Long form of thymic stromal lymphopoietin of keratinocytes is induced by protein allergens

A growing body of evidence suggests that epicutaneous sensitization of protein allergens induces immediate-type hypersensitivity (IHS) following induction of Type 2 immune responses in animals and humans. Thymic stromal lymphopoietin (TSLP) derived from keratinocytes is a cytokine that can activate dendritic cells and has been implicated in development of inflammatory Type 2 helper T-cells. However, there is no direct evidence that allergens directly regulate TSLP expression in keratinocytes. This study aimed to evaluate the response of TSLP to protein allergens in cultured human keratinocytes and to identify appropriate endpoints for IHS. The transcription of long-form TSLP (loTSLP) was strongly induced by ovalbumin, wheat gluten (WG), acid-hydrolyzed WG (acid-HWG), and extracts from feces of Dermatophagoides pteronyssinus and D. farina, and trypsin, but not by rare allergens, human serum albumin (HSA), or extracts of mite bodies. In acid-HWG, loTSLP mRNA was significantly augmented by acid hydrolysis of WG for 0.5 h compared to WG. However, prolonged acid hydrolysis attenuated this induction similarly to that reported in previous animal studies. These results suggested that intense loTSLP transcriptional induction was a characteristic of a high-allergenic protein. Additionally, TSLP production was induced by exposure to ovalbumin, WG, and acid-HWG in combination with a trio of cytokines, i.e. interleukin (IL)-4, IL-13, and tumor necrosis factor (TNF)-alpha. However, no TSLP protein was detected following exposure to HSA, even in the presence of these cytokines. With acid-HWG, TSLP protein release was consistent with loTSLP transcription. Thus, intense loTSLP transcriptional induction and TSLP protein expression are each effective indicators that can be used for in vitro screening of IHS.