Mechanisms of Airway Inflammation in HPIV Infection Immune system responds to HPIV infection by secreting high levels of inflammatory cytokines including tumor necrotic factor - alpha, IL-2 and IL-6, and interferon alpha. The inflammatory cytokines secrete for 7-10 days at peak after initial exposure. In severe cases, IL-8 and IP-10 are released. In pediatric patients, the nasal secretions reveal chemokines such as macrophage inflammatory protein (MIP)–K and RANTES (regulated upon activation, normal T-cell expressed and secreted). Pathologic features in airway inflammation include; - Sloughing and necrosis of respiratory epithelium - Excessive mucous production - Edema - Interstitial infiltration of lung - Stridor (feature of croup) After primary infection, HPIV continues to excrete in respiratory exudates for 3-16 days. However, after re-infection HPIV excretes for 1-4 days after infection.