Immunohistochemical characterisation of pulmonary hyaline membrane in various types of interstitial pneumonia

Aims: Hyaline membrane (HM) in diffuse alveolar damage (DAD) pattern is frequently detected in the acute stage of interstitial pneumonia (IP). To determine the exact nature of HM, we investigated immunohistochemically 25 cases of HM-containing IP. Methods: The cases examined using various kinds of antibodies were four cases associated with rheumatoid arthritis, five with usual interstitial pneumonia, two with dermatomyositis, five with viral infection, one case with progressive systemic sclerosis and eight cases caused by other agents. Results: HM mostly reacted with antibodies to PE10 (SP-A), Factor VIII, KL-6 and EMA and, interestingly, stained for AE1/AE3, CK19, and Hup-1 in some cases, but was negative for PTAH staining. However, the immunoreactivities of HM varied even within the same disease or section. Conclusions: The immunohistochemical heterogeneity of HM suggests that HM may be formed by different mechanisms in various types of IP. Our findings also suggest that the main components of HM are derived from alveolar epithelial cells and their proteins, some including cytoplasmic element of CK19, and also from serum factors, but not fibrin. The immunohistochemical characteristics of HM in DAD pattern will aid understanding of the significance of HM formation in IP.