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Vitamin D3 binding protein (group-specific component) is a precursor for the macrophage-activating signal factor from
1Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140.
Abstract:
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.
Insights
Lysophosphatidylcholine (lyso-PC) activates macrophages by modifying vitamin D3 binding protein (Gc). This process involves B and T cells, generating a potent macrophage-activating factor that enhances phagocytic activity.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages play a crucial role in the immune system, particularly in phagocytosis.
- Lysophosphatidylcholine (lyso-PC) is a bioactive lipid with known immunomodulatory effects.
- Vitamin D3 binding protein (Gc), also known as group-specific component, is a serum protein with diverse functions.
Purpose of the Study:
- To investigate the mechanism by which lysophosphatidylcholine (lyso-PC) rapidly activates macrophages.
- To identify the role of serum factors, specifically vitamin D3 binding protein (Gc), in this activation process.
- To elucidate the intercellular signaling pathways involving B and T cells in generating a macrophage-activating factor.
Main Methods:
- Treatment of mouse peritoneal cells with lysophosphatidylcholine (lyso-PC).
- Cultivation of adherent macrophages and analysis of Fc receptor-mediated phagocytic activity.
- Incubation of vitamin D3 binding protein (Gc) with B and T cell components and enzymes (beta-galactosidase, sialidase).
- Administration of the generated macrophage-activating factor to mice and assessment of macrophage ingestion activity.
Main Results:
- Lysophosphatidylcholine (lyso-PC) treatment rapidly enhances macrophage phagocytic activity.
- Macrophage activation requires a serum factor, vitamin D3 binding protein (Gc).
- B cells modify Gc protein into a proactivating factor, which T cells convert to a macrophage-activating factor.
- Enzymatic modification of Gc protein by beta-galactosidase and sialidase generates the macrophage-activating factor.
- In vivo administration of the factor significantly increases macrophage ingestion.
Conclusions:
- Lysophosphatidylcholine (lyso-PC) triggers a rapid, Gc-dependent pathway for macrophage activation.
- A novel macrophage-activating factor is generated through the enzymatic modification of Gc protein by B and T cells.
- This pathway highlights a new mechanism of immune cell communication and macrophage potentiation.