The findings may help explain the many health effects reported by tea drinkers -- including tea's reputed anticancer effect.
Lisa Ann Beltz, PhD, of the University of Northern Iowa, and colleagues exposed both leukemia cells and normal cells to extracts of green tea, black tea, oolong tea, and the tea compound epigallocatechin gallate (EGCG).
All of the tea extracts and the EGCG inhibited the growth of cancerous white blood cells called leukemia cells. But they didn't have much of an effect on a normal kind of white blood cell called a T lymphocyte. These cells contribute to immune defenses in various ways. Instead, the tea extracts and the EGCG caused these cells to put out six to eight times more of a chemical messenger called interleukin-2 (IL-2) --potent substances that help boost the immune system to recognize cancer cells as foreign.
Further study is needed to make sure that it's EGCG, and not some other tea ingredient, that has this major effect on immune cells. But EGCG looks like it will be getting a lot of future attention.
"EGCG may act to kill not only tumor cells but also certain infectious agents," Beltz and colleagues speculate.