Dysregulation of Innate Immune Responses by Borrelia burgdorferi:A Role for IL-10

描述(申请人提供)：大多数感染伯氏疏螺旋体(BB)的人会患上莱姆病，这种疾病占美国所有媒介传播疾病的90%，每年直接医疗费用和生产力损失高达10-20亿美元。这种感染会引发强大的先天和获得性免疫反应，但往往无法清除细菌，从而导致目标组织的持续感染和疾病。通过先天免疫细胞上的Toll样受体2早期识别BB脂蛋白似乎是细菌从宿主组织中清除的关键，然而我们目前还不清楚对于预防莱姆病至关重要的特定先天反应。我们先前的研究表明，IL-10缺陷小鼠(IL-10-/-)对宿主组织中BB水平的控制明显好于野生型(WT)小鼠，从而使IL-10成为唯一显著影响BB清除的细胞因子。我们的初步数据进一步表明，1)活的(但不是被杀死的)BB能从小鼠巨噬细胞(MX)和树突状细胞(DC)诱导高水平的IL-10，2)分泌的IL-10水平可以显著抑制随后驻留的MX的激活，3)在感染后24小时内在小鼠皮肤中检测到显著的IL-10水平，以及4)IL-10-/-小鼠没有表现出这些抑制作用，导致MX活性和免疫清除增强。我们推测，IL-10是为了应对BB感染而产生的，它抑制了宿主的先天性免疫反应，而这种免疫反应对于有效地清除宿主组织中的BB是至关重要的，并且MX和DC功能是这种失调的宿主反应的核心。这项建议的总体目标是：1)确定在小鼠组织中最初检测并对BB做出反应的细胞类型，2)确定哪些细胞类型负责在感染过程中产生IL-10，3)描述哪些免疫细胞类型受到BB诱导的IL-10的不利影响，以及哪些免疫机制受到失调。为了达到这些目标，目标1将比较IL-10对MX和DC摄取、内部运输和体外介导BB杀伤能力的影响，包括激活/成熟标志物的表达。目的2将利用一些基因突变的小鼠品系来描述在体内BB感染过程中造血细胞和非造血细胞以及MX、DC和T细胞产生IL-10和/或响应IL-10的相对重要性。目的3将严格测试IL-10受体阻断抗体是否可以用于治疗感染BB的小鼠。这些研究应该阐明在莱姆病发展过程中被抑制的特定宿主免疫机制，从而导致新的治疗方法的开发。与公共卫生相关的伯氏杆菌感染导致宿主组织显著增加IL-10的产生，这抑制了宿主的免疫反应，阻碍了宿主清除这种感染的能力，导致莱姆病的发生。IL-10是目前已知的唯一显著影响莱姆病发生发展的细胞因子，是了解莱姆病免疫逃避机制的重要线索。这些研究旨在确定产生IL-10的宿主细胞以及受IL-10失调的免疫细胞，从而确定可能有针对性地治疗莱姆病患者的机制。

DESCRIPTION (provided by applicant): Most people infected with Borrelia burgdorferi (Bb) will develop Lyme disease, which accounts for >90% of all vector-borne illnesses in the United States, and e $1-2 billion each year in direct medical expenses and lost productivity. This infection elicits potent innate and adaptive immune responses that often fail to clear the bacteria, leading to persistent infection and disease in targeted tissues. Early recognition of Bb lipoproteins through Toll-like receptor 2 on innate immune cells appears to be crucial for bacterial clearance from host tissues, however we currently have no clear understanding of the particular innate responses that are critical for preventing Lyme disease. Our previous studies revealed that IL-10-deficient mice (IL-10-/-) control Bb levels in host tissues significantly better than wild type (WT) mice, thus making IL-10 the only cytokine shown to significantly affect Bb clearance. Our preliminary data further indicate that 1) viable (but not killed) Bb elicit high IL-10 levels from murine macrophages (MXs) and dendritic cells (DCs), 2) that the secreted levels of IL-10 can significantly inhibit subsequent activation of resident MXs, 3) that significant IL-10 levels are detected in mouse skin within 24h of infection, and 4) that IL-10-/- mice do not exhibit these suppressive effects, leading to enhanced MX activity and immune clearance. We hypothesize that the IL-10 elaborated in response to Bb infection, suppresses host innate immune responses that are crucial for efficient Bb clearance from host tissues, and that MX and DC functions are central to this dysregulated host response. The overall goals of this proposal are: 1) to identify the cell types that initially detect and respond to Bb in murine tissues, 2) to determine which cell types are responsible for producing IL-10 during the course of infection, and 3) to delineate which immune cell types are adversely affected by Bb-elicited IL-10 and which immune mechanisms are dysregulated. To approach these goals, Aim 1 will compare IL-10 effects on the abilities of MXs and DCs to ingest, internally traffic, and mediate killing of Bb in vitro, including the expression of activation/maturation markers. Aim 2 will utilize a number of genetically mutated mouse lines to delineate the relative importance of hemopoietic and nonhemopoietic cells, as well as MXs, DCs, and T cells to both produce IL-10 and/or respond to IL-10 during Bb infection in vivo. Aim 3 will rigorously test whether administration of IL-10 receptor-blocking antibodies could be used as a curative therapy for mice infected with Bb. These studies should clarify specific host immune mechanisms that are suppressed during the development of Lyme disease, leading to the development of novel treatments. PUBLIC HEALTH RELEVANCE Infection with B. burgdorferi causes host tissues to significantly increase IL-10 production, which suppresses the host immune responses and hinders their ability to clear this infection, leading to the development of Lyme disease. IL-10 is the only cytokine that is currently known to significantly affect the development of Lyme disease and represents an important clue into the immune evasion mechanism of this pathogen. These studies intend to identify the host cells that produce IL-10, as well as the immune cells that are dysregulated by IL-10, thus identifying mechanisms that could be targeted to treat Lyme disease patients.