A new Mel-CAM (CD146)-specific monoclonal antibody, MN-4, on paraffin-embedded tissue

Mel-CAM (also termed CD146 or MUC18) is a cell-adhesion molecule belonging to the immunoglobulin gene superfamily. It mediates cell-cell interaction through heterophilic Mel-CAM/ligand adhesion. Previous studies showed Mel-CAM immunoreactivity in normal and neoplastic human tissues, but an extensive assessment of Mel-CAM distribution was not performed because of the lack of a Mel-CAM-specific monoclonal antibody that could be used in routinely processed, formalin-fixed, paraffin-embedded tissues. Therefore, we developed a mouse monoclonal antibody, MN-4, that specifically recognized a fixation-resistant epitope in the second extracellular (C2) domain of Mel-CAM. We performed immunohistochemical staining on 467 paraffin-embedded tissue samples with this MN-4 antibody and avidin-biotin peroxidase. MN-4 immunoreactivity was seen in normal tissues, including endothelium, smooth muscle, epithelial and myoepithelial cells of the breast, Schwann cells, ganglion cells, cerebellar cortex, implantation-site intermediate trophoblast, external root sheath of hair follicles, basal cells of bronchial epithelium, parathyroid glands, subcapsular epithelium of thymus, follicular dendritic reticulum cells, skeletal muscles, epithelium of lens, and glial cell fibers in the central nervous system in early embryos. In malignant tumors, MN-4 immunostaining was consistently present in all melanomas, angiosarcomas, Kaposi's sarcomas, leiomyosarcomas, mucoepidermoid carcinomas of salivary gland, placental-site trophoblastic tumors, and choriocarcinomas. Three of 8 squamous cell carcinomas, 2 of 2 small cell carcinomas of the lung, 2 of 11 of infiltrating breast carcinomas, and 4 of 11 of germinomas were focally and weakly positive for MN-4 antibody. In contrast, a wide variety of other carcinomas, sarcomas, lymphomas, leukemias, and neuroendocrine tumors failed to show MN-4 immunoreactivity. In conclusion, MN-4 is a specific monoclonal antibody that recognizes Mel-CAM on paraffin sections. This antibody is useful in retrospective studies of Mel-CAM expression in archival tissue sections and might provide a diagnostic and prognostic marker for human neoplasms.