Which cytokine is predominantly elevated in the exudative phase of ARDS and plays a central role in neutrophil recruitment and alveolar inflammation?

Explanation

## Inflammatory Mediators in ARDS Pathogenesis **Key Point:** TNF-α is the primary pro-inflammatory cytokine in the early exudative phase of ARDS, driving endothelial injury, increased vascular permeability, and massive neutrophil infiltration into the alveolar space. ### Role of TNF-α in ARDS 1. **Endothelial activation** → increased expression of adhesion molecules (ICAM-1, VCAM-1) 2. **Neutrophil recruitment** → chemotaxis via C5a and IL-8 (also TNF-α-dependent) 3. **Increased vascular permeability** → disruption of tight junctions and alveolar-capillary barrier 4. **Activation of coagulation cascade** → tissue factor expression, microthrombi formation 5. **Oxidative stress** → release of reactive oxygen species (ROS) and proteases **High-Yield:** TNF-α levels correlate with ARDS severity and mortality. Elevated TNF-α in bronchoalveolar lavage (BAL) fluid and plasma are markers of poor prognosis. **Clinical Pearl:** The exudative phase (first 7 days) is dominated by TNF-α, IL-1β, and IL-6. The fibroproliferative phase (after 7 days) shifts toward TGF-β, which drives fibrosis and recovery or progression to pulmonary fibrosis. **Mnemonic:** **TNF = Trouble in the Neutrophil Front** — TNF-α initiates the inflammatory cascade that recruits and activates neutrophils, the hallmark of early ARDS. [cite:Robbins 10e Ch 15]