Figure 1.

Graphical representation of the multi-level mathematical model of bacterial lung infection. The upper left panel displays processes at the tissue level of the model. It incorporates two lining fluid layers between which bacteria can transition (light blue layers). In both layers, the bacterial cell wall sheds factors (small orange particles) that attract nearby macrophages. In addition, when bacteria (red-orange oval) are attached to the epithelial cell layer (purple rectangles), they trigger the release of chemokine (pink concentric ovals) from the host epithelial cells; these chemokines act as a secondary attractive stimulus to macrophages (large gray structure). Bacteria can transition to the upper flowing layer (arrow-shaped blue layer), where they are moved by the flow toward the alveolar opening, and back again to the lower layer to re-attach at another site. The bottom right panel displays the intracellular level, containing the signaling pathway of the epithelial cells for production of the chemokine that attracts macrophages (MCP-1). For a more detailed scheme of the intracellular model, see Supplementary Material Figure S1.