Determinants and regulating processes in bronchial hyperreactivity.

Bronchial hyperresponsiveness (BHR) can be considered as a feature of asthma, although only a loose relationship is present with symptoms and severity of the disease. Epidemiology of BHR may inform about determining factors in BHR and its role as a risk factor. BHR is found already at a young age, mostly diminishes with age, and increases in many asthmatic patients after midlife. Genetic determinants are suggested by familial segregation and twin studies. Allergy, respiratory infections, and cigarette smoking are found to induce increase in BHR and to modify its degree at the long run. The mechanisms in BHR are being unraveled gradually. A chronic inflammation with an important role for eosinophils, mast cells, and others, is thought to modify bronchial mechanisms, such as smooth muscle, epithelium, and autonomic systems. Growing evidence supports that T lymphocytes are implicated and may determine many of the inflammatory cells, such as eosinophils, neutrophils, and mast cells.