High TSLP responses in the human infant airways are associated with pre-activated airway epithelial IFN antiviral immunity
Introduction: Thymic Stromal Lymphopoietin (TSLP) is a primarily epithelial-derived cytokine that drives type 2 allergic immune responses. Early life viral respiratory infections elicit high TSLP production, which leads to the development of type 2 inflammation and airway hyperreactivity. The goal of this study was to examine in vivo and in vitro the human airway epithelial responses leading to high TSLP production during viral respiratory infections in early infancy. Methods: A total of 129 infants (<1m – 24m, median age 10m) with severe viral respiratory infections were enrolled for in vivo (n=113), and in vitro studies (n=16). Infants were classified as “high TSLP” or “low TSLP” for values above or below the 50th percentile. High vs. low TSLP groups were compared in terms of type I-III IFN responses and production of chemokines promoting antiviral (CXCL10), neutrophilic (CXCL1, CXCL5, CXCL8), and type 2 responses (CCL11, CCL17, CCL22). Human infant airway epithelial cell (AEC) cultures were used to define the transcriptomic (RNAseq) profile leading to high vs. low TSLP responses in vitro. Results: Infants in the high TSLP group had greater in vivo type III IFN airway production (median type III IFN in high TSLP 183.2 pg/ml vs. 63.4 pg/ml in low TSLP group, p= 0.007) and increased in vitro type I-III IFN AEC responses after stimulation with a viral mimic (poly I:C). Our RNAseq data showed that infants in the high TSLP group had significant baseline upregulation of IFN signature genes (e.g., IFIT2, IFI6, MX1) and pro-inflammatory chemokine genes prior to viral mimic stimulation. Infants in the high TSLP group also showed a baseline AEC pro-inflammatory state characterized by increased production of all the chemokines assayed (e.g., CXCL10, CXCL8) in the absence of viral stimuli. Conclusion: High TSLP responses in the human infant airways are associated with pre-activated airway epithelial IFN antiviral immunity and increased baseline AEC production of pro-inflammatory chemokines. These findings present a new paradigm underlying the high production of TSLP in the human infant airway epithelium and shed light on the pathogenesis of viral respiratory illnesses during early infancy and beyond childhood. Overall design: To investigate the immune response initiated by TSLP, in infants, before and after introduction of viral mimic (Poly I:C; PIC), differential expression was performed between high and low TSLP groups at no treatment (NT), 3 hr PIC and 24 hour PIC treatment respectively.