Vitamin D3 binding protein (group-specific component) is a precursor for the macrophage-activating signal factor from lysophosphatidylcholine-treated lymphocytes.
A brief (30 min) treatment of mouse peritoneal cells (mixture of nonadherent lymphocytes and adherent macrophages) with 1-20 micrograms of lysophosphatidylcholine (lyso-PC) per ml in serum-supplemented RPMI medium 1640, followed by a 3-hr cultivation of the adherent cells alone, results in a greatly enhanced Fc receptor-mediated phagocytic activity of macrophages. This rapid process of macrophage activation was found to require a serum factor, the vitamin D3 binding protein (the human protein is known as group-specific component; Gc). Efficient activation of macrophages was achieved by using medium containing purified human Gc protein. Analysis of intercellular signal transmission among nonadherent (B and T) cells revealed that lyso-PC-treated B cells modify Gc protein to yield a proactivating factor, which can be converted by T cells to the macrophage-activating factor. This rapid generation process of the macrophage-activating factor was also demonstrated by stepwise incubation of Gc protein with lyso-PC-treated B-cell ghosts and untreated T-cell ghosts, suggesting that Gc protein is modified by preexisting membranous enzymes to yield the macrophage-activating factor. Incubation of Gc protein with a mixture of beta-galactosidase and sialidase efficiently generated the macrophage-activating factor. Stepwise incubation of Gc protein with B- or T-cell ghosts and sialidase or beta-galactosidase revealed that Gc protein is modified by beta-galactosidase of B cells and sialidase of T cells to yield the macrophage-activating factor. Administration to mice of a minute amount (4-10 pg per mouse) of in vitro, enzymatically generated macrophage-activating factor resulted in a greatly enhanced (3- to 7-fold) ingestion activity of macrophages.
Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140.
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Yamamoto
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S
Homma
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media; D005260:Female; D006026:Glycoside Hydrolases / Q000378:metabolism; D066298:In Vitro Techniques; D008214:Lymphocytes / Q000502:physiology*; D008222:Lymphokines / Q000502:physiology*; D008244:Lysophosphatidylcholines / Q000494:pharmacology*; D008262:Macrophage Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D011498:Protein Precursors / Q000378:metabolism; D014809:Vitamin D-Binding Protein / Q000378:metabolism*
D003470:Culture Media; D008222:Lymphokines; D008244:Lysophosphatidylcholines; D011498:Protein Precursors; D014809:Vitamin D-Binding Protein; D006026:Glycoside Hydrolases