Figure 1.

State-based model of avian whole-blood infection. Schematic picture of the state-based model (SBM) for the immune response in avian whole blood upon infection with either of the three pathogens S. aureus and E. coli or C. albicans. The states (circles) represent the different cell populations of pathogens (P) and the two immune cell types of monocytes (M_i,j) and heterophils (He_i,j) with i alive and j killed pathogens. The model contains respective states for extracellular pathogens that are alive (P_AE) or killed (P_KE) as well as immune evasive pathogens that are alive (P_AIE) or have been killed (P_KIE). The SBM for fungal infection additionally contains states for alive pathogens in hyphal form (P_AHy) that can be killed by extracellular factors (P_KHy) (see right gray box). In the bacterial SBM, alive extracellular pathogens can proliferate (dark green arrow) (see left gray box). Connections between the states refer to possible state transitions that represent biological reactions during infection. Alive and killed extracellular pathogens can be phagocytosed (green and red arrows). The purple connections indicate killing of pathogens either in extracellular space or within immune cells. The dark blue connections represent the different mechanisms of immune cell killing. These are heterophil killing by stress factors with rate ${\kappa }_{stress}^{He}$ (dotted lines), immune cell killing by extracellular peptides (dashed lines) and immune cell killing by lysis induced by alive intracellular pathogens (solid lines).