Antigenic variation of TprK

本计划项目申请的重点是梅毒病原体梅毒螺旋体的平行12个成员TPR家族。有证据表明，这些基因及其编码的蛋白质是重要的抗原和毒力因子。我们建议研究Tpr家族成员之一的TprK，作为第一个在梅毒螺旋体中描述的无源变异系统。TprK是细胞免疫和体液免疫的主要靶点，用重组TprK免疫兔可显著抑制梅毒螺旋体皮内攻击后的病变发展。TprK在菌株间和菌株内是异质性的*，序列变异限制在7个离散变量(V)，这些变量是抗体反应的目标。序列变异的分子机制被提出，即位于染色体上tprD附近的供体位点的基因转化导致单个tprK表达位点发生突变。用一种新的方法获得梅毒螺旋体克隆分离株，我们证明了tprK V区序列在感染过程中发生变化，并且变异在免疫压力下积累。这些发现有力地提示了tprK变异在免疫逃避和感染持久性中的作用。在本次续费申请中，我们提出了以下具体目标：1)。比较三株梅毒螺旋体在感染过程中和连续传代过程中tprK序列的变化规律和变化率；确定免疫抑制是否能防止感染期间变异序列的积累；3)。确定V区特异性免疫压力是否选择具有不同tprK序列的生物；4)。确定TprK V区序列多样性在异源感染或免疫逃避易感性中的作用。这些研究与项目1-3的目标一致，将有助于确定这种重要感染的发病机制和持久性。

This Program Project application focuses on the paralogous 12-mernber tpr family of Treponema pallidum, the causatiye;agent of syphilis. Evidence suggests; that these: genes; and their encoded proteins, are important antigens and virulence factors. We propose to examine TprK, one member of the Tpr family, as:the first angenic variation system to bedescribed in Treponema pallidum. TprK is a major target of both cellular and humoral immunity and immunization rabbits with recombinant TprK results in significant attenuation of lesion development following intradermal challenge with viable Treponema pallidum. TprK is heterogeneous among and within strains* with sequence variation limited to 7 discrete variable (V) that are targets of the antibody response. A molecular mechanism has been proposed for the sequence variation, with mutations arising in the single tprK expression site by gene conversion of donor sites located near tprD on the chromosome. Using a novel method for derivation of clonal isolates of T. pallidum, we have demonstrated that the tprK V region sequences change during infection, and that variation accumulates under immune pressure. These findings strongly suggest the role of tprK variation in immune evasion and persistence of infection. In this renewal application, we propose the following Specific Aims: 1). Compare the pattern and rate of tprK sequence change among three strains of T. pallidum during the course of infection and during serial passage; 2). Determine whether immunosuppression prevents accumulation of variant sequences during infection; 3). Determine whether V region-specific immune pressure selects for organisms with variant tprK sequences; 4). Determine the contribution of TprK V region sequence diversity in susceptibility to heterologous infection or immune escape. These studies, in concert with the aims of Projects 1-3, will help to define mechanisms of pathogenesis and persistence of this important infection.