Mechanisms of IVIG Protection in Viral Encephalitis

描述（由申请人提供）：与易感的129 S6（129）和BALB/c相比，C57 BL/6（B6）小鼠对致死性HSV脑炎（HSE）具有遗传抗性。我们已经表明，致命的HSE在129只小鼠的结果，涉及巨噬细胞和中性粒细胞的高度炎症反应，抑制HSV复制的阿昔洛韦在很大程度上是无效的，对HSE的保护。缺乏B和T细胞的B6-Rag小鼠比仅比129野生型（wt）小鼠稍微更易感的129-Rag小鼠更具抗性。我们报告说，单剂量的合并人免疫球蛋白（IVIG）给予感染后24小时（PI）完全保护野生型129小鼠从致命的HSE。IVIG几乎保护了所有B6-Rag小鼠，而129-Rag小鼠即使给予多剂量IVIG或补充有阿昔洛韦（ACV）的IVIG也没有保护作用。我们认为IVIG保护的机制在B6和129小鼠中根本不同，并且进一步地，Rag小鼠中不存在的细胞类型需要类似于IVIG处理的wt 129中所见的长期保护。我们提出了一个双组分模型IVIG保护涉及的机制，抑制炎症和抑制HSV复制的神经元;这两种机制是在129小鼠，而只有第二种机制是在B6小鼠的操作。我们假设IVIG激活了一个“传感器”DC，该DC进而直接或通过诱导的调节性T细胞（TcB）调节先天效应细胞（巨噬细胞和单核细胞），以实现控制感染的受控炎症反应，而没有旁观者免疫病理。我们的特定目的是为了测试所提出的解释IVIG的抗炎活性的假设。IVIG抑制HSV复制的机制将在单独的应用中进行研究。在目的1中，将在未治疗和用IVIG或其衍生物（唾液酸化IgG、抗体亚类等）治疗的小鼠中表征对HSV的炎症应答。将评估IVIG对存活、病毒载量、病变形成的影响，此外，将在模拟和HSV感染的WT 129和129/B6-Rag中比较IVIG的生物分布。目的3：采用过继转移的方法筛选IVIG的“感受器”细胞（sDC），并研究其在免疫保护中的作用，包括诱导T细胞活化和调节Fc？Rs、细胞因子、趋化因子及其受体，以确定IVIG在过度炎症引起的病毒性脑炎模型中的抗炎机制。迄今为止的研究结果表明，IVIG将用于治疗HSE和其他免疫介导的HSV疾病，如疱疹性基质角膜炎（HSK）。本文提出的研究结果将揭示IVIG抑制神经炎症的机制，揭示其应用于治疗广谱CNS炎性疾病的潜力。公共卫生相关性：单纯疱疹病毒（HSV）广泛分布于人群中，这是由于其能够引起潜伏感染并随后重新激活导致进一步传播。HSV是散发性脑炎的主要原因，尽管使用抗病毒药物治疗，但仍与高死亡率（约20%）和许多幸存者的严重神经系统后遗症相关。HSV感染在免疫抑制的个体和免疫力低下的新生儿中特别危险。我们已经令人信服地表明，致命的HSV脑炎（HSE）在易感的129 S6小鼠的致病性炎症反应的结果。最重要的是，用合并的人IgG（IVIG）治疗129只感染的小鼠完全保护了小鼠免于死亡。IVIG治疗还保护了>80%的缺乏B&T细胞的抗性C57 BL/6（B6）Rag小鼠，但即使给予多剂量的IVIG或补充有阿昔洛韦（ACV）的IVIG，它也不能保护129-Rag小鼠。这个意想不到的结果表明，遗传因素决定了IVIG治疗的疗效，我们独特的模型将使我们能够剖析IVIG在具有不同遗传背景的小鼠中的保护机制，包括代表免疫受损个体的Rag小鼠。这些研究的结果对于IVIG作为神经炎性疾病（包括由HSV和其他病毒（如西尼罗河病毒）引起的脑炎）的治疗非常重要，这些病毒是潜在的生物恐怖主义制剂。

DESCRIPTION (provided by applicant): C57BL/6 (B6) mice are genetically resistant to fatal HSV encephalitis (HSE) compared to 129S6 (129) and BALB/c that are susceptible. We have shown that fatal HSE in 129 mice results from hyper-inflammatory responses involving macrophages and neutrophils and that acyclovir which inhibits HSV replication is largely ineffective in protection against HSE. B6-Rag mice lacking B and T cells are more resistant than 129-Rag that are only slightly more susceptible than 129 wild type (wt) mice. We report that a single dose of pooled human immunoglobulin (IVIG) given at 24 h post infection (PI) completely protected wild type 129 mice from fatal HSE. IVIG protected virtually all B6-Rag mice, while 129-Rag mice were not protected even when given multiple doses of IVIG or IVIG supplemented with acyclovir (ACV). We suggest that the mechanism(s) of IVIG protection differs fundamentally in B6 and 129 mice and further, that a cell type absent in Rag mice is required for long-term protection akin to that seen in IVIG treated wt 129. We propose a two-component model for IVIG protection involving a mechanism to suppress inflammation and a mechanism to suppress HSV replication in neurons; both mechanisms are operative in 129 mice whereas only the second mechanism is operative in B6 mice. We hypothesize that IVIG activates a 'sensor' DC that in turn modulates innate effector cells (macrophages and monocytes) either directly of via induced regulatory T cells (Tregs) to achieve controlled inflammatory responses that control infection without bystander immune pathology. Our Specific Aims are designed to test the hypothesis proposed to explain IVIG's anti-inflammatory activity. The mechanism whereby IVIG suppresses HSV replication will be studied in a separate application. In Aim 1, the inflammatory response to HSV will be characterized in untreated and mice treated with IVIG or its derivatives (sialylated IgG, antibody subclasses, etc). IVIG effects on survival, virus load, lesion formation will be assessed and additionally, biodistribution of IVIG will be compared in mock and HSV infected WT 129 and 129/B6-Rag. In Aim 3, the IVIG 'sensor' cells (sDC) will be identified using an adoptive transfer strategy, it's role in protection will be investigated, including induction of Tregs and modulation of expression of Fc?Rs, cytokines, chemokines and their receptors in hematopoietic cells to define the anti-inflammatory mechanism(s) of IVIG in this model of viral encephalitis caused by excessive inflammation. Results from studies done thus far suggest IVIG will be useful for treating HSE and other immune mediated HSV diseases such as herpes stromal keratitis (HSK). Results from studies proposed here will uncover the mechanisms of suppression of neuroinflammation revealing the potential for application of IVIG to treat a broad spectrum of CNS inflammatory diseases. PUBLIC HEALTH RELEVANCE: Herpes simplex virus (HSV) is widely distributed in the human population as result of its ability to cause latent infections and subsequently reactivate leading to further spread. HSV is the major cause of sporadic encephalitis, which despite treatment with antiviral drugs is still associated with high mortality (~20%) and serious neurological sequelae in many survivors. HSV infections are particularly dangerous in immunosuppressed individuals and neonates with compromised immunity. We have shown convincingly that fatal HSV encephalitis (HSE) in susceptible 129S6 mice results from pathogenic inflammatory responses. Most importantly, treatment of 129 infected mice with pooled human IgG (IVIG) totally protected the mice from death. IVIG treatment also protected >80% of resistant C57BL/6 (B6) Rag mice that lack B&T cells but it failed to protect 129-Rag mice even when multiple doses of IVIG or IVIG supplemented with acyclovir (ACV) were given. This unexpected result shows that genetic factors determine the efficacy of IVIG treatment and our unique model will allow us to dissect the mechanism(s) of IVIG protection in mice with different genetic backgrounds, including Rag mice representative of immunocompromized individuals. Results from these studies will be important for making the case for IVIG as a treatment for neuroinflammatory diseases including encephalitis caused by HSV and other viruses like West Nile virus that are potential bioterrorism agents.