Skin sensitization (manifested primarily by allergic contact dermatitis) and respiratory sensitization (such as asthma) are two main types of allergic responses to xenobiotic exposures. The assessment of the toxic potential of chemicals involves determining their ability to cause respiratory and skin sensitization. Traditional tests to achieve this involve animal research models. However, application of the 3Rs of animal research (refinement, replacement, and reduction of animal experimentation) is implemented to limit the use of animal experimentation.
In vitro assays exist to help predict the sensitizing potential of chemicals, but these approaches do not differentiate between respiratory and skin sensitizers. Therefore, a group of scientists developed an assay capable of discerning respiratory from skin sensitizers based on differences between the two systems’ mechanisms of sensitization. For example, the T helper 2 immune response is an important feature of respiratory sensitization. Therefore, scientists developed a three-dimensional (3-D) coculture system that mimics human upper airway epithelium for use in measuring T helper 2 differentiation in this culture model.
The 3-D system consists of a human airway epithelial cell line, human dendritic cells, and a human fibroblast cell line. Using a commercially available scaffold, the cells were cultured in individual scaffolds then assembled into a 3D tissue model. Well-known skin sensitizers (oxazolone, formaldehyde, and dinitrochlorobenzene) and respiratory sensitizers (ortho-phthaldialdehyde, hexamethylene diisocyanate, and trimellitic anhydride) were individually tested in the 3-D coculture system. After 9 hours of stimulation, the scaffold was disassembled, and real-time RT-PCR was performed in individual scaffolds to determine the expression levels of T helper 2 differentiation-related molecules (OX40 ligand (OX40L), interleukins (IL)-4, IL-10, and IL-33, and thymic stromal lymphopoietin).
The results showed that OX40L expression was significantly and consistently upregulated by stimulation with the studied respiratory sensitizers as compared to stimulation to skin sensitizers. Therefore, OX40L upregulation in dendritic cells may serve as a reliable marker to differentiate chemically induced respiratory sensitization potential from skin sensitization. The analysis of OX40L for T helper 2 differentiation in dendritic cells may serve as a valuable in vitro method to test chemical sensitization.
Mizoguchi, I., Ohashi, M., Chiba, Y., Hasegawa, H., Xu, M., Owaki, T., & Yoshimoto, T. (2017). Prediction of Chemical Respiratory and Contact Sensitizers by OX40L Expression in Dendritic Cells Using a Novel 3D Coculture System. Frontiers In Immunology, 8. doi:10.3389/fimmu.2017.00929