Macrophage Fcγ Receptors Expression Is Altered by Treatment with Dopaminergic Drugs

Macrophage Fcγ receptors have an important role in host defense and the pathophysiology of immune mediated disorders. Alteration of splenic macrophage Fcγ receptors expression predisposes to severe infection. Inhibition or blockade of splenic macrophage Fcγ receptors is one of the mechanisms by which immune cytopenias improve. Dopaminergic drugs have clinically significant regulatory functions on the immune response. Using an experimental model in the guinea pig we assessed the effect of commonly used dopaminergic drugs on the expression of macrophage Fcγ receptors. Three dopa-antagonists, bromocryptine, leuprolide, and pergolide, and seven dopa-antagonists, chlorpromazine, SCH 23390, metochlopramide, sulpiride, veralipride, alizapride, and cisapride, were studied. Following guinea pig treatment with dopaminergic drugs, the clearance of IgG-sensitized RBCsin vivo,thein vitrobinding of IgG-sensitized RBCs by isolated splenic macrophages and flow cytometry with monoclonal antibodies were performed. Treatment with dopa-agonists enhanced the clearance of IgG-sensitized RBCs, thein vitrobinding of IgG-sensitized RBCs by isolated splenic macrophages, and the cell surface expression of both macrophage Fcγ receptors, and vice versa, dopa-antagonists impaired macrophage Fcγ receptors expression. Macrophage FcγR1,2 was more sensitive than FcγR2 to such dopaminergic effect. These alterations of macrophage Fcγ receptors expression are mediated by both D1 and D2 dopamine receptors, with a major participation of D2 receptors. Dopaminergic drugs alter the clearance of IgG-coated cells by an effect at the expression of splenic macrophage Fcγ receptors.     

Effects of androgen treatment on expression of macrophage Fcgamma receptors

Macrophage Fcgamma receptors (FcgammaRs) play an important role in the host defense against infection and in the pathophysiology of immune cytopenias. Modulation of macrophage FcgammaR expression is a potential therapeutic approach to immune disorders. Glucocorticoids and progesterones decrease macrophage FcgammaR expression. We assessed the effect of treatment with androgens and antiandrogens on the expression of macrophage FcgammaRs using an experimental guinea pig model. Four androgens (testosterone, dihydrotestosterone, mesterolone, and danazol) and five antiandrogens (flutamide, nilutamide, cyproterone acetate, spironolactone, and finasteride) were studied. Following in vivo treatment of guinea pigs, we determined the clearance of immunoglobulin G (IgG)-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic macrophage FcgammaR cell surface expression. All of the androgens impaired the clearance of IgG-sensitized erythrocytes by decreasing splenic macrophage FcgammaR expression. Dihydrotestosterone and mesterolone were more effective than testosterone or dihydrotestosterone. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that the androgens decreased the cell surface expression of FcgammaR1,2 more than that of FcgammaR2. Antiandrogens did not significantly alter macrophage FcgammaR expression. Nevertheless, antiandrogens counteracted the effects of androgens on macrophage FcgammaR expression. These data indicate that androgens impair the clearance of IgG-coated cells by decreasing splenic macrophage FcgammaR expression. Thus, androgens other than danazol are candidate drugs for the treatment of immune disorders.     

Enhancement of splenic-macrophage Fcgamma receptor expression by treatment with estrogens.

Splenic-macrophage Fcgamma receptors (FcgammaRs) participate in the pathophysiologies of immune-complex diseases and in host defense against infection. Modulation of macrophage FcgammaR expression is an immuno-therapeutic target. Glucocorticoids, sex steroids, and dopaminergic drugs modulate macrophage FcgammaR expression. Previous data indicate that estradiol increases macrophage FcgammaR expression. Nevertheless, the effects of clinically used estrogens upon macrophage FcgammaR expression are unknown. We assessed the effects of treatment with commonly used estrogens on the expression of macrophage FcgammaRs using a guinea pig experimental model. Six estrogens have been studied: ethynylestradiol (Et), mestranol (M), chlortianisene (Ct), promestriene, 17-epiestriol, and 17beta-estradiol. Following in vivo treatment of guinea pigs, we determined the clearance of immunoglobulin G (IgG)-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic-macrophage FcgammaR cell surface expression. Estrogens enhance the clearance of IgG-sensitized erythrocytes by increasing splenic-macrophage FcgammaR expression. Et, M, and Ct were more effective than the other estrogens. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that estrogens increase the cell surface expression of FcgammaR1 and -2 more than that of FcgammaR2. These data indicate that treatment with commonly used estrogens enhances the clearance of IgG-sensitized cells by improving splenic-macrophage FcgammaR expression.     

Effects of Androgen Treatment on Expression of Macrophage Fcγ Receptors

Macrophage Fcγ receptors (FcγRs) play an important role in the host defense against infection and in the pathophysiology of immune cytopenias. Modulation of macrophage FcγR expression is a potential therapeutic approach to immune disorders. Glucocorticoids and progesterones decrease macrophage FcγR expression. We assessed the effect of treatment with androgens and antiandrogens on the expression of macrophage FcγRs using an experimental guinea pig model. Four androgens (testosterone, dihydrotestosterone, mesterolone, and danazol) and five antiandrogens (flutamide, nilutamide, cyproterone acetate, spironolactone, and finasteride) were studied. Following in vivo treatment of guinea pigs, we determined the clearance of immunoglobulin G (IgG)-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic macrophage FcγR cell surface expression. All of the androgens impaired the clearance of IgG-sensitized erythrocytes by decreasing splenic macrophage FcγR expression. Dihydrotestosterone and mesterolone were more effective than testosterone or dihydrotestosterone. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that the androgens decreased the cell surface expression of FcγR1,2 more than that of FcγR2. Antiandrogens did not significantly alter macrophage FcγR expression. Nevertheless, antiandrogens counteracted the effects of androgens on macrophage FcγR expression. These data indicate that androgens impair the clearance of IgG-coated cells by decreasing splenic macrophage FcγR expression. Thus, androgens other than danazol are candidate drugs for the treatment of immune disorders.     

Enhancement of Splenic-Macrophage Fcγ Receptor Expression by Treatment with Estrogens

Splenic-macrophage Fcγ receptors (FcγRs) participate in the pathophysiologies of immune-complex diseases and in host defense against infection. Modulation of macrophage FcγR expression is an immuno-therapeutic target. Glucocorticoids, sex steroids, and dopaminergic drugs modulate macrophage FcγR expression. Previous data indicate that estradiol increases macrophage FcγR expression. Nevertheless, the effects of clinically used estrogens upon macrophage FcγR expression are unknown. We assessed the effects of treatment with commonly used estrogens on the expression of macrophage FcγRs using a guinea pig experimental model. Six estrogens have been studied: ethynylestradiol (Et), mestranol (M), chlortianisene (Ct), promestriene, 17-epiestriol, and 17β-estradiol. Following in vivo treatment of guinea pigs, we determined the clearance of immunoglobulin G (IgG)-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic-macrophage FcγR cell surface expression. Estrogens enhance the clearance of IgG-sensitized erythrocytes by increasing splenic-macrophage FcγR expression. Et, M, and Ct were more effective than the other estrogens. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that estrogens increase the cell surface expression of FcγR1 and -2 more than that of FcγR2. These data indicate that treatment with commonly used estrogens enhances the clearance of IgG-sensitized cells by improving splenic-macrophage FcγR expression.     

Antigen presentation by a macrophage-like cell line persistently infected with respiratory syncytial virus

Severe infection by the human respiratory syncytial virus (RSV) early in life is associated with subsequent recurrent airway disease presumably mediated by dysregulation of the local immune response. Dysfunction of the immune response may be related to impaired macrophage functions. We have previously reported that RSV persistence in a macrophage culture (MPhiper) alters Fcgamma receptors (FcgammaR)-mediated phagocytosis and the production of pro-inflammatory cytokines. Here, we determined whether the ability of macrophages to process and present antigens and to stimulate RSV-specific CD8(+) T cells was altered in MPhiper. We also examined the level of expression of MHC class I molecules in MPhiper and the ability of these cells to present viral antigens to specific T lymphocytes. Our results showed that antigen processing and presentation were not altered by chronic RSV infection, and suggested that MPhiper were able to stimulate RSV-specific CD8(+) T lymphocytes.     

Differentiation of the human monocyte cell line,U937, with dibutyryl cyclicAMP induces the expression of the inhibitory Fc receptor,FcgammaRIIb

FC receptor for IgG receptor (Fcgamma) mediated activation of macrophages is essential for the clearance of immune complexes and control of inflammation. However, activated macrophages play an integral role in tissue destruction associated with autoimmune and inflammatory disease processes. Understanding the mechanisms which balance activating and inhibitory signals generated by immune complexes are therefore of critical importance to human disease. Here, we demonstrate that differentiation of the human monocytic U937 cell line to a macrophage phenotype with dibutyryl cyclicAMP induces both mRNA and protein expression of the inhibitory IgG receptor, FcgammaRIIb1. We further demonstrate that, following receptor aggregation, FcgammaRII transiently recruits the 5'-inositol phosphatase, SHIP. These data define a role for FcgammaRIIb in the modulation of immune complex mediated macrophage activation in a human model system.     

Monocyte-dependent cell death of T lymphocyte subsets in chronic hepatitis C

Much evidence indicates that atherosclerotic lesions are largely of an inflammatory nature. Activated macrophages and macrophage-derived foam cells laden with cholesterol esters are a major constituent of these lesions and can influence lesion formation via several potential mechanisms. One such mechanism is Fcgamma receptor activation and/or Fcgamma receptor-mediated clearance of immune complexes containing cholesterol, such as lipoprotein immune complexes. That this mechanism contributes to lesion formation would be further supported if Fcgamma receptor expression in arterial lesions were demonstrated. We therefore used monoclonal antibodies and immunocytochemical methods to analyze frozen sections of human arterial lesions for expression of each of the three primary classes of mononuclear phagocyte Fcgamma receptors. Approximately 800 sections of aorta, carotid, and coronary arteries obtained from five elderly donors were analyzed. The presence of macrophages was determined by assaying reactivity of a monoclonal antibody specific to CD163, which is expressed only on cells of the human mononuclear phagocyte lineage. Results indicate that highly cellular preatheromatous lesions contained numerous macrophages in the zone of proliferation that expressed each class of Fcgamma receptor (FcgammaRIA, FcgammaRIIA, and FcgammaRIIIA). Fcgamma receptor-positive cells were also present in medial and adventitial areas. Fcgamma receptor staining was both punctate and diffuse, the latter suggesting that soluble receptors were present in the extracellular matrix. These data further support that Fcgamma receptor-mediated clearance of immune complexes can occur in arterial lesions during atherogenesis. Expression of both the high affinity (FcgammaRIA) and lower affinity (FcgammaRIIA/FcgammaRIIIA) receptors indicates that mono- and multivalent IgG-containing immune complexes could engage Fcgamma receptors and influence lesion formation through several different inflammatory mechanisms triggered by receptor activation.     

Persistence of respiratory syncytial virus in macrophages alters phagocytosis and pro-inflammatory cytokine production

Functions of macrophage are known to be altered by acute infection with respiratory syncytial virus (RSV). However, it is unknown whether the persistent presence and expression of the RSV genome have any effect on the functions of these cells. We used a murine macrophage-like cell line (P388D1) persistently infected with RSV to determine: (i) phagocytic activity mediated by Fcgamma receptors, (ii) expression of Fcgamma receptors, and (iii) production of IL-1beta, IL-6 and TNF-alpha. Viral persistence was found to increase phagocytosis, expression of Fcgamma receptors and the production of IL-1beta and IL-6. In contrast the biological activity of secreted TNF-alpha decreased. In this study we give novel evidence that RSV persistence alters the biological activities of macrophages.     

Differential kinase requirements in human and mouse Fc-gamma receptor phagocytosis and endocytosis

Fc gamma receptors (FcgammaRs) contribute to the internalization of large and small immune complexes through phagocytosis and endocytosis, respectively. The molecular processes underlying these internalization mechanisms differ dramatically and have distinct outcomes in immune clearance and modulation of cell function. However, it is unclear how the same receptors (FcgammaR) binding to identical ligands (IgG) can elicit such distinct responses. We and others have shown that Syk kinase, Src-related tyrosine kinases (SRTKs) and phosphatidyl inositol 3-kinases (PI3K) play important roles in FcgammaR phagocytosis. Herein, we demonstrate that these kinases are not required for FcgammaR endocytosis. Endocytosis of heat-aggregated IgG (HA-IgG) by COS-1 cells stably transfected with FcgammaRIIA or chimeric FcgammaRI-gamma-gamma (EC-TM-CYT) was not significantly altered by PP2, piceatannol, or wortmannin. In contrast, phagocytosis of large opsonized particles (IgG-sensitized sheep erythrocytes, EA) was markedly reduced by these inhibitors. These results were confirmed in primary mouse bone marrow-derived macrophages and freshly isolated human monocytes. Levels of receptor phosphorylation were similar when FcgammaRIIA was cross-linked using HA-IgG or EA. However, inhibition of FcgammaR phosphorylation prevented only FcgammaR phagocytosis. Finally, biochemical analyses of PI3K(p85)-Syk binding indicated that direct interactions between native Syk and PI3K proteins are differentially regulated during FcgammaR phagocytosis and endocytosis. Overall, our results indicate that FcgammaR endocytosis and phagocytosis differ dramatically in their requirement for Syk, SRTKs, and PI3K, pointing to striking differences in their signal transduction mechanisms. We propose a competitive inhibition-based model in which PI3K and c-Cbl play contrasting roles in the induction of phagocytosis or endocytosis signaling cascades.     

Requirements for Vav guanine nucleotide exchange factors and Rho GTPases in FcgammaR- and complement-mediated phagocytosis

Vav guanine nucleotide exchange factors (GEFs) have been implicated in cell adhesion by integrin and immune response receptors through the regulation of Rho GTPases. Here, we examine the role of Vav and Rho GTPases in phagocytosis by using primary murine macrophages. The genetic deletion of Rac1 and Rac2 prevents phagocytosis mediated by integrin and Fcgamma receptors (FcgammaR), whereas the genetic deletion of Vav1 and Vav3 only prevents integrin-mediated phagocytosis through the complement receptor alpha(M)beta(2). In addition, a Rac1/2 or Vav1/3 deficiency blocks Arp2/3 recruitment and actin polymerization at the complement-induced phagosome, indicating that these proteins regulate early steps in phagocytosis. Moreover, constitutively active Rac is able to rescue actin polymerization and complement-mediated phagocytosis in Vav-deficient macrophages. These studies indicate that Rac is critical for complement- and FcgammaR-mediated phagocytosis. In contrast, Vav is specifically required for complement-mediated phagocytosis, suggesting that Rac is regulated by GEFs other than Vav downstream of the FcgammaR.     

A novel phenotype for an activated macrophage: the type 2 activated macrophage

Activated macrophages were used as antigen presenting cells (APCs) to determine the extent to which these APCs could influence an adaptive immune response. We show that activated macrophages induced a strong polarized Th1-like T cell response that was predominated by IFN-gamma. However, when antigen was targeted to Fcgamma receptors on these macrophages, their phenotype changed, and they now induced a T cell response that was predominated by IL-4. The initial biasing by activated macrophages toward a Th1-like response was a result of activation of the innate immune response, as macrophages from MyD88(-/-) mice failed to produce Th1-inducing cytokines. The reversal of the Th1 biasing was a result of FcgammaR ligation, as macrophages lacking the FcR common gamma chain failed to reverse this biasing. To show that this biasing could occur in vivo, mice were injected with activated macrophages or activated macrophages whose FcgammaR had been ligated with an irrelevant immune complex. Mice injected with FcgammaR-ligated macrophages made more antibody than those receiving conventionally activated macrophages, and the antibody was predominantly of the IgG1 isotype. These studies demonstrate that FcgammaR ligation on activated macrophages can change the phenotype of these APCs to cells that preferentially drive a Th2-like response. We have termed these cells type 2 activated macrophages.     

Role of Syk in Fc gamma receptor-coupled tyrosine phosphorylation of Cbl in a manner susceptible to inhibition by protein kinase C.

Fcgamma receptors (FcgammaR) of guinea pig neutrophils were ligated and anti-Cbl immunoprecipitates prepared therefrom were assayed for the associated protein tyrosine kinase activity, which increased upon ligation of FcgammaR. The increases were overcome upon activation of cellular protein kinase C by simultaneous addition of phorbol 12-myristate 13-acetate (PMA) to the ligated cells. Syk proved to be the most important tyrosine kinase bound to Cbl that served as the major substrate; essentially no tyrosine phosphorylation occurred in the anti-Cbl immunoprecipitates prepared from the cell lysate that had been depleted of Syk by prior immunoprecipitation with anti-Syk antibodies. Exposure of the (32)P-labeled cells to PMA resulted in phosphorylation of cellular Cbl on serine residues. Thus, protein kinase C-induced serine phosphorylation of Cbl suppressed its tyrosine phosphorylation by Syk as a result of tyrosine kinase inhibition by unknown mechanisms, leading to inhibition of Cbl-mediated signaling such as phosphatidylinositol 3-kinase activation.     

Membrane changes in murine macrophages after in-vivo stimulation and activation.

The expression of various receptors and other surface determinants on resident, glycogen-and Corynebacterium parvum- elicited mouse peritoneal macrophages has been described. Macrophage Fc (IgG2b) receptors and I-A antigens were slightly increased after stimulation and a more marked increase was shown after activation with C. parvum. Complement receptor expression was enhanced after stimulation but was markedly reduced after activation. C. parvum-elicited macrophages, and to a lesser extent glycogen-elicited macrophages, showed a reduction in lectin-like receptors which recognize bacterial cell-wall sugars. Surface mannosyl determinants of the macrophage membrane were apparently increased after activation. The environment thus can be seen to influence the expression of macrophage surface receptors and antigens. These alterations are likely to influence the role of the macrophage in the immune response.     

Fc receptor-mediated accumulation of macrophages in crescentic glomerulonephritis induced by anti-glomerular basement membrane antibody administration in WKY rats

Anti-glomerular basement membrane (GBM) glomerulonephritis induced in WKY rats is characterized by glomerular accumulation of CD8(+) T cells and monocytes/macrophages, followed by crescent formation. The mechanism of leukocyte accumulation after antibody binding to GBM is still unclear. To unveil an involvement of Fcgamma receptors (FcgammaR) in leukocytes recruitment we examined the expression of FcgammaR in glomeruli and the effects of the administration of F(ab')(2) fragment of anti-GBM antibody or FcgammaR blocking on the initiation and progression of this model. A gradual increase of FcgammaR mRNA expression in glomeruli during the time course of disease suggested their significance in the development of glomerulonephritis. Glomerular lesions and proteinuria were induced only in rats injected with intact IgG of anti-GBM antibody, but not with the F(ab')(2) fragment. In vivo blocking of FcgammaR by administering heat-aggregated IgG led to the decrease of mRNA expression for all types of FcgammaR (types 1, 2 and 3) and a significant amelioration of glomerulonephritis manifestations. By flow cytometry and immunohistochemistry FcgammaR2-expressing cells in glomeruli were identified as macrophages, but not CD8(+) T cells. The expression of FcgammaR1 and 3 was significantly decreased, and that of FcgammaR2 became undetectable in CD8(+) T cell-depleted rats. Thus, CD8(+) T cells may stimulate FcgammaR expression on macrophages, contributing to their glomerular accumulation and injury. These studies provide direct evidence for a crucial involvement of IgG Fc-FcgammaR interaction in glomerular recruitment of macrophages and following induction of anti-GBM glomerulonephritis in WKY rats.     

Interaction of membrane-bound Fc gamma receptors with the cytoskeletal matrix

Binding of ligands to cell surface receptors may induce an interaction of the receptors with the cell cytoskeleton. This interaction may decrease the solubility of the receptors in nonionic detergents. We studied effect of binding of various 125I-labeled immunoglobulin ligands to Fc gamma receptors on guinea pig peritoneal macrophages and human placental syncytiotrophoblast plasma membranes on an interaction of these receptors with the cytoskeletal matrix. The receptor-cytoskeleton association was evaluated by measurement radioactivity of bound ligands in pellets and supernatants obtained after lysis of cells or membranes in a nonionic detergent NP-40. Binding of soluble immune complexes or crosslinking of IgG bound induces much stronger insolubilization of the receptors than binding of monomeric or aggregated IgG. It shows that the interaction of the receptors with the cytoskeletal matrix strongly depends on the degree of cross-linking of the Fc gamma receptors by ligands bound. The observed effects were IgG Fc region-specific. Isolated, purified putative Fc gamma receptors from guinea pig peritoneal macrophages and from human placental syncytiotrophoblast plasma membranes do not interact with free G or F actin. We also studied association of the guinea pig peritoneal macrophage Fc gamma receptor with the cytoskeleton, before and after shedding of macrophage membrane proteins. The results obtained showed that the macrophages have only one class of Fc gamma receptors interacting with the cytoskeletal matrix. Effect of a cytoskeleton-destabilizing buffer and DNAse I on release of the receptors from the cytoskeleton suggests that insolubilization of ligand-Fc gamma R complexes was caused, at least partially, by an interaction of the receptors with actin filaments in the cytoskeleton. The results presented in this paper suggest that the cytoskeleton might play a role in transmission of signals from Fc gamma receptors to the cells. They underline the role of immune complexes as physiological ligands for Fc receptors and correlate well with activation of cells via their Fc receptors (e.g. superoxide burst) observed by other authors after treatment of the cells with immune complexes, but not with monomeric or aggregated IgG.     

Clearance of red cells by monoclonal IgG3 anti-D in vivo is affected by the VF polymorphism of Fcgamma RIIIa (CD16)

Human red cells (RBC) coated with IgG anti-D are cleared from the circulation to the spleen by macrophages which express IgG receptors (Fcgamma R). Polymorphisms of Fcgamma RIIa and Fcgamma RIIIa affect IgG binding in vitro, and may alter the efficiency of clearance of immune complexes in vivo. In a RBC clearance study, 22 Rh D-negative subjects were given 100-400 micro g human monoclonal or polyclonal IgG anti-D i.m. followed 48 h later by 51Cr-labelled D+ RBC. The half lives of the infused D+ RBC were determined, together with the coating levels of anti-D on the D+ RBC. Fcgamma RIIA and FcgammaRIIIA genotyping was performed. Large ranges of phagocytosis and extracellular lysis of RBC in vitro, and of half lives of RBC in vivo, were observed. Clearance of RBC coated with monoclonal IgG3 anti-D (BRAD-3) was more rapid in five subjects homozygous for Fcgamma RIIIa-F/F158 than in three subjects expressing the Fcgamma RIIIa-V158 allele (P = 0.024). This effect was not observed, however, for those individuals given polyclonal anti-D. There was also no significant difference in the efficiency of RBC destruction in vitro or of RBC clearance in vivo between the subjects analysed for individual genotypes or alleles or combinations of alleles. In conclusion, the presence of the Fcgamma RIIIa-V158 allele compromised the efficiency of removal of RBC coated with IgG3 anti-D.     

Phagocytic efficacy of macrophage-like cells as a function of cell cycle and Fcgamma receptors (FcgammaR) and complement receptor (CR)3 expression

Previous studies have shown that the efficiency of phagocytosis is a function of cell cycle and that phagocytosis promotes cell cycle progression. Because phagocytosis is dependent on cellular receptors we hypothesized that Fcgamma receptors (FcgammaR) and complement receptors (CR) expression varied with cell cycle. Consequently, we used centrifugal elutriation of macrophage-like cells, fluorescence activated cell sorting analysis and receptor staining to investigate expression of FcgammaR and CR as a function of cell cycle. We confirmed that FcgammaR expression on macrophage-like cells increased as the cells progressed from G1 to G2 phases. Moreover, CR3 expression varied as a function of cell cycle in a manner similar to FcgammaR. Correlation of receptor expression with cell size showed that FcgammaR and CR3 expression on macrophages was determined largely by cell size enlargement during the cell cycle. The efficacy of both Fc- and complement-mediated phagocytosis of live Cryptococcus neoformans (Cn) showed a biphasic pattern with the efficacy of phagocytosis decreasing when the cells approached the G1-S interface, which paralleled the changes in receptor surface expression when cells exited G1 phase. Live Cn cells were significantly more resistant to phagocytosis than dead cells at all stages of macrophage-like cell cycle. In contrast to live cells, the efficacy of phagocytosis of dead Cn decreased as surface receptor expression increased. Hence, the efficacy of phagocytosis in this system as function of cell cycle is not related to phagocytic receptor expression.     

Fcγ receptor expression on splenic macrophages in adult immune thrombocytopenia

Splenic macrophages play a key role in immune thrombocytopenia (ITP) pathogenesis by clearing opsonized platelets. Fcγ receptors (FcγR) participate in this phenomenon, but their expression on splenic macrophages and their modulation by treatment have scarcely been studied in human ITP. We aimed to compare the phenotype and function of splenic macrophages between six controls and 24 ITP patients and between ITP patients according to the treatments they received prior to splenectomy. CD86, human leucocyte antigen D‐related (HLA‐DR) and FcγR expression were measured by flow cytometry on splenic macrophages. The major FcγR polymorphisms were determined and splenic macrophage function was assessed by a phagocytosis assay. The expression of the activation markers CD86 and HLA‐DR was higher on splenic macrophages during ITP compared to controls. While the expression of FcγR was not different between ITP and controls, the phagocytic function of splenic macrophages was reduced in ITP patients treated with intravenous immunoglobulin (IVIg) within the 2 weeks prior to splenectomy. The FCGR3A (158V/F) polymorphism, known to increase the affinity of FcγRIII to IgG, was over‐represented in ITP patients. Thus, these are the first results arguing for the fact that the therapeutic use of IVIg during human chronic ITP does not modulate FcγR expression on splenic macrophages but decreases their phagocytic capabilities.     

Upregulation of the macrophage scavenger receptor in response to different forms of injury in the CNS

Summary The monoclonal antibody 2F8 was used to localize the macrophage scavenger receptor by immunohistochemistry. In control adult mice, macrophage scavenger receptor expression in the brain was restricted to stromal and epiplexus macrophages of the choroid plexus, meningeal macrophages and to perivascular sites. Microglia did not express the receptor. In the developing mouse brain, macrophage scavenger receptor expression was high on meningeal macrophages and detectable on immature microglia in the supraventricular corpus callosum, cingulum, cavum septum and the periaqueductal area. In the aged mouse brain, the pattern of macrophage scavenger receptor expression was no different from that in the young adult brain. Macrophage scavenger receptor expression on resident microglia and recruited macrophages was detected 24 h after an intrahippocampal injection of either lipopolysaccharide or kainic acid. Macrophage scavenger receptor expression was also detected in microglia 3 days after optic nerve crush both in the nerve segment distal to the crush site and in the superior colliculus. These studies indicate a potential role for the macrophage scavenger receptor in the CNS in the clearance of debris during acute neuronal degeneration.