If the monocytes were indeed acting as a Trojan horse, the scientists would expect to see the parasite breach the blood-brain barrier. To test this, the team infected monocytes with a form of Toxo, labeled red, that can’t reproduce, then introduced those cells into mice. The researchers also wanted to revisit the Trojan horse hypothesis, to see if, as had been proposed, infected monocytes, a type of immune cell, might be responsible for carrying the parasite into the brain. In additional experiments, they were able to visualize parasites bursting out of infected endothelial cells, thereby introducing the parasite into the brain. Two weeks post-infection, they saw that parasites appeared in the brain tissue adjacent to the endothelial cells. They then infected the mice with modified Toxoplasma that expressed a red fluorescent protein.Īfter a week, they saw endothelial cells in the brain that were infected, as well as evidence that the parasite was reproducing inside those cells. In these studies, they used mice that had been specially bred to express a fluorescent green protein in their endothelial cells. Konradt used Penn Vet’s multi-photon microscope, which allows them to peer deep into living tissues without damaging them, to try to witness the parasite’s invasion in action. Another idea, “beloved of microbiologists,” Hunter said, is the Trojan horse hypothesis, in which the parasite hitches a ride across the barrier while hidden inside an infected host cell. Some believe the parasite squeezes between the barrier cells, while others think the parasite goes directly through a cell. Hunter was the senior author on the study, which was led by Christoph Konradt, a post-doctoral researcher in Hunter’s laboratory.Ī few different theories have been considered to explain how Toxoplasma could enter the brain. The study appears in Nature Microbiology. It’s something that no one had seen before.”īy illuminating the pathogen’s path into the brain, the research helps inform what treatment strategies may be most effective at combatting the parasite before it wreaks its worst damage.
“And yet it happens and we have now been able to visualize these events. “Crossing the blood-brain barrier is a rare event in part because this structure is designed to protect the brain from pathogens,” said Christopher Hunter, the Mindy Halikman Heyer President’s Distinguished Professor at Penn Vet. Using a powerful imaging technique that allowed the scientists to track the presence and movement of parasites in living tissues, the researchers found that Toxoplasma infects the brain’s endothelial cells, which line blood vessels, reproduces inside of them, and then moves on to invade the central nervous system. Now, researchers from the University of Pennsylvania School of Veterinary Medicine and colleagues from across the country have identified how the parasite makes its way in.
But scientists have debated exactly how the parasite crosses the blood-brain barrier, a physical obstacle intended to keep pathogens out of the brain. It’s known that “Toxo” can affect the brain, even influencing the behavior of its hosts. Pregnant women can also pass an infection to their unborn children, putting the babies at risk of severe neurological disease.
Most people live with the infection without noticeable effect, but it can be life-threatening for people with suppressed immune systems, such as people on cancer therapies or who have HIV/AIDS. A blond futanari wakes up to a giant zombie Apocalypse with her the only one in the city not infected.An estimated 30 percent of the world’s population is chronically infected with the parasite Toxoplasma gondii.
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