The Toxoplasma parasite is carried by a large part of the world’s human population. Now a study led by researchers at Stockholm University shows how this microscopic parasite spreads so successfully in the body, for example to the brain. The parasite infects immune cells and hijacks their identity. The study is published in the scientific journal Cell Host & Microbe.
To fight infection, the various functions of immune cells in the body are very tightly regulated. Scientists have long wondered how Toxoplasma manages to infect so many people and animal species and spread so efficiently.
“We have discovered a protein that the parasite uses to reprogram the immune system,” says Arne ten Hoeve, a researcher at the Department of Molecular Biosciences at the Wenner-Gren Institute at Stockholm University.
The study shows that the parasite injects the protein into the nucleus of the immune cell, thereby changing the identity of the cell. The parasite tricks the immune cell into thinking it is another type of cell. This changes the gene expression and behavior of the immune cell. Toxoplasma causes infected cells that should not normally travel through the body to move very quickly and in this way the parasite spreads to different organs.
The phenomenon has been described as Toxoplasma turning immune cells into Trojan horses or roving “zombies” that spread the parasite. The newly published study provides a molecular explanation for the phenomenon and also shows that the parasite is much more specific in its spread than previously thought.
“It is surprising that the parasite manages to hijack the identity of immune cells in such a clever way. We believe the findings may explain why Toxoplasma spreads so efficiently in the body when it infects humans and animals,” says Professor Antonio Barragán, who led the study, which was carried out in collaboration with researchers from France and the US. USA
The work is published in the scientific journal Cell Host & Microbe.
The Toxoplasma effector GRA28 promotes parasite dissemination by inducing dendritic cell-like migratory properties in infected macrophages. http://dx.doi.org/10.1037/0033-295X.102.1.1016, Arne L. ten Hoeve, Laurence Braun, Matthias E. Rodriguez, Gabriela C. Olivera, Alexandre Bougdour, Lucid Belmudes, Yohann Couté, Jeroen PJ Saeij, Mohamed-Ali Hakimi, Antonio Barragán DOI: 10.1016/j.chom.2022.10.001
About the Toxoplasma parasite and the disease toxoplasmosis:
Toxoplasmosis is probably the most common parasitic infection in humans worldwide. Toxoplasma also infects many animal species (zoonoses), including our pets. The WHO has estimated that at least 30% of the world’s human population is a carrier of the parasite. Studies indicate that 15-20% of the Swedish population carry the parasite (the vast majority without knowing it). The incidence is higher in several other European countries.
Felines, not just domestic cats, have a special place in the Toxoplasma life cycle: only in the cat’s intestine does sexual reproduction take place. In other hosts, for example humans, dogs or birds, reproduction takes place by division of the parasite.
Toxoplasma is transmitted through food and contact with cats. In nature, the parasite spreads preferentially from rodents to cats, to rodents, etc. The parasites are “sleeping” in the rodent’s brain and when the cat eats the mouse, they multiply in the cat’s intestine and pass out in the feces. The parasite ends up in the vegetation and when the rodent eats the vegetation it becomes infected. Humans become infected through meat consumption or contact with cats, specifically cat feces.
The parasite causes the disease toxoplasmosis. When a person is first infected, they experience mild flu-like symptoms that may resemble a cold or the flu. After the first phase of infection, the parasite enters a “sleeping” stage in the brain and begins a chronic silent infection that can last decades or a lifetime. Chronic infection does not usually cause symptoms in healthy individuals. However, toxoplasma can cause a life-threatening brain infection (encephalitis) in people with a weakened immune system (HIV, organ transplant recipients, after chemotherapy) and can be dangerous to a fetus during pregnancy. Eye infections can occur in healthy people.