from Aspergillus oryzae (LP) and an amylase from Bacillus subtilis (AM) and to a fourth protein, bovine serum albumin (BSA), which is considered usually not to cause respiratory sensitization. Under conditions where all proteins provoked IgG antibody responses, only OVA, LP and AM elicited specific IgE antibody. As judged by passive cutaneous anaphylaxis (PCA) assay, BSA failed to induce an IgE response. In contrast to chemical respiratory sensitizers, the protein allergens examined here failed to cause a substantial increase in the serum concentration of IgE; OVA and AM induced no increase in serum IgE and LP only a comparatively modest increase relative to control values. In conclusion, these data demonstrate that while protein respiratory allergens are able to provoke specific IgE antibody, they fail to cause a marked increase in the concentration of this immunoglobulin in the sera of treated mice. It would appear, therefore, that the mouse IgE test, which seeks to evaluate chemical respiratory sensitization potential as a function of induced changes in the concentration of serum IgE, will be inappropriate for the identification of protein respiratory allergens. Nevertheless, identification of protein allergens may be possible by exploiting the observations reported here that such proteins induce in mice specific IgE antibody responses.

Allergens↗

PubMed1994

Interleukin-6 production by draining lymph node cells following primary contact sensitisation of mice: relationship to the proliferative response.

Interleukin-6 (IL-6) production and proliferative responses by draining lymph node cells were studied in mice exposed topically to a series of chemicals. Chemicals with the capacity to induce sensitisation, but not non-sensitisers, promoted both IL-6 production and lymph node cell proliferation ex vivo. The responses exhibited similar kinetics, were dependent upon the dose of topically applied allergen, and correlated significantly. We demonstrate that the main source of IL-6 within draining lymph nodes is not proliferating T lymphocytes. The induction of a strong IL-6 response, and the relationship of this to cellular proliferation indicate that production of this cytokine within the lymph node is closely associated with the induction of contact sensitivity in mice.

Animals↗

PubMed1994

The kinetics of cytokine production by draining lymph node cells following primary exposure of mice to chemical allergens.

Skin sensitization with chemical allergens is associated with the activation and proliferation of lymphocytes in lymph nodes draining the site of exposure. As lymphocyte activation is regulated by the action of cytokines, we have investigated the nature and kinetics of cytokine production by draining lymph node cells (LNC) from mice, following their primary exposure to chemical allergens. Both interleukin-1 (IL-1) and IL-6 were induced in a biphasic manner following primary exposure of mice to oxazolone or to dicyclohexylmethane-4,4'-diisocyanate (HMDI). The initial phase of production occurred when LNC were prepared from mice 8-20 hr following exposure, while the second peak was coincident with the maximal proliferative response at 72 hr. Increased IL-4 production was observed only when LNC were prepared 96 hr following sensitization. Despite vigorous lymphocyte proliferation there was no evidence for IL-2 production by draining LNC. The ordered and transient pattern of cytokine production that occurs during the afferent phase of contact sensitization suggests that sequential cytokine signals may be involved in regulating the characteristics of the response generated within the draining lymph node.

Allergens↗

PubMed1994

Inducible interleukin-4-secreting cells provoked in mice during chemical sensitization.

It has been demonstrated previously that chemical contact and respiratory allergens differ with respect to the quality of immune responses they will provoke in mice. Trimellitic anhydride (TMA), a human respiratory allergen, induces in mice responses consistent with the preferential activation of Th2-type cells, resulting in the production of IgE anti-hapten antibody and an increase in the serum concentration of IgE. In contrast, oxazolone (OX), a potent contact allergen considered not to cause respiratory hypersensitivity, induces instead Th1-type responses in mice characterized by vigorous IgG2a antibody production and a failure to elicit IgE. In the present study we have extended these investigations and have examined the capacity of these chemicals to stimulate inducible interleukin-4 (IL-4) production by draining lymph node cells (LNC). IL-4 was measured in the supernatants of draining LNC cultured for various periods in the presence or absence of concanavalin A (Con A). Following primary topical exposure to the chemical allergens, Con A-stimulated LNC from OX-treated mice secreted significantly more IL-4 than did LNC from mice exposed to trimellitic anhydride (TMA). A different pattern of IL-4 secretion was observed following culture with Con A of LNC prepared from lymph nodes draining the sites of secondary exposure to these chemicals. In this case significantly higher concentrations of IL-4 were produced by TMA-treated mice. Detectable levels of IL-4 (> 300 pg/ml) were not found following culture of draining LNC from sensitized mice in the absence of Con A or following culture of LNC from naive mice with or without Con A. These data demonstrate that chemical allergens of different types stimulate discrete and changing patterns of inducible IL-4 synthesis consistent with the selective activation of Th-cell subpopulations.

Allergens↗

PubMed1994

Interactions of IFN-gamma with IL-3 and IL-4 in the regulation of serotonin and arachidonate release from mouse peritoneal mast cells.

We have examined the interactions between interferon-gamma (IFN-gamma), interleukin-3 (IL-3) and interleukin-4 (IL-4) in the regulation of IgE/antigen-induced secretory responses of mouse peritoneal mast cells. The cytokines were added either alone or in various combinations to cultured mast cells sensitized passively with IgE antibody. In experiments with unfractionated peritoneal cells (containing approx. 1% mast cells), IL-3 and IL-4 enhanced in an additive manner antigen-induced release of serotonin (5-HT), while IFN-gamma inhibited release regardless of whether IL-3 and/or IL-4 were present. In experiments employing mast cells purified to > 90%, IL-3 and IL-4 retained their enhancing activities whereas the inhibitory effect of IFN-gamma was considerably diminished. Nevertheless, IFN-gamma still inhibited significantly IL-4-enhanced secretion. The effects of IL-3 and IL-4 +/- IFN-gamma on arachidonate release were identical to those seen for 5-HT release, indicating that the secretion of both preformed mediators and newly synthesized eicosanoids is regulated in a similar way by these cytokines.

Animals↗

PubMed1993

Mechanistic relationship among mutagenicity, skin sensitization, and skin carcinogenicity.

Twenty organic Salmonella mutagens, seven of which (including benzo[a]pyrene) are established skin carcinogens, and one of which (2-chloroethanol) is a well-defined noncarcinogen to skin, have been evaluated for skin-sensitizing activity using the local lymph node assay. The relative mutagenicity of the agents to Salmonella was also established. Fourteen of the chemicals were positive in the local lymph node assay, including the seven skin carcinogens. 2-Chloroethanol was inactive as a sensitizing agent. We suggest that a variety of factors contributes to the lack of sensitizing activity of the remaining six bacterial mutagens: extremes of intrinsic chemical reactivity, high water solubility reducing dermal translocation, and inappropriate dermal metabolism. Two reference skin-sensitizing agents (an oxazolinone and fluorescein isothiocyanate) were established as in vitro clastogens after their recognition as nonmutagens to Salmonella. These data imply that mutagenicity, rather than simply activity in the Salmonella assay, is a primary stimulus for electrophilic sensitization and carcinogenic initiation in the skin. We conclude that genotoxicity data for an agent can provide indications of the agent's potential to induce skin sensitization and that genotoxins which are skin-sensitizing agents have an enhanced potential to initiate skin carcinogenesis. We suggest that common, albeit individually distinct, structure-activity relationships underpin genotoxicity, skin sensitization, and the initiation of skin carcinogenesis. These relationships should simplify the hazard evaluation of chemicals and contribute to a reduction in animal usage. Several predictions of skin carcinogenicity are made based on the data presented.

Animals↗

PubMed1993

Influence of sodium lauryl sulphate on 2,4-dinitrochlorobenzene-induced lymph node activation.

The influence of the anionic surfactant sodium lauryl sulphate (SLS) on the ability of the contact allergen 2,4-dinitrochlorobenzene (DNCB) to provoke draining lymph node cell proliferative responses, a correlate of skin sensitizing potential, has been examined in mice. Topical application of 10% SLS with 0.1% DNCB caused a more vigorous proliferative response than did exposure to 0.1% DNCB alone. Lower concentrations (0.1% or 1%) of SLS were ineffective and 10% SLS failed to influence proliferative responses to higher concentrations (0.5% or 1%) of DNCB. Using an in vitro model for measurement of percutaneous absorption 10% SLS was shown not to increase the skin penetration of 0.1% DNCB. We therefore examined the influence of SLS on the accumulation of dendritic cells (DC) in lymph nodes draining the site of exposure, an important early event during the induction phase of skin sensitization. The frequency of DC in draining nodes was measured following topical application of SLS, DNCB or a combination of both. Epicutaneous exposure to 0.1% DNCB caused only a modest increase in the number of lymph node DC. However, 10% SLS or a mixture of 10% SLS with 0.1% DNCB each resulted in a significant elevation of DC numbers. It is proposed that SLS augments the skin sensitizing potential of sub-irritant concentrations of DNCB via an increase in the number of immunostimulatory DC which reach the draining nodes.

Administration, Cutaneous↗

PubMed1993

Approaches to the identification and classification of chemical allergens in mice.

During the last 10 years understanding of the immunobiological mechanisms whereby chemicals induce allergy has increased significantly. In parallel there have emerged opportunities to develop alternative methods for the prospective identification and classification of chemical contact and respiratory allergens. Attention has focused largely on the mouse, and several novel approaches to the identification of contact allergens have been described, among them the local lymph node assay, the mouse ear swelling test and, most recently, the noninvasive mouse ear swelling assay (MESA). Progress has been made also in defining methods for measuring respiratory sensitization potential in mice. Recent evidence indicates that respiratory and contact allergens provoke qualitatively different immune responses characteristic of selective T helper (Th) cell activation. Evaluation of the nature of immune responses induced in mice by chemicals may permit not only assessment of allergenic potential, but also prediction of the form allergic reactions will take.

Allergens↗

PubMed1993

Sensitization of mice to chemical allergens modulates the responsiveness of isolated mast cells to IgE-dependent activation.

It is known that the release of granule-associated inflammatory amines by isolated mouse tissue-type mast cells is subject to regulation in vitro by a number of cytokines that are produced during the immune response. In this study we investigated whether mast cell secretory function might also be subject to regulation in vivo during active sensitization. Mice were sensitized with one of three chemical allergens (trimellitic anhydride, TMA; 2,4-dinitrochlorobenzene, DNCB; or oxazolone) all of which induce contact sensitization and one of which (TMA) in addition causes immediate hypersensitivity. Peritoneal mast cells isolated from treated mice and sensitized passively with IgE released a greater proportion of cellular serotonin (5-HT) on stimulation either by anti-IgE or by specific antigen than did cells isolated from vehicle-treated controls. These results show that the function of mast cells is susceptible in vivo to regulatory influences that result from induction of an immune response.

Allergens↗

PubMed1992

The cellular and molecular basis for divergent allergic responses to chemicals.

Chemicals vary with respect to the nature of allergic reactions which they will elicit preferentially. A wide variety of environmental and industrial chemicals are known to cause allergic contact dermatitis (contact sensitivity). Some of these are able also to induce respiratory allergy. This article reviews the characteristics of immune responses to different classes of chemical allergens and the role which functional subpopulations of T helper (TH) cells and their soluble cytokine products play in the induction of allergic sensitization. In addition, new opportunities to identify and classify chemical allergens based upon characterization of divergent allergic responses is discussed.

Allergens↗

PubMed1992

Variable effects of chemical allergens on serum IgE concentration in mice. Preliminary evaluation of a novel approach to the identification of respiratory sensitizers.

A wide variety of chemicals may induce allergic contact dermatitis (contact sensitivity). Some chemical allergens may, in addition, cause respiratory sensitization. Topical exposure of mice to contact and respiratory chemical sensitizers results in the initiation of divergent immune responses characteristic of preferential activation of different functional subpopulations of T helper (TH) cells. In the present study we have sought to make use of these differences, particularly differences in the ability of contact and respiratory allergens to provoke IgE responses, and to question whether opportunities exist for the identification of chemicals with the potential for respiratory sensitization. We have examined alterations in the serum concentration of IgE following topical exposure of mice to seven chemical allergens; trimellitic anhydride (TMA), phthalic anhydride, diphenylmethane-4,4'-diisocyanate (MDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), isophorone diisocyanate (IPDI), oxazolone and 2,4-dinitrochlorobenzene (DNCB). Three of these--TMA, phthalic anhydride and MDI--are known human respiratory sensitizers. The other four--HMDI, IPDI, oxazolone and DNCB--appear not to cause respiratory allergy, or at least have a very limited potential to do so. At the concentrations tested, exposure to all chemicals caused a lymphocyte proliferative response in lymph nodes draining the site of application. However, exposure only to TMA, phthalic anhydride and MDI resulted in a substantial increase in the concentration of serum IgE. Treatment with HMDI and IPDI failed to induce any change in serum IgE concentration. DNCB and oxazolone caused only small and transient elevations of IgE that were considerably less marked than those observed with respiratory sensitizers.(ABSTRACT TRUNCATED AT 250 WORDS)

Allergens↗

PubMed1992

Characterization of murine immune responses to allergenic diisocyanates.

Chemicals may cause contact allergy. Some allergens may, in addition, cause respiratory sensitization. In previous investigations we have found that contact and respiratory sensitizers induce differential immune responses in mice characteristic of TH1 and TH2 T helper cell activation, respectively. In the present study we have examined immune responses in mice following topical exposure to three allergenic diisocyanates; diphenylmethane-4,4'-diisocyanate (MDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), and isophorone diisocyanate (IPDI). All three chemicals are contact allergens. MDI is in addition a known human respiratory allergen. HMDI and IPDI appear not to induce respiratory sensitization or at least do so very rarely. Exposure of mice to all chemicals resulted in a vigorous lymphocyte proliferative response in lymph nodes draining the site of application, and each caused contact sensitization. In common with other respiratory allergens, MDI induced an increase in the serum concentration of IgE and provoked considerably more IgG2b than IgG2a anti-hapten antibody; responses consistent with a preferential activation of TH2 cells. In contrast, under conditions where both caused lymph node cell proliferation and contact sensitization, neither HMDI nor IPDI induced a measurable antibody response of any class. These data provide additional evidence that different classes of chemical allergen cause divergent immune responses in mice. The possibility that these characteristics may facilitate not only the identification, but also classification, of chemical allergens is discussed.

Allergens↗