How do Treg cells know which Th cell to suppress?

Several models have been proposed to explain how Treg cells know which Th cells to suppress. 

• The Cross regulation model suggests that Treg cells are autoreactive and exhibit antigen specificity in suppressing conventional Th cells. The suppression mechanism in this model is based on the interaction between three partners – the Treg cell, the antigen-presenting cells, and the Th cell to be suppressed.   
• The TCR signal strength model proposes that Treg cells suppress the normal activation of autoreactive T cells that have weak signal strength, whereas T cells activated during inflammatory responses with strong signaling are resistant to this suppression mechanism. 
• The Toll-like receptor (TLR)-mediated blockade of Treg suppression model, suggests that TLR activation on dendritic cells (DCs) block the suppressive function of Treg cells, which activates pathogen-specific immune responses. A similar later model suggested that during infections, Treg cells are directly inactivated when microbial products bind to TLR2 on Treg cell surfaces. However, a significant issue with both models is their implication that immune responses to pathogens should always trigger autoimmunity. This is because microbial infections deactivate Treg cells responsible for maintaining peripheral T-cell tolerance.
• According to Matzinger's effector class regulation model, dendritic cells (DCs) serve as intermediaries between orally immunized regulatory T cells (Tregs) and naive CD4+ T cells. Matzinger suggests that Treg cells aren't a distinct lineage dedicated to suppression. Instead, Treg cells represent new subsets of T helper cells that are capable of both suppression and activation of immune functions.