Application of the popliteal lymph node assay (PLNA) for evaluation of the antigenicity of water-soluble food colors

Abstract

The mouse popliteal lymph node assay (PLNA) has been proposed as an immunotoxicological test to predict the allergenicity of chemicals without additional adjuvant. Although a PLN response in the primary PLNA is also observed in association with non-specific activation induced by some irritants, the PLN response in the secondary PLNA in previously sensitized animals is used to detect memory immune responses without using adjuvant. In this study PLNA was applied to evaluate the allergenicity of water-soluble food colors. The PLN cellularity index of an individual dye was calculated from the cell count of exposed and control PLNs of mice. The xanthene dyes Food Red No.3, Food Red No.104, and Food Red N0.105, but not Food Red No.106 gave a high PLN cellularity index. The azo dyes and triphenylmethane dyes were not associated with any increase in PLN cellularity index. Indigo Carmine (Food Blue No.2) also had a high PLN cellularity index. The reactivity of the PLNA correlated well with the chemical structure category of the synthetic dyes. The high PLN cellularity index was considered to be associated with protein binding. Corresponding author: Megumi Hamano Nagaoka, National Institute of Health Sciences, Kamiyoga 1-18-1, Setagaya, Tokyo 158-8501, Japan. Japanese Journal of Food Chemistry, Vol. 13(1), 2006