Airway epithelium expresses interleukin-18

Interleukin(IL)‐18 is an interferon (IFN)‐γ‐inducing cytokine suggested to be important in regulating inflammatory responses. This study investigated the pulmonary expression of IL‐18 under conditions characterized by T‐helper (Th)1 (lipopolysaccharide (LPS) treatment/sarcoidosis) and Th2 (ovalbumin (OVA) challenge/asthma) cytokine production. In situ hybridization and immunocytochemistry were used to determine the number of cells expressing IL‐18, IFN‐γ, IL‐5 and major basic protein (MBP) within lung tissue from Balb/c mice stimulated with LPS, OVA and in normal control mice. Bronchial biopsies from patients with sarcoidosis, asthma and control individuals were also examined. IL‐18 was localized primarily to airway epithelium and mononuclear cells. Constitutive expression was observed within the lungs of control mice. Animals challenged with LPS exhibited more IL‐18 messenger ribonucleic acid (mRNA)‐positive and IFN‐γ immunoreactive cells, compared to control mice (p