Shear Forces Enhance Toxoplasma gondii Tachyzoite Motility on Vascular Endothelium

Abstract

Toxoplasma gondii is a highly successful parasite that infects approximately one-third of the human population and can cause fatal disease in immunocompromised individuals. Systemic parasite dissemination to organs such as the brain and eye is critical to pathogenesis. T. gondii can disseminate via the circulation, and both intracellular and extracellular modes of transport have been proposed. However, the processes by which extracellular tachyzoites adhere to and migrate across vascular endothelium under the conditions of rapidly flowing blood remain unknown. We used microfluidics and time-lapse fluorescence microscopy to examine the interactions between extracellular T. gondii and primary human endothelial cells under conditions of physiologic shear stress. Remarkably, tachyzoites adhered to and glided on human vascular endothelium under shear stress conditions. Compared to static conditions, shear stress enhanced T. gondii helical gliding, resulting in a significantly greater displacement, and increased the percentage of tachyzoites that invaded or migrated across the endothelium. The intensity of the shear forces (from 0.5 to 10 dynes/cm2) influenced both initial and sustained adhesion to endothelium. By examining tachyzoites deficient in the T. gondii adhesion protein MIC2, we found that MIC2 contributed to initial adhesion but was not required for adhesion strengthening. These data suggest that under fluidic conditions, T. gondii adhesion to endothelium may be mediated by a multistep cascade of interactions that is governed by unique combinations of adhesion molecules. This work provides novel information about tachyzoite interactions with vascular endothelium and contributes to our understanding of T. gondii dissemination in the infected host.

Endothelial cells are a replicative niche for entry of Toxoplasma gondii to the central nervous system

“…Microfluidic devices were fabricated using polydimethylsiloxane and coverglass, coated with fibronectin, and seeded with human umbilical vein endothelial cells (HUVECs, Lonza), as described previously 42 . In the Lodoen laboratory, mycoplasma screening was performed in all parasite and cell culture lines, monthly and whenever they obtained or thawed new lines.…”

Parasite pathogenesis: Breaching the wall for brain access

“…In vivo, brain ECs are usually exposed to shear forces, enhancing the barrier properties of the BBB and dislodging invading parasites. Using primary human umbilical vein endothelial cells cultured in a microfluidic chamber with varied shear stress 8 , the authors observed that free parasites indeed adhere better when subject to lower shear forces. In particular, the conditions for adhesion and invasion are better at bifurcations, where velocities are lower and therefore less challenging.…”

From the blood to the brain: avenues of eukaryotic pathogen dissemination to the central nervous system

“…Extracellular T. gondii tachyzoites can adhere to human vascular endothelium in conditions of shear stress by using the parasite adhesin MIC2 [7]. After adhesion, tachyzoites may either transmigrate across the endothelial barrier [8] or invade endothelial cells [9], and invasion appears to predominate [7].…”