Smooth muscle hypercontractility in airway hyperresponsiveness: innate, acquired, or nonexistent?

From introduction: Asthma symptoms are triggered or exacerbated by a range of environmental factors, such as allergens, viruses, fungi, exercise, aspirin, pollutants, and occupational irritants and sensitizers. While traditionally considering an intrinsic disease, in more recent years asthma has been viewed by many as a genetically associated environmental lung disorder with a heterogeneous pathogenesis. With the exception of the severe cases, the diagnostic signature of asthma is the reversibility of airway obstruction by agents that relax airway smooth muscle (ASM), which attests to the importance of this tissue in the pathobiology of the airflow obstruction.