Transbronchial biopsy as a tool to evaluate small airways in asthma

Small airway (SA) inflammation in asthmatics is poorly understood. Surgical biopsies to obtain peripheral lung tissue are seldom justified in asthmatics. Therefore, the authors hypothesised that transbronchial biopsy could be an alternative approach to evaluate SA in asthma. Transbronchial and endobronchial biopsy tissue samples (TBBX and EBBX) from 12 severe asthmatics were evaluated for airway and parenchymal total inflammatory cell count expressed as the sum of immunostained T-cells (CD3), macrophages (CD68), mast cells (tryptase AA1), neutrophils (neutrophil elastase) and cosinophils (EG2) per mm(2). The large airways (LA) were evaluated in EBBXs, while SA, medium airways (MA) and alveolar tissue (AT) were evaluated in TBBXs. When cell counts from SA, MA, LA and AT were compared, SA had a significantly higher cell count than MA or LA (SA 1011.mm(-2) (539-1,290), MA 346.min(-2) (223-415), LA 332.mm(-2) (189-416), AT 464.min(-2) (298-834)). The cell density and pattern of the inflammatory cell distribution in subjects with TBBXs appeared similar to those in three severe asthmatics whose inflammatory cells were analysed in surgical tissue samples. This study suggests that small airway may be identified and analysed in transbronchial biopsy tissue samples and therefore transbronchial biopsy tissue samples could expand the analysis of inflammation and tissue remodelling in asthma.