For the local lymph node assay (LLNA), female BALB/c mice were dosed for 3 days with vehicle (acetone) or increasing concentrations of PPD (0.05-1.0 % ) on the dorsal ear pinnae. Following injection of [3H]-thymidine, draining lymph nodes were radioassayed on day 6. In a phenotypic analysis assay, mice were similarly exposed to 0.05 − 6.0 % PPD through intact or abraded skin for 4 days. On day 10 post-exposure, lymph nodes were excised to evaluate B220+ and IgE+B220+ cell populations. In a 3-week time course study, mice were exposed to PPD through intact or abraded skin and tail bled for serum IgE analysis at 2 and 3 weeks post initial exposure.
A significant response was observed in the LLNA and phenotypic analysis assays at concentrations as low as 0.5 and 2.0 % , respectively. Following 3 weeks of PPD exposure, IgE levels reached statistical significance (p<0.05) in the high dose abraded skin group, however only a modest increase in IgE was observed.
These studies revealed that PPD is a potent contact sensitizer in BALB/c mice while demonstrating only weak IgE inducing potential even when exposure is through abraded skin.