being those that express CD4, CD25, and FOXP3 (CD4⁺CD25⁺ regulatory T cells). These T_reg cells are different from helper T cells. Another regulatory T cell subset is T_reg17 cells. Regulatory T cells are involved in shutting down immune responses after they have successfully eliminated invading organisms, and also in preventing autoimmunity.

CD4⁺ FOXP3⁺ CD25(high) regulatory T cells have been called "naturally