[Improvement of local lymph node assay for cosmetics safety evaluation]

To improve the local lymph node assay (LLNA) as an alternative method to detect chemicals for both sensitization and irritation.

The following chemicals: one negative control: 4-Aminobenzoic Acid, three sensitizers: 2,4-dinitrochlorobenzene (DNCB), Hexyl cinnamic aldehyde (HCA), 2-Aminophenol (2-APC) and two irritations: potassium hydroxide (KOH), sodium lauryl sulphate (SLS) were selected. According to the normal LLNA, groups of female Balb/c mice were treated with test solutions. The thickness of each ear was measured and each auricle was weighed. On the sixth day, the bilateral draining auricular lymph nodes were excised and weighed. The single cell suspensions were prepared, the lymphocyte were counted and the proliferations of lymph cells were detected by cell counting kit-8 (CCK-8).

Significant increase in ear thickness and weight were found in groups of KOH, SLS and DNCB (above 0.5%) (P < 0.05), which could be considered as irritants, whereas irritation were not found in 2-APC and HCA. In the allergic test, three sensitizers showed positive, but different sensitivity were found among each index. HCA, DNCB and 2-APC could all obviously augment the weight of lymph node and the lymphocyte count in different groups (P < 0.05). Conspicuous proliferation of lymphocyte were found in DNCB (all group), HCA (above the middle dose) and 2-APC (high dose) by CCK-8.

The reformed LLNA using auricle thickness and weighing as observed markers for irritation, and using lymph nodes weighing and proliferation of lymphocyte as observed markers for sensitization, could evaluate both sensitization and irritation at the same time.