There are more than 400 flavonoids in the human diet. Flavonoids have potent anti-inflammatory and antioxidant properties. Today I would like to focus on two flavonoids that are important for T-reg cell that play a key role in immunity.
The first flavonoid is found in tea.
The regulatory T cells (T-regs ), formerly known as suppressor T cells, are a subpopulation of T cells which modulate the immune system, maintain tolerance to self-antigens, and prevent autoimmune disease. T-regs are immunosuppressive and generally suppress or downregulate induction and proliferation of effector T cells

The ability of tea flavonoids to combat inflammation has been studied for many decades. Back in 2010, university of California researchers measured the function and the number of T-regs in the blood of over weight and lean people. Both function and number were impaired by obesity and restored by exposing blood cells to tea flavonoids. [Ref: 1]

Researchers at Tufts university demonstrated similar effects when they fed low doses of tea flavonoids to mice [Ref: 2]

Lab research has also shown the increase in T-regs produced by tea flavonoid causes a reduction in blood levels of the IgE antibody, indicating a functional anti-allergic effect. [Ref: 3]

Low doses of tea flavonoids appear to work better at reducing inflammation than very high doses [Ref: 4]
This is why it makes perfect sense to get your flavonoids by enjoying a cup or two of tea and not from dietary supplements.

Although green tea is well known source of this flavonoids, the studies show that partially fermented oolong tea is just as rich in these flavonoids. [Ref: 5]

In addition, the inhibitory activity of GCG catechin is found greater than that of EGCG, which is well known to be an antiallergic constituent in tea suggesting that GCG may be a novel antiallergic constituent among tea catechins, and also the most potent and that tea could provide a significant protection against the type-I allergic reaction. [Ref6]

1. https://www.ncbi.nlm.nih.gov/pubmed/20175943 / Effects of epigallocatechin gallate on regulatory T cell number and function in obese v. lean volunteers.
2. https://www.ncbi.nlm.nih.gov/pubmed/22056360 / Epigallocatechin-3-gallate ameliorates experimental autoimmune encephalomyelitis by altering balance among CD4+ T-cell subsets. 3.https://www.ncbi.nlm.nih.gov/pubmed/?term=25151997 / Immunomodulatory effects of EGCG fraction of green tea extract in innate and adaptive immunity via T regulatory cells in murine model.
4. https://www.ncbi.nlm.nih.gov/pubmed/21684134 / Dietary supplementation with high dose of epigallocatechin-3-gallate promotes inflammatory response in mice.
5. https://www.ncbi.nlm.nih.gov/pubmed/15656692 / Comparative studies on the hypolipidemic and growth suppressive effects of oolong, black, pu-erh, and green tea leaves in rats.
6. https://www.ncbi.nlm.nih.gov/pubmed/9261215 / [Effect of tea extracts, catechin and caffeine against type-I allergic reaction].