Department of Molecular Biology and Biochemistry and Institute for Immunology, University of California, Irvine, California 92697, USA.
J Leukoc Biol. 2013 May;93(5):789-800. doi: 10.1189/jlb.1012517. Epub 2013 Mar 13.
Toxoplasma gondii actively infects circulating immune cells, including monocytes and DCs, and is thought to use these cells as Trojan horses for parasite dissemination. To investigate the interactions of T. gondii-infected human monocytes with vascular endothelium under conditions of shear stress, we developed a fluidic and time-lapse fluorescence microscopy system. Both uninfected and infected monocytes rolled, decelerated, and firmly adhered on TNF-α-activated endothelium. Interestingly, T. gondii-infected primary human monocytes and THP-1 cells exhibited altered adhesion dynamics compared with uninfected monocytes: infected cells rolled at significantly higher velocities (2.5- to 4.6-fold) and over greater distances (2.6- to 4.8-fold) than uninfected monocytes, before firmly adhering. During monocyte searching, 29-36% of infected monocytes compared with 0-11% of uninfected monocytes migrated >10 μm from the point where they initiated searching, and these "wandering" searches were predominantly in the direction of flow. As infected monocytes appeared delayed in their transition to firm adhesion, we examined the effects of infection on integrin expression and function. T. gondii did not affect the expression of LFA-1, VLA-4, or MAC-1 or the ability of Mn(2+) to activate these integrins. However, T. gondii infection impaired LFA-1 and VLA-4 clustering and pseudopod extension in response to integrin ligands. Surprisingly, a single intracellular parasite was sufficient to mediate these effects. This research has established a system for studying pathogen modulation of human leukocyte adhesion under conditions of physiological shear stress and has revealed a previously unappreciated effect of T. gondii infection on ligand-dependent integrin clustering.
刚地弓形虫主动感染循环免疫细胞，包括单核细胞和树突状细胞，并被认为利用这些细胞作为寄生虫传播的特洛伊木马。为了研究在切应力条件下感染弓形虫的人单核细胞与血管内皮的相互作用，我们开发了一种流体和延时荧光显微镜系统。未感染和感染的单核细胞在 TNF-α 激活的内皮上滚动、减速和牢固黏附。有趣的是，与未感染的单核细胞相比，感染弓形虫的原代人单核细胞和 THP-1 细胞表现出改变的黏附动力学：感染细胞的滚动速度明显更高（2.5 至 4.6 倍），滚动距离也更长（2.6 至 4.8 倍），然后才牢固黏附。在单核细胞搜索过程中，与未感染的单核细胞（0-11%）相比，29-36%的感染单核细胞从开始搜索的点迁移超过 10μm，这些“游走”搜索主要是朝向流动的方向。由于感染的单核细胞在向牢固黏附的转变中似乎延迟，我们研究了感染对整合素表达和功能的影响。弓形虫不会影响 LFA-1、VLA-4 或 MAC-1 的表达，也不会影响 Mn2+ 激活这些整合素的能力。然而，弓形虫感染会损害 LFA-1 和 VLA-4 的聚集以及对整合素配体的伪足延伸。令人惊讶的是，单个细胞内寄生虫就足以介导这些效应。这项研究建立了一种在生理切应力条件下研究病原体调节人白细胞黏附的系统，并揭示了弓形虫感染对配体依赖性整合素聚集的先前未被认识的影响。
