Allergic contact dermatitis

Lymph node cell proliferation assay in guinea pigs for the assessment of sensitizing potentials of chemical compounds

The efficacy of a lymph node cell proliferation assay in the guinea pig as a first stage screening method of predicting sensitizing potentials of chemicals was studied by using several haptens. Animals were sensitized by a single 24-hr occlusive patch (24 cp), intradermal injection (id) and a combination of id and 24 cp, at a concentration used for guinea pig conventional contact hypersensitivity assay methods. Control animals were treated with vehicle(s) only. Suspensions of the lymph node cells (LNC) were individually prepared and cultured with [3H]methyl thymidine ([3H]TdR). [3H]TdR incorporation was measured and a stimulation index (SI) was calculated as a ratio of the mean [3H]TdR incorporation in sensitized animals and the mean [3H]TdR incorporation in control animals. LNC sensitized by 24 cp with 2,4-dinitrochlorobenzene proliferated maximally and significantly at day 5, whereas this occurred at day 7 after id sensitization. Significant LNC proliferation and high SI values were obtained successively by a combination of 24 cp and id. Moreover, strongly sensitizing chemicals increased significant LNC proliferation (SI > 2.0); weakly to moderately sensitizing chemicals also induced significant LNC proliferation (SI = 1.3-1.7). On the other hand, a primary irritant, sodium dodecyl sulfate, failed to encourage LNC proliferation (SI approximately 1.0).

Immunopathological study on equine insect hypersensitivity ("kasen") in Japan

Equine "kasen" is a chronic dermatitis that occurs especially during the summer months. In the present study, skin lesions of kasen that were collected by biopsy from May to October were classified histopathologically into three stages: initial (Group I, 30 cases), developing (Group II, 48 cases) and regressing (Group III, 13 cases). The characteristic lesions were hyperkeratosis, an increase in the number of T-lymphocytes and Langerhans cells (positive for class II MHC) at the epidermo-dermal junction, oedema of the dermis and perivascular infiltration of eosinophils and mast cells. Ultrastructurally, numerous Birbeck granules were observed in the cytoplasm of Langerhans cells. These lesions were striking in Group II and less so in Group III. Kasen is therefore considered to be similar to Queensland itch and sweet itch as described in Australia and Britain, respectively. The histological features were characteristic of a type I and type IV allergic dermatitis.

Challenge assay in vitro using lymphocyte blastogenesis for the contact hypersensitivity assay

To confirm positivity in routine guinea pig studies, contact allergenicity was investigated by a challenge assay in vitro using a co-culture of autologous lymphocytes passed through a nylon-wool column and antigen-presenting cells (APCs) modified with or without antigen. Proliferation of the lymphocytes primed with ovalbumin and/or 2,4-dinitrochlorobenzene was antigen specific and dependent on the presence of APCs (peripheral blood monocytes, splenic macrophages and macrophages induced by liquid paraffin). For another nine haptens, primed lymphocytes proliferated significantly more than control lymphocytes; the stimulation index (SI; ratio between [3H]methylthymidine ([3H]TdR) incorporation of lymphocytes with antigen-modified APCs and [3H]TdR incorporation of lymphocytes with APCs not modified by antigen) was 1.6-4.8 in sensitized animals whereas it was about 1.0 in control animals. Sodium dodecyl sulfate did not cause lymphocyte proliferation. The SI value in vitro was correlated with both the positive rate in vivo (r = 0.736) and the mean response score in vivo (r = 0.645). Thus, it was possible to confirm that positivity in routine experiments was a true sign of allergy. A combination of this assay and short-term animal studies would provide an efficient assessment of the allergic potential of chemicals.

Antigen-specific IgG1-mediated epidermal cell injury: a component of contact hypersensitivity reactions in guinea pigs, measurable in vitro in full-thickness skin explants

Guinea pigs were sensitized by the topical application of either dinitrochlorobenzene (DNCB) or oxazolone on days 1, 2, 3, and 10. Seventeen days after the first treatment with the sensitizer, full-thickness 1.0-cm2 explants of untreated areas of skin were topically exposed in vitro to these contactants. Compared to the response of skin from control guinea pigs, skin from specifically sensitized animals showed a dose-related increase in the number of epidermal cells containing vacuoles. A specific increase in epidermal microblistering paralleled the increase in epidermal vacuolization. In addition, skin explants from sensitized animals (exposed to the contactant) showed a specific decrease in the incorporation of [14C]leucine. Full-thickness skin explants from unsensitized guinea pigs were sensitized in vitro by the intradermal injection of serum IgG1 fraction from oxazolone-sensitized guinea pigs. In such passively sensitized explants, the specific contactant produced an increase in the number of epidermal vacuoles, an increase in the amount of microblistering, and a decrease in the number of mast cells detectable by Giemsa staining. To elicit this specific response, the concentration of the specific contactant had to be mildly injurious, as well as antigenic. This requirement for nonspecific injury could be met by topically exposing skin explants to a nonspecific irritant followed by a sub-threshold concentration of the specific contactant. In contrast to vacuole formation and blistering, contactant-specific degranulation of mast cells (measured by the decrease in their number) did not require irritant levels of the contactant. These studies show that several components of contact sensitivity reactions can be reproduced in vitro by the passive transfer of sera containing antigen-specific immunoglobulins. Banks of such sera might, therefore, be useful in identifying (in human populations) many pre-existing sensitivities to chemical compounds.

Examination of tetrachlorosalicylanilide (TCSA) photoallergy using in vitro photohapten-modified Langerhans cell-enriched epidermal cells

Lymphocytes from BALB/c mice photosensitized in vivo to tetrachlorosalicylanilide (TCSA) were investigated to determine whether they could be stimulated to proliferate when cultured with Langerhans cell-enriched cultured epidermal cells (LC-EC) photohapten-modified in vitro with TCSA + UVA radiation. Cultured LC-EC were photohapten-modified in vitro by irradiation in TCSA-containing medium using a 1000-watt solar simulator equipped with filters to deliver primarily UVA radiation (320-400 nm). Lymphocytes from TCSA-photosensitized mice were incubated with LC-EC that had been treated in vitro with 0.1 mM TCSA and 2 J/cm2 UVA radiation (TCSA + UVA). Responder lymphocytes demonstrated a significant increase in their blastogenesis response compared to lymphocytes that were incubated with LC-EC irradiated with UVA prior to treatment with TCSA (UVA/TCSA) or with LC-EC that had received no treatment. Lymphocytes from naive mice or mice photosensitized with musk ambrette (MA) demonstrated a significantly lower response to LC-EC modified with TCSA + UVA, indicating the specificity of the response. Maximum blastogenesis response was achieved when LC-EC were treated with 0.1 mM TCSA and a UVA radiation dose of at least 0.5 J/cm2. Epidermal cells depleted of LC by treatment with anti-Ia antibody plus complement or by an adherence procedure were unable to stimulate this blastogenesis response. Epidermal cells treated in vitro with TCSA + UVA demonstrated enhanced fluorescence compared to control cells. The fluorescence observed was not restricted to any specific epidermal cell type; however, fluorescence microscopy studies revealed that dendritic Ia-positive cells, presumably LC, were also TCSA fluorescent. Flow cytometry showed that Ia-positive epidermal cells demonstrated the greatest UV fluorescence when treated with TCSA + UVA compared to both cells irradiated with UVA and subsequently treated with TCSA and untreated cells. This is consistent with the enhanced antigen presentation capability of TCSA + UVA treated LC-EC, which leads to the conclusion that LC photohapten-modified in vitro with TCSA + UVA demonstrate enhanced TCSA fluorescence and are capable of stimulating lymphocytes from TCSA photosensitized mice in an antigen-specific manner.

Cross-antigenicity between the scabies mite, Sarcoptes scabiei, and the house dust mite, Dermatophagoides pteronyssinus

This study demonstrated that antigens of the parasitic mite Sarcoptes scabiei (SS) cross-react with antigens of the house dust mite Dermatophagoides pteronyssinus (DP). Crossed immunoelectrophoresis (CIE) reaction of SS extract with rabbit anti-DP serum resulted in multiple immunoprecipitates. Reciprocal CIE reactions gave similar results. Immunoprecipitates from both reactions bound IgE in the sera of dust-mite-sensitive patients who had no history of scabies. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis resolved protein/peptide bands of both SS and DP also bound serum IgE from dust-mite-allergic patients following immunoblotting. Non-allergic control sera gave no IgE binding to either SS or DP antigens. These results indicate that patients with atopy to dust mites exhibit circulating antibodies built to DP but that recognize determinants on SS antigens. It is highly probable that scabietic patients build antibodies to SS antigens that also recognize DP antigens. These results raise questions concerning the reported isotypic antibody responses to SS because the sensitivity of scabietic patients to house dust mites has not been previously evaluated. This cross-reactivity may play an important role in the susceptibility to scabies and its clinical manifestations.

Depletion and repopulation of Langerhans cells in nonsegmental type vitiligo

The role of Langerhans cells in the pathogenesis of nonsegmental type vitiligo is still unknown. In this study, biopsies were taken from 26 patients at various stages of nonsegmental type vitiligo and morphometrically observed to investigate the kinetics of Langerhans cells in patients at various stages of the disease. A marked depletion of OKT6-positive and ATPase-positive epidermal dendritic cells was noted in patients with active nonsegmental type vitiligo. A repopulation of both OKT6-positive and ATPase-positive epidermal dendritic cells was noted in patients with stable nonsegmental type vitiligo. Profound depletion of epidermal OKT6-positive and ATPase-positive dendritic cells was noted in patients with repigmenting nonsegmental type vitiligo receiving treatments involving topical use of 0.05% Fluocinonide cream or PUVA photochemotherapy. Transmission electron microscopy confirmed the absence of epidermal dendritic cells (Langerhans cells and intermediate cells) in patients with active and repigmenting nonsegmental type vitiligo. In active nonsegmental type vitiligo, two possible explanations are proposed for the depletion of OKT6-positive and ATPase-positive epidermal dendritic cells (presumptive Langerhans cells): 1) the cells are destroyed by cytotoxic factors released during the course of destruction of melanocytes in active vitiligo, and/or 2) they leave the epidermis and migrate to regional lymph nodes to present certain antigens which are released from certain destroyed epidermal cells (keratinocytes or melanocytes) during the course of active vitiligo. The repopulated epidermal Langerhans cells may result from phenotypically transformed dermal dendritic cells in the depigmented lesions of patients with stable vitiligo. Since various therapies which result in repigmentation deplete the density of epidermal Langerhans cells markedly, it is suggested that depletion of epidermal Langerhans cells in stable vitiligo may aid in repigmentation. It is also proposed that the repopulated epidermal Langerhans cells may play a role in inhibiting the proliferation of epidermal melanocytes in depigmented lesions of stable vitiligo, thus various methods of treatment which deplete the Langerhans cells may eventually aid in the repigmentation of nonsegmental type vitiligo.

Optimization of an in vitro lymphocyte blastogenesis assay for predictive assessment of immunologic responsiveness to contact sensitizers

Current methods for the predictive and diagnostic assessment of contact sensitization rely on the visual scoring of skin reactions. Predictive animal tests, generally using guinea pigs, require a relatively large number of animals to produce a sufficient database for interpreting skin reaction scores. In vitro assays have the potential of being more quantitative than skin testing and, if so, would require fewer animals. However, although in vitro assays are commonly used to study the cellular immune response to strong contact sensitizers, there has been little effort to validate them for predictive assessment purposes. We have optimized an in vitro lymphocyte blastogenesis assay for detecting the response of mouse lymphocytes to strong contact sensitizers with the eventual objective of applying this assay to moderate and weak sensitizers as well. Lymph node lymphocytes from mice sensitized to the strong contact allergens, dinitrochlorobenzene (DNCB), dinitrofluorobenzene (DNFB), or trinitrochlorobenzene (TNCB), responded [greater than or equal to 12,000 counts per minute (CPM) above background] when cultured with water soluble chemical analogues, di- or trinitrobenzene sulfonic acid (DNBS or TNBS). However, the strong sensitizer, oxazolone (OXAZ), has no water soluble analogue and lymphocytes from mice sensitized to OXAZ responded poorly in vitro (less than 2000 CPM) to an ethanol-solubilized OXAZ preparation in spite of very strong in vivo sensitization (ear swelling assay). To increase the assay sensitivity, for OXAZ, we modified the antigen presentation conditions by using 1) solubilized antigen-modified adherent spleen cells, 2) dendritic cells from the draining lymph nodes of antigen painted mice, and 3) antigen-modified Langerhans cell-enriched cultured epidermal cells (EC). These approaches increased OXAZ-directed responses to greater than 7000, greater than 20,000, and greater than 100,000 CPM, respectively, under culture conditions optimized for cell density, responder: stimulator cell ratio, culture duration, and responder cell type. Our results represent a first attempt to directly modify cultured epidermal cells with OXAZ and use these cells to stimulate OXAZ-directed blastogenesis in microtiter plate cultures. This optimized assay is now under evaluation for predictive assessment of contact sensitizers relevant to occupational and consumer exposures.

Zinc effects on nickel dermatitis in the guinea pig

Prevention of NiSO4 induced allergic contact dermatitis (ACD) using ZnSO4 in drinking water was studied in a guinea pig model. Without ZnSO4 interventions, nickel (Ni)-exposure resulted in significantly higher (p less than 0.05) stimulation indices (SIs) as compared to non-exposed controls, using NiSO4 as an allergen in the lymphocyte transformation test (LTT). Oral intake of ZnSO4 at both 250 micrograms/ml double-distilled deionized water (DDD) and 500 micrograms/ml DDD resulted in lower SIs than those of control guinea pigs drinking only DDD; the 250 micrograms/ml group had significantly lower SIs (p = 0.025) than controls. There was no significant correlation between intradermal test responses and the SI values of individual guinea pigs exposed to NiSO4. Mean zinc (Zn) concentrations in skin and in whole blood were not statistically different between the NiSO4 exposed control and Zn supplemented groups, nor between Ni-sensitive and non-sensitive animals within groups. The rôle of Zn homeostasis, rôle of the Langerhans cell, effect of Zn supplementation on Ni ACD in other species, and possible blocking effects of other metals should be investigated in future studies.

The allergenicity of complex cations

A homologous series of eight quaternary ammonium salts (quats) were used as complex cations in a survey of contact hypersensitivity in guinea pigs. Two of the quats tested were found to be strong allergens which was due to stable association with membrane lipids at the surface of epidermal cells. This surface complexation reaction was studied in detail by using a spin-labelled quat of intermediate allergenicity. Electron spin resonance was used to show that stable "ion pairs" are formed between membrane receptor sites and the two strong allergens. Information was obtained on the specificity and kinetics of immunogenic complex formation as well as on the position and orientation of these haptens on epidermal receptor sites in vivo.