Comparison of flow cytometry and immunohistochemistry in non-radioisotopic murine lymph node assay using bromodeoxyuridine

Non-radioisotopic local lymph node assay (LLNA) employing 5-bromo-2′-deoxyuridine (BrdU) with flow cytometry (FACS) or immunohistochemistry (IHC) is gaining attention due to a regulatory issue of using radioisotope, 3H-thymidine, in vivo in traditional LLNA. In this study, to compare the performance of these non-radioisotopic endpoints, 7 chemicals with known sensitizing potencies were examined in LLNA. Mice were topically treated with chemicals or vehicle on both ears for 3 days. After intraperitoneal injection of BrdU, bilateral lymph nodes were isolated separately and undergone respectively, FACS or IHC to determine BrdU incorporated lymph node cells (LNCs). Weight and histology of treated ears were also examined to evaluate chemical-induced edema and irritation. Both FACS and IHC could successively identify the skin sensitizers from non-sensitizers. Comparison of FACS and IHC with traditional LLNA revealed that FACS has a higher sensitivity although both assays produced comparable sensitivity and performance to traditional LLNA. In conclusion, non-radioisotopic LLNA using FACS and IHC can successfully detect sensitizers with a good correlation to traditional LLNA. Notably, FACS showed almost equivalent sensitivity and accuracy to traditional LLNA.