Bronchoscopy as a research tool for the study of asthma pathogenesis and effects of antiasthma drugs.

Fiberoptic bronchoscopic methods have greatly improved our understanding of asthma pathogenesis and of the mode of action of established and experimental antiasthma drugs. It is probably most appropriate to study bronchoalveolar lavage (BAL) and bronchial biopsy simultaneously because there are major differences between the airway lumen and tissue compartments: for example, T cells are the most abundant cells in endobronchial biopsy samples but form only 10% to 20% of total BAL cells, and eosinophils and mast cells are more numerous in the airway tissue than in the lumina. Immunostaining is currently the most reliable method for enumerating cells and assessing their activation state with a panel of cell surface and intracellular activation markers. In situ hybridization can be used to study a cell's capacity for cytokine production. Newer techniques allow immunohistochemistry of adjacent cell sections to co-localize staining with different antibodies, showing for example that mast cells contain preformed cytokines IL-4, IL-5, and IL-6 and tumor necrosis factor-alpha A combination of immunohistochemistry and in situ hybridization can colocalize messenger RNA transcription to individual cell types; this approach is useful for T cells, which do not have storage capacity and cannot be shown by immunohistochemistry to contain cytokines. An additional tool to assess cellular activity is reverse transcriptase polymerase chain reaction, which has recently been used to confirm a predominant TH2-type cytokine profile in allergic disease.