Meri T, Cutler S J, Blom A M, Meri S, Jokiranta T S
Haartman Institute, Department of Bacteriology and Immunology, P.O. Box 21, University of Helsinki, FIN-00014 Helsinki, Finland.
Infect Immun. 2006 Jul;74(7):4157-63. doi: 10.1128/IAI.00007-06.
Relapsing fever is a rapidly progressive and severe septic disease caused by certain Borrelia spirochetes. The disease is divided into two forms, i.e., epidemic relapsing fever, caused by Borrelia recurrentis and transmitted by lice, and the endemic form, caused by several Borrelia species, such as B. duttonii, and transmitted by soft-bodied ticks. The spirochetes enter the bloodstream by the vector bite and live persistently in plasma even after the development of specific antibodies. This leads to fever relapses and high mortality and clearly indicates that the Borrelia organisms utilize effective immune evasion strategies. In this study, we show that the epidemic relapsing fever pathogen B. recurrentis and an endemic relapsing fever pathogen, B. duttonii, are serum resistant, i.e., resistant to complement in vitro. They acquire the host alternative complement pathway regulator factor H on their surfaces in a similar way to that of the less serum-resistant Lyme disease pathogen, B. burgdorferi sensu stricto. More importantly, the relapsing fever spirochetes specifically bind host C4b-binding protein, a major regulator of the antibody-mediated classical complement pathway. Both complement regulators retained their functional activities when bound to the surfaces of the spirochetes. In conclusion, this is the first report of complement evasion by Borrelia recurrentis and B. duttonii and the first report showing capture of C4b-binding protein by spirochetes.
回归热是由某些疏螺旋体引起的一种迅速进展且严重的败血症性疾病。该疾病分为两种形式，即由回归热疏螺旋体引起、通过虱子传播的流行性回归热，以及由几种疏螺旋体（如达顿疏螺旋体）引起、通过软蜱传播的地方性回归热。螺旋体通过媒介叮咬进入血液，即使在特异性抗体产生后仍持续存在于血浆中。这导致发热复发和高死亡率，清楚地表明疏螺旋体利用了有效的免疫逃避策略。在本研究中，我们表明流行性回归热病原体回归热疏螺旋体和地方性回归热病原体达顿疏螺旋体具有血清抗性，即在体外对补体具有抗性。它们以与血清抗性较低的莱姆病病原体狭义伯氏疏螺旋体类似的方式在其表面获取宿主替代补体途径调节因子H。更重要的是，回归热螺旋体特异性结合宿主C4b结合蛋白，这是抗体介导的经典补体途径的主要调节因子。当这两种补体调节因子与螺旋体表面结合时，它们都保留了其功能活性。总之，这是关于回归热疏螺旋体和达顿疏螺旋体逃避补体的首次报道，也是螺旋体捕获C4b结合蛋白的首次报道。
