Figure 6

Smad7 is the key for the regulation of tolerance and immunity. Figure 6-1: A previous study has reported that Smad7 is a mediator that controls the tolerance and immunity pathways [26]. The time course of Smad7 expression demonstrated a significant increase during secondary infection, suggesting that in zebrafish injected with a higher pathogen dose, the immune response was triggered to defend against the invading pathogen rather than to promote infection tolerance. Figure 6-2: According to a previous study [10], the regulation of TGF-β, the innate immune response, and the adaptive immune response may be considered as a feedback system. Figure 6-3: Smad7 was found to be a key protein during secondary infection. Smad7 attenuates TGF-β-mediated inhibition of cells in the adaptive immune system, resulting in the proliferation of T and B cells that promote host defense by the adaptive immune system challenged with a higher dose of the pathogen.