Reproducible prediction of contact allergenic potency using the local lymph node assay

A considerable body of data has been accumulated which demonstrates that the local lymph node assay (LLNA) can provide a valuable estimation of the contact allergenic potency of a substance. This estimate is obtained via interpolation of the LLNA dose-response curve and is expressed as the concentration of the chemical required to evince a 3-fold stimulation of proliferation in lymph nodes draining the site of application compared to the vehicle-treated controls (EC3). It has also been shown that the EC3 estimates are reproducible and are stable over time. In the present work, we have extended this information by a demonstration of the inherent biological variability surrounding EC3 estimation, using data derived (from a single laboratory) from the testing of isoeugenol as a positive control. Isoeugenol gave EC3 values ranging from 0.5 to 2.6% (n = 29), with a mean and standard deviation of 1.2 +/- 0.6%. Given that EC3 values for a variety of contact allergens range over several orders of magnitude, these results further endorse the utility of EC3 values as a reliable indicator of human contact allergenic potency.