Immunohistochemical study of idiopathic bronchiolitis obliterans organizing pneumonia

Abstract

To examine the characteristics of idiopathic BOOP and to compare them with those of organizing pneumonia (OP) with known causes, immunohistochemical examinations using monoclonal antibodies against T- and B-lymphocytes which are available for formaldehyde-fixed and paraffin-embedded sections, and polyclonal antibodies against human IgG, IgA and IgM, and bovine S-100 protein, were carried out, along with conventional histopathological examinations. Histopathological observations demonstrated that both of the 7 BOOP cases and 5 OP cases had polypoid masses of organizing tissue in the lumen of small airways, alveolar ducts, and some alveolar sacs, and infiltration of pulmonary interstitium by a large number of lymphocytes and moderate number of plasma cells, eosinophils and mast cells. Degree of bronchiolo-alveolitis was greater in idiopathic BOOP. Immunohistochemically, the majority of lymphocytes which had diffusely infiltrated into the interstitium were T-lymphocytes, the degree of which was higher in the cases of BOOP. On the other hand, B-lymphocytes were seen mainly in the lymphoid follicles. Furthermore, S-100 protein positive dendritic cells were noted in the lymphocyte rich interstitium in the all cases of both groups, and similarly between two groups. Immunoglobulin (Ig) positive plasma cells were also seen, but there was no evidence indicating the preferential increase of plasma cells which produce a particular class of Ig. These observations suggest that there might be some immunological mechanisms in the pathogenesis of BOOP in which T-lymphocytes, mast cells and eosinophils are involved.