Surface Lipoproteins and Serum Resistance in Borrelia burgdorferi

描述（由申请方提供）：莱姆病由螺旋体引起，螺旋体分为三种不同的基因种，伯氏疏螺旋体，B。afzelii和B. garinii。有趣的是，所有这三个基因种似乎在感染期间在哺乳动物宿主中占据不同的生态位。例如，B。burgdorferi和B.阿氏杆菌通常与涉及心脏、关节和皮肤的疾病有关，而B.伽氏病常引起中枢神经系统异常。最近的研究表明，B。burgdorferi和B. afzelii在细胞表面结合宿主血清补体抑制因子H，这可能增强了它们对血清的抗性。相比之下，大多数B.伽氏分离物不结合H因子，并被哺乳动物血清杀死。这一观察结果导致了这样的建议，即B。伽氏微生物持续感染中枢神经系统，因为它是细胞毒性补体有限的环境。最近，几家B. Burgdorferi外表面脂蛋白（Osp）被我们和其他人鉴定为可以在体外结合因子H。最相关的因子H结合蛋白包括与OspE相关的脂蛋白家族以及称为CspA的疏螺旋体表面脂蛋白。与它们结合因子H的能力一致，所有这些表面脂蛋白都已显示出增强血清抵抗力。我们和其他人以前曾报道过表达B。在血清敏感的B.加氏菌株导致对血清介导的杀伤的抗性增加。我们还表明，突变B强毒株中的cspA基因。burgdorferi导致对血清介导的杀伤非常敏感的突变体。此外，我们最近还表明，CspA表达是B所必需的。因为蜱虫大量吸食哺乳动物的血液，所以它们无法在蜱虫的中肠中生存。合并的观察结果与我们的假设一致，即CspA和OspE表面脂蛋白是B中血清抗性的组成部分。burgdorferi。直接检验这一潜在假设，并进一步检验这些蛋白质在B传递中所起的机制作用。从蜱到哺乳动物，我们提出以下两个具体目标。在具体目标1中，我们将使用我们最近产生的几种新菌株，使用莱姆病小鼠模型来研究CspA在毒力和疾病发病机制中的作用。在特定目标2中，我们将检查在两种野生型B中均缺乏OspE相关脂蛋白表达的菌株。在我们的CspA突变株中，以更好地评估它们在疏螺旋体地方性流行周期期间在血清抗性和莱姆病发病机制中的作用。最后，在修订后的提案中，我们纳入了更多基于机制的研究，以确定与CspA和OspE结合的H因子是否实际上增强了该生物体表面上C3b降解为iC3b，这是该领域目前的教条。自从我们上次提交以来，我们已经产生了有趣的数据，表明因子H结合蛋白可能不会增强B表面上iC3 B的生成。我们将在修正后的目标2中更详细地考察这一观察结果。 公共卫生相关性：综合研究可能会导致识别新的机制，使莱姆病细菌在感染后逃避最初的宿主免疫监视系统。从拟议的研究中获得的信息可用于产生一种新的疫苗或莱姆病的疾病调节治疗。鉴于莱姆病是美国最流行的蜱传感染，拟议研究的独特见解可能导致莱姆病的新疫苗策略，这将大大有利于美国和国外的整体公共卫生。

DESCRIPTION (provided by applicant): Lyme disease is caused by spirochetes that have been grouped into three different genospecies, Borrelia burgdorferi, B. afzelii, and B. garinii. Interestingly, all three genospecies seem to populate different niches in the mammalian host during infection. For example, B. burgdorferi and B. afzelii are commonly associated with disease involving the heart, joints, and skin, while B. garinii often causes central nervous system abnormalities. It was recently shown that both B. burgdorferi and B. afzelii bind host serum complement inhibitor factor H on their cell surface, which possibly enhances their resistance to serum. By contrast, most B. garinii isolates do not bind factor H and are killed by mammalian serum. This observation has led to the suggestion that B. garinii organisms persistently infect the central nervous system because it is an environment limited in cytotoxic complement. Recently, several B. burgdorferi outer surface lipoproteins (Osp) were identified by us and others that can bind factor H in vitro. The factor H binding proteins that are most relevant include a family of lipoproteins related to OspE as well as a borrelial surface lipoprotein designated CspA. Consistent with their ability to bind factor H, all of these surface lipoproteins have been shown to enhance serum resistance. We and others have previously reported that expressing the B. burgdorferi strain 297 OspE protein in a serum sensitive B. garinii strain results in increased resistance to serum-mediated killing. We also have shown that mutating the cspA gene in a virulent strain of B. burgdorferi results in a mutant that is exquisitely sensitive to serum-mediated killing. Furthermore, we also have recently shown that CspA expression is required for B. burgdorferi to survive in the midgut of ticks as they engorge on mammalian blood. The combined observations are consistent with our hypothesis that CspA and the OspE surface lipoproteins are integral to serum resistance in B. burgdorferi. To directly examine this underlying hypothesis and further examine the mechanistic role played by these proteins in transmission of B. burgdorferi from the tick to mammal, we propose the following two Specific Aims. In Specific Aim 1 we will use several novel strains we recently generated to examine the role of CspA in virulence and disease pathogenesis using the mouse model of Lyme disease. In Specific Aim 2 we will examine a strain that lacks expression of the OspE-related lipoproteins in both wild type B. burgdorferi and in our CspA mutant strain to better assess their role(s) in serum resistance and Lyme disease pathogenesis during the borrelial enzootic cycle. Finally, in the revised proposal we have included more mechanism-based studies to determine if factor H binding to CspA and OspE actually enhances degradation of C3b to iC3b on the surface of this organism, which is the current dogma in the field. Since our last submission, we have generated interesting data indicating that factor H binding proteins may not enhance generation of iC3b on the surface of B. burgdorferi after all, and we will examine this observation in more detail in our revised Aim 2. PUBLIC HEALTH RELEVANCE: The combined studies could result in the identification of new mechanisms that allow Lyme disease bacteria to evade the initial host immune surveillance system after infection. Information derived from the proposed studies could be used to generate a new vaccine or disease modulating therapeutic for Lyme disease. Given that Lyme disease is the most prevalent tick-borne infection in the United States, unique insight from the proposed studies that could lead to a new vaccine strategy for Lyme disease could greatly benefit overall public health in the United States and abroad.