Results with OECD recommended positive control sensitizers in the maximization, Buehler and local lymph node assays

The guinea pig maximization test and the Buehler occluded patch test are used widely to identify the sensitization potential of new chemicals. This information enables toxicologists and/or regulatory authorities to determine whether a chemical should be classified formally as a skin sensitizer. Both to improve and to harmonize these assessments internationally, the OECD has recommended recently that moderate rather than strong contact sensitizers are used as positive control substances. The purpose is to ensure an adequate level of sensitivity in sensitization assays performed at specific testing establishments. Results from two laboratories reported here show that the minimum acceptable standard laid down by the OECD can be achieved and indeed commonly exceeded by a substantial margin. Furthermore, results with these positive controls in a new method, the local lymph node assay, also appear to satisfy similar criteria, suggesting results from this assay, including negative data, should be acceptable for classification purposes. However, a review of the way in which results with new chemicals will be interpreted for regulatory purposes, in the context of positive control data, reveals that considerable inadequacies still exist. It is recommended that ultimately, sensitization data can only be interpreted meaningfully (i.e. to protect humans from sensitization hazards) by considering the potency of the contact allergen in the context of the sensitivity of the assay performed at the particular testing institution.