A 72-year-old patient was reported to have ‘saber-sheath-type’ acquired tracheobronchomalacia after irradiation therapy for laryngeal cancer. The pathogenetic features of this case were demonstrated immunohistopathologically using CD68, HLA-DR, UCHL1, L26 and Ki-67 antibodies. The principal features were (a) selective destruction ofthe cartilage with Ki-67 stainability from the trachea to the segmental bronchi with inflammatory infiltrations of predominant T lymphocytes (UCHL1-positive) and activated macrophages (CD68-positive with marked HLA class II antigen) and (b) replacement by collagen fibers through the affected lesion. The tissues, except for the cartilage in the airway tract, were preserved without marked change, including the membranous portion. The cartilage at organs other than the airway showed no changes. We first clarified the immunohistopathology of tracheobronchomalacia. We proposed that the characteristic cell-mediated immunity against cartilage with T lymphocytes and activated macrophages in the pathogenetic features may be related to a cancer-healing tendency.

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