Dermal exposure to cinnamaldehyde alters lymphocyte subpopulations, number of interferon-γ-producing cells, and expression of B7 costimulatory molecules and cytokine messenger RNAs in auricular lymph nodes of B6C3F1 mice

Background: Although the Murine Local Lymph Node Assay (LLNA) is efficient in identifying chemicals with sensitizing potential, there is increasing need for alternative end points. Cinnamaldehyde (CIN) was chosen for evaluation based on its moderate potency and extensive use in fragrance materials. Objectives: The purpose of the present studies is to incorporate some alternative end points, such as phenotypic analysis and cytokine production, into a modified LLNA/irritancy assay (IA) to evaluate the sensitization of female B6C3F1 mice to CIN. Methods: Several nontraditional end points, including the analysis of lymphocyte subpopulations, B7 costimulatory molecule and cytokine messenger RNA (mRNA) expression, and intracellular interferon-γ (IFN-γ) levels, were incorporated into a modified murine local lymph node (LLNA)/irritancy assay (IA) to evaluate the sensitization of female B6C3F1 mice to cinnamaldehyde (CIN). Results: The alternate end points used in these studies support the classification of CIN as a moderately potent sensitizer. Dermal treatment with CIN resulted in an increase in the percentage of B cells in the auricular lymph nodes (ALNs) and expression of the costimulatory molecule, B7-2, on B cells. Lymph node cells also showed increased transforming growth factor-β1, migration-inhibition factor, and mild increases in IFN-γ and interleukin-2 cytokine mRNA expression. Although the increase in IFN-γ mRNA expression did not translate into increased intracellular IFN-γ levels, the absolute number of T cells producing IFN-γ in the ALNs increased. Conversely, the MEST did not classify CIN as a contact allergen. Conclusion: The nontraditional end points used in the LLNA/IA were not as sensitive as the traditional radioisotope method used to assess cell proliferation. However, they may help identify compounds inappropriately classified as sensitizers or nonsensitizers by the LLNA and MEST.