Figure 5.

Simulation of case scenarios of tolerance and resistance and simulation under increased metabolic demand. Panel d-f shows a bifurcated case in which the infection leads to a constant high infection-inflammation and immune response (Black line trajectory) or a low infection-inflammatory and immune response (dash green line). The intersections of the upper and lower nullclines show two bifurcated setpoints. That is there can be two possible stable states or setpoints for the infection response. The green line setpoint lies on a zero-immune response level and with a low infection-inflammatory reaction and this trajectory predicts a tolerant host response. While the black line shows the trajectory for a higher setpoint for the immune and infection-inflammatory response leading to a resistant host response. In the case, the metabolic rate parameter, M, has been reduced from 10 to 2. Panel a shows the phase plane and simulated trajectories (panels b and c) of Eqs. (1) and (2), respectively. Here, M is reduced stepwise from 2 to 0, which reduces the gradient in the left plot, causing the infection response to increase in the central plot and the immune response to drop in the right plot. In all cases (v₀,u₀) = (1.1,0). This shows the production of an immune response depends critically on the metabolism producing energy to enable the response.