FURTHER EVALUATION OF THE LOCAL LYMPH-NODE ASSAY IN THE FINAL PHASE OF AN INTERNATIONAL COLLABORATIVE TRIAL

The local lymph node assay (LLNA) is a method used for the prospective identification in mice of chemicals that have the potential to cause skin sensitization. We report here the results of the second and final phase of an international trial in which the performance of the assay has been evaluated using seven test materials in five independent lab oratories. The additional chemicals examined here included compounds w hich are considered less potent allergens than some of those tested in the first phase of the investigation, and includes hexylcinnamic alde hyde (HCA), a chemical recommended by the Organization for Economic Co operation and Development (OECD) as a positive control for skin sensit ization studies. In each laboratory all skin sensitizing chemicals exa mined (2,4-dinitrochlorobenzene ( DNCB), HCA, oxazolone, isoeugenol an d eugenol) elicited positive responses of comparable magnitude as judg ed by the derived lowest concentration of test chemical required to el icit a 3-fold or greater increase in the proliferative activity of dra ining lymph node cells compared with vehicle-treated controls. We obse rved that sodium lauryl sulphate, considered to be a non-sensitizing s kin irritant, also induced a positive response in the assay. Para-amin obenzoic acid (pABA), a nonsensitizing chemical, was negative at all t est concentrations in each laboratory. Some laboratories incorporated minor modifications into the standard assay procedure, including the e valuation of lymph nodes pooled from individual mice rather than treat ment groups and the use of statistical analyses. The use of statistics did not markedly change the determination of the lowest concentration yielding a positive response. These data confirm that the local lymph node assay is robust and yields equivalent results when performed ind ependently.