Exudative Phase (1–7 days): After the initial insult to the alveoli, immune cells (neutrophils and macrophages) are recruited to the alveoli, which can cause more damage through their nonspecific defensive mechanisms. Since the epithelial lining is damaged it allows plasma and proteins to leak in to the airspace, accumulating fluid (otherwise known as edema). Additionally, since the epithelial lining is damaged there is limited ability to pump this edema out of the airspace and back in to the interstitium.