T helper 17 (TH17) cells have well-described roles in autoimmune disease. However, TH17 is not stable in some physiological or pathological courses. Also, TH17 cells can reciprocally modulate and convert into other helper T cell subpopulations. The fully exploring the reciprocal regulatory effects and its immunoregulatory mechanisms are becoming interesting topics in the immunological study. In this review, we summarized reciprocal modulation pattern between TH17 cell and other helper T cell subpopulations in the mouse model of autoimmune diseases and human diseases. J. Cell. Physiol. 226: 8–13, 2010. © 2010 Wiley-Liss, Inc.