It has been suggested that fibronectin plays a role in clearing particles from the circulation by promoting binding to phagocytes of the reticuloendothelial system . By use of a well-defined system to investigate the possible opsonic role of fibronectin, we have studied the uptake of gelatin-coated latex particles by a murine macrophage cell line (P388D 1 ) .Fibronectin promotes binding of gelatin-coated beads to these cells in both suspension and monolayer cultures . In both cases there is a requirement for heparin as a cofactor . Other glycosaminoglycans (chondroitin sulfates A and C, dermatan sulfate, and keratan sulfate) were inactive, whereas heparan sulfate was somewhat active .Proof that beads were actually endocytosed was obtained by electron microscopy, which showed beads internalized in membrane-bounded vesicles, and by immunofluorescence analyses, using antibodies to fibronectin to stain external beads. Two rapid assays for the opsonic activity of fibronectin were developed based on differential centrifugation of cellassociated beads and on the immunofluorescence procedure . Binding and endocytosis were time-and temperature-dependent and varied with the amount of gelatin on the beads and with the concentrations of fibronectin and heparin added, and could be inhibited by F(ab') 2 antifibronectin . These studies provide a sound basis for a detailed analysis of the interaction of fibronectin with the cell surface and of its involvement in endocytosis.Phagocytosis is the process by which particles (bacteria, damaged cells, fibrin aggregates, etc .) are bound and endocytosed by phagocytic cells . Recognition of these particles by the cells is due to the presence of humoral factors (opsonins) such as immunoglobulins or complement, which coat the particles and promote their phagocytosis (44). Recently, an a-2-globulin from plasma has been shown to facilitate clearance of certain particles from the circulation (31,32,42) . It also promotes the binding of particles to liver slices (12,16,31,40) and the uptake of gelatin-coated particles by rat peritoneal macrophages (13,18) . This a-2-globulin has recently been purified from rat and human sera and found to be immunologically and functionally identical with plasma fibronectin (2, 33), a dimeric glycoprotein with subunits of 230,000 daltons (3) . Fibronectin is known to be involved in adhesion of cells to solid substrata and has specific binding sites for gelatin, glycosaminoglycans (i .e ., heparin), fibrinogen, and fibrin, and can be crosslinked to fibrin or collagen by Factor XIII (reviewed in references 17, 21, 35, 32 47, 49) . Fibronectin has also been shown to bind to bacteria' (27, 36), but has not been shown to promote phagocytosis of bacteria .To define the conditions necessary for endocytosis of fibronectin-coated particles, we have studied an established mouse macrophagelike cell line (P388D,) by using a centrifugation assay, as well as electron and immunofluorescence microscopy. We find that endocytosis of gelatin-conjugated latex beads...

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Malting-quality barley samples of the varieties Harrington, Manley, and TR118, each from two locations in Saskatchewan, were collected directly from the producers and sent to China for storage. At regular intervals samples were shipped back to Canada for analysis consisting of germination studies, alpha-amylase tests, magnetic resonance imaging (MRI), and magnetic relaxation (NMR) studies. Samples showing a decrease in germinative energy and elevated levels of alpha-amylase also showed a rapid uptake of water in the area between the embryo and the endosperm as observed by MRI. Using NMR relaxation experiments, viable and nonviable barley samples could be distinguished after 2 h of imbibition.