Is suppression by Treg cells antigen-specific?

Yes, suppression by Treg cells is antigen-specific, which means the ability of Treg cells to suppress immune responses is triggered by specific antigens. 

Studies show that the activation of Treg cells is triggered by specific antigens, indicating that their suppressive activity is also antigen-specific. While Treg cells have been observed to effectively suppress Th cells with different antigen specificities, there is a higher likelihood that suppression is more effective when both, the Treg cell and the suppressed Th cell recognize the same antigen. Further in vivo studies with Treg cells having defined antigen specificities need to be carried out to better understand the Treg cell suppression mechanism.