TSLP and IL-33 Reciprocally Regulate Each Other’s Lung Protein Expression and Receptor Expression on ILC2 following Aeroallergen Challenge in Mice

Synergistic relationship between TSLP and IL-33/ST2 signaling pathways in allergic rhinitis and the effects of hypoxia

BACKGROUND

The World Health Organization (WHO) has noted that allergic diseases are a major health problem of the 21st century. Allergic rhinitis (AR) is a type I allergic disease characterized by nasal mucosa and immune system abnormalities. AR is mediated by various inflammatory cells and is mainly characterized by altered secretion of cytokines. Thymic stromal lymphopoietin (TSLP) and the interleukin-33/stimulation-expressed gene 2 (IL-33/ST2) signaling pathway are cytokines that play pivotal roles in many inflammatory responses and allergic reactions. There have been reports of interactions between the 2 pathways in many diseases. Hypoxia is a common pathologic manifestation of AR. The aim of this study was to explore the relationship and expressions and biologic functions of TSLP and IL-33/ST2 in AR, and also to determine the effects of hypoxia on these cytokines.

METHODS

The rat nasal mucosal epithelium was obtained from Wistar rats. Cells were cultured in groups under hypoxia and normoxia conditions. Identification of rat nasal epithelial cell (RNEpC) and protein expressions was done by immunohistochemistry and immunofluorescence methods. Cell proliferation and migration were examined using the cell counting kit-8 (CCK-8) and Transwell kit. Detection of apoptosis was tested using a fluorescence apoptosis kit. Enzyme-linked immunoassay (ELISA) and Western blot analysis ELISA were used to measure cell secretion and protein expressions. For these experiments, TSLP was knocked down by lentivirus transfection and IL-33 blocked with its antagonist.

RESULTS

TSLP, IL-33, and ST2 expressions were significantly higher in nasal mucosa epithelial cells from AR rats than in those from control rats. Hypoxia further promoted their expression. Increased TSLP and IL-33/ST2 promoted cell proliferation, inhibited cell apoptosis, and enhanced cell migration. In addition, the downregulation of TSLP expression effectively attenuated expression of the IL-33/ST2 axis and, through use of IL-33 antagonists, could also reduce TSLP expression, a synergistic effect more obvious under hypoxia.

CONCLUSION

Our data indicate that TSLP and IL-33/ST2 signaling pathways interact with each other in the pathogenesis and pathologic development of AR. TSLP inhibition is a key factor in AR treatment. Inhibiting hypoxia-induced pathologic processes could represent a therapeutic effect by inhibiting IL-33/ST2 expression via downregulating TSLP.

Innate lymphoid cells in organ fibrosis

Innate lymphoid cells (ILCs) are a recently identified family of lymphoid effector cells. ILCs are mainly clustered into 3 groups based on their unique cytokine profiles and transcription factors typically attributed to the subsets of T helper cells. ILCs have a critical role in the mucosal immune response through promptly responding to pathogens and producing large amount of effector cytokines of type 1, 2, or 3 responses. In addition to the role of early immune responses against infections, ILCs, particularly group 2 ILCs (ILC2), have recently gained attention for modulating remodeling and fibrosis especially in the mucosal tissues. Herein, we overview the current knowledge in this area, highlighting roles of ILCs on fibrosis in the mucosal tissues, especially focusing on the gut and lung. We also discuss some new directions for future research by extrapolating from knowledge derived from studies on Th cells.