Animal Models for Predicting Sensitization Potential.ppt

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1、Animal Models for Predicting Sensitization Potential,Judith C. Stadler Haskell Laboratory, DuPont Company Newark, DE,Dermal Sensitization,Regulatory Acceptance Guinea Pig Buehler Maximization Test Mouse Local Lymph Node Assay,Dermal Sensitization (continued),Other Tests Guinea Pigs Open Epicutaneous

2、 Mauer Optimization Test Split Adjuvant Technique Freunds Complete Adjuvant Test Draize Sensitization Mice Mouse Ear Swelling Test,Guinea Pig Tests,Based on common principles Chemical induction Rest phase Dermal Challenge Skin Reaction Assessment Erythema, edema,Guinea Pig Tests,Guinea Pig Tests,Adv

3、antages Measures skin reactions similar to human response Large data base for comparison of many chemicals Correlates well to human responseDisadvantages Requires large numbers of animals Subjective evaluation Assessment of colored materials difficult,Mouse Local Lymph Node Assay,Based on responses

4、during induction rather than elicitation phase of sensitization Measures induction of the T-lymphocyte proliferative response in skin draining lymph nodes,Local Lymph Node Assay,Sequence of Events Topical application, generally to the ear Epidermal cells release cytokines Mobilize Langerhans cells A

5、ntigen transported from skin to draining lymph nodes Responsive T-cells activated and divide Radioactivity incorporated during clonal expansion,Local Lymph Node Assay,Advantages Smaller numbers of animals required Quantitative assay Several doses can be evaluated Colored materials can be assayed Dis

6、advantages Insoluble or systemically toxic materials may not test well Tests not predictive for metals,Local Lymph Node Assay Regulatory Status,U.S. EPA has approved its use as a stand-alone assay Europe has approved for registrations if the assay is positive. If the assay is negative, a follow-up g

7、uinea pig assay is required This requirement expected to change by the end of 2000,Respiratory Sensitization,No tests have been validated for regulatory testing Use of animal models primarily for research and mechanistic studies Evaluation of models for predictive assays continues,Animal Models of R

8、espiratory Sensitization,Some use as predictive assays Mouse Guinea pig Rat,Primarily used in asthma research rabbit dog sheep primate,Occupational respiratory allergic disorders,Wide spectrum of disease asthma hypersensitivity pneumonitis Pulmonary infiltrates with eosinophilia Pulmonary institial

9、fibrosis Mechanisms IgE, IgG4, cell-mediated immunity Extent and duration of exposure related to likelihood of sensitization,Guinea pig,Similar to humans Histaminic bronchoconstriction at antigen challenge Exhibits airways hyperreactivity Late-phase responses can be elicited Lung eosinophilia,Guinea

10、 pig use with chemical and protein workplace allergens,Isocyanates Various methods of induction Inhalation challenge with chemical or the protein conjugates Detergent enzymes Inhalation induction model Intratracheal test,Guinea pig,Advantages Ease of sensitization Immunologically robust Multifactori

11、al Disadvantages IgG-dependent mechanism Hyper eosinophilia Dissociation between airway hyperreactivity and eosinophilia Biological variability (outbred strains) Cost prohibitive,Mouse,Similarities of the model to human Influx of eosinophils and T-cells histological features following acute exposure

12、s similar to human Epithelial denudation Interstitial airway edema Thick basement membrane Goblet cell hyperplasia Mucus hypersecretions Repeated exposure results in histological features of chronic asthma,Mouse,Advantages Molecular and immunological assays available Acute bronchoconstriction and ai

13、rway hyperreactivity can be elicited from antigen challenge Disadvantages Large doses required for antigen challenge Difficult to measure eosinophil degranulation, rarely in airways,Brown Norway Rat,Similarities to human sensitization Serotonergic bronchoconstriction IgE mediated Early and late phas

14、e reactions Airway hyperreactivity Tissue + BAL accumulation of neutrophils, eosinophils, lymphocytes,Brown Norway Rat,Advantages Good inflammatory responses Disadvantages Induction of airway hyperreactivity difficult,Regulatory Status,No one model has been validated for prediction of respiratory se

15、nsitization New concerns may place higher priority on this area and encourage methods validation Childrens Health issues Food allergy,Future direction,Emphasis on structure-activity relationships Assay development molecular biology other in vitro screening,References/Suggested Reading,OECD Guideline

16、s for the Testing of Chemicals 406 Skin Sensitisation (17-JUL-92)OPPTS Health Effects Test Guidelines. OPPTS 870.2600 Skin Sensitization (5-AUG-98)Dearman, R.J. D.A. Basketter, and I. Kimber (1999) Local lymph node assay: use in hazard and risk assessment REVIEW. J. Appl Toxicol. 19, 299-306.Kimber,

17、 I, I.L. Bernstein, M.H. Karol, M.K. Robinson, K. Sarlo, and M.K. Selgrade (1996) Identification of respiratory allergens. Fund. and Appl Tox 33, 1-10.Padrid, Philip. Animal models of asthma. in Lung Biol. Health Dis. (1996), 96(Genetics of Asthma), 211-233. Selig, William M.; Chapman, Richard W. Asthma. in In Vivo Models of Inflammation (1999), 111-135.,