title: Conversion of vitamin D3 binding protein (group-specific component) to a macrophage activating factor by the stepwise action of beta-galactosidase of B cells and sialidase of T cells.
abstract: Highly conserved DBP (human DBP is known as Gc) of serum alpha 2-globulin fraction can be converted to a potent macrophage activating factor by stepwise modification of Gc glycoprotein with beta-galactosidase of B cells and sialidase of T cells. These glycosidases, beta-galactosidase and sialidase, are membrane bound and not soluble in culture medium. Thus, consecutive contact of Gc protein with B cells and T cells, presumably via specific receptors, is required for conversion of Gc glycoprotein to the macrophage activating factor. The essential role of T cell sialidase in macrophage activation was confirmed by the finding that peritoneal nonadherent cells of SM/J mouse, whose T cells are deficient in sialidase activity, were unable to convert Gc protein to the macrophage activating factor and thus did not activate macrophages. Treatment with sialidase of a conditioned medium of lipid metabolite-treated SM/J mouse nonadherent cells efficiently generated the macrophage activating factor. When Gc protein was first treated with soluble or immobilized sialidase and used in a medium for 2 h cultivation of lipid metabolite-treated SM/J mouse nonadherent cells or BALB/c mouse B cells, the resultant conditioned media contained a large amount of the macrophage activating factor. These results support the hypothesis that Gc protein carries a dibranched trisaccharide with galactose and sialic acid termini.
authors.affiliation: Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140.
authors.forename: N
authors.initials: N
authors.lastname: Yamamoto
authors.forename: R
authors.initials: R
authors.lastname: Kumashiro
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology*; D005260:Female; D005989:Glycerides / Q000494:pharmacology; D007848:Laurates / Q000494:pharmacology; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D008262:Macrophage Activation; D016215:Macrophage-Activating Factors / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D050178:Monoglycerides; D009439:Neuraminidase / Q000378:metabolism*; D013601:T-Lymphocytes / Q000201:enzymology*; D014809:Vitamin D-Binding Protein / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism*
chemical_list: D005989:Glycerides; D007848:Laurates; D008244:Lysophosphatidylcholines; D016215:Macrophage-Activating Factors; D050178:Monoglycerides; D014809:Vitamin D-Binding Protein; C020777:monolaurin; D009439:Neuraminidase; D001616:beta-Galactosidase