Characterization of BATF functions in plasmacytoid dendritic cell development and type I interferon production in antiviral immune responses

浆细胞样树突状细胞（pDCs）具有产生大量I型干扰素（ifn）的能力。因此，pDCs在病毒感染介导保护性免疫反应或引起免疫病理中发挥着重要而复杂的作用。此外，pDCs的激活失调与自身免疫性疾病有关。pDC介导的免疫调节的细胞和分子机制尚不清楚。为了确定pDC功能的新调控因子，我们发现在产生IFN β的pDC中Batf（碱性亮氨酸拉链转录因子，atf样）的高表达。BATF与BATF2和BATF3组成了AP-1转录因子的一个亚家族。已知它可以负向调节AP-1介导的基因转录，但也可以通过与其他转录因子如IRF家族成员相互作用发挥积极的转录活性。BATF已被证明在辅助性T细胞（Th）类型的分化和细胞因子的产生以及B细胞的类开关重组中是必不可少的。到目前为止，还不知道BATF对pDC开发或功能的影响。在初步研究中，我们做了以下观察：(i) BATF在i型IFN产生的pDCs中高表达，（ii）在Flt3-L培养和来自BATF -缺陷（BATF -/-）小鼠的次级淋巴器官中Toll样受体（TLR） 9激活后，pDCs的频率增加，（iii） DC标记CD11c在BATF -/- pDCs上的表面表达水平降低。（iv）在TLR9的体外激活下，Batf-/- pDCs产生的I型IFN数量增加，并且存在于被淋巴细胞性脉络丛脑膜炎病毒（LCMV）感染的Batf-/-小鼠的血清中；(v)与Batf-/- pDCs相比，Batf-/- pDCs的体外病毒感染率分别降低。此外，（vi）在Batf-/-与Batf+/+ pDCs的初步转录组分析中，可以看到I型IFN特征和DC分化基因表达的差异。本研究将明确batf介导的pDC发育和抗病毒免疫效应的作用机制。我们设想的双轨工作计划涵盖分子和细胞方面：在第一个轨道中，我们将定义Batf介导的pDCs中I型IFN产生的调节的分子机制，并在激活后对Batf-/-与Batf+/+ pDCs的转录和表观遗传时间模式进行全基因组谱分析，并确定激活复合体内Batf-相互作用的伙伴。第二个方向是利用pDC特异性BATF缺陷小鼠和竞争性骨髓嵌合体研究BATF在pDC发育和分化中的作用，并表征pDC特异性BATF在LCMV感染中的功能。详细分析BATF在pDCs中调控的功能和途径，将为控制BATF在感染性疾病和干扰素病变中的功能提供重要信息。

Plasmacytoid dendritic cells (pDCs) harbor the capacity to produce high amounts of type I interferons (IFNs). Thereby, pDCs play an important and complex role in viral infections mediating protective immune responses or causing immunopathology. Also, dysregulated activation of pDCs is associated with autoimmune diseases. The cellular and molecular mechanisms of pDC mediated immune regulation are poorly understood. In aiming to identify novel regulators of pDC functions we discovered a high expression of Batf (Basic leucine zipper transcription factor, ATF-like) in IFN beta-producing pDCs. BATF together with BATF2 and BATF3 comprise a subfamily of the larger group of AP-1 transcription factors. It is known to negatively regulate AP-1 mediated gene transcription, but also to exert positive transcriptional activities by interacting with other transcription factors such as IRF family members. BATF has been shown to be essential in the differentiation and cytokine production of T helper (Th) cell types and in class switch recombination in B cells. No implications for BATF in pDC development or function are known so far.In preliminary studies we made the following observations: (i) BATF is highly expressed in type I IFN producing pDCs, (ii) frequencies of pDCs are increased in Flt3-L cultures and after Toll like receptor (TLR) 9 activation in secondary lymphoid organs from Batf-deficient (Batf-/-) mice, (iii) surface expression levels of the DC marker CD11c are reduced on Batf-/- pDCs, (iv) increased amounts of type I IFN are produced by Batf-/- pDCs in response to TLR9 activation in vitro and present in the serum of lymphocytic choriomeningitis virus (LCMV) infected Batf-/- mice, and (v) viral infection rates in vitro in the presence of Batf-/- pDCs are reduced, as compared to Batf+/+ littermate controls, respectively. Also, (vi) a type I IFN signature and differences in the expression of DC differentiation genes are visible in preliminary transcriptome profiling of Batf-/- vs. Batf+/+ pDCs.The proposed study will define the mechanisms of BATF-mediated functions in pDC development and effector functions in anti-viral immunity. Our envisaged twin-track work programme covers molecular and cellular aspects: In the first track we will define the molecular mechanisms of BATF-mediated regulation of type I IFN production in pDCs and perform genome wide profiling of transcriptional and epigenetic temporal patterns in Batf-/- vs. Batf+/+ pDCs after activation and identify BATF-interaction partners within the activating complex. The second track investigates the role of BATF in pDC development and differentiation using pDC specific BATF-deficient mice and competitive bone marrow chimeras and characterizes pDC specific BATF functions in LCMV infection.Detailed analyses of the functions and pathways regulated by BATF in pDCs will provide critical information for controlled manipulation of BATF functions in infectious diseases and interferonopathies.