Use of induced sputum has been already useful to understand certain mechanisms of asthma. Eosinophils and metachromatic cells are only weekly associated with bronchial hyperresponsiveness to methacholine but to be closely associated with changes in airway hyperresponsiveness after allergen challenge. Exacerbations of asthma induced by tapering the dose of i n haled steroids are associated with increased eosinophilic inflammation, whereas wild exacerbations of asthma are sometimes associated with neutrophilic inflammation. Responses to corticosteroid treatment may differ in the two types of inflammation, as shown in preliminary studies in COPD patients. Therefore induced sputum may be a valuable tool to help investigating patients in the cl ni c.
Induced sputum can help to investigate the anti inflammatory effects of new medications in asthma.
Studies performed after allergen challenge or mild exacerbations of asthma have shown that long acting 2 agonists, despite their prolonged effect on baseline respiratory function and airway hyperresponsiveness, do not abolish the inflammatory reaction, whereas inhaled corticosteroid do. These may be valuable models to investigate the antinflammatory effects of new antilenkotrienes or new phospho-diestarase inhibitors. In conclusion, induced sputum is a reliable non invasive valid and reproducible way to have direct access to the lower airways. Because it should be performed very carefully and sputum processing needs more assesament and improvement, it is still a research tool. However it may become a clinica l tool in the near future. .