Increased numbers of dendritic cells in the bronchiolar tissues of diffusepanbronchiolitis

Dendritic cells (DCs) are potent antigen-presenting cells (APCs); they are considered to be the most important APC in the lung. Recently, the number o f DCs in the large airways was demonstrated to increase in patients with at opic asthma, leading to the concept that DCs play an important role in airw ay inflammation. However, little is known about the distribution of lung DC s in the small airways under other pathological conditions. The aim of the present study was to examine the distribution of DCs in the bronchiolar tis sues in patients with diffuse panbronchiolitis (DPB), which is a chronic in flammatory disorder of the airways histologically characterized by peribron chiolitis. We investigated the distribution of DCs in the bronchiolar tissu es of the lungs in 11 patients with DPB and 7 control subjects with normal lungs using immunohistochemical methods. Marked increases in the number of CD1a(+), CD1c(+) and CD83(-) DCs were found in both the bronchiolar epithel ium and submucosal tissues of patients with DPB, compared with control subj ects with normal lungs. The most striking increase occurred in the number o f DCs expressing CD83, a marker of mature DCs in the submucosal tissues of patients with DPB. The increases of these positive cells in patients with D PB were more marked in the submucosal tissues than in the epithelium. The b ronchiolar epithelial cells in patients with DPB strongly expressed GM-CSF protein, which is an important cytokine for the differentiation and functio n of DCs, suggesting that the increased local production of CM-CSF may be r esponsible for the accumulation and differentiation of DCs in the bronchiol ar tissues of patients with DPB. These results suggest that increased DCs i n the bronchiolar tissues, together with their phenotypical maturation, may play an important role in the mucosal immune response in patients with DPB through their potent antigen-presenting function.