The suitability of hexyl cinnamic aldehyde as a calibrant for the murine local lymph node assay

The murine local lymph node assay (LLNA) for the prospective identification of contact allergens assesses skin sensitization potential as a function o f proliferative activity induced in lymph nodes draining the site of topica l exposure to test chemical. This method has been endorsed recently as a st and alone test for the identification of contact allergens. We have now exa mined the suitability of hexyl cinnamic aldehyde (HCA), a recommended posit ive control for skin sensitization testing, as a calibrant for comparing th e consistency of LLNA responses with time, and between laboratories, and th us for the routine assessment of assay reliability Standard LLNAs were perf ormed with CBA strain mice in 3 independent laboratories over a period of 8 years. Dose-response curves were used to derive mathematically the EC3 val ue (the estimated concentration of chemical necessary to cause a stimulatio n index (SI) of 3 compared with proliferation induced by concurrent vehicle controls). In each laboratory, 6 separate experiments were conducted using a single concentration of HCA (25%). Very similar stimulation indices were achieved, with mean values of 9.0, 6.5 and 6.6 recorded. A total of 10 dos e-response experiments were performed independently in the 3 laboratories a nd these revealed that l:here was very little inter-laboratory, or temporal , variation in EC3 values. These data confirm that HC:A responses in the LL NA are very stable and demonstrate that HCA provides a suitable calibrant f or determining assay sensitivity and performance.