Antigenic Variation in Mycoplasmas

描述（由申请人提供）：支原体在自然界中广泛分布，通常会产生具有相当大经济影响的疾病，但有关致病机制的信息很少，也没有有效的控制方法。许多支原体的表面蛋白发生快速变化，这些蛋白被认为对疾病的发病机制很重要。这些支原体蛋白的变异主要是免疫回避的机制还是产生具有不同功能的细胞的机制（例如，组织向性）尚未得到解决。在鼠病原体肺支原体中，涉及高度重复的V-1表面抗原变化的高频表型变异影响菌落形态、生物体对支原体病毒的易感性、支原体对红细胞的吸附和毒力。我们的实验室已经表明，V-1抗原是由一个名为vsa（可变表面抗原）的基因家族编码的。位点特异性DNA倒位通过将不同的基因与vsa表达位点重组来改变vsa基因的表达，从而导致Vsa蛋白质的相位可变产生。最近，我们已经表明，Vsa蛋白具有保护支原体免受补体杀伤的作用。我们的长期目标是了解支原体表型变异的分子基础和致病意义。本提案的具体目的是研究Vsa变异的致病意义。(i)将通过比较免疫活性小鼠和免疫功能低下小鼠（rag和诱导型一氧化氮合酶缺陷突变体）中出现的支原体种群，检查Vsa变异在免疫回避中的作用。(ii)Vsa变异在疾病慢性化中的作用将通过确定不具有Vsa变异能力的支原体突变体是否具有减弱的维持长期感染的能力来检查。(iii)将在一系列体外试验中检查Vsa蛋白在支原体-补体相互作用中的作用。(iv)通过确定对补体杀伤的敏感性是否与小鼠呼吸道定殖能力降低相关，评价支原体细胞对补体敏感性的致病意义。

DESCRIPTION (provided by applicant): Mycoplasmas are widely distributed in nature and commonly produce diseases of considerable economic impact, yet little information is available concerning mechanisms of pathogenesis and effective methods of control are unavailable. Many mycoplasmas undergo rapid variations in surface proteins that are thought to be important to disease pathogenesis. The issue of whether variations in these mycoplasmal proteins is primarily a mechanism for immune avoidance or instead a mechanism for creating cells with varied functions (e.g., tissue tropism) has not been addressed. In the murine pathogen Mycoplasma pulmonis, high-frequency phenotypic variations involving changes in the highly repetitive V-1 surface antigens affect colony morphology, the susceptibility of the organism to mycoplasma viruses, the adsorption of mycoplasmas to red blood cells, and virulence. Our laboratory has shown that the V-1 antigens are encoded by a family of genes designated vsa (variable surface antigen). Site-specific DNA inversions serve to vary vsa gene expression by recombining different genes with the vsa expression site, resulting in the phase-variable production of the Vsa proteins. Recently, we have shown that the Vsa proteins have a role in protecting the mycoplasma from killing by complement. Our long-range goals are to understand the molecular basis and pathogenic significance of phenotypic variations in mycoplasma. The specific aims of the current proposal are to study the pathogenic significance of Vsa variation. (i) The role of Vsa variation in immune avoidance will be examined by comparing the mycoplasma populations that arise in immuno-competent and immunocompromised mice (rag and inducible nitric oxide synthase-deficient mutants). (ii) The role of Vsa variation in disease chronicity will be examined by determining whether a mycoplasmal mutant that is not capable of Vsa variation has a diminished ability to sustain a long-term infection. (iii) The role of the Vsa proteins in mycoplasma-complement interactions will be examined in a series of in vitro assays. (iv) The pathogenic significance of the susceptibility of mycoplasma cells to complement will be evaluated by determining whether sensitivity to complement killing correlates with a diminished ability to colonize the mouse respiratory tract.