Found on a discussion list:

"Who Knew Tea Did THIS?

Tea fights colds. Tea fights the flu. Tea fights cancer.

Maybe it's time to switch from coffee to tea. Drink five to six cups of tea a day--green or black, hot or iced--and you'll get a significant boost to your immune system that will allow you to better fight off diseases from viruses to tumors, according to a new research study presented to the American Chemical Society.

HealthDayNews reports that scientists from Harvard Medical School and Brigham and Women's Hospital have conducted the first study to link immunity with tea. A molecule that is in tea, as well as bacteria and parasites, activates certain components of the immune system called gamma delta T lymphocytes, which are very important as the first line of defense against infection and tumors.

The study:
Dr. Jack F. Bukowski and his team assembled a group of volunteers who did not drink tea or coffee. They were told to drink five to six cups of black tea infusion or instant coffee for either two weeks or four weeks. Blood samples were taken to test the activity of the immune system against bacteria.

The results: The blood samples of the tea drinkers were five times better able to react against bacteria than the coffee drinkers by making the protein interferon gamma, a molecule that fights bacteria, viruses, and tumors.

Bukowski's next study will go one step further and try to show how drinking tea can actually protect you from getting sick.

Bukowski cautions that tea can't be seen as a cure, but it could be viewed as a vitamin for the immune system."