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publicado em 22/09/2011 às 20h11:00
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Discovered the parasite that "hijacks" the host immune cells

Parasites can invade the body of the host and promote behavioral changes related to neuroticism

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Parasite Toxoplasma gondii can invade the bloodstream, invade the brain and promote behavioral changes related to the imprudence of neuroticism. These highly contagious protozoan infect more than half the world's population, and most of the immune systems of people expelled the intruders.

Cornell researchers have recently discovered as T. gondii escapes our defenses with the help of hackers cells of the immune system, making it the first parasite known to control the immune system of its host. Immunology at the Faculty of Veterinary Medicine at Cornell Univesity in the United States, published the study in this month in the journal PLoS Pathogens, describes a forced partnership between parasite and host, which challenges the common conception of how pathogens interact with the body.

"Gondii parasite is a particularly promiscuous," said Eric Denkers, professor of immunology. "It infects almost all species of warm-blooded, most types of nucleated cells and much of the human population. Although he lives in the brain and muscle tissue, usually causes no obvious reactions. Infections can seriously harm people with weak immune systems, but most hosts do not have any obvious symptoms because Toxoplasma found a way to act in cooperation. "

Famous for its manipulative powers, T. gondii have altered the brain chemistry of rats so that they were not afraid to chase cats. Cats eat rodents, delivering the parasites to their breeding grounds in the intestines of cats. Manipulations appeared in similar studies linking human infections with T. gondii to behavioral and personality changes, schizophrenia and variations of the population, including cultural differences and unsafe sex. According to the new study, T. gondii have the ability to manipulate the immune cells at the molecular level.

"We found that Toxoplasma calms the alarm system of their host by blocking the production of certain cytokines - proteins that stimulate inflammation - made by cells of the immune system." Denkers said. "Cytokines are two-edged swords: They summon reinforcements from the immune system, but its accumulation can damage the body that are trying to defend and a dysregulated immune response can kill you."

When immune cells are intruders they release cytokines that summon more immune cells, which produce more cytokines, rapidly causing inflammation. T. gondii must release a sufficient amount of cytokines to trigger an immune response in order to maintain their own numbers in check and ensure the survival of the host. But many cytokines cause an overwhelming response of the immune system that could damage the host or eliminate the parasites.

"The Toxoplasma hijacks cells of the immune system to enforce a mutually beneficial equilibrium," said Denkers. "Until recently we thought that the parasite was removed within the cells without interacting with its environment. It is now clear to us that the parasite sends messages to cells so that their behavior changes.

To prove this, Barbara Butcher, a senior researcher who worked with Denkers, immune cells in exposed laboratory for bacterial factors that normally stimulate the release of inflammatory cytokines.

"The Toxoplasma-infected cells did not produce any messages to trigger inflammation," said Denkers. "Our colleagues at Stanford University found that Toxoplasma produces a specific protein called ROP16 to suppress the inflammatory response. In collaboration with parasitologists at Dartmouth Medical School, found that ROP16 Toxoplasma send to infiltrate the communication channels in immune cells , causing them to lower production of cytokines.

"We are excited to have found the non-bacterial pathogen able to exercise such control," said Denkers. "If the Toxoplasma can do this, other parasites may also do so. This is the first indication that the whole process of manipulation of the immune system is close to being fully mapped at the molecular level."

This map can help guide future research on how pathogens interact with the host, revealing the inner workings of a spectrum of infectious diseases.

   Palavras-chave:   Parasite    Toxoplasma gondii    Bloodstream    Brain    Behavioral changes    Search   
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