TEMPORAL STABILITY OF LOCAL LYMPH-NODE ASSAY RESPONSES TO HEXYL CINNAMIC ALDEHYDE

The local lymph node assay is an alternative method for the prospectiv e identification of chemicals that have the potential to cause skin se nsitization. Activity in the assay is measured as a function of prolif erative responses by draining lymph node cells induced by topical expo sure of mice to the test chemical. Positive responses are defined as t hose where a test chemical, at one or more application concentrations, is able to induce a stimulation index of 3 or greater compared with c oncurrent vehicle-treated control values. Although the method has been evaluated extensively, the stability over time of responses induced i n the local lymph node assay has not previously been addressed formall y. It was the purpose of the investigations described here to consider this issue and, to this end, responses provoked in the local lymph no de assay by hexyl cinnamic aldehyde (HCA)-a skin sensitizing chemical of moderate potency-were assessed in five separate experiments conduct ed in a single laboratory over a 10-month period. In each case, HCA el icited a positive response. Although some significant interexperimenta l variation was recorded, this was attributable entirely to the stimul ation by HCA of slightly more vigorous responses in one of the five ex periments. When the results of this experiment were excluded from the data set, significant variations were lost, Finally, for each experime nt an EC3 value was derived, this being the estimated concentration of test chemical required to induce a stimulation index of 3, Similar EC 3 values were derived in each experiment. These data demonstrate the r elative stability over time of activity in the local lymph node assay, (C) 1998 John Wiley & Sons, Ltd.