CXCL8 and acute respiratory distress syndrome: In the acute, or exudative, phase of ARDS/ALI (Figure 3), the alveoli become filled with protein-rich edema fluid and resident macrophages (a type of white blood cell) secrete pro-inflammatory proteins and cytokines [e.g., interleukin-8 (IL-8)], which recruit the innate immune cells (primarily neutrophils).