Summerfield, VL; (2015) Characterisation of keratinocyte-derived epidermal signals in the initiation of contact hypersensitivity to chemicals. Doctoral thesis , UCL (University College London).

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Abstract

Contact hypersensitivity reactions result from an adaptive immune response following topical exposure to chemical allergen. The initiation of this response requires the production of an inflammatory micro-environment, however the contribution of epidermal keratinocytes in creating this environment is not well-characterised. In particular, the molecular processes that regulate inflammatory mediator release in response to chemical allergen, and the function of keratinocyte-derived mediators in dendritic cell migration and maturation, have not been fully explored. Keratinocytes (HaCaT cell line) and three-dimensional reconstructed human epidermis were evaluated as possible models for investigating these questions. We have found that, in response to chemical allergen, keratinocytes transcribe and release inflammatory mediators (interleukin-6 (IL-6) and IL-8), and a cytokine known to induce dendritic cell migration (IL-1). Furthermore, the production of these mediators was greater than that induced by a simple chemical irritant, and different to lipopolysaccharide/interferon- stimulation. Transcriptomic analysis was performed to investigate the molecular mechanisms behind the inflammatory mediator release. Principal component analysis of the data showed distinct clustering of gene expression profiles associated with different doses of 2,4-dinitrochlorobenzene (DNCB, allergen) and sodium dodecyl sulfate (SDS, irritant) exposed keratinocytes. Many of the differentially expressed genes that were found in response to DNCB map to components of stress-induced pathways such as nuclear factor -light-chain-enhancer of activated B cells (NF-B) and nuclear factor erythroid 2-related factor 2 (Nrf2). Investigation of the upstream signal transduction cascades revealed activation of mitogen-activated protein kinase (MAPK) pathways, specifically phosphorylation of p38MAPK and c-Jun N-terminal kinase (JNK), with a simultaneous decrease in the phosphorylation level of extracellular-signal-regulated kinase (ERK). There was also evidence of partial activation of the NF-B pathway. The mechanism by which chemical allergens initiate these responses is unknown, however we have identified two possible triggers: production of reactive oxygen species, and activation of a receptor tyrosine kinase.

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