IgG-coated erythrocytes augment the lipopolysaccharidestimulated increase in serum tumor necrosis factor-alpha

Differential effect of Fc gamma receptor ligation on LPS-stimulated TNF-alpha secretion by hepatic, splenic, and peritoneal macrophages

Lipopolysaccharide (LPS) increases serum TNF-alpha levels due to TNF-alpha secretion by macrophages. The serum TNF-alpha response to LPS was augmented 10x when FcgammaR ligation was induced by the intravenous injection of Gig-coated erythrocytes (IgG) prior to the administration of LPS. The macrophage population responsible for the augmented TNF-alpha secretion was determined by isolating Kupffer cells, splenic macrophages and peritoneal macrophages from mice that had been given ElgG prior to LPS and determining TNF-alpha secretion ex vivo. The intravenous injection of ElgG augmented LPS-stimulate TNF-alpha secretion by Kupffer cells and splenic macrophages. In contrast, LPS-stimulated TNF-alpha secretion by peritoneal macrophages was not altered by either the intravenous or intraperitoneal injection of ElgG. In vitro phagocytosis of ElgG by isolated peritoneal macrophages also did not augment LPS-stimulated TNF-alpha secretion. These results show that FcgammaR ligation augments LPS-stimulated TNF-alpha secretion by Kupffer cells and splenic macrophages but not by peritoneal macrophages. Thus, the ability of FcgammaR ligation to influence TNF-alpha secretion may be specific to the tissue source of the macrophages.

Fcgamma-receptor signaling augments the LPS-stimulated increase in serum tumor necrosis factor-alpha levels

The phagocytosis of IgG-coated erythrocytes (EIgG) has been shown to augment the bacterial lipopolysaccharide (LPS)-stimulated increase in serum tumor necrosis factor-alpha (TNF-alpha) levels. The present study evaluated the role of Fcgamma-receptor (FcgammaR) signaling and complement activation in the effect of EIgG on the TNF-alpha response to LPS. The role of FcgammaR was determined using FcR gamma-chain knockout mice that lack functional FcgammaRI and FcgammaRIII. In wild-type animals, EIgG caused a 16-fold augmentation of the serum TNF-alpha response to LPS, whereas there was no augmentation in the FcgammaR-deficient animals. Heat-damaged erythrocytes also augmented the TNF-alpha response to LPS. This effect was absent in FcgammaR-deficient animals. An IgG antibody against heated erythrocytes was detected in mouse serum. The complement activation caused by EIgG had little effect on the LPS-stimulated increase in serum TNF-alpha levels as indicated by activation of complement with cobra venom factor or IgM-coated erythrocytes as well as studies with C5-deficient mice. These results indicate that FcgammaR signaling primarily mediates the augmented serum TNF-alpha response to LPS caused by EIgG.

Adsorbed IgG: a potent adhesive substrate for human macrophages

Previous reports from our laboratory have demonstrated qualitatively that preabsorbed IgG can enhance long-term macrophage adhesion in vitro. This investigation further characterizes and quantifies the biological effect of adsorbed human IgG on human macrophages and probes the potential mechanisms. Ten-day human monocyte/macrophage cultures on Plastek M (PM), a normally poor cellular substrate for macrophages, confirmed the ability of preabsorbed IgG to dramatically enhance long-term macrophage adhesion. An adsorption solution concentration of 200 microg/mL of IgG was necessary to provide a consistent, optimal cellular response. (125)I adsorption studies indicated Langmuir-style IgG adsorption at low concentrations; however, no adsorption maximum was observed. Additional adsorption analysis revealed that the IgG fragments Fab, F(ab')(2), and Fc adsorb at levels only 20-40% that of the whole molecule. Despite the lower adsorption levels, both preabsorbed Fab and F(ab')(2) were shown to be as effective as whole molecule IgG at enhancing long-term macrophage adhesion. Surprisingly, the preabsorbed Fc fragment demonstrated no IgG-like activity, thereby eliminating the possibility of an Fc receptor-based mechanism. Other possible mechanisms, such as macrophage lectins, novel macrophage Fab receptors, and complement activation by adsorbed IgG and IgG fragments, are discussed.

Regulation of protein phosphorylation and pathogen phagocytosis by surfactant protein A

Surfactant protein A (SP-A), a pulmonary member of the collectin family of proteins, facilitates the rapid clearance of pathogens by upregulating immune cell functions in the lungs. SP-A binds to bacteria and targets them for rapid phagocytosis by alveolar macrophages, but the mechanism by which this stimulation occurs is not clear. To characterize the intracellular events that may be involved, we examined the roles of protein phosphorylation and cytoskeletal polymerization in SP-A-stimulated phagocytosis. In rat alveolar macrophages, SP-A stimulated rapid tyrosine phosphorylation of specific proteins in a dose- and time-dependent manner. The pattern of proteins that were phosphorylated in response to SP-A, as resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was similar to that observed for immunoglobulin G (IgG)-stimulated macrophages. Both SP-A and IgG stimulated increases in phagocytosis of Streptococcus pneumoniae above levels in the absence of added protein by 394% +/- 81% and 200% +/- 25%, respectively. Phagocytosis in both cases was dependent on tyrosine kinases, protein kinase C, and actin polymerization but not on microtubule activity. These studies show that SP-A utilizes pathways similar to those used by IgG to increase macrophage phagocytosis of bacteria.