Fig. 3

“Yin-Yang” theory and immune system. According to the opposing attributes of Yin and Yang, immune-activating cells and molecules, such as M1 macrophages, Th17s, and pro-inflammatory cytokines like IL-1β and IL-17, as well as immune activation-related molecules such as TLR4 and CD80, along with the transcription factor RORγT, are associated with Yang, represented by the white “fish”. Immunosuppressive cells and molecules such as M2 macrophages, Treg, immunosuppressive cytokines such as IL-10, inhibitory receptors PD-1 and CTLA-4, and the transcription factor Foxp3, are associated with Yin, represented by the black “fish”. Furthermore, Yin and Yang are mutually inclusive, represented by the black circle in Yang (Yin within Yang) and the white circle in Yin (Yang within Yin). Therefore, IL-10-producing Th17 can be viewed as a manifestation of Yang within Yin, whereas IL-17-producing Treg can be seen as Yin within Yang. Besides, the transformation of Yin and Yang are also reflected in the study of IL-17-producing Treg and IL-10-producing Th17 as IL-17-producing Treg and IL-10-producing Th17 represent intermediate forms in the transformation between Treg and Th17