Thrombosis and hemodynamic changes in the CNS during Toxoplasma gondii infection

Mammalian circulation relies on a closed high-pressure system to deliver oxygen to tissues via red blood cells within blood vessels lined by endothelial cells. However, this high-pressure system makes us vulnerable to hemorrhage if a blood vessel is damaged. Therefore, we have a mechanism to rapidly seal a damaged vessel with a platelet-fibrin clot in a physiological process called hemostasis. However, clots can form in an intact blood vessel and obstruct blood flow, in a pathological process called thrombosis. Such clots can be life threatening if they interfere with blood flow in critical organs, such as the brain (i.e., ischemic stroke). However, recent research has revealed that thrombosis can be involved in augmenting and supporting the innate immune response to control infection through immunothrombosis. As recent work has demonstrated that Toxoplasma gondii infects and lyses central nervous system endothelial cells that form the blood-brain barrier (BBB), T. gondii-infection is a good model to study the interplay between coagulation, immunity, and infection. However, little is known about the effect of T. gondii infection on the BBB and the functional consequences of infection on cerebral blood flow (CBF) during the different stages of infection. To study CBF changes during T. gondii infection longitudinally we developed a surgical method to achieve chronic optical access for >100 days. Then, using an in vivo infection model in mice, we demonstrated that brain endothelial upregulate the adhesion molecules ICAM-1 and VCAM-1 and become morphologically more tortuous during T. gondii infection. Longitudinal two-photon imaging of cerebral blood vessels during infection revealed vascular occlusion in the brain, prompting an analysis of the coagulation cascade. We detected platelet-fibrin clots within the cerebral vasculature during acute infection. Longitudinal analysis of CBF using laser-speckle imaging during T. gondii infection demonstrated that CBF decreased during acute infection, recovered during stable chronic infection, and decreased again during reactivation of the infection. Finally, we demonstrate that treatment of mice with an anticoagulant, during infection partially rescued CBF in T. gondii-infected mice. These data provide insight into the host-pathogen interactions of a CNS pathogen within the brain vasculature and suggest that thrombosis and changes in cerebral hemodynamics may be an unappreciated aspect of infection with T. gondii