The local lymph node assay: an interlaboratory evaluation of interleukin 6 (IL-6) production by draining lymph node cells

Aerofloral studies and allergenicity of dominant pollen types in Taraba and Bauchi States of Northeastern Nigeria

Pollen and spores have been identified as major airborne bio-particles inducing respiratory disorders including allergic rhinitis and atopic dermatitis among hypersensitive individuals. The present study was conducted with a view to investigating monthly depositional rate of atmospheric palynomorphs to determine the influence of the immediate vegetation on airborne pollen distribution; allergenic activities of dominant atmospheric pollen types at selected study locations in Taraba and Bauchi States, Northeastern Nigeria. Bioaerosols were collected using Tauber-like pollen traps and subjected to standard palynological treatment procedures, microscopy and photomicrography. Plant enumeration within the surrounding vegetation revealed that some airborne pollen types were produced by local plants at the study locations. Spores of Nephrolepis sp., Pteris sp. and a trilete fern, as well as diatoms were also recovered. Crude protein contents of some dominant pollen types; Borreria verticillata (L.) G.F.W. Meyer and Panicum maximum Jacq. for Taraba State; Leucaena leucocephala (Lam.) de Wit. and Terminalia catappa L. for Bauchi State, were quantified and extracted to sensitize Mus musculus mice for serology (ELISA) and haematology (differential and total white blood cell counts). Statistical significance was tested and recorded in the correlation between levels of serological and haematological parameters elicited by each test group; differences between levels of these parameters elicited by each test group and those of the control, as well as at varying sensitization periods. In the Leucaena leucocephala test group, swollen body and histopathological morbid features showing more extensive areas of inflammatory cells and alveoli filled with fluid in the lungs, were recorded in two dead M. musculus, respectively. The study revealed that all the tested pollen types are possible allergens at the study locations, establishing a complexity of interaction among allergy mediators at varied periods of mice sensitization and forming a paradigm of human immune response to the different pollen allergens.

A highly sensitive and selective high pressure liquid chromatography with tandem mass spectrometry (HPLC/MS-MS) method for the direct peptide reactivity assay (DPRA)

While the HPLC/UV (high performance liquid chromatography coupled with ultra-violet spectrometry)-based DPRA (Direct Peptide Reactivity Assay) identifies dermal sensitizers with approximately 80% accuracy, the low selectivity and sensitivity of the HPLC/UV-based DPRA poses challenges to accurately identify the sensitization potential of certain chemicals. In this study, a high performance liquid chromatography coupled with tandem mass spectrometry (HPLC/MS-MS)-based DPRA was developed and validated according to the test guideline (OECD TG 442C). The final results were compared with the results from the traditional HPLC/UV-based guideline DPRA. This HPLC/MS-MS-based DPRA demonstrated similar performance compared to HPLC/UV-based DPRA using known dermal sensitizers and non-sensitizers according to the test guideline (OECD TG 442C). Following the validation, a challenge set of chemicals with either overlapping retention time with peptides, or higher hydrophobicity or chemicals potentially forming non-covalent interactions with peptides were assessed for dermal sensitization potential using both methods and the results were compared to existing in vivo data. The HPLC/MS-MS-based DPRA correctly predicted these chemicals as sensitizers or non-sensitizers; however, the HPLC/UV-based DPRA resulted in false-positive predictions for hydrophobic substances, chemicals with UV peaks overlapping with those of the peptide(s), and compounds that non-covalently interact with the peptides. These findings demonstrate the broader applicability and better sensitivity and selectivity of the LC/MS-MS-based DPRA over the traditional HPLC/UV-based guideline DPRA.

Comparison of flow cytometry and immunohistochemistry in non-radioisotopic murine lymph node assay using bromodeoxyuridine

Non-radioisotopic local lymph node assay (LLNA) employing 5-bromo-2'-deoxyuridine (BrdU) with flow cytometry (FACS) or immunohistochemistry (IHC) is gaining attention due to a regulatory issue of using radioisotope, (3)H-thymidine, in vivo in traditional LLNA. In this study, to compare the performance of these non-radioisotopic endpoints, 7 chemicals with known sensitizing potencies were examined in LLNA. Mice were topically treated with chemicals or vehicle on both ears for 3 days. After intraperitoneal injection of BrdU, bilateral lymph nodes were isolated separately and undergone respectively, FACS or IHC to determine BrdU incorporated lymph node cells (LNCs). Weight and histology of treated ears were also examined to evaluate chemical-induced edema and irritation. Both FACS and IHC could successively identify the skin sensitizers from non-sensitizers. Comparison of FACS and IHC with traditional LLNA revealed that FACS has a higher sensitivity although both assays produced comparable sensitivity and performance to traditional LLNA. In conclusion, non-radioisotopic LLNA using FACS and IHC can successfully detect sensitizers with a good correlation to traditional LLNA. Notably, FACS showed almost equivalent sensitivity and accuracy to traditional LLNA.

Intracellular expression of cytokines and granzyme B in auricular lymph nodes draining skin exposed to irritants and sensitizers

The murine local lymph node assay (LLNA) has been extensively utilized to evaluate sensitizing chemicals. However, there have been some concerns that its use to discriminate between classes of chemicals is minimal. It is thus desirable to identify better or alternative immune endpoints with in LLNA itself. Here, we evaluated the protein and/or mRNA levels of cytokines and granzyme B (GzmB), a cytotoxic lymphocyte product, to discriminate between sensitizers and irritants and to characterize the chemical sensitizers when used as supplemental indicators in LLNA endpoints. For this, CBA/N mice were topically treated daily with a well-known chemical sensitizer such as a strong contact sensitizer 1-chloro-2,4-dinitrobenzene (DNCB), a skin contact sensitizer 2-phenyl-4-ethoxymethylene-5-oxazolone (OXA), and a skin or respiratory sensitizer toluene 2,4-diisocyanate (TDI), and the non-sensitizing irritants, croton oil (CRO) and nonanoic acid (NA), for 3 consecutive days. The protein and/or mRNA levels in auricular lymph nodes draining the ear skin were then analyzed by real-time RT-PCR and immunoassay. The sensitizers, but not the irritants, evoked pronounced interleukin (IL)-2, IL-3 and IL-4 or interferon (IFN)-gamma. Significantly, different sensitizers evoked different cytokine patterns of IL-4 and IFN-gamma, as DNCB strongly up-regulated both IFN-gamma and IL-4, OXA up-regulated IFN-gamma strongly but IL-4 weakly, and TDI up-regulated IL-4 strongly but IFN-gamma weakly. The sensitizers also strongly up-regulated GzmB mRNA, while the irritants had a much weaker effect. Thus, these cytokines and GzmB mRNA may be useful as additional endpoints for discriminating between irritants and sensitizers or contact and respiratory sensitizers in the LLNA.

Clinical relevance of preclinical testing for allergic side effects

Immune-mediated hypersensitivity reactions include exaggerated humoral or cell mediated responses to specific antigens and may culminate in adverse, potentially life threatening effects. The immune status of the host and presence of infections or other disorders can alter the kind and extent of immune mediated side effects in individuals. Such variability in the immune status may influence the type of idiosyncratic reaction(s) that patients manifest. The issues typically encountered from a drug development standpoint include the potential for contact hypersensitivity, respiratory sensitivity, systemic hypersensitivity, photoallergy, and pseudoallergy. There are no accepted in vitro or in vivo models available to measure and predict all types of hypersensitivity reactions in humans. There is a need for the development of preclinical models to predict all types of hypersensitivity reactions in humans. The FDA immunotoxicology guidance document recommends doing preclinical testing in animal models for topical and inhalational drugs before initiation of multiple dose studies in humans. Any signs of potential immune related drug hypersensitivity should be further evaluated in an attempt to further understand the potential for hypersensitivity reactions in humans. In summary, existing preclinical models have limited capability for prediction of drug allergy in humans except for topical and inhalational drugs. Additional tools are needed to evaluate drugs in early development and improve performance of existing assays.

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.

Local lymph node assay with non-radioisotope alternative endpoints

The local lymph node assay has recently been accepted by regulatory agencies as a stand-alone alternate method for predicting allergic contact dermatitis. To compare the sensitivity of non-radioisotope methods with that of the standard assay, we determined if these modified methods would affect evaluation of sensitization potency. For this reason, we used 2,4-dinitrochlorobenzene (DNCB) and benzocaine for different sensitizing criteria. Female CBA mice were treated for 3 days with a test compound or vehicle applied to each side of both ears. Bilateral auricular lymph node proliferative activity was assessed by the following endpoints with incorporation of 3H-methyl thymidine (3H-TdR), bromodeoxyuridine (BrdU) in vivo, and BrdU ex vivo, IL-2 production, and proliferating cell nuclear antigen (PCNA) expression. Ear thickness was also tested. The strong sensitizer DNCB was detectable by any of the non-radioisotope endpoints as well as by radioisotope-dependent standard assay. On the other hand, when evaluating the weak sensitizer benzocaine, significant changes were evident in BrdU incorporation ex vivo and in vivo, and IL-2 production. We believe that these non-radioisotope methods can assess allergic contact dermatitis caused by chemicals even in the laboratory, where it can be difficult to handle radioisotopes.

IL-6 secretion by ex vivo whole blood cultures upon allergen stimulation

Allergen induced IL-6 synthesis by whole blood cultures was compared with skin prick allergen test results for the same group of individuals. Whole blood cultures from both allergic and non-allergic individuals secrete IL-6 at high allergen concentrations. When whole blood cultures from controls were incubated with serial dilutions of allergens it was found that IL-6 induction was abolished at lower allergen dilutions (allergen threshold concentration or ATC). When whole blood cultures from patients with allergic rhinitis were stimulated with ATC it was found that some allergens induced IL-6 secretion. The allergens inducing IL-6 and the level of IL-6 secreted were dependent on the patient. The induction of IL-6 secretion by the cultures at ATC correlated very significantly with the patient's skin prick test results (r = 0.71 1; p = 0.0003).

ICCVAM evaluation of the murine local lymph node assay. Conclusions and recommendations of an independent scientific peer review panel

The validation status of the murine local lymph node assay (LLNA), a method for assessing the allergic contact dermatitis potential of chemicals, was evaluated by an independent peer review panel (Panel) convened by the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM). The LLNA measures lymphocyte proliferation using incorporation of radioactive thymidine or iododeoxyuridine into cells of the draining lymph nodes of mice topically exposed to a test article. The Panel concluded that the assay performed as well as currently accepted guinea pig methods [guinea pig maximization test (GPMT)/Buehler assay (BA)] for the hazard identification of strong to moderate chemical sensitizing agents, but that it might not correctly identify all weak sensitizers or metals (potential false negative response) or all strong irritants (potential false positive response). The Panel concluded also that the LLNA involves less pain and distress than conventional guinea pig methods. The Panel unanimously recommended the LLNA as a stand-alone alternative for contact sensitization hazard assessment, provided that certain protocol modifications were made. These included collection of individual, rather than pooled, animal response data; the inclusion of a concurrent positive control; and consideration of dose-response information and statistical analyses. A standardized LLNA protocol is provided.

Local lymph node assay: use in hazard and risk assessment

The murine local lymph node assay (LLNA) was developed as an alternative method for the identification of chemicals that have the ability to cause skin sensitization and allergic contact dermatitis. The assay now has been evaluated extensively in the context of both national and international inter-laboratory collaborative trials and has been the subject of detailed comparisons with guinea pig test methods and human skin sensitization data. On the basis of these evaluations the LLNA has been endorsed recently by the US Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) as a stand-alone method for skin sensitization testing. The assay offers a number of important benefits compared with conventional guinea pig test methods, among these being provision of an objective and quantitative endpoint. Moreover, the LLNA provides advantages in the context of animal welfare; compared with guinea pig tests, fewer animals are required and these animals are subject to less trauma. It is important now that the validation status of the LLNA is recognized and the method applied widely so that these advantages may be realized. Hazard identification represents only the first step in the risk assessment process. A full toxicological evaluation of skin sensitization activity requires an understanding of relative potency. Guinea pig methods do not lend themselves readily to assessment of potency, and interest recently has focused on the utility of the LLNA for this purpose. Contained within this review article are brief descriptions of the history of the LLNA and the immunobiological basis for the method, together with detailed accounts of the conduct and interpretation of the assay. Procedural modifications to, and alternative endpoints for, the LLNA are considered also. Finally, the current regulatory status of the LLNA is summarized and the application of the method for the purposes of defining relative potency and developing risk assessments is reviewed.

Cytokine endpoints for the local lymph node assay: consideration of interferon-gamma and interleukin 12

The murine local lymph node assay (LLNA) is a method for the prospective identification of contact allergens. Skin sensitization potential is assessed as a function of induced proliferative responses in lymph nodes draining the site of topical exposure measured in situ by incorporation of radiolabelled thymidine ([3H]thymidine). The results of previous investigations have demonstrated that the analysis of [3H]thymidine incorporation represents a robust and reliable endpoint for the LLNA for the assessment of skin sensitizing activity for strong and moderate allergens and, in addition, many weaker sensitizers. The aim of the current experiments was to explore the utility of the production of the cytokines interferon-gamma (IFN-gamma) and interleukin 12 (IL-12) by draining lymph node cells (LNC) as alternative readouts for the LLNA. Animals were exposed to a range of skin sensitizers at two application concentrations. The first of these was chosen on the basis of results from previous investigations to stimulate a strong proliferative response (tenfold or greater increase in proliferation compared with concurrent vehicle controls). The second concentration of test material in each case was the amount of chemical estimated to be necessary mathematically for elicitation of a stimulation index of 3 (EC3 value); the induction of a threefold or greater increase in proliferation is the current criterion for a positive response in the LLNA. In addition, analyses were conducted with para-aminobenzoic acid (PABA), a non-sensitizing chemical shown previously not to induce LLNA responses. Secretion of IFN-gamma and the p40 subunit of IL-12 by draining LNC was measured by cytokine-specific enzyme-linked immunosorbent assay. In parallel experiments, LNC activity was assessed as a function of [3H]thymidine incorporation in situ. All the chemical allergens tested provoked robust proliferative responses, with the stimulation indices recorded at both test concentrations reflecting only small changes in activity compared with previously recorded data. Exposure to vehicle (4:1 acetone:olive oil, AOO) alone resulted in detectable, although variable, expression of both IFN-gamma and IL-12. Treatment with chemical allergen in each case caused a marked increase in IFN-gamma secretion, with particularly vigorous production of cytokine being stimulated following exposure to oxazolone or hexyl cinnamic aldehyde. In contrast, application of chemical allergens was not generally associated with elevated IL-12 p40 secretion. Exposure of mice to PABA did not result in increased IFN-gamma or IL-12 production compared with vehicle-treated controls. In general, however, cytokine secretion did not correlate closely with the induction of LNC proliferation. These data indicate that expression by allergen-activated LNC of IFN-gamma or IL-12 does not provide a reliable or sufficiently sensitive endpoint for the LLNA compared with [3H]thymidine incorporation in situ.

Development of a non-radioactive endpoint in a modified local lymph node assay

A murine local lymph node assay (LLNA) has been developed as an alternative to guinea pig models for contact sensitization testing. Although the LLNA appears to be a little less sensitive than the most stringent of guinea pig assays, it provides a rapid, objective, quantitative and cost-effective method for screening strong contact sensitizers and has advantages with respect to animal welfare. However, a potential disadvantage is the need for the use of radioactive material. We have reported previously that an ex vivo assay based on similar principles to the original in vivo LLNA, but using a non-radioactive endopoint, was valid for the prediction of strong sensitizers. This ex vivo assay was not sensitive enough to allow prediction of moderately potent ones. In this study, we propose a new parameter, Corrected IL-2 Index (CII), for the prediction of moderate sensitizers. To obtain CII the IL-2 release in the supernatant of the cell culture is corrected for lymph node weight ratio and ratio of CD4-positive subset. We found that CII predicted the allergenicity of moderate sensitizers, including the ones recommended by the OECD in guideline 406, such as mercaptobenzothiazole and hexyl cinnamic aldehyde. The allergenicity of metal salts, such as potassium dichromate, ammonium tetrachloroplatinate and cobalt chloride, was also predicted by the CII. We conclude that the use of CII as an index significantly increases the sensitivity of the ex vivo method so that moderate sensitizers may also be detected.

An integrated model for the differentiation of chemical-induced allergic and irritant skin reactions

Contact and photocontact allergic as well as irritant and photoirritant skin reactions represent a major problem in clinical dermatology and during the development of new pharmaceuticals. Furthermore, there is a lack of in vitro and in vivo assays that provide a clear differentiation between allergic and irritant skin reactions. Here, we describe an integrated model to differentiate between chemical-induced allergic and irritant skin reactions by measuring objective and easy-to-determine parameters within both skin and skin-draining lymph nodes. Dose-response studies with standard contact and photocontact allergens as well as irritants and photoirritants revealed that irritants predominantly induced skin inflammation, which in turn stimulated draining lymph node cell proliferation. In contrast, the induction phase of contact or photocontact allergy was characterized by marginal skin inflammation, but a marked activation and proliferation of skin-draining lymph node cells. Therefore, a differentiation index (DI) was defined describing the relation between skin-draining lymph node cell activation (lymph node cell count index) and skin inflammation (ear swelling). A DI > 1 indicates an allergic reaction pattern whereas DI < 1 demonstrates an irritant potential of a chemical. Experiments with the contact allergen oxazolone, the photocontact allergen TCSA + UVA, the irritant croton oil, and the photoirritant 8-methoxypsoralen + UVA confirmed the predictive value of DI. Furthermore, flow cytometric analysis of lymph node-derived T- and B-cell subpopulations revealed that contact sensitizer, but not irritant, induced the expression of CD69 on the surface of I-A+ cells. In conclusion, further studies with a broad range of irritants and allergens will be required to confirm general applicability.

A local lymph node assay to analyse immunosuppressive effects of topically applied drugs

Topical glucocorticosteroids represent the mainstay of antiinflammatory therapy in the treatment of inflammatory skin diseases. Their clinical use, however, is limited by local and systemic side-effects. Thus, in dermatopharmacology there is a large demand for alternative non-steroidal antiinflammatories. Other than transplantation models, most of the frequently used in vivo test systems for assessment of drug-induced immunosuppression measure changes in inflammatory skin responses by means of skin erythema and edema after challenge of sensitized animals. The aim of this study was to develop an alternative mouse model to detect and analyse immunosuppressive effects of topically applied drugs. On the basis of a modified local lymph node assay, we analysed effects of topical hydrocortisone, dexamethasone, mometasone furoate and FK506 (tacrolimus) during the induction phase of contact hypersensitivity. On 4 consecutive days, NMRI mice were treated on the dorsal surfaces of both ears with increasing concentrations of test compound. During the last 3 days, the mice received in addition the contact sensitizer, oxazolone (1%). On day 5, draining auricular lymph nodes were removed in order to assess lymph node cell counts and perform flow cytometric analysis of lymph node cell subpopulations (CD4+/CD25+, Ia+/CD69+, Ia+/B220+). All test compounds proved to exert significant immunosuppressive effects after topical application, but showed differences in their immunomodulatory potential. In conclusion, the local lymph node assay serves as an appropriate model to characterize immunosuppressive effects of topically applied drugs by measuring immunologically relevant end-points.