Eighteen species of rickettsiae are reported to cause infections in humans. One of these is Rickettsia helvetica, which is endemic in European and Asian countries and transmitted by the tick Ixodes ricinus. Besides fever, it has been demonstrated to cause meningitis and is also associated with perimyocarditis. One of the initial targets for rickettsiae after inoculation by ticks is the macrophage/monocyte. How rickettsiae remain in the macrophages/monocytes before establishing their infection in vascular endothelial cells remains poorly understood. The main aim of the present study was to investigate the impact on and survival of R. helvetica in a human leukemic monocytic cell line, THP-1. Our results show that R. helvetica survives and propagates in the THP-1 cells. The infection in monocytes was followed for seven days by qPCR and for 30 days by TEM, where invasion of the nucleus was also observed as well as double membrane vacuoles containing rickettsiae, a finding suggesting that R. helvetica might induce autophagy at the early stage of infection. Infected monocytes induced TNF-α which may be important in host defence against rickettsial infections and promote cell survival and inhibiting cell death by apoptosis. The present findings illustrate the importance of monocytes to the pathogenesis of rickettsial disease.

18种立克次体的报告给人类造成感染。其中之一是立克次体Helvetica字体，这是在欧洲和亚洲国家流行，并通过蜱传播篦子硬蜱。除了发烧，它已被证明导致脑膜炎和也与perimyocarditis相关。一个用于由蜱接种后立克次氏体的初始目标是巨噬细胞/单核细胞。立克次体如何保持在巨噬细胞/血管内皮细胞建立自己的感染之前的单核细胞仍然知之甚少。本研究的主要目的是研究上的影响和存活R.黑体在人白血病单核细胞系，THP-1。我们的研究结果显示，立克生存和传播在THP-1细胞。在单核细胞的感染之后七天通过qPCR和通过TEM，其中核的侵袭也观察到，以及含有立克次氏体双膜液泡，这一发现表明30天立克可能在早期诱导自噬感染。被感染的单核细胞分泌TNF-α这可能是对立克次体感染的宿主防御重要的凋亡促进细胞存活和抑制细胞死亡。目前的发现说明了单核细胞对立克次体病发病机制的重要性。