Immune Divergences Between the Skin Sensitizer 2,4-Dinitrochlorobenzene and the Respiratory Sensitizer Phthalic Anhydride Revealed by Mouse Single-Cell Transcriptomics.

BACKGROUND: Chemical-induced sensitization is a major health concern. To date, no internationally accepted method is able to discriminate a skin from a respiratory sensitizer. The identification of an immune profile specific to skin or respiratory sensitizers is therefore scientifically relevant. METHODS: Female BALB/c mice were dermally exposed to a skin (2,4-dinitrochlorobenzene, DNCB) or to a respiratory sensitizer (phthalic anhydride, PA) at day 0 (D0) and D5 to initiate allergic sensitization and at D10, D11, and D12 to induce elicitation. Auricular lymph nodes (LNs) were collected at D0, D3, D7, D10, and D13. Single-cell transcriptomic and flow cytometric analyses were performed in order to identify immune cell proportions and marker expression. Enrichment analyses were performed at D13 on dendritic and T cells. Cytokine measurements were performed in LN cells' supernatant by bead array cytometry. RESULTS: Exposure to both sensitizers induced a strong immune reaction demonstrated by an increase of mature B cells and an evolution of the T cell subpopulations, with an increase of follicular and memory T cells. The proportion of NKT, Th2, and Th9 cells and the levels of IgE increased specifically during PA exposure. Follicular, memory, and helper T cells showed distinct transcriptomic responses to DNCB or PA. The proportion of dendritic cells (DCs) strongly increased starting from D10 in mice exposed to DNCB, and those cells showed a specific transcriptomic signature towards the skin sensitizer. Enrichment analyses suggested a metabolic shift in DCs exposed to DNCB. Single-cell transcriptomic data were confirmed by flow- and bead array cytometry. CONCLUSION: A distinct transcriptomic signature was identified in immune cells during sensitization to DNCB or PA in this study.