ZNRF1在TLR7/9主導之免疫反應中所扮演的角色

Abstract

漿狀樹突細胞(plasmacytoid dendritic cells)是一種特化的先天免疫細胞，其在病毒感染時能夠產生大量的第一型干擾素(type I interferons)。 第七型和第九型類鐸受體（Toll-like receptor 7 and 9）在漿狀樹突細胞中高度表現，並且能夠分別偵測單股核糖核酸(single strand RNA)和未甲基化的CpG位點去氧核醣核酸(CpG DNA)。我們先前的研究發現ZNRF1在脂多糖（Lipopolysaccharide）刺激後會增強前發炎激素(pro-inflammatory cytokines)的製造並抑制抗發炎激素 (anti-inflammatory cytokines) 的產生，顯示ZNRF1在第四型類鐸受體(Toll-like receptor 4)主導的免疫反應中具有正向調節功能。然而，ZNRF1在胞內體型類鐸受體主導的免疫反應中所扮演的角色仍不清楚。在這篇研究中，我們顯示當漿狀樹突細胞中的第七型和第九型類鐸受體藉由配體刺激或是病毒感染活化後，ZNRF1缺失會增強第一型干擾素產生而前發炎激素則不受影響。增強的第一型干擾素反應也促進ZNRF1缺失的人類漿狀樹突細胞抵抗第一型單純皰疹病毒(herpes simplex virus 1)感染的能力。此外，ZNRF1的泛素連接酶活性對於其調控第七型類鐸受體主導第一型干擾素的製造是必須的。最後，我們發現ZNRF1缺失會導致IKKα的活性增加，並延遲IKKα和LC3B之間的分離。總結以上，我們的結果顯示ZNRF1在第七型和第九型類鐸受體主導的免疫反應中扮演負向調控的角色，並有可能作為治療第一型干擾素相關自體免疫疾病的新標靶。

Plasmacytoid dendritic cells (pDCs) are a specialized population of innate immune cells, which are capable of producing large amounts of type I interferons (IFNs) following viral infection. Toll-like receptor (TLR) 7 and 9 are highly expressed in pDCs and are able to sense single strand RNA (ssRNA) and unmethylated CpG DNA, respectively. Our previous studies demonstrated that ZNRF1 enhanced the production of pro-inflammatory cytokines and suppressed anti-inflammatory cytokines production after LPS challenge, suggesting its positive regulatory function in TLR4-triggered inflammatory reposes. However, the regulatory role of ZNRF1 in endosomal TLRs-mediated immune responses remains unclear. Here we demonstrated that ZNRF1 deficiency enhanced type I IFNs production whereas the production of pro-inflammatory cytokines remained unaffected in pDCs after TLR7 and TLR9 activation induced by both ligands and virus infection. Consistently, enhanced type I IFNs production in ZNRF1 -/- CAL-1 promoted the host defense against HSV-1 infection. Furthermore, we showed that the E3 ubiquitin ligase activity of ZNRF1 was required for its regulatory function in TLR7-mediated type I IFNs production, which worked through modulating IKKα activity. Finally, immuno-fluorescence images showed that the disassociation of IKKα and LC3B was delayed in ZNRF1 -/- CAL-1. Taken together, our results suggested that ZNRF1 is a negative regulator of TLR7/9-driven immune response in pDCs and may serve as a novel therapeutic target for type I IFNs-mediated autoimmune diseases.