ROLE OF VITAMIN-D-3-BINDING PROTEIN IN ACTIVATION OF MOUSE MACROPHAGES

When mouse peritoneal nonadherent (lymphocytes) cells were treated wit h lysophosphatidylcholine (lyso-Pc) and cultured with adherent cells ( macrophages) in 1% fetal calf serum (FCS)- or adult mouse serum (AMS)- supplemented medium for 3 h, markedly enhanced phagocytic and superoxi de-generating capacities of macrophages were observed. Stepwise cultiv ation of lyso-Pc-treated B cells and untreated T cells with an FCS-sup plemented medium generated a macrophage-activating factor (MAF), where as cultivation of lyso-Pc-treated B cells alone in AMS-supplemented me dium was sufficient to generate the MAF. The accumulated evidence sugg ests that lyso-Pc-inducibie beta-galactosidase of B lymphocytes and th e Neu-1 sialidase of T lymphocytes modified the bovine serum vitamin D -3-binding protein (DBP) to yield the MAF, a protein with N-acetylgala ctosamine as the remaining sugar. In contrast, the lyso-Pc-inducible b eta-galactosidase of B cells alone modified mouse DBP to yield the MAF . These observations led us to conclude that bovine DBP carries a tris accharide com posed of N-acetylgalactosamine, galactose, and sialic ac id, whereas mouse DBP carries a disaccharide composed of N-acetylgalac tosamine and galactose. Thus, macrophages of a T-cell-deficient nude ( BALB/c nu/nu) mouse and a T-cell Neu-1 sialidase-deficient SM/J mouse were efficiently activated by administration of lyso-Pc.