Phase portraits of iTreg versus effector dynamics over 20 days. (a) Phase portraits for five different precursor frequencies, T0(0) = 0.0004, 0.004, 0.04, 0.4, and 4k/μL. The curve for T0(0) = 0.04 shows the same dynamics as Fig. 18. (b) Phase portraits for three different precursor frequencies, T0(0) = 0.004, 0.04, and 0.4k/μL, corresponding to T cell dynamics under persistent antigen stimulation, i.e., b = 1,000 days.