Pulmonary surfactant in asthma

Pulmonary surfactant is vital in human respiration. It maintains alveoli and terminal conducting airways open and therefore promotes an efficient gas exchange and low resistance in the airways during breathing dynamics. Lack or dysfunction of the pulmonary surfactant system is associated with severe lung disorders. Surfactant ability to maintain low surface tension at the respiratory air-liquid interface, with subsequent good compliance and low resistance in the airways, is extremely important for asthmatic patients. A growing series of experimental evidence indicates that surfactant dysfunction, either associated with the causes or as a consequence of asthma, can contribute to constriction of airways and exacerbation of asthma. Modulation by surfactant of the innate and induced immune response is also an important element defining propensity, but also the resolution of asthmatic crisis. Limited trials indicate that administration of exogenous therapeutic surfactant may offer favorable pharmacological effects to asthmatic patients, possibly by two different mechanisms. On the one hand, it can restore endogenous surface activity and, on the other hand, properly modulate the immune system. The objective of the present review has been to summarize and update available concepts and evidence that support the relationship between pulmonary surfactant and asthma, with particular attention to the role of pulmonary surfactant in the mechanisms of asthma manifestations as well as in the design of innovative future therapies.