Toxoplasma uses tough love

Parasites are known for outwitting their hosts in unexpected ways, and Toxoplasma gondii is no exception. To ensure that it does not kill its host prematurely, T. gondii secretes a protein that induces a strong host cellular immune response. This response slows the infection—and enables the parasite to complete its life cycle. Now, Julio Aliberti, Jesus Valenzuela, Alan Sher, and colleagues (NIH, Bethesda, MD) have identified the T. gondii protein that triggers the immune response and found that it mimics a chemokine.

The T. gondii protein, cyclophillin-18 (C-18), binds to the CCR5 receptor on the surface of dendritic cells and induces the expression of high levels of IL-12, a positive regulator of cell-mediated immunity. The fact that C-18 works through a chemokine receptor is unusual. “In general this sort...