Immunohistochemical Analyses of Masson Bodies in Organizing Pneumonia Pattern in Interstitial Pneumonias

Abstract

ABSTRACT

To clarify the intimate relationship between the formation of Masson bodies (MBs) and alveolar mouths (AMs), we carried out detailed immunohistochemical analyses of MBs from 17 cases with various kinds of pneumonia. The cases comprised idiopathic or secondary organizing pneumonia (OP).

Immunohistochemical analyses revealed the heterogeneous components of each MB in each individual case of pneumonia. Initially, the thin epithelial cells of AMs were damaged by endogenous or exogenous stimuli, and tissue exudate, fibrin, cell debris, macrophages, and aspirated materials from the airway were gradually organized revealing continuity with AMs. The MBs comprised surface alveolar epithelial cells, which were extended by the mitoses of the alveolar epithelial cells including those of AMs, and maturational processes, such as Krebs von den Lungen-6(KL-6) and surfactant protein A( SP-A) positivity, occurred on their surfaces. Blood vessels, mesenchymal interstitial cells, fibroblastic cells, and some inflammatory cells extended into the MBs through the AMs. The MBs contained collagen fibers produced by fibroblasts, but not elastic fibers. Myofibroblasts were concentrically arranged in the MBs, which were connected directly with the AMs, and they transformed into collagen fiber-producing fibroblasts. Therefore, AMs may play an important role in the formation of MBs in OP patterns of (interstitial) pneumonia.

Key words:Organizing pneumonia, Masson body, Immunohistochemistry, Alveolar mouths