VITAMIN D-3-BINDING PROTEIN AS A PRECURSOR FOR MACROPHAGE ACTIVATING FACTOR IN THE INFLAMMATION-PRIMED MACROPHAGE ACTIVATION CASCADE IN RATS

When rat peritoneal nonadherent cells were treated with inflammatory l ipid metabolites and cultured with adherent cells in 1% fetal calf ser um (FCS) supplemented medium RPMI 1640 (FCS medium) for 3 hr, markedly enhanced phagocytic and superoxide generating capacities of macrophag es were observed. Stepwise preparation of conditioned medium of lysoph osphatidylcholine (lyso-Pc)-treated B cells and untreated T cells in F CS medium generated a potent macrophage activating factor whereas cult ivation of lyse-Pc-treated B cells alone in a 1% adult rat serum suppl emented medium efficiently generated the macrophage activating factor. Generation of macrophage activating factor requires a precursor prote in, serum vitamin D-3-binding protein (DBP), as well as participation of lymphocyte glycosidases. The lyse-Pc-inducible beta-galactosidase o f B lymphocytes and the Neu-1 sialidase of T lymphocytes modified bovi ne DBP (bDBP) to yield the macrophage activating factor, a protein wit h N-acetylgalactosamine as the remaining sugar, In contrast, lyso-Pc-i nducible beta-galactosidase of B cells alone modified rat DBP (rDBP) t o yield the macrophage activating factor, a protein with N-acetylgalac tosamine as the remaining sugar, Thus, we conclude that bDBP carries a trisaccharide composed of N-acetylgalactosamine, galactose, and siali c acid while rDBP carries a disaccharide composed of N-acetylgalactosa mine and galactose. (C) 1996 Academic Press, Inc.