Use of an optimized in vitro lymphocyte blastogenesis assay to detect contact sensitivity to nickel sulfate in mice

Preclinical skin sensitization testing of antihistamines: guinea pig and local lymph node assay responses

Preclinical test methods for allergic contact sensitivity have been widely used for sensitization hazard identification and, with consideration of human exposure conditions, have also been valuable tools for sensitization risk assessment. For many years, the guinea pig has been the test species of choice with a variety of test methods developed to assess the sensitization response. More recently the local lymph node assay (LLNA) in mice has been developed to provide a more objective index of sensitization potential. The standardized methods have proven to be very well suited to most situations in which potential skin sensitization of a chemical needs to be assessed before human exposure. A potential difficulty with all these relatively limited exposure preclinical test methods, however, is in the ability to detect weak contact allergens that prove to be significant clinical allergens due to chronic topical exposure, exposure to compromised skin, and/or highly exaggerated exposure through transdermal delivery. This has been shown with the transdermal drug clonidine and might also be the case for topical antihistamines. The latter are considered significant clinical contact allergens, although predictive preclinical test data are minimal or lacking. A series of guinea pig (modified Buehler) tests with two common antihistamine compounds (triprolidine and diphenhydramine) and LLNA on these and two other compounds (chlorpheniramine and promethazine) was conducted. Positive Buehler test results required use of penetrating vehicle systems and a modified nine-induction patch regimen. Positive LLNA responses were obtained with all four materials (to varying degrees) only if the application site was pre-abraded or a penetrating vehicle (dimethylformamide) was used. These data support the notion that preclinical sensitization test methods can be modified to increase sensitivity. This may be critical for preclinical assessment of topical/transdermal drugs or other materials with chronic or high-concentration exposures in man.

Assessment of contact sensitivity of four thiourea rubber accelerators: comparison of two mouse lymph node assays with the guinea pig maximization test

Contact sensitivity of four thiourea rubber accelerators, diphenylthiourea (DPTU), dilaurylthiourea (DLTU), dibutylthiourea (DBTU) and diethylthiourea (DETU), was evaluated by a new sensitive mouse lymph node assay (SLNA) and the murine local lymph node assay (LLNA). The results of the SLNA and LLNA were compared with the data of the guinea pig maximization test (GPMT). In the LLNA and SLNA, the sensitizing activity was measured as a function of draining lymph node activation following application of the test chemicals. Of these four thioureas, three (DETU, DBTU and DPTU) were not classified as skin sensitizers in the LLNA. The SLNA successfully detected the sensitivity of all thioureas tested. This result indicated that the SLNA was, in these cases, more sensitive than the LLNA for identification of contact allergens. The order of sensitization potential observed from the SLNA was DPTU (greatest), DLTU, DBTU and then DETU (least). The predictions of sensitizing potential and the order of the sensitizing capacity of four thioureas by the SLNA and the GPMT are very similar.

Kinetics and specificity of nickel hypersensitivity in the murine model

Nickel contact dermatitis appears to be almost exclusively a disease of females despite the increasing exposure of males to nickel. Successful murine models of nickel allergic contact dermatitis have been described. The purpose of this study is to investigate the kinetics and specificity of the response in this model and to examine if any differences exist between male and female. Mice were sensitised epicutaneously with nickel sulphate in aqueous solution of varying concentration, volume and duration of application. Following intradermal challenge, dose dependent response kinetics which approximated linearity were demonstrated upto the point of toxicity. Sensitised mice were challenged with Cobaltous chloride, Chromic chloride and Cupric sulphate and demonstrated no evidence of cross sensitivity to cobalt or chrome. Copper produced an irritant response making interpretation difficult. Earlier and stronger responses were observed in female mice, however these differences fell short of statistical significance. The results of the present study therefore establishes a reliable model for nickel hypersensitivity, that demonstrates both specificity and dose dependent kinetics without significant sex differences.

A sensitive mouse lymph node assay with two application phases for detection of contact allergens

A predictive test using mice for the identification of contact sensitizing chemicals was developed. Contact sensitizing activity is measured as a function of draining lymph node activation following application of test chemical. Experimental conditions for assessment of induced lymph node cell (LNC) responses have been optimized. BALB/c mice were initially treated with intradermal injections of test chemical in Freund's complete adjuvant emulsion. Five days after intradermal injection, mice were exposed topically to chemical in vehicle on the ears daily for 3 consecutive days. Next day following the final exposure, changes in lymph node weight, total cell number in the draining lymph nodes and LNC proliferation for 24 h culture were assessed. The performance of the method was evaluated with ten sensitizing chemicals and a non-sensitizing irritant, sodium lauryl sulfate (SLS). The LNC proliferation induced by combination of intradermal injection and topical application of sensitizing chemicals was more clearly increased than that following only topical application. With the single exception of sulfanilic acid, the method developed was able to detect the sensitizing capacity of chemicals that failed to induce sensitization in the local lymph node assay. Under the conditions used, SLS did not induce measurable lymph node responses. These results suggest that the mouse lymph node assay can provide a sensitive screening test for weak to moderate sensitizers. In addition, the assay offers the advantages of objective and quantitative endpoints, and is suitable for the evaluation of colored or irritant chemicals.

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.

Oral induction of tolerance to nickel sensitization in mice

Antigen contact via the alimentary tract prior to sensitization may result in systemic immunologic unresponsiveness ("oral tolerance"). The induction of oral tolerance seems an attractive strategy to combat undesired immune responses, such as allograft rejection and autoimmune and allergic diseases. We describe clear and reproducible sensitization to nickel in mice reared under nickel-free conditions. Hypersensitivity was induced by injecting nickel sulfate intradermally into the flank skin and elicited by injecting the metal salt into the pinnae of the ears. The effectiveness of orally induced hyporesponsiveness could be inferred from a low degree of hypersensitivity obtained with mice raised and maintained in cages with nickel-releasing covers and water nipples. This mouse model for the assay of nickel hypersensitivity was used for oral tolerance studies by administrating non-toxic doses of nickel sulfate in drinking water or intragastrically prior to sensitization. In these animals, the development of delayed-type hypersensitivity was suppressed in a dose-dependent way, and the hyporesponsiveness could be transferred by CD8+ cells. The antigen specificity of this oral tolerance could be demonstrated by the concomitant use of sensitization and challenge procedures for nickel and chromium. The hypersensitivity assay described provides a versatile, highly reproducible experimental model to study immunoregulation of oral tolerance to clinically relevant metal allergens.

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.

Detection of contact sensitivity of metal salts using the murine local lymph node assay

The local lymph node assay (LLNA) is a predictive test for the detection of contact allergens. Nickel and chromium sensitization are common cases in man. However, in a previous study topical application of nickel sulfate and potassium dichromate in aqueous solution failed to induce activation in the draining lymph node. This study describes the application of LLNA to evaluate the contact sensitivity of metal salts. The metal salts were applied in dimethylsulfoxide or aqueous ethanol solution. In some experiments, the skin of the ears was gently abraded using a needle prior to application of metal salts. The ability of seven metal salts to induce lymph node cell (LNC) proliferation was compared. Nickel, cobalt, chromium and copper salts increased LNC proliferation, whereas zinc, manganese and iron salts failed to induce LNC proliferation in this assay.

Skin sensitization--a critical review of predictive test methods in animals and man

With the exception of the Draize Test, the guinea-pig test methods currently accepted by regulatory authorities worldwide are well able to predict the potential of a material to cause skin sensitization. Nevertheless, (a) some methods are more sensitive than others (e.g. adjuvant tests are generally more sensitive than non-adjuvant tests); (b) methods cannot be sufficiently standardized to give full reproducibility of results between laboratories; and (c) most methods are based on subjective visual grading of skin reactions--difficulties thus arise when testing coloured or irritant materials. Laboratories must be able to show the sensitivity of the method(s) they use by demonstrating that positive reactions occur with mild/moderate contact allergens rather than the strong/extreme sensitizers currently recommended in certain guidelines, specifically in the EEC Test Method. The sensitivity of the adjuvant tests is such that it is possible to halve the minimum number of animals required by present regulatory guidelines without compromising the capacity of the tests to detect weak/mild sensitizers. A similar review has not yet been made for non-adjuvant tests. Alternative test methods, including some recently developed mouse models, offer several advantages, including more objective endpoints. These tests have not been extensively validated and this precludes their use at present for regulatory purposes other than to confirm the sensitization potential of a material. Two new test methods using mice, the Mouse Ear-swelling Test and the Local Lymph Node Assay, appear promising. They should undergo rigorous interlaboratory testing to determine their sensitivity and specificity. In vitro methods do not represent a viable alternative in the foreseeable future. An approach using quantitative structure-activity relationships is the most likely route to a non-animal model, but this will require considerable research, development and validation. Human sensitization tests have generally not been used for the classification of substances as non-sensitizers. This is because of an absence of internationally agreed test protocols, the lack of positive controls and because the methods for establishing the sensitivity of human tests are less developed than for animal tests. Nevertheless, for products for which direct human contact is intended, predictive tests in human volunteers can be considered. The EEC Directive for the Classification, Packaging and Labelling of Dangerous Substances provides a reasonable approach to the evaluation of skin sensitizers.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunosuppressive effects of clonidine on the induction of contact sensitization in the balb/c mouse

The clonidine transdermal therapeutic system (clonidine-TTS) has been associated with a significant incidence of allergic contact sensitization. This incidence was not predicted by premarket skin sensitization testing in animals or humans. One possible explanation lies in recent findings in guinea pigs that clonidine exposure could inhibit the elicitation of skin reactions to unrelated strong contact sensitizers. However, these studies also showed that clonidine pretreatment did not appear to affect the induction of contact sensitization. On this basis, we sought to specifically evaluate the induction phase of sensitization to clonidine as an alternative means of assessing its sensitization properties. The method selected was the assay of in situ lymphocyte proliferation in lymph nodes draining the sites of clonidine exposure, a method recently promoted as an alternative means to assess contact allergenic potential. Utilizing various induction application techniques and regimens, we were consistently unable to demonstrate clonidine's allergenic potential through such an assessment of lymphocyte proliferation. We were also unable to demonstrate sensitization by in vivo ear swelling or in vitro lymphocyte blastogenesis assay techniques. However, a subsequent assessment of the effect of clonidine exposure on the induction of sensitization to unrelated strong contact allergens demonstrated a consistent 40-70% inhibition of the proliferative response to the contact allergens oxazolone and trinitrochlorobenzene. This was similar to the degree of suppression produced by the corticosteroids fluocinonide and hydrocortisone when they were tested at 80 and 10 times lower concentrations. In addition, we observed a comparable inhibition of the ear swelling response to oxazolone. These data extend our knowledge of the immunomodulatory effects of clonidine and offer additional mechanistic insights into the failure of short-term predictive patch-test methods to detect this chemical's potential to induce allergic contact sensitization.