A shift towards a type I immune response in chronic atopic dermatitis favours an IL-15 dependent tissue resident memory cell niche.

BACKGROUND

Tissue resident memory (TRM) cells are of interest in chronic inflammatory skin diseases as they are believed to facilitate flares in the same anatomical area. IL-15 is an essential growth factor for the survival of TRM in the skin compartment. A main source of IL-15 are tissue-resident cells.

OBJECTIVE

The purpose of this study was to explore the role of IL-15 in the chronification process of atopic dermatitis (AD).

METHODS

Primary human keratinocytes and fibroblasts were cultured and exposed to a range of stimuli in order to assess their IL-15 expression and production, which were measured by qPCR and ELISA, respectively. RNAseq and PCR were performed from lesional and non-lesional atopic dermatitis (AD) biopsies.

RESULTS

We tested a range of type I and type II response-associated cytokines and PAMPs on primary human fibroblasts and keratinocytes. The main inducer for IL-15 in keratinocytes proved to be IFNγ, while fibroblasts showed responsiveness to long-term exposure to IL-4. Transcriptomic analyses of AD skin biopsies confirmed that IL-15 was associated with a higher IFN signature and longer disease duration, and a significant correlation was observed between IL-15 and the TRM molecules CCR8 and CD69.

CONCLUSION

The epidermal compartment responds to IFNs with IL-15 expression. Analysis of patient-derived skin biopsies highlights higher expression of IL-15 in the context of a Th1 shift known to occur in chronic AD. These data suggest that flares require prompt intervention to avoid consolidation of an IFNγ-driven tissue memory.