Modification of alpha 2-macroglobulin into a macrophage-activating factor through the action of liposome-stimulated B-cell membranous glycosidases.
The serum glycoprotein alpha 2-macroglobulin can be converted into a potent macrophage-activating factor that promotes the Fc gamma receptor-mediated phagocytosis of macrophages, through modification of the sugar moiety with liposome-treated B-cell glycosidase(s). This paper discusses the activation mechanism of B-cell membranous glycosidase by liposomes using mouse splenic B cells. B-cell membranous beta-galactosidase and beta-N-acetylglucosaminidase were significantly activated by liposome treatment, and this process can be regulated by trypsin-sensitive protein. To clarify the contribution of trypsin-sensitive protein to enzyme activities, the B-cell surface antigen receptor was studied. With the addition of a Fab' fragment of anti-mouse IgM but not IgD antibody, the activation of both glycosidases induced by liposomes was significantly inhibited and was essentially the same as that of saline-treated glycosidase activities. Consequently, interactions of liposomes with cell-surface IgM may cause B-cell membranous glycosidase activation. A significant decrease in membrane fluidity, particularly near the membrane surface rather than deep within the membrane, was observed in liposome-treated B cells using electron spin resonance. Liposomes would thus appear to interact with B cells via cell-surface IgM, with a consequent decrease in membrane fluidity, as well as the activation of B-cell membranous glycosidases, causing alpha 2-macroglobulin to be converted into a macrophage activating factor.
Murai
M
M
School of Pharmacy, Tokyo University of Pharmacy and Life Science, Hachioji, Japan.
Aramaki
Y
Y
Tsuchiya
S
S
D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology*; D002462:Cell Membrane / Q000201:enzymology; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006596:Hexosaminidases / Q000378:metabolism; D007075:Immunoglobulin M / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism*; D008262:Macrophage Activation; D016215:Macrophage-Activating Factors / Q000378:metabolism*; D008297:Male; D008560:Membrane Fluidity; D051379:Mice; D008807:Mice, Inbred BALB C; D000511:alpha-Macroglobulins / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism; D048828:beta-N-Acetyl-Galactosaminidase
D007075:Immunoglobulin M; D008081:Liposomes; D016215:Macrophage-Activating Factors; D000511:alpha-Macroglobulins; D006026:Glycoside Hydrolases; D006596:Hexosaminidases; D001616:beta-Galactosidase; D048828:beta-N-Acetyl-Galactosaminidase