Comparison of BALB/c and CBA/J mice for the local lymph node assay using bromodeoxyuridine with flow cytometry (LLNA: BrdU-FCM).

ABSTRACT

The local lymph node assay using 5-bromo-2-deoxyuridine (BrdU) with flow cytometry (LLNA BrdU-FCM) is a modified LLNA that is used to identify skin sensitizers by counting BrdU-incorporated lymph node cells (LNCs) with flow cytometry. Unlike other LLNA methods (OECD TG 429, 442A and 442B) in which the CBA/J mouse strain is used, LLNA BrdU-FCM was originally designed to be compatible with BALB/c, a mouse strain that is more widely used in many countries. To justify the substitution of CBA/J for BALB/c, the equivalence of the test results between two strains shall be established prior to the official implementation of LLNA BrdU-FCM. This study aims to compare the test results of LLNA BrdU-FCM produced in BALB/c mice with those in CBA/J mice for 18 reference substances, including 13 sensitizers and 5 non-sensitizers, listed in OECD Test Guideline 429. Based on the LLNA BrdU-FCM test procedure, we selected an appropriate solvent and then performed preliminary tests to determine the non-irritating dose ranges for the main study, which revealed the difference in the irritation responses to 8 of the 18 chemicals between the two strains. In the main study, we measured the changes in the number of total LNCs, which indicated differences in the responses to test chemicals between the two strains. However, the stimulation index obtained with the counts of BrdU-incorporated LNCs with 7-AAD using flow cytometry yielded comparable results and 100% concordance between the BALB/c and CBA/J mouse strains was achieved, suggesting that the performance of LLNA BrdU-FCM using BALB/c mice was equivalent to that with CBA/J mice.