Insulin inhibits phagocytosis in normal human neutrophils via PKCalpha/beta-dependent priming of F-actin assembly.

OBJECTIVE: This study investigated the effects of insulin on the phagocytosis of C3bi - and IgG-opsonized yeast particles in normal human neutrophils. METHODS: Neutrophils were incubated in different insulin concentrations for 30 minutes and stimulated by C3bi - or IgG-opsonized yeast particles. Phagocytosis was quantified by both light microscopy and FACscan flow cytometry. Laser confocal microscopy was used for quantification of F-actin levels. RESULTS: Elevated insulin concentrations decreased neutrophil phagocytosis of both types of targets. This defect was shown to be in part due to a delayed phagocytosis in the presence of insulin. Following a 30 minute incubation, insulin was found to increase the accumulation of cortical F-actin, without affecting the total cellular F-actin content. The specific PKCalpha/beta inhibitor, Go6976, abolished the insulin-mediated increase in cortical F-actin content and both Go6976 and the PKCalpha/beta/delta/epsilon-specific inhibitor GF109203X reversed the inhibitory effects of insulin on phagocytosis. CONCLUSION: Hyperinsulinemia in vitro can inhibit phagocytosis of opsonized targets in normal human neutrophils. This effect of insulin is dependent on activation of PKCalpha and/or PKCbeta, and these insulin signals may interfere with the dynamic assembly/disassembly and/or distribution of F-actin, which is required for the phagocytosis process.

Target cell CD47 regulates macrophage activation and erythrophagocytosis.

The ubiquitously expressed cell surface glycoprotein CD47 (integrin-associated protein, IAP) was originally identified as a regulator of integrin-dependent leukocyte responses to extracellular matrix proteins. However, it has been shown that CD47 has several important functions in addition to regulating integrin activation. Extensive studies in murine systems have shown that CD47 on erythrocytes and other cells can function as a regulator of target cell phagocytosis, by binding to the inhibitory receptor SIRPalpha on macrophages. In this way, macrophages are less likely to phagocytose an autoimmune sensitized cell with CD47 on its surface than a CD47-deficient cell where this inhibitory mechanism will not be engaged. The CD47-SIRPalpha interaction seems to be important in limiting destruction of host cells in experimental models of autoimmune diseases like autoimmune hemolytic anemia (AIHA) or immune thrombocytopenia, where macrophages destroy antibody or complement opsonized cells.

CD47 (integrin-associated protein) engagement of dendritic cell and macrophage counterreceptors is required to prevent the clearance of donor lymphohematopoietic cells.

Integrin-associated protein (CD47) is a broadly expressed protein that costimulates T cells, facilitates leukocyte migration, and inhibits macrophage scavenger function. To determine the role of CD47 in regulating alloresponses, CD47(+/+) or CD47(-/-) T cells were infused into irradiated or nonconditioned major histocompatibility complex disparate recipients. Graft-versus-host disease lethality was markedly reduced with CD47(-/-) T cells. Donor CD47(-/-) T cells failed to engraft in immunodeficient allogeneic recipients. CD47(-/-) marrow was unable to reconstitute heavily irradiated allogeneic or congenic immune-deficient CD47(+/+) recipients. These data suggested that CD47(-/-) T cells and marrow cells were cleared by the innate immune system. To address this hypothesis, dye-labeled CD47(-/-) and CD47(+/+) lymphocytes or marrow cells were infused in vivo and clearance was followed. Dye-labeled CD47(-/-) cells were engulfed by splenic dendritic cells and macrophages resulting in the clearance of virtually all CD47(-/-) lymphohematopoietic cells within 1 day after infusion. Host phagocyte-depleted CD47(+/+) recipients partially accepted allogeneic CD47(-/-) T cells. Thus, dendritic cells and macrophages clear lymphohematopoietic cells that have downregulated CD47 density. CD47 expression may be a critical indicator for determining whether lymphohematopoietic cells will survive or be cleared.

CD47-signal regulatory protein alpha (SIRPalpha) regulates Fcgamma and complement receptor-mediated phagocytosis.

In autoimmune hemolytic anemia (AIHA), circulating red blood cells (RBCs) opsonized with autoantibody are recognized by macrophage Fcgamma and complement receptors. This triggers phagocytosis and elimination of RBCs from the circulation by splenic macrophages. We recently found that CD47 on unopsonized RBCs binds macrophage signal regulatory protein alpha (SIRPalpha), generating a negative signal that prevents phagocytosis of the unopsonized RBCs. We show here that clearance and phagocytosis of opsonized RBCs is also regulated by CD47-SIRPalpha. The inhibition generated by CD47-SIRPalpha interaction is strongly attenuated but not absent in mice with only residual activity of the phosphatase Src homology 2 domain-containing protein tyrosine phosphatase (SHP)-1, suggesting that most SIRPalpha signaling in this system is mediated by SHP-1 phosphatase activity. The macrophage phagocytic response is controlled by an integration of the inhibitory SIRPalpha signal with prophagocytic signals such as from Fcgamma and complement receptor activation. Thus, augmentation of inhibitory CD47-SIRPalpha signaling may prevent or attenuate RBC clearance in AIHA.

Different effects of glucose on extracellular and intracellular respiratory burst response in normal human neutrophils activated with the soluble agonist fMet-Leu-Phe.

AIMS: The study evaluated the effects of glucose concentration on the extracellular and intracellular activation of the respiratory burst in fMet-Leu-Phe-stimulated normal human neutrophils. METHODS: Specific extracellular respiratory burst activity was measured as superoxide dismutase (SOD)-inhibitable cytochrome c reduction. Intracellular respiratory burst activity was studied using luminol-enhanced chemiluminescence in the presence of SOD and catalase, to quench extracellular chemiluminescence activity. Myeloperoxidase (MPO) release from activated neutrophils was studied by using the guaiacol technique. RESULTS: The extracellular respiratory burst following activation with 1 microM fMet-Leu-Phe was significantly reduced at 15 and 25 mM D-glucose (9.5 +/- 1.0 and 8.5 +/- 0.8 nmol/10(6) cells and 10 min; P < 0.01 and P < 0.001, respectively) as compared with that at 5 mM glucose (10.3 +/- 1.0 nmol/10(6) cells and 10 min). When specifically studying the intracellular respiratory burst, no difference was found between the responses at 5, 15 or 25 mM glucose. Increasing glucose concentrations also reduced the secretion of MPO from fMet-Leu-Phe-activated neutrophils. CONCLUSIONS: Elevated glucose concentrations inhibit the generation of extracellularly released reactive oxygen metabolites but have no effects on the intracellular respiratory burst in fMet-Leu-Phe-stimulated normal human neutrophils.

Role of CD47 as a marker of self on red blood cells.

The immune system recognizes invaders as foreign because they express determinants that are absent on host cells or because they lack "markers of self" that are normally present. Here we show that CD47 (integrin-associated protein) functions as a marker of self on murine red blood cells. Red blood cells that lacked CD47 were rapidly cleared from the bloodstream by splenic red pulp macrophages. CD47 on normal red blood cells prevented this elimination by binding to the inhibitory receptor signal regulatory protein alpha (SIRPalpha). Thus, macrophages may use a number of nonspecific activating receptors and rely on the presence or absence of CD47 to distinguish self from foreign. CD47-SIRPalpha may represent a potential pathway for the control of hemolytic anemia.

Effects of insulin on N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-stimulated production of reactive oxygen metabolites from normal human neutrophils.

OBJECTIVE AND DESIGN: To further understand the mechanisms behind defective neutrophil function in diabetes mellitus, the ability of insulin to affect the production and metabolism of reactive oxygen metabolites in normal human neutrophils was studied. MATERIALS AND METHODS: Neutrophil granulocytes from healthy adults were studied for their N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-stimulated production of reactive oxygen metabolites and release of myeloperoxidase or elastase following treatment with insulin. RESULTS: Preincubation of the neutrophils for 30 min with insulin (40-320 microU/ml), before activation with 1 microM fMet-Leu-Phe, revealed that the hormone at 80 and 160 microU/ml reduced the luminol-enhanced chemiluminescence without affecting the superoxide secretion. The insulin-induced reduction of the chemiluminescence response was reversed by the addition of exogenous peroxidase and was also paralleled by a reduced myeloperoxidase activity, with no effect on the elastase activity, in cell-free supernatants from fMet-Leu-Phe-stimulated neutrophils. Superoxide dismutase removed the inhibitory effect of insulin on myeloperoxidase activity. CONCLUSIONS: These results suggest that elevated levels of insulin do not affect the NADPH-oxidase activity but, together with superoxide anions, interfere with myeloperoxidase availability and a subsequent myeloperoxidase-dependent generation of reactive oxygen metabolites in fMet-Leu-Phe-stimulated normal human neutrophils.

Hyperglycemia in vitro attenuates insulin-stimulated chemokinesis in normal human neutrophils. Role of protein kinase C activation.

This study was performed to test whether the inhibitory effect of elevated D-glucose concentrations on insulin-stimulated chemokinesis in normal human neutrophils is mediated by increase in protein kinase C (PKC) activity. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) at 0-100 nM dose-dependently inhibited neutrophil random locomotion in the absence of insulin. Sub-optimal concentrations of PMA (0.1-0.5 nM) inhibited the chemokinetic effect of 160 microU/mL insulin in a dose-dependent way. The specific PKC inhibitor bisindolylmaleimide (GF 109203x) did not affect the insulin-stimulated chemokinesis at 5 mM glucose but restored the chemokinetic effect of insulin at 15 mM glucose. These results therefore suggest that glucose-induced PKC activation may mediate the inhibitory effects of high glucose levels on insulin-stimulated chemokinesis in normal human neutrophils.

The glucose concentration modulates N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-stimulated chemokinesis in normal human neutrophils.

The effects of glucose concentration on the chemokinetic effects of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) was evaluated for normal human neutrophils using a direct microscopic assay. fMet-Leu-Phe increased the rate of locomotion in the absence of glucose, but the chemokinetic effect of fMet-Leu-Phe was most potent at 5 mM glucose and not further changed at 15 mM glucose. The chemokinetic effects of fMet-Leu-Phe and glucose were essentially the same in blood clot-isolated and gradient-isolated neutrophils. However, in gradient-isolated neutrophils, the rate of locomotion under different experimental conditions was strictly negatively correlated to the fraction of non-locomoting cells and the degree of adhesion to the substratum. These results indicate that the chemokinetic effects of fMet-Leu-Phe are regulated by the glucose concentration by inducing locomotor activity in otherwise non-locomoting cells and by improving adhesion to the substratum.

Insulin-stimulated chemokinesis in normal human neutrophils is dependent on D-glucose concentration and sensitive to inhibitors of tyrosine kinase and phosphatidylinositol 3-kinase.

This study shows that D-glucose and insulin, alone and in certain combinations, have chemokinetic effects on neutrophil granulocytes from healthy humans. A stimulatory chemokinetic effect of insulin was present at 40-160 microU/mL insulin but only in the presence of 5 mM, and not at 15 mM, D-glucose. D-Glucose alone dose-dependently increased the neutrophil locomotion, showing a maximum effect at 5-15 mM and a return toward the basal locomotion at 25 mM glucose. Because the stimulatory chemokinetic effects of 5 and 15 mM D-glucose alone were the same, it seems that the high glucose level does not inhibit the basic motile properties of the cells but may generate intracellular signals interfering with the signal transduction underlying the insulin effect. The tyrosine kinase inhibitor, genistein, or the phosphatidylinositol 3-kinase inhibitor, wortmannin, abolished the chemokinetic effect of 160 microU/mL insulin in the presence of 5 mM D-glucose. This indicates that the insulin effect on locomotion is indeed mediated by receptor-associated tyrosine kinase activation and involving phosphatidylinositol 3-kinase.

Effects of D-glucose on chemokinesis and resting production of reactive oxygen species in neutrophil granulocytes of lean or obese-hyperglycemic mouse.

The response to D-glucose (0-21 mM) was studied in neutrophil granulocytes from obese, hyperglycemic and hyperinsulinemic Umeå ob/ob mice and their lean, littermate controls in order to further elucidate the effects of in vivo and in vitro hyperglycemia on neutrophil function. Neutrophil random locomotion on glass and neutrophil resting luminol-enhanced chemiluminescence in cell suspension were studied. Random locomotion was stimulated by D-glucose in neutrophils from both Umeå ob/ob and control mice but the locomotive activity in Umeå ob/ob mouse neutrophils was significantly higher than that found in the controls at 4-21 mM glucose. In both types of mice, the stimulatory effect of D-glucose on random locomotion was diminished at 21 mM glucose (not significantly different from that at 0 mM glucose). Resting chemiluminescence from mouse neutrophils was also stimulated by glucose but here the magnitude of response was similar in neutrophils from both types of mice. These results indicate that chronic hyperglycemia and hyperinsulinemia in the Umeå ob/ob mouse may be associated with an increased neutrophil random locomotive activity but a similar resting production of reactive oxygen species, as compared with neutrophils from control mice at physiological and hyperglycemic glucose concentrations in vitro.

D-glucose but not insulin reduces N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-induced shape changes in suspended human neutrophils.

The effects of glucose (5-25 mM) and insulin concentration (40-320 microU/ml) on the cell shape of neutrophil granulocytes from healthy humans were studied. Both non-activated and N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-activated neutrophils in suspension were used as a model for initial chemotactic activation of neutrophil locomotion. D-glucose, but not the non-metabolizable analogue 3-O-methyl-D-glucose, dose-dependently reduced the fMet-Leu-Phe-induced (10(-8)M) neutrophil elongation. Insulin, either alone or in combination with 25 mM D-glucose, was without effect on the fMet-Leu-Phe-induced neutrophil elongation. Furthermore, the inhibitory effect of D-glucose was observed already after 1 min of exposure to D-glucose and fMet-Leu-Phe. D-glucose diminished the fraction of neutrophils with elongated locomotor shape by changing it into an irregular cell shape, suggesting that at least part of the D-glucose effect could be associated with mechanisms determining the typical locomotor shape. The present results suggest that D-glucose through its metabolism, but without the involvement of insulin, reduces chemotactically induced elongation to a locomotor neutrophil shape, and thus neutrophil motility, and that this effect of glucose appears prior to adhesion. This glucose-induced inhibition of the neutrophil chemotactic response may be involved in the neutrophil deficiency seen in diabetes mellitus.