Lin Mingqun, Rikihisa Yasuko
Department of Veterinary Biosciences, The Ohio State University, Columbus, OH 43210, USA.
Cell Microbiol. 2007 Apr;9(4):861-74. doi: 10.1111/j.1462-5822.2006.00835.x. Epub 2006 Nov 3.
Ehrlichia chaffeensis is an obligate intracellular bacterium which replicates in monocytes or macrophages, the primary producers of reactive oxygen species (ROS). However, effects of ROS on E. chaffeensis infection and whether E. chaffeensis modulates ROS generation in host monocytes are unknown. Here, E. chaffeensis was shown to lose infectivity upon exposure to O(2)(-) or hydrogen peroxide. Upon incubation with human monocytes, E. chaffeensis neither induced O(2)(-) generation by human monocytes, nor colocalized with nicotinamide adenine dinucleotide phosphate (NADPH) oxidase components. Instead, it actively blocked O(2)(-) generation by monocytes stimulated with phorbol myristate acetate and caused the rapid degradation of p22(phox), a component of NADPH oxidase. These effects were not seen in neutrophil, which is another potent ROS generator, but a cell type that E. chaffeensis does not infect. Trypsin pretreatment of monocytes prevented the inhibition of O(2)(-) generation by E. chaffeensis. The degradation of p22(phox) by E. chaffeensis was specific to subsets of monocytes with bound and/or intracellular bacteria, and the degradation could be reduced by heat treatment of the bacterium, lipopolysaccharide pretreatment of monocytes, or the incubation with haemin. The degradation of p22(phox) by E. chaffeensis and its prevention by haemin or protease inhibitors also occurred in isolated monocyte membrane fractions, indicating that host cytoplasmic signalling is not required for these processes. The amount of gp91(phox) was stable under all conditions examined in this study. These findings point to a unique survival mechanism of ROS-sensitive obligate intraleucocytic bacteria that involves the destabilization of p22(phox) following the binding of bacteria to host cell surface proteins.
恰菲埃立克体是一种专性细胞内细菌，在单核细胞或巨噬细胞（活性氧（ROS）的主要产生者）中复制。然而，ROS对恰菲埃立克体感染的影响以及恰菲埃立克体是否调节宿主单核细胞中ROS的产生尚不清楚。在此研究中，发现恰菲埃立克体在暴露于超氧阴离子（O₂⁻）或过氧化氢后会丧失感染力。与人单核细胞共孵育时，恰菲埃立克体既不诱导人单核细胞产生O₂⁻，也不与烟酰胺腺嘌呤二核苷酸磷酸（NADPH）氧化酶成分共定位。相反，它会积极阻断佛波酯肉豆蔻酸酯刺激的单核细胞产生O₂⁻，并导致NADPH氧化酶成分p22⁽ᵖʰᵒˣ⁾快速降解。在中性粒细胞（另一种有效的ROS产生细胞，但恰菲埃立克体不感染的细胞类型）中未观察到这些效应。对单核细胞进行胰蛋白酶预处理可防止恰菲埃立克体抑制O₂⁻的产生。恰菲埃立克体对p22⁽ᵖʰᵒˣ⁾的降解作用特定于带有结合和/或胞内细菌的单核细胞亚群，并且通过对细菌进行热处理、对单核细胞进行脂多糖预处理或与血红素共孵育可减少这种降解。恰菲埃立克体对p22⁽ᵖʰᵒˣ⁾的降解及其被血红素或蛋白酶抑制剂的抑制作用在分离的单核细胞膜组分中也会发生，这表明这些过程不需要宿主细胞质信号传导。在本研究检测的所有条件下，gp91⁽ᵖʰᵒˣ⁾的量都是稳定的。这些发现指出了对ROS敏感的专性白细胞内细菌的一种独特生存机制，该机制涉及细菌与宿主细胞表面蛋白结合后p22⁽ᵖʰᵒˣ⁾的不稳定。
