COMPARISON OF 125-IODODEOXYURIDINE ((125)IUDR) AND [H-3] THYMIDINE ([H-3]TDR) FOR ASSESSING CELL-PROLIFERATION IN THE MURINE LOCAL LYMPH-NODE ASSAY

The murine local lymph node assay (LLNA) evaluates the dermal sensitiz ation potential of chemicals by assessing the cell proliferation withi n the auricular lymph nodes following topical application of a chemica l to the ears. Traditionally, [H-3]thymidine ([H-3]TdR) is used to mea sure proliferation. Because of its long half-life and the resulting ex pense of disposing of [H-3]TdR waste, the usefulness, reliability, sel ectivity, and sensitivity of 125-iododeoxyuridine ((125)IUdR) was eval uated as an alternative radiolabel in the LLNA. An optimal response wa s obtained using the following: daily exposure on the dorsum of both e ars for 3 days; 2 days of rest; on the sixth day IV injection of 2 mu Ci/mouse (125)IUdR; removal of nodes after 5 h. Female CBA/J mice were exposed to either vehicle or 1,6-diisocyanatohexane (HDI), 2-hydroxye thyl acrylate (HEA), methyl salicylate (MS), potassium dichromate (PD) , or dinitrochlorobenzene (DNCB); injected IV with 20 mu Ci [H-3]TdR o r 2 mu Ci (125)IUdR; and proliferation in the pooled auricular lymph n odes from individual mice was assessed. Stimulation indices (SI) of gr eater than or equal to 3 indicated a positive response. Both an SI gre ater than or equal to 3 and statistical significance were observed for the known sensitizers HDI and HEA using either (125)IUdR or [H-3]TdR. For the nonsensitizer MS, neither an SI greater than or equal to 3 no r statistical significance was detected using (125)IUdR or [H-3]TdR. B oth isotopes detected a positive response based on statistical analysi s at 0.5 and 0.25% PD, while (125)IUdR detected further significance a t 0.1% PD, An SI greater than or equal to 3 was detected by both isoto pes at 0.5% PD, while (125)IUdR detected an SI greater than or equal t o 3 at 0.25% PD. Statistical significance was observed for [H-3]TdR at 0.025, 0.05, 0.1, and 0.25% DNCB and at 0.1 and 0.25% DNCB for (125)I UdR. An SI greater than or equal to 3 was observed at 0.05, 0.1, and 0 .25% DNCB for [H-3]TdR and at 0.1 and 0.25% DNCB for (125)IUdR. (125)I UdR is a suitable, cost-effective alternative radiolabel to [H-3]TdR f or assessing cell proliferation in the LLNA.