IL-9 and IL-24 biomarkers in the transcriptional signature of contact dermatitis to methylisothiazolinone

Taynah Cohen De Melo¹Mirian Nacagami Sotto²Iara Fernandes¹Emanuella Sarmento Alho de Sousa³Frederico Moraes Ferreira⁴Gabriel Benevides Simões¹Yasmim Álefe Leuzzi Ramos¹Marcella Soares Pincelli⁵Vitor Manuel Silva dos Reis⁵Maria Notomi Sato^1*

• ¹Laboratory of Medical Investigation 56, Department of Dermatology, University of São Paulo Medical School, São Paulo, Brazil
• ²Laboratory of Medical Investigation 50, Department of Pathology, University of São Paulo Medical School, São Paulo, Brazil
• ³Department of Immunology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
• ⁴Cellular, Genetic, and Molecular Nephrology Laboratory (LIM-29), Hospital das Clínicas, University of São Paulo Medical School, São Paulo, Brazil
• ⁵Department of Dermatology, University of São Paulo Medical, São Paulo, Brazil

Allergic contact dermatitis (ACD) is a cutaneous inflammatory condition mediated by memory T cells specific to the allergen, triggered after prior exposure to sensitizers. Methylisothiazolinone (MI), a preservative found in industrial and cosmetic products, has been responsible for a significant increase in ACD cases, standing out as a prominent sensitizing agent in the compound Kathon CG. There are a few investigations of MI cutaneous response. This study aimed to investigate the innate immune components, such as cytokines and signaling pathways induced by MI in the skin test of individuals with MI-sensitized ACD, comparing them to healthy controls. Individuals initially testing positive only for MI were recruited at the Contact Dermatitis Clinic at Hospital das Clínicas of São Paulo, re-exposed to MI or saline, and biopsied 48 hours after exposure. Negative controls for the patch test were also exposed to MI and saline for comparison. Histopathological and transcriptomic (RNAseq) analyses identified two groups among the ACD patients: high responder to MI (ACD-A), with more pronounced histopathological features such as spongiosis and micro vesicles, and low responder to MI (ACD-B), which showed milder reactions and absence of spongiosis. In ACD-A MI, a total of 1588 genes were upregulated and 2090 downregulated in response to MI, compared to ACD-B MI. These differentially expressed genes (DEGs) were associated with innate immunity and inflammation, such as IL-24, IL-9, IL-13, and NTRK1, while IL-37 and IL-18 were downregulated. Similarly, ACD-A MI compared to the MI-negative ACD group showed 1169 upregulated and 321 downregulated genes. DEG validation in ACD-A through qPCR confirmed increased expression of NTRK1 and IL-9, with a reduction in IL-18. Protein analysis of IL-9 and IL-24 revealed higher expression in the dermal layer of ACD-A. These results indicate distinct transcriptional profiles in MI-sensitized individuals, despite positive patch tests in all cases. The observed heterogeneity, not previously described in ACD, points to as IL-9 and IL-24 be better explored, in order to understand the pathogenesis of ACD.