Modeling Treg cell therapy. A)Healthy configurations: while the system is moving clockwise on a spiral trajectory that moves towards the equilibrium point, the model was perturbed with an impulse of Treg cells (only a portion of the trajectory is shown for clarity). The perturbation was introduced near to the maximum possible value of activated Treg. After the impulse, the system jumps to a more distant spiral, where the new maximum value reached by the activated Teff is greater than that on the initial trajectory. B)In the healthy configuration reversible and irreversible damage result almost imperceptible. C) Autoimmune configuration: while the Teff-Treg loop is driving an autoimmune regime, the model was perturbed with the same impulse as above. The effect of the perturbation was qualitative similar to that in the healthy regime, but not quantitatively, showing the hypersensitivity of this kind of regime in the model. D)Both reversible and irreversible damage resulted evident when the system was working under autoimmune conditions.