On the expression of haptoglobin in the human lungs

Abstract

Introduction: The acute phase protein Haptoglobin (Hp) consists of two different polypeptide chains. Originating from the liver; the biological function is binding free hemoglobin (Hb) and preventing oxidative stress. Elevated amounts of Hp in plasma were observed were infection, inflammation and malignant diseases. Purpose of this study was to investigate protein and mRNA expression within human lung tissues and tumors. Methods: We performed immunohistochemistry, in situ hybridization and RT-PCR analyzing 115 tissue samples. 47 adenocarcinomas, 42 squamous cell carcinomas, 13 small cell lung cancers and 13 tumor-free lungs were investigated. After lobectomy/pneumonectomy tissues were fixed and paraffin-embedded using formalin (immunohistochemistry) or the HOPE-solution (other methods). Results: Immunohistochemistry and in situ hybridization revealed a high level of Hp expression in adenocarcinomas (40.4%) in contrast to squamous cell carcinomas (4.8%, expression in alveolar epithelial cells type II surrounding the tumor). One small cell carcinoma showed Hp expression. In tumor-free lungs we located Hp in alveolar macrophages; alveolar epithelial cells type II and bronchi. RT-PCR results confirmed elevated expression. Discussion: We characterized that Hp protein expressed in lung cancers and tumor-free lungs showing an extra hepatic function. Due to the known immunosuppressive properties of Hp, its broad synthesis is strongly suggestive for a function as a fundamental, pulmonary, local defense element and confirms recent reports that haptoglobin plays an important role in protection processes and repairing mechanisms of injured tissues.