There are actually several kinds of T cells, and the ones Tarleton and his colleagues studied are the cytotoxic T cell, which scientists call CD8+. What they discovered is that the T cell response in T. cruzi is highly focused on a relatively small set of cellular features called "epitopes," which are part of a macromolecule that is recognized by the immune system. The specific epitopes involved are ones encoded by the trans-sialidase (or "ts") family of genes.
"The function of the ts genes is crucial for the parasite," said Tarleton, "because the parasite must have sialic acids to invade cells and infect the host. But since it doesn't have it, it must steal it from the host cells." The problem is that T. cruzi potentially expresses more than a thousand ts genes, and this pool varies from parasite to parasite--making this set of proteins a poor choice for vaccine development, Tarleton said.
The importance of the new research, however, isn't in specifically what happens in T. cruzi and Chagas Disease. Rather, it is a new understanding of how T cells react to infection in all parasitic diseases, including malaria, which may cause as many as 500 million infections and three million deaths annually in humans. The entire area has been little understood because of the almost impenetrable complexity of the problem.
In organisms like viruses and bacteria, which have relatively small genomes, analysis can be more direct; however, understanding the targets of the T cell response in complex pathogens such as T. cruzi requires much more. Sc
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Contact: Kim Carlyle
kcarlyle@uga.edu
706-542-8083
University of Georgia
28-Aug-2006