Figure 2.

Disease progression model with normal immune responses during the initial mild symptoms phase (see 1–3). Antigen presenting cells migrate to the lymph nodes to activate T cells (2a). The progression gate to moderate and server disease is the infection of phagocytic immune cells (3a) leading to immune dysregulation (4b). In the lungs, chemokines attract additional dendritic cells and immature macrophages that are subsequently infected in an positive feedback-loop infection cascade (4b). Infected phagocytic immune cells disseminate throughout the body infecting additional organs (5 & 6). Levels of chemokine and cytokines in the lungs from infected cells can create a cytokine storm (6).