Food coloring may suppress immune system

12/09/05 Very high doses of a caramel food coloring suppress the immune system, new research finds.

The discovery, in a study involving mice, might lead to the development of new drugs that achieve selective suppression of the immune system. Such suppression would be useful after an organ transplant, the researchers noted.

"The amounts [of caramel coloring] used [in the study] were far greater than what is found in foods," noted study author Jason Cyster, a professor of microbiology and immunology at the University of California, San Francisco School of Medicine.

Cyster and his team fed mice the caramel food colorant, called THI (2-acetyl-4-tetrahydroxybutylimidazole), which inhibits the movement of white blood cells from the lymph nodes into the bloodstream, where they typically move to fight infection in the body.

What was already known, Cyster said, is that THI prevents the movement of the white blood cells from the thymus gland to peripheral lymphoid organs such as the lymph nodes and the tonsils. And it was also known that the signaling molecule called S1P (for sphingosine-1-phosaptae) is involved in the white blood cell migration from the lymph nodes.

Cyster's work helps explain how S1P is involved in the immune system regulation. He said the THI prevents the white blood cell movement by inhibiting an enzyme that breaks down S1P. That enzyme is called S1P lyase. The THI, Cyster said, "decreases the activity of an enzyme that controls the abundance of S1P."

"When you give the caramel food coloring, the S1P accumulates in the lymph nodes," Cyster said. "They stay in the lymphoid organs. They can't get out. And if, for example, you had a transplant at that time, they wouldn't be able to fight the transplant."

The findings appear in the Sept. 9 issue of Science.