Effects of Coffee and Tea on the Immune System

Looking at how tea effects the immune system is a relatively new idea, with little study so far. But it's looking promising, nonetheless.

The chemistry involved is somewhat complicated for me to explain here, but there is a compound in tea (L-theanine) that reacts in the liver to create another chemical that is involved in the production of T-cells. T-cells are a large part of our bodies response mechanism to bacterial infection. Both black and green tea contain L-theanine.

Drinking approximately 5 cups of tea per day would markedly improve your bodies response to disease.

References:
Tea Helps Fight Off Infection
Tea May Sharpen Immune System<