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Abstract

During my PhD, I firstly explored the crosstalk of type I and III interferons (IFNs) signaling. Intestinal epithelial cells (IECs) are primarily responsive to enteric viruses in human intestine. The virus infection results in the induction of both type I and type III IFNs. Subsequently, the IFNs induce a series of antiviral molecules to prevent IECs from viral propagation. Currently, whether there is a crosstalk between these two cytokine pathways remains unsolved. Using either type I or type III receptor-deficient human intestinal epithelial cells, the results showed that the two cytokine pathways are interconnected at the level of ISG induction and potent of antiviral activity. Moreover, in human IECs, type I IFN receptor upregulates type III IFN siganling whereas type III IFN downregulates type I IFN signaling. These findings indicate that human intestinal cells are preferentially protected by type III IFN signaling. Subsequently, I investigated how the newly discovered IFN-λ4 and its variants impact cytokine signaling and the conservation between them. Human IFN-λ4 is very divergent and only shares about 30% homology with IFN-λ1-3. Interestingly, IFN-λ4 variants are related to the outcome of HCV infection in humans. In this study, I determine whether human IFN-λ4 and its variants have differences in antiviral signalling compared to IFN-λ3. My results demonstrate that human IFN-λ4 and its variants P70S and K154E induce a distinct magnitude and kinetics of ISG production in human hepatocyte and intestinal cells. In addition, antiviral response induced by IFN-λ4 is faster yet transient compared to IFN-λ3. Furthermore, the distinct antiviral potency was also found in non-human primate IFN-λs and cell lines. Modifications in IFN-λ1 receptor-interacting interface do not alter its kinetic profile. Together, the results emphasis the possibility of IFN-λs in tissue specialisation. My third project is to explore the interaction between interleukin-22 and IFN-λ. In this project, I employed human cell lines and human intestinal organoids to reveal several important findings about the interaction. I found that co-treatment of IL-22 and IFN-λ can induce more p-STAT1 than individual treatment of IL-22 or IFN-λ, but IL-22 cannot enhance IFN-λ-induced ISGs and antiviral activity in vitro. Using RNA-seq, I found signaling induced by IL-22 and IFN-λ are relatively independent even though they share a receptor and activate the same JAK/STAT pathways. Subsequently, I applied human intestinal organoids to validate the cell proliferation function induced by IL-22 which is found in the RNA-seq. I demonstrate IL-22 can promote the proliferation and regeneration of human intestinal organoids. Notably, IL-22 can promote stem cell proliferation marked by the increase in OLFM4 expression in the organoids. Subsequent smRNAFish in OLFM4 confirms the result in organoids. These results indicate a new finding concerning IL-22 in human intestinal cells and intestinal organoids.