Study of bronchus-associated lymphoid tissue in patients with diffuse panbronchiolitis.

Bronchus-associated lymphoid tissue (BALT) is thought to affect local immunologic defense mechanisms. Studies of BALT, however, have mainly been focused on animals, and information detailing the BALT structure and functions in humans is scanty. Therefore, the purpose of this study is to clarify BALT morphology and immunologic findings in patients with diffuse panbronchiolitis (DPB) and compare them with BALT findings in animals. Thus, in 17 patients diagnosed with DPB, open-lung biopsy specimens were reviewed, and lymphoid follicles with a lymphoepithelium that was determined as BALT were identified in 12 patients. BALT was found mostly at bifurcations from nonrespiratory bronchioles to respiratory bronchioles. This lymphoepithelium was devoid of cilia and was diffusely infiltrated with CD4-positive (helper/inducer) T cells. The majority of T cells were confined to the parafollicular area with a predominance of helper T cells. Also, a few high endothelial venules were recognized in the parafollicular area. Further, in a follicular area situated in the center of the BALT, a number of sigM-positive cells were found to be heavily distributed, suggesting that this follicular area has the characteristics of a B cell zone equivalent to a germinal center of the peripheral lymph nodes. These observations are comparable with BALT findings in animals and suggest that BALT is at least partially related to the local immune response.