Figure 2.

Infection outcomes as the initial immune state varies across values of ${\chi }_1,{\chi }_2$ and ${\iota }_{12}={\iota }_{21}$ . For the ‘high Th2’ outcome, the immune system is polarized towards a Th2 response and the parasite is extinct (acute infection). For the ‘high Th1+2’ outcome, there is a high level of both Th1 and Th2 immune cells and the parasite biomass is very low. For the ‘high Th1’ outcome, the immune system is polarized towards a Th1 response and parasite biomass is very high (chronic infection). For the ‘low Th1+2’ outcome, there is a low level of both Th1 and Th2 immune cells and the parasite biomass is high.