Different Effects of Fibronectin on the Phagocytosis of Staphylococcus aureus and Coagulase‐Negative Staphylococci by Murine Peritoneal Macrophages

Abstract

Fibronectin is known to be an important factor in colonization by Staphylococcus aureus of host tissues as well as other extracellular matrix proteins such as collagen and laminin. We investigated the effect of fibronectin on the phagocytosis of the S. aureus Cowan I strain by macrophages and of coagulase-negative staphylococci (CNS) strains for comparison. Fibronectin-reduced serum in place of normal serum lowered the phagocytic activity of the macrophages on the Cowan I strain. Purified fibronectin enhanced the phagocytic activity of the strain in a dose-dependent manner. On the other hand, fibronectin did not show any opsonic effect on the ingestion of CNS strains, though the binding of fibronectin occurred equally well in CNS strains and the Cowan I strain. Fibronectin-binding protein (FnBP), the specific fibronectin receptor on the surface on S. aureus, was detected in both the Cowan I strain and CNS strains. Polymerase chain reaction confirmed that not only the Cowan I strain, but also CNS strains possessed the FnBP gene.These results indicate that fibronectin shows an opsonic effect on the S. aureus, Cowan I strain but not on CNS strains, and suggest that the binding of fibronectin to FnBP is not sufficientfor efficient phagocytosis of the staphylococci strains by macrophages.

Fibronectin Bound to the Surface of Staphylococcus aureus Induces Association of Very Late Antigen 5 and Intracellular Signaling Factors with Macrophage Cytoskeleton

“…Macrophages were obtained as previously described (37). In brief, 1 ml of 3% thioglycolate medium (Difco, Detroit, Mich.) was injected intraperitoneally into female ICR mice (5 weeks of age; purchased from Charles River Japan Inc.), and peritoneal exudate cells were collected on day 4 by flushing the cavity with 3 ml of ice-cold Dulbecco's modified Eagle's medium (Life Technologies, Grand Island, N.Y.).…”

“…However, the number of bacteria ingested by macrophages increased only when the macrophages interacted with FN-bound S. aureus, whereas FN showed no effect on the ingestion of CNS (37). In the present study, the response of the adhesion architecture of macrophages after binding to FN-bound staphylococci was investigated.…”

Expression and Distribution of Very Late Antigen‐5 in Mouse Peritoneal Macrophages upon Ingestion of Fibronectin‐Bound Staphylococcus aureus

“…Macrophages were obtained as previously described (35). Briefly, 1 ml of 3% TGC medium (Difco, Mich., U.S.A.) or 10% proteose peptone (Sigma, Mo., U.S.A.) was injected intraperitoneally into female ICR mice (5 weeks of age; Charles River Japan, Inc., Yokohama, Japan), and peritoneal exudate cells were collected on the appropriate day by flushing the cavity with 3 ml of ice-cold Dulbecco's Modified Eagle's Medium (Life Technologies, N.Y., U.S.A.).…”

“…Fetal calf serum FN was prepared as previously described (35). The fractions eluted from the GCL-2000-m column were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions, and fractions containing only dimers were selected (28).…”

“…Previously, we demonstrated that FN treatment of S. aureus remarkably increases the phagocytic activity of TGC-induced murine peritoneal macrophages (35). RGD peptide and anti-VLA-5 antibody dose-dependently reduced the number of ingested bacteria, indicating that this activation was mediated by VLA-5.…”