Characterization of Human Gc Protein- Derived Macrophage Activation Factor (GcMAF) and Its Functional Role in Macrophage Tumoricidal Activity

Macrophages are essential for host defense and play an important role in orchestrating immune response of the host against threat signals. Macrophages are also known to have a critical role in antitumor immunity, can infiltrate into tumor, and are found in most tumor sites. Meanwhile, Gc protein (also known as vitamin D-binding protein) is a serum protein with multifunctional properties and has been reported as a precursor for macrophage activation factor. Gc protein can be converted by an inducible s-galactosidase of B cells and neuraminidase of T cells to a potent macrophage activating factor (GcMAF), a protein with N-acetylgalactosamine (GaINAc) as the remaining sugar moiety. Activated macrophages express tumoricidal activity by ingestion of tumor cells and release of reactive oxygen species (ROS) and reactive nitrogen species (RNS), or both. We reported that in situ modification of Gc protein with B-galactosidase and neuraminidase increased the release of superoxide in thioglycolate-elucidated mouse peritoneal macrophage. Yamamoto et al. reported the possibility of using GcMAF as an immunomodulator for cancer treatment, so it is important to provide an assay for GcMAF. Kanan et al. reported the quantitative analysis of GcMAF from human serum. However, the sugar moiety of GcMAF has never been qualitatively studied. Here we present the study of qualitative analysis of GcMAF from purified human serum as well as its influence on the macrophage activity.