Bronchus-associated lymphoid tissue (BALT) is well
defined in animals. In humans, however, BALT has been reported to be
inducible under pathologic conditions, such as chronic respiratory
infection, although it is not present in healthy adults. Thus, induced
BALT is considered to be involved in the mucosal immunity of the human
lung under these conditions. However, there have been few studies to
investigate BALT development in hypersensitivity pneumonitis. The aim
of this study was to examine the presence of BALT in hypersensitivity
pneumonitis, especially in its chronic form.
The subjects included five patients with chronic hypersensitivity
pneumonitis (CHP) diagnosed from clinical and histologic findings. We
investigated histologically the development of BALT in these patients.
Further, the cellular distribution of BALT was also examined by
Results: BALT was present in
three of five patients with CHP. Immunohistochemical examination
revealed the follicular area of BALT to be composed mainly of B cells,
while the parafollicular area comprised predominantly T cells.
Centroblasts located in the germinal center of BALT expressed Ki-67
antigen, a marker of cell proliferation, suggesting that these cells
were actively proliferating after antigenic stimulation. Cells
expressing bcl-2, which is present primarily on memory B cells, were
confined to the follicular area, devoid of any germinal centers.
S-100-positive, CD1a-negative interdigitating dendritic cells were
observed in the dome area of BALT.
observations suggest that chronic antigenic stimulation and/or
inflammation in CHP may cause BALT development, which, in turn, is
likely to play an important role in the mucosal immune response of this
Abbreviations:BALT = bronchus-associated lymphoid tissue; CHP = chronic
hypersensitivity pneumonitis; DPB = diffuse panbronchiolitis;
GALT = gut-associated lymphoid tissue