Expression of the acute phase protein haptoglobin in human lung cancer and tumor-free lung tissues

Besides its main function, i.e., the binding of free hemoglobin and prevention of oxidative stress, the acute phase protein haptoglobin acts as a potent immunoreactive modulator. As part of an investigation that aimed at illuminating the role of acute phase proteins in the local defense of the lungs, this study is the first to describe the expression and synthesis of haptoglobin in human lung tissues and lung tumors. Prompted by the results obtained from a transcription array study, we analyzed 115 lung (cancer) specimens using immunohistochemistry. Thirty-seven specimens were subjected to mRNA- in situ hybridization. 40.4% of the adenocarcinomas showed distinct granular and perinuclear staining of the tumor cells. By contrast, only 4.8% of the squamous cell carcinomas showed haptoglobin within tumor cells, but 19% displayed haptoglobin expressing alveolar epithelial cells type II surrounding the tumor. One small cell lung cancer displayed haptoglobin expression. In tumor-free lungs, we located haptoglobin in alveolar macrophages, alveolar epithelial cells type II, and bronchiolar cells. In situ hybridization verified the results of immunohistochemistry. The results were further verified by RT-PCR and Western blot compared to liver tissues, which both showed comparable amounts of haptoglobin mRNA and protein in NSCLC and in liver, while tumor-free lung tissues showed lower expression. Due to the known immunomodulatory effects of haptoglobin, its broad expression and synthesis within human lung tissues strongly suggests a function as a fundamental pulmonary local defense element.