The role of an alpha2-macroglobulin of rat serum in the phagocytosis of colloidal particles

The Molecular Dance of Fibronectin: Conformational Flexibility Leads to Functional Versatility

Fibronectin, a large multimodular protein and one of the major fibrillar components of the extracellular matrix, has been the subject of study for many decades and plays critical roles in embryonic development and tissue homeostasis. Moreover, fibronectin has been implicated in the pathology of many diseases, including cancer, and abnormal depositions of fibronectin have been identified in a number of amyloid and nonamyloid lesions. The ability of fibronectin to carry all these diverse functionalities depends on interactions with a large number of molecules, including adhesive and signaling cell surface receptors, other components of the extracellular matrix, and growth factors and cytokines. The regulation and integration of such large number of interactions depends on the modular architecture of fibronectin, which allows a large number of conformations, exposing or destroying different binding sites. In this Review, we summarize the current knowledge regarding the conformational flexibility of fibronectin, with an emphasis on how it regulates the ability of fibronectin to interact with various signaling molecules and cell-surface receptors and to form supramolecular assemblies and fibrillar structures.

An in vitro assay based on surface plasmon resonance to predict the in vivo circulation kinetics of liposomes

The adsorption of blood proteins onto liposomes and other colloidal particles is an important process influencing the circulation time. Proteins adsorbed to the surface of liposomes can mediate recognition of the liposomes by macrophages of the reticuloendothelial system (RES) facilitating their clearance from the circulation. Coating liposomes with poly(ethylene glycol) (PEG) decreases the blood clearance considerably, most likely due to reduced protein adsorption and/or liposome aggregation. By using the relation between clearance and protein binding, the present study introduces an in vitro assay measuring interactions of liposomes with proteins to predict their blood clearance in vivo. Such assay is valuable since it limits time and costs, and importantly reduces the number of animals required for pharmacokinetic investigations of new formulations. In the current study, Surface Plasmon Resonance (SPR) and fluorescence Single Particle Tracking (fSPT) were used to study liposome-protein interactions and blood induced liposome aggregation in vitro. By means of SPR the interactions between proteins and liposomes coated with PEG of different molecular weights and at different densities (PEG(2000) in 2.5%, 5% and 7%; PEG(5000) in 0.5%, 1.5% and 2.5%), were measured for several plasma proteins: human serum albumin (HSA), apolipoprotein E (ApoE), α2-macroglobulin (α2-M), β2-glycoprotein (β2-G) and fibronectin (Fn). Liposomes coated with PEG interacted less with all proteins, an effect which increased with the PEG surface density. In parallel, fSPT analysis showed that the exposure of liposomes to full blood did not change the liposome size, indicating that aggregation is not a strong attributive factor in the clearance of these liposomes. In addition, the SPR measurements of the interactions between liposomes and proteins were correlated with the blood clearance of the liposomes. For each protein, the degree of protein-liposome interaction as determined by SPR showed a moderate to strong positive correlation with the clearance of the liposome type.

Parameters influencing the stealthiness of colloidal drug delivery systems

Over the last few decades, colloidal drug delivery systems (CDDS) such as nano-structures have been developed in order to improve the efficiency and the specificity of drug action. Their small size permits them to be injected intravenously in order to reach target tissues. However, it is known that they can be rapidly removed from blood circulation by the immune system. CDDS are removed via the complement system and via the cells of the mononuclear phagocyte system (MPS), after their recognition by opsonins and/or receptors present at the cell surface. This recognition is dependent on the physicochemical characteristics of the CDDS. In this study, we will focus on parameters influencing the interactions of opsonins and the macrophage plasma membrane with the surface of CDDS, whereby parameters of the polymer coating become necessary to provide good protection.

Serum-mediated recognition of liposomes by phagocytic cells of the reticuloendothelial system - The concept of tissue specificity

The mechanisms responsible for the clearance and recognition of intravenously injected liposomes by phagocytic cells of the reticuloendothelial system are presently not well understood. Here, we address a multiplicity of physicochemical and physiopathological factors which influence the clearance kinetics and tissue distribution of liposomes administered into the circulation. Emphasis is particularly drawn towards the concept of liposome-blood protein interaction and its role in liposome recognition by various phagocytes of the reticuloendothelial system.

Effect of surface charge of small unilamellar liposomes on uptake and transfer of carboxyfluorescein across the perfused human term placenta

We aim to investigate the effect of surface charge of small unilamellar liposomes on transfer and uptake of a low molecular weight, hydrophilic and polar molecule carboxyfluorescein in an in vitro model of perfused human term placenta. Carboxyfluorescein-encapsulated neutral liposomes were prepared by using an equimolar concentration of lecithin and cholesterol. Anionic and cationic liposomes were prepared by adding dicetylcholine and stearylamine, respectively. Size distribution, encapsulation efficiency, and stability of liposomes in blood-based medium were determined. The transfer kinetics of free carboxyfluorescein and liposomally encapsulated carboxyfluorescein were studied in a dually perfused isolated lobule of human term placenta. The concentration of carboxyfluorescein was measured fluorometrically. The maternal to fetal transfer and placental uptake of free carboxyfluorescein was 1.6 +/- 0.1% and 4.2 +/- 0.1% of the initial dose, respectively. This constitutes the control data. The placental transfer of carboxyfluorescein was significantly increased by neutral (2.5 +/- 0.1%; p < 0.01) and anionic liposomes (3.1 +/- 0.2%; p < 0.001), whereas cationic liposomes prevented its transfer (0.4 +/- 0.1%; p < 0.001). The placental uptake of neutral (14.9 +/- 2.3%; p < 0.001) and anionic liposomes (21.1 +/- 1.2%; p < 0.001) were significantly higher than the cationic liposomes (2.3 +/- 0.6%) and control group (p < 0.001). The placental uptake of cationic liposomes was comparable with the control data. These results indicate that placental uptake of small unilamellar liposomes depends upon their surface charge, and transfer of carboxyfluorescein is enhanced by anionic and impeded by cationic liposomes.

Distinction between the depletion of opsonins and the saturation of uptake in the dose-dependent hepatic uptake of liposomes

Opsonins play a role in the hepatic uptake of particles such as bacteria, lipid emulsion, and liposomes. The objective of this study was to distinguish between opsonin depletion and uptake saturation in the dose-dependent hepatic uptake of liposomes. The uptake of opsonized and unopsonized liposomes was determined in the isolated perfused liver. Serum (2.9 mL) was required to opsonize 1 mumol liposomes fully, indicating that a rat (250 g with 10 mL of serum) can opsonize 3.5 mumol liposomes. Next the dose effect on hepatic uptake of opsonized and unopsonized liposomes was examined. Saturation of uptake was found only for the opsonized liposomes. On the other hand, the hepatic uptake clearance decreased dose dependently from 4.31 to 0.79 (mL/min), with increasing doses from 0.075 to 17 mumol/250 g, respectively, after i.v. administration. Thus, the decrease in the hepatic uptake clearance at the medium dose was due to the saturation of uptake alone, and at the high dose it was due to opsonin depletion as well. These results show that the saturation of liposomal uptake in the liver and the depletion of opsonins occurred at different liposome dosage levels.

Sinusoidal endothelial cells from guinea pig liver synthesize and secrete cellular fibronectin in vitro

Endothelial liver cells were obtained from guinea pig by enzymatic digestion and centrifugal elutriation. Cells were cultured on gelatin and fibronectin pretreated culture vessels. Endothelial cells were characterized by phase-contrast microscopy, electron microscopy and the presence of Factor VIII-related antigen. Fibronectin secretion was determined in cell-free supernatants by a sensitive and specific ELISA and localized on fixed cultured cells by immunofluorescence. [35S]Methionine endogeneously labeled fibronectin was immunoprecipitated from supernatants and cellular lysates and displayed on sodium dodecyl sulfate polyacrylamide slab gel electrophoresis. After attachment to the culture vessel, one day after plating, endothelial cells start to produce fibronectin as measured by ELISA and demonstrated by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Secretion of fibronectin increases as cells proliferate to form a confluent monolayer. By immunofluorescence, fibronectin is visualized inside permeabilized cells and as a fibrillar network on the cell surface. Underneath the cell bodies, fibronectin-positive material is present as short strands. From supernatants and cellular lysates, fibronectin is immunoprecipitated with an apparent Mr of about 235,000 obviously larger than plasma fibronectin with an Mr of 220,000, which behaves electrophoretically like fibronectin isolated from early hepatocyte cultures. As endothelial cells incorporate [3H]fucose in fibronectin, whereas hepatocytes do not, we conclude that endothelial cells in contrast to hepatocytes produce cellular fibronectin. Endothelial cells, therefore, are probably the cellular source of the fibronectin present in the space of Disse. The significance of this finding with respect to fibrotic liver disease is discussed.

Stimulation of rat macrophage interleukin 1 secretion by plasma fibronectin

Purified plasma fibronectin (Fn) enhanced the secretory activity of rat peritoneal exudate macrophages as measured by 35S-methionine incorporation into protein released into culture supernatants. Enhancement of protein secretion was dose-dependent and increased with time in culture. Addition of various concentrations of supernatant from cultures of macrophages with Fn resulted in a significant increase in thymocyte proliferation elicited by phytohaemagglutinin. The stimulatory activity of the supernatant was Fn dose-dependent and increased with increasing concentrations of macrophages. This thymocyte stimulatory effect was not due to the presence of Fn in the culture supernatant or to the minimal contamination with endotoxin detected in the Fn preparations. These data suggest that the inflammatory macrophage interaction with Fn results in the release of interleukin-1. They also are consistent with the reported ability of Fn to stimulate lymphocyte transformation.

Evidence for the recycling nature of the fibronectin receptor of macrophages

Plasma fibronectin (pFN) has been shown to mediate phagocytosis of several types of artificial particles and tissue debris by macrophages. In the present investigation some of the dynamic aspects of this receptor-mediated cellular process have been studied. Plasma fibronectin did not bind specifically to fibronectin (FN)-receptors of rat peritoneal macrophages at either 4 degrees C or 37 degrees C. On the other hand, pFN aggregated on the surface of gelatin-coated latex beads (gLtx) and 125I-labeled pFN covalently coupled to latex beads (pFN-Ltx) bound strongly to macrophages at both temperatures. Both of these particles were also internalized at 37 degrees C. Treatment of macrophages by chymotrypsin, thermolysin, or trypsin in a protein-free tissue culture medium did not affect either of the above reactions; however, pronase treatment strongly reduced both the binding and internalization of the pFN-coated particles. The pronase-treated macrophage monolayers in time regained their ability to bind and internalize pFN-gLtx when incubated in fresh tissue culture medium. Such recovery, however, did not take place when the medium contained cycloheximide. On the other hand, phagocytosis of pFN-gLtx was not affected directly by cycloheximide with untreated macrophages; this suggests that the FN-receptor recycles during sustained phagocytosis. This assumption was substantiated by the observations that some of the established lysosomotropic amines--i.e., chloroquine, dansylcadaverine, and dimethyldansylcadaverine--caused total inhibition of internalization without affecting the binding of particles to macrophages. Furthermore, chloroquine protected the FN-receptors against destruction by pronase. Together these results suggest that macrophage receptors for FN are protein, present both on the cell surface and intracellularly, and recycle between the plasma membrane and intracellular sites during phagocytosis.

Trypanosoma cruzi: modulation of parasite-cell interaction by plasma fibronectin

Treatment of either rat peritoneal macrophages (RPM), cloned 3T3 fibroblasts (3T3FR) or Trypanosoma cruzi trypomastigote culture forms with human plasma fibronectin (huFN) enhanced their association with the untreated counterpart and this related to the concentration of huFN used. When treatment was performed at 4 degrees C, the enhancing effect of huFN on parasite-cell interaction was greater than that observed at 37 degrees C. This observation could be related to the indirect immunofluorescence antibody assay showing that a significant increase of fibronectin staining was observed on the cell and parasite surfaces upon incubation with huFN and that the extent of fibronectin staining was greater at 4 degrees C. Incubation of huFN-treated or nontreated parasites or cells with anti-huFN antibodies exerted an inhibitory effect on the parasite-cell association. The region of fibronectin that interacts with the trypomastigote surface is unknown. Inhibition experiments suggested that the domain of fibronectin which interacts with parasite surface receptors would probably be localized close to the NH2-terminal region of the molecule. Taken together, these results suggest that fibronectin may play a role in the binding of parasites to the vertebrate host cell surface.

Fibrinmonomer binding to macrophages mediated by fibrin-binding fibronectin fragments

Binding of 125-I-fibrinmonomer to peritoneal macrophages was investigated in dependence of plasma fibronectin and of its thrombin- or plasmin-derived fragments. Plasma fibronectin failed to enhance cell binding of 125-I-fibrinmonomer. In contrast, 30kD-fragments derived from the N-termini of the fibronectin subunits improved binding considerably. The association with the cell surface was completely inhibited by EDTA, 2-5 mM putrescine and to about 40 per cent by 0.1 mM dansylcadaverine suggesting that a transamidase-catalyzed cross-linking reaction was involved. Thrombin-derived 200kD-remnants of the fibronectin subunit chains failed to mediate cell binding of 125-I-fibrinmonomer provided they had been deprived of residual thrombin activity. Otherwise they were active and their activity was inhibited by the thrombin inhibitor hirudin. Plasmin-derived 200 kD-fragments were inactive as well.

Biological and physical properties of fibronectin pasteurized in the presence of stabilizers

Interest in human plasma fibronectin (Fn) as a potential clinical product for replacement therapy in septic patients has prompted the search for stabilizers to protect the protein from heat denaturation during pasteurization designed to inactivate hepatitis viruses. Fn was pasteurized (60 degrees C, 10 h) in the presence of either citrate, tricarballylate, sucrose or four mixtures of lysine, glucarate, gluconate or citrate which had been found to increase the denaturation temperature of Fn by greater than or equal to 19 degrees C. All but a citrate/gluconate mixture were effective in preventing aggregation as measured by dye fluorescence, light scattering, gel filtration and electrophoresis. Binding to gelatin was retained and immunological activity was only slightly diminished compared to a sample heated without stabilizers. Opsonic activity was measured as ability to mediate the uptake of 125I-gelatin-coated polystyrene beads by attached human monocytes. Fn heated without stabilizers underwent a transient increase in activity which was traced to formation of aggregates having elevated specific activities. Pasteurized samples had slightly elevated opsonic activities with no detectable aggregates present, while the unstabilized control was inactive. These results indicate that the physical properties of Fn as well as the functional activities of the gelatin- and cell-binding domains can be protected against thermal denaturation by various compounds.

Role of fibronectin in human monocyte and macrophage bactericidal activity

Fibronectin is a high-molecular-weight glycoprotein found as a soluble dimer in plasma and as an insoluble multimer in tissues. It has been proposed that plasma fibronectin facilitates phagocytic removal of lysed cells and damaged tissues. Fibronectin binds avidly to several species of gram-positive bacteria and enhances staphylococcal and streptococcal attachment to cultured cells. Determination of whether fibronectin will enhance the bactericidal activity of monocytes and macrophages has not been reported. The bactericidal activity of freshly isolated monocytes, cultured monocytes, or lymphokine-activated macrophages was tested in the presence of either dimeric or multimeric fibronectin. Freshly isolated monocytes and lymphokine-activated macrophages killed Staphylococcus aureus effectively in the absence of fibronectin or whole serum. In contrast, monocytes cultured for 7 to 10 days had diminished staphylocidal capacity. When the monocytes were cultured with either dimeric or multimeric fibronectin, however, bactericidal capacity was maintained. Thus, although fibronectin did not enhance the bactericidal activity of mononuclear phagocytes, both multimeric and dimeric fibronectin were effective at maintaining the bactericidal capacity.

A critical assessment of fibronectin's opsonic role for bacteria and microaggregates

Within recent years, the physiological roles of fibronectin (Fn) have begun to be elucidated. This review examines Fn's opsonic capabilities with respect to bacteria and microparticulates. Fn's ability to promote the phagocytosis of these targets by monocytes, macrophages, and neutrophils is discussed in detail, as are the possible mechanisms through which Fn mediates these interactions. The controversies concerning the physiological importance of Fn for host homeostasis and its use as an indicator of reticuloendothelial system function are also addressed in this review.

Effect of the nonionic surfactant poloxamer 338 on the fate and deposition of polystyrene microspheres following intravenous administration

The blood clearance and organ deposition of polystyrene microspheres in the rabbit following intravenous injection has been investigated using the technique of gamma scintigraphy, blood and organ level measurements, and histology. Uncoated microspheres of 1.27-microns diameter were cleared rapidly from the blood and were taken up primarily by the reticuloendothelial system in the liver. Coating of the microspheres with the nonionic surface-active agent poloxamer 338 reduced the uptake in the liver and gave a corresponding increase in the lungs.

Fibronectin--mediator between cells and connective tissue

Fibronectin, previously also termed LETS-protein, is a high-molecular-weight protein (mol. w. ca. 450,000) present in the form of thin fibrils in the pericellular space of fibroblasts and other adherent cells, as well as in distinct areas of the connective tissue. A soluble form, immunologically identical and chemically at least very similar to the cell-attached protein, is found in plasma in a concentration of about 300 micrograms/ml. It is also denominated cold-insoluble globulin. The protein has affinity both to cell surfaces and to various matrix substances such as fibrin and collagen and, therefore, is capable of mediating cell attachment to these substrates. In addition, it serves as an opsonin for the phagocytosis of gelatin-containing compounds and probably is essential for the removal of soluble fibrin from the circulating blood by the reticulo-endothelial system. Bacterial cell walls are also recognized by fibronectin. A conversion of soluble fibronectin to fibrils is achieved by heparin which also enhances the binding of soluble fibronectin to cells. Heparin or, as suggested, the related heparan sulfate present on the surface of various cells, appears to function as a cofactor in the formation of pericellular fibrils. The fibronectin fibrils precipitated with heparin, compared to soluble fibronectin, show a considerably improved affinity to native collagen, especially to type III. Hyaluronic acid has an antagonistic function which, at higher concentrations, prevents the fibronectin fibrils from interacting with collagen and cell surfaces. Masking of fibronectin fibrils was also achieved by sulfated proteoglycans of cartilage. Virus-transformed fibroblasts produce less fibronectin and are less capable of maintaining surface pericellular fibrils. A reasonable explanation is that they have an elevated secretion of hyaluronic acid. The transformed cells attach only weakly to a surface and exhibit a rounded shape in contrast to healthy ones. This phenotype can be corrected to a great extent with fibronectin. It is suggested that fibronectin also influences the formation of connective tissue by accumulating collagen precursors on the surface of fibroblasts and facilitating fibrillogenesis.

Fibronectin binding to protein A-containing staphylococci

Fibronectin (Fn) was found to bind to protein A-containing isolates of Staphylococcus aureus, but not to mutant strains devoid of this protein nor to clinical isolates of S. epidermidis. Fn was purified from human plasma by affinity chromatography on gelatin-Sepharose. After elution with 4 M urea, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified material detected no immunoglobulin contamination. This purified Fn was radiolabeled with 125I and used in binding assays. Quantitatively, Fn binding was directly correlated with the cellular protein A content of the various strains tested. Mannitol salt broth preculture or organisms resulted in a reduction of their cellular protein A and a decrease in Fn binding by these cells. However, soluble protein A maximally inhibited the binding of radiolabeled Fn to protein A-positive strains of staphylococci by only 50%, indicating the possibility of multiple Fn binding sites. Fn's binding to protein A-containing S. aureus strains may play a role in the pathogenicity of these organisms by promoting their attachment to and subsequent invasion of host tissues.

Phagocytosis of gelatin-latex particles by a murine macrophage line is dependent on fibronectin and heparin

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 (P388D1). 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 cell-associated 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-promoting activity of avian plasma and fibroblastic cell surface fibronectins

The purpose of this investigation was to determine whether fibronectin preparations from both chicken plasma and cell surface of fibroblasts can promote phagocytosis of gelatin-coated latex particles. Chicken plasma fibronectin was isolated (a) by ammonium sulfate fractionation, chromatography on Sepharose-4B followed by purification on a Sepharose-4B-heparin column; (b) by affinity chromatography on a Sepharose-4B-rat-antifibronectin column; (c) by affinity chromatography on Sepharose-4B-gelatin followed by molecular sieve separation on Sepharose-CL4B; (d) by a dual affinity chromatographic method using a Sepharose-4B-gelatin column and a Sepharose-4B-heparin column. Chicken cell surface fibronectin from fibroblast cultures was purified by ammonium sulfate precipitation followed by chromatography on Sepharose-CL4B. The purity of preparations was examined by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate; all samples showing high purity. The opsonic activities of the preparations were measured by the uptake of 125I-labeled gelatin coated latex particles in conjunction with rat liver slice, and peritoneal macrophage monolayer systems. Both the plasma fibronectin and cell surface fibronectin preparations showed substantial opsonic activities in the test systems. Fresh chicken plasma did not reveal any phagocytosis promoting activity due to the presence of some unidentified inhibitor(s). The results showed that an opsonically active protein can be isolated from chicken plasma or serum and this protein is identical to plasma fibronectin. Furthermore, it could be concluded that cell surface fibronectin from chicken fibroblasts also can serve as an opsonin for gelatin coated particles.

Fibronectin-mediated uptake of gelatin-coated latex particles by peritoneal macrophages

The present study demonstrates the ability of plasma fibronectin or cold-insoluble globulin (Clg) to promote the uptake of 125I-labeled, gelatin-coated latex beads (g-Ltx*) by monolayers of peritoneal macrophages (PM). The uptake of g-Ltx* by PM was enhanced by Clg in a concentration-dependent fashion and required the presence of heparin (10 U/ml) as an obligatory cofactor for maximal particle uptake. Treatment of PM monolayers with trypsin (1 mg/ml) for 15 min at 37 degrees C after particle uptake removed less than 15% of the radioactivity incorporated by the monolayers. However, a similar trypsin treatment of the monolayers before the addition of latex particles depressed Clg-dependent uptake by greater than 75%. Pretreatment of PM monolayers with inhibitors of glycolysis effectively reduced the Clg-dependent uptake of latex. Similarly, pretreatment of monolayers with either inhibitors of protein synthesis or agents that disrupt cytoskeletal elements also significantly depressed Clg-dependent particle uptake. Phagocytosis of g-Ltx* by PM in the presence of Clg and heparin was confirmed by electron microscopy. Finally, g-Ltx* could also be effectively opsonized with Clg at 37 degrees C before their addition to the monolayers. These studies suggest that the recognition of g-Ltx* in the presence of Clg required cell surface protein(s) and that subsequent phagocytosis of these particles by PM was energy dependent and required intact intracellular cytoskeleton elements. Thus, PM monolayers provide a suitable system for further studies on the function of Clg in the recognition and phagocytosis of gelatin-coated particles by phagocytic cells.

Plasma fibronectin (opsonic glycoprotein): its synthesis by vascular endothelial cells and role in cardiopulmonary integrity after trauma as related to reticuloendothelial function

Progressive multiple organ failure in association with septic complications in the surgical, trauma and burn patient is of major clinical importance. Reticuloendothelial system host defense mechanisms are abnormal following severe trauma and burn. Failure in systemic host defense is, in part, mediated by a deficiency in a circulating opsonic alpha 2 surface binding (SB) glycoprotein. This opsonic deficiency and reticuloendothelial host defense failure appears etiologic in the genesis of organ failure with sepsis. Opsonic alpha 2SB glycoprotein is identical to cold-insoluble globulin or plasma fibronectin. Plasma fibronectin is antigenically related to cell surface fibronectin which appears to be synthesized by both fibroblasts and vascular endothelial cells. Although these two proteins are antigenically related, they may or may not be identical with respect to biochemical properties and function. Cell surface fibronectin appears to be an adhesive glycoprotein mediating cell-cell interaction and cell adhesion to a substratum. Plasma fibronectin is a more soluble form which mediates reticuloendothelial or macrophage clearance of particulates such as fibrin microaggregates, collagenous debris, perhaps other bacterial or nonbacterial particulates. Since opsonic glycoprotein is identical to cold-insoluble globulin which can be readily concentrated in plasma cryoprecipitate, it has been shown that cryoprecipitate infusion can reverse opsonic deficiency in the injured patient with sepsis. Reversal of opsonic deficiency by cryoprecipitate infusion results in a marked improvement in cardiopulmonary function which includes a decline in the pulmonary shunt, a decrease in the physiologic dead space, an increase in limb blood flow, an increase in reactive hyperemia of the peripheral circulation and an increase in limb oxygen consumption. This cardiopulmonary response is paralleled by a decline in the septic state and normalization of other hematologic parameters. These studies suggest an important homeostatic role for fibronectins in organ and microvascular integrity, especially in the septic injured patient. Cell surface fibronectin which participates in cell adhesion may, in part, modulate microvascular integrity, vascular permeability and would repair. In contrast, the more soluble plasma fibronectin or opsonic alpha 2SB glycoprotein may mediate reticuloendothelial clearance of blood-borne particulates to prevent pulmonary and peripheral vascular microembolization and organ injury. Thus, reversal of opsonic deficiency may be an effective modality of therapy in the septic injured patient with organ failure.

Cryoprecipitate reversal of opsonic alpha2-surface binding glycoprotein deficiency in septic surgical and trauma patients

Human opsonic alpha2-surface binding glyoprotein (alphs2SB-glycoprotein), a molecule having immunologic identity with an amino acid composition similar to cold-insoluble globulin, is concentrated in a cryoprecipitate of plasma. Septic surgical and trauma patients manifesting opsonic alpha2SB-glycoprotein deficiency and associated reticuloendothelial system dysfunction were treated by intravenous infusion of cryoprecipitate. This therapy restored circulating bioreactive and immunoreactive opsonin and improved their septicemia, pulmonary insufficiency, and duration of recovery. Cryoprecipitate infusion may offer a new approach to the treatment of septic injured patients in preventing multiple organ failure; measurement of immuno-reactive serum opsonic alpha2SB-glycoprotein may provide a noninvasive index of reticuloendothelial system function and patient status during servere sepsis that follows trauma.