Granzyme A potentiates chemokine production in IL-17-stimulated keratinocytes.

Plaque psoriasis presents with focal skin inflammation, partially maintained by IL-17-mediated interactions between infiltrating epidermal T cells and activated keratinocytes. Here we show that the majority of lesional epidermal CD8 T cells express granzyme A, alone or in combination with IL-17. To assess proinflammatory properties of granzyme A in psoriasis, primary human keratinocytes were stimulated with granzyme A in the presence or absence of IL-17. Out of 33 analysed keratinocyte-derived inflammatory mediators, granzyme A potentiated IL-17-induced secretion of CXCL 1, CXCL 12 and CCL 4. Intriguingly, all three chemokines are implicated in psoriasis pathogenesis and are involved in recruitment of T cells, neutrophils and pDCs into inflamed tissues. Our results indicate that granzyme A produced by lesional CD8 T cells specifically increase the chemokine production from inflamed keratinocytes, thereby amplifying a chemotactic inflammatory loop that sustains psoriasis lesions.