Friendly gut bacteria lend a hand to fight infection

http://www.eurekalert.org/pub_releases/2009-08/usmc-fgb081809.php

Public release date: 19-Aug-2009
Contact: Kristen Holland Shear
UT Southwestern Medical Center
, UT Southwestern study suggests

IMAGE: Immunology researchers led by Dr. Felix Yarovinsky (left) and including Alicia Benson have found that bacteria in the human gut helps battle the parasite responsible for toxoplasmosis. Generally a mild...
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DALLAS – Aug. 19, 2009 – Immunology researchers at UT Southwestern Medical Center have found that bacteria present in the human gut help initiate the body's defense mechanisms against Toxoplasma gondii, the parasite responsible for toxoplasmosis.

Toxoplasmosis is generally a mild infection, but it can have serious and potentially fatal effects in pregnant women, their fetuses and others with weakened immune systems.

In mice, T gondii directly activates a specific immune protein in the host, called toll-like receptor 11 (TLR-11), which helps control the animals' immune response to the parasite. Humans, however, don't have an active form of this receptor. Exactly how the body senses T gondii has remained unclear because the parasite doesn't activate any of the functioning toll-like receptors that humans do possess.

In a new study appearing online and in the Aug. 20 issue of Cell Host & Microbe, researchers at UT Southwestern suggest that instead of activating toll-like receptors directly, T gondii's first interaction in the human gut is with the helpful bacteria that live inside us. Those bacteria then release signaling molecules, alerting the human host to the invader.