BRONCHUS-ASSOCIATED LYMPHOID-TISSUE (BALT) IN HUMAN LUNG - ITS DISTRIBUTION IN SMOKERS AND NONSMOKERS

Background-Bronchus associated lymphoid tissue (BALT) is a normal comp onent of the lung's immune system in many animals and may be analogous to gut associated lymphoid tissue (GALT). This study aimed at assessi ng the nature and extent of BALT in human lung and determining whether its expression is induced within the human airway in response to smok ing. Methods-Paraffin embedded, formalin fixed full thickness bronchia l wall sections were examined from 31 whole lung specimens derived fro m both smokers and non-smokers. Samples were taken from throughout the bronchial tree to include main stem bronchi, lobar bronchi and segmen tal bronchi, as well as first to third generation carinae. Standard 4 mum step sections were stained by haematoxylin and eosin and immunocyt ochemical methods to show foci of BALT. Results-Examination of 256 air way sites detected 46 foci of BALT. These differed from those describe d in other mammals in being distributed throughout the bronchial tree, in being found in relation to bronchial glandular epithelium as well as luminal bronchial epithelium, and in lacking any accompanying M cel ls. Analysis by smoking status showed that the expression of BALT was significantly more common in smokers than non-smokers (82% (14117) v 1 4% (2/14) respectively). Conclusions-The findings support the view tha t BALT in humans is an integral feature in a comparatively small propo rtion of lungs from non-smokers while being significantly more promine nt in lungs from smokers. The tissue shows several important differenc es from that described in other mammals.