Human potency predictions for aldehydes using the local lymph node assay

The murine local lymph node assay (LLNA) assesses skin sensitization potent ial as a function of proliferative responses induced in lymph nodes drainin g the site of topical exposure to test chemical. It has been shown that int erpolation of LLNA dose-response data to define the concentration of test c hemical required to induce a 3-fold stimulation of proliferation (EC3) offe rs the prospect of a quantitative index of the relative potency of a contac t allergen. Initial studies have demonstrated that there exists a strong (i nverse) correlation between EC3 values and contact allergenic potency in hu mans. Thus, materials with a low EC3 value were more potent contact allerge ns in humans. However, it is necessary to examine a wide range of allergens to demonstrate that such correlations are generally true. Thus, in the pre sent study, 10 aldehydes of varying degrees of allergenicity in man were ev aluated in the LLNA and their EC3 values derived. Formaldehyde was regarded as the strongest allergen in man and also had the lowest EC3 value, 0.35% (equivalent to 0.93% formalin). In contrast, the extremely weak allergen va nillin and the non-sensitizer ethyl vanillin both had EC3 values of >50%. F or the remaining 7 aldehydes, there was a close similarity between what is judged to be their rank order of allergenicity in humans and EC3 values der ived from analysis of LLNA data. These results support further the utility of EC3 determinations in the LLNA as a measure of the relative potency of a contact allergen.