Aberrant expression of macrophage-associated antigens (CD68 and Ki-M1P) by Schwann cells in reactive and neoplastic neural tissue. Light- and electron-microscopic findings.

The monoclonal antibodies KP1 (CD68), PG-M1 (CD68), and Ki-M1P can be used to detect normal and neoplastic monocytes/macrophages in formalin-fixed, paraffin-embedded tissue. However, systematic investigations undertaken on various tissues have revealed that reactivity with these antibodies is also found in a few cells that do not belong to the mononuclear phagocyte system. The immunoreactivity of normal, reactively altered, and neoplastic Schwann cells with these antibodies was investigated using intact peripheral myelinated nerves, nerves exhibiting Wallerian degeneration, traumatic neuromas, appendixes with neurogenic appendicopathy, granular cell tumors, neurofibromas, and neurogenic sarcomas. The results obtained by light microscopy showed that Schwann cells of nerves with Wallerian degeneration and those in traumatic neuroma, neurofibroma, and granular cell tumor exhibit intracytoplasmic immunoreactivity, which is usually intense, with KP1, Ki-M1P, and PG-M1, but normal myelinated nerves, neurogenic sarcoma, and Schwann cells in neurogenic appendicopathy do not react with these antibodies. No Schwann cells were stained by MAC387 or anti-lysozyme. The site of immunoreactivity with these antibodies was also investigated by electron microscopy. One of the granular cell tumors and macrophages in lymphoid tissue were investigated by the immunogold technique using both pre- and postembedding methods. In granular cell tumor the reaction product was located in phagolysosomes; in macrophages it was found in phagosomes and/or lysosome-like granules. Our findings therefore indicate that immunoreactivity with KP1, Ki-M1P, and PG-M1 can also be expected in cells that do not belong to the mononuclear phagocyte system if they exhibit phagocytosis and/or autophagy.