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P Chien

Publications and source records attributed to P Chien.

At least 37 records · Page 2Linked to original sources
PubMed1993

In the absence of other Fc receptors, Fc gamma RIIIA transmits a phagocytic signal that requires the cytoplasmic domain of its gamma subunit.

The transmembrane isoform of Fc gamma RIII, Fc gamma RIIIA, is found on NK cells, cultured monocytes, and tissue macrophages in association with a dimer of an accessory subunit, either gamma or zeta. Functions of individual Fc receptors have been difficult to analyze due to coexpression of the receptors on hematopoietic cells and permanent cell lines expressing Fc receptors. cDNAs for the alpha and gamma subunits of Fc gamma RIIIA were cotransfected into COS-1 cells, which lack endogenous Fc receptors, to evaluate receptor-mediated phagocytosis and changes in [Ca2+]i. Transfectants both bound and phagocytosed IgG-sensitized erythrocytes and, following activation of Fc gamma RIIIA, increased [Ca2+]i. The gamma subunit was essential both for the surface expression of the receptor and for transduction of the phagocytic signal. Truncation of the gamma subunit cytoplasmic domain (amino acids 65-80) eliminated phagocytic function. Phorbol ester inhibited phagocytosis in a concentration-dependent manner, but did not affect IgG-sensitized erythrocytes binding, suggesting that a protein kinase C-dependent pathway inhibits phagocytosis. The data indicate that a tyrosine containing cytoplasmic domain within the gamma subunit is required for phagocytosis by Fc gamma RIIIA.

Amino Acid Sequence↗
PubMed1993

Conserved cytoplasmic tyrosine residues of the gamma subunit are required for a phagocytic signal mediated by Fc gamma RIIIA.

Fc receptors for immunoglobulins are found on many cells and are important in host defense. We transfected Fc gamma RIIIA, present on macrophages and natural killer (NK) cells, into COS-1 cells to study its role in phagocytosis and calcium mobilization in the absence of other Fc gamma receptors. Human Fc gamma RIIIA-alpha (CD16) was cotransfected with its associated chains, either Fc gamma RIIIA gamma or zeta. Both gamma and zeta were observed to induce a phagocytic signal, but gamma was at least sixfold more effective than zeta. Conservative substitution by phenylalanine of either one of the two cytoplasmic tyrosine residues in the gamma chain resulted in markedly diminished phagocytosis and calcium mobilization. Tyrphostin 23, an inhibitor of tyrosine kinases, reversibly inhibited phagocytosis. Further, in vitro kinase assays with the wild type and mutant gamma chains demonstrated that the wild type gamma chain, but not the mutant gamma chains, is phosphorylated. These results suggest that the cytoplasmic tyrosine residues and tyrosine phosphorylation are required for Fc gamma RIIIA to mediate two signal transduction events: phagocytosis and calcium mobilization.

Amino Acid Sequence↗
PubMed1992

Granulocyte Fc gamma receptor recognition of cell bound and aggregated IgG: effect of gamma-interferon.

Granulocyte Fc gamma receptors are important components in the recognition of IgG-coated cells and immune complexes. Two proteins have been identified on resting human granulocytes which function as Fc gamma receptors, Fc gamma RII (CD32) and Fc gamma RIII (CD16). A third protein, Fc gamma RI (CD64), is not constitutively expressed on resting granulocytes, but can be induced by activation with gamma-interferon. We examined the role of these three Fc gamma receptors on human granulocytes in the binding of both IgG-sensitized erythrocytes and soluble oligomeric IgG. In these studies we employed anti-Fc gamma receptor antibodies which complete for the Fc gamma RII and Fc gamma RIII ligand binding sites. Preincubation of granulocytes with saturating concentrations of high-affinity anti-Fc gamma RII monoclonal antibody did not alter the recognition of IgG sensitized human cells by granulocytes. Furthermore, ligand binding studies demonstrated that anti-Fc gamma RII antibody altered neither the number nor the affinity of granulocyte binding sites for human trimeric IgG. In contrast, Fab anti-Fc gamma RIII inhibited the binding of both IgG (anti-D) sensitized human RBCs and IgG sensitized sheep RBCs. Similarly, a reduction in the expression of Fc gamma RIII by treatment with phosphatidyl-inositol specific phospholipase C reduced PMN recognition of IgG-sensitized cells. Also, anti-Fc gamma RIII decreased the number of granulocyte binding sites for human IgG trimer without a change in receptor affinity. Fc gamma RI, which was induced by gamma-IFN, increased granulocyte recognition of both IgG sensitized RBCs and IgG trimer. These data suggest that Fc gamma RIII is the primary Fc gamma receptor on granulocytes which recognizes IgG sensitized RBCs and low molecular weight complexes of IgG. With gamma-interferon activated granulocytes, Fc gamma RI appears to enhance this recognition process.

Antibodies, Monoclonal↗
PubMed1992

Operative treatment of unstable pelvic fractures.

Unstable pelvic fractures are serious injuries. Non-operative treatment gives poor early and late results. We report the results of operative treatment of 28 unstable pelvic fractures; eight were rotatory unstable and 20 were both rotatory and vertically unstable. The average age of the patients was 33 years. All the patients underwent operation according to a definite protocol for internal fixation. Mobilization was started within 2 weeks after the operation; the average hospital stay was 9.8 weeks. With an average follow-up of 19 months, there was no mortality. In 20 patients there was no discomfort, five patients had moderate back pain and four patients walked with a limp due to leg length inequality and back pain. Twenty patients returned to gainful employment. Complications included one deep wound infection, two superficial wound infections, one dislodgement of the external fixator, and residual interval rotatory deformity of the hemipelvis. We conclude that operative treatment of unstable pelvic fractures is safe and that the early and late results are much better than those treated by non-operative means.

Adult↗
PubMed1992

Calcium signalling by the high affinity macrophage Fc gamma receptor requires the cytosolic domain.

Hematopoietic cells express multiple receptors which bind the Fc domain of IgG. We utilized transfection of COS-1 cells, a cell line which lacks endogenous Fc receptors, to study the expression and function of Fc gamma RI, the high affinity Fc gamma receptor in the absence of other Fc gamma receptors. Fc gamma RI was efficiently expressed in transiently transfected COS-1 cells as measured by flow cytometry and the binding of IgG sensitized RBCs (EA). In addition, analysis at the single cell level demonstrated that individually transfected COS-1 cells release cytosolic free Ca2+ [(Ca2+)i] upon activation with anti-Fc gamma RI antibody. The calcium response required Fc gamma RI cross-linking. COS-1 cells transfected with mutant Fc gamma RI lacking the cytosolic domain expressed Fc gamma receptors and bound EA as well as wild type receptors, but failed to induce an increase in [Ca2+]i. These data indicate that Fc gamma RI in the absence of other Fc gamma receptors mediates a calcium signal and that the cytoplasmic domain of Fc gamma RI contains the elements required for calcium dependent signal transduction.

Amino Acid Sequence↗
PubMed1992

Characterization of Fc gamma receptors on a human erythroleukemia cell line (HEL).

It has been established that human platelets express a single class of Fc gamma receptors that has been designated Fc gamma RII. However, the function of this receptor on these cells and its regulation are less certain. Studies to further investigate Fc gamma RII on platelets are limited by the inability to culture platelets in vitro. Therefore, identification of a human cell line that expresses Fc gamma RII as its only Fc gamma receptor as well as other platelet characteristics would be of potential importance. To this end, we examined Fc gamma receptor expression by the human erythroleukemia (HEL) cell line, which expresses platelet/megakaryocyte surface proteins. Flow cytometry studies on HEL cells with anti-Fc gamma receptor monoclonal antibodies revealed that, similar to platelets and megakaryocytes, Fc gamma RII is the only Fc gamma receptor expressed on the cell surface. Furthermore, Northern blot analysis revealed that Fc gamma RII is the only Fc gamma receptor mRNA present. Stimulation with dimethylsulfoxide (DMSO) or 12-O-tetradecanoylphorbol-13-acetate (TPA) did not alter Fc gamma RII protein or mRNA expression. Ligand binding studies with [125I]IgG trimer indicated that HEL cells express 92,240 +/- 5030 binding sites per cell, with a kd of 1.94 +/- 0.31 x 10(-8) M. Similar to human platelets, HEL cells preferentially bound oligomeric IgG, and this binding was ionic strength dependent. These observations are similar to those previously observed with Fc gamma RII on human platelets and suggest that the HEL cell Fc gamma receptor is similar, if not identical to the platelet Fc gamma RII receptor. HEL cells may serve as a model for the study of platelet/megakaryocyte Fc gamma RII.

Humans↗
PubMed1991

Human Fc gamma RII, in the absence of other Fc gamma receptors, mediates a phagocytic signal.

Fc gamma receptors are important components in the binding and phagocytosis of IgG-sensitized cells. Studies on the role of these receptors have been limited by the fact that most hematopoietic cells express more than one Fc gamma receptor. We studied the role of Fc gamma RIIA in isolation on a human erythroleukemia cell line (HEL) which expresses Fc gamma RIIA as its only Fc gamma receptor. HEL cells were observed to bind and phagocytose IgG-sensitized red blood cells (RBCs) in a dose-dependent manner. We then examined the role of Fc gamma RI and Fc gamma RII in isolation and in combination, in transfected COS-1 cells. Fc gamma RIIA-transfected COS cells also mediated both the binding and phagocytosis of IgG-sensitized RBCs. In contrast, phagocytosis was not observed in Fc gamma RI-transfected cells, although these cells avidly bound IgG-sensitized RBCs. Furthermore, coexpression of both receptors by doubly transfected cells did not affect the phagocytic efficiency of Fc gamma RIIA. These studies establish that Fc gamma RIIA can mediate phagocytosis and suggest that transfected COS-1 cells provide a model for examining this process. Since HEL cells exhibit characteristics of cells of the megakaryocyte-platelet lineage, including expression of Fc gamma RII as the only Fc gamma receptor, Fc gamma RIIA on megakaryocytes and platelets may be involved in the ingestion of IgG-containing immune complexes. Furthermore, these studies indicate that Fc gamma RI and Fc gamma RIIA differ in their requirements for transduction of a phagocytic signal.

Antigens, Differentiation↗
PubMed1990

Monocyte/macrophage Fc gamma RIII, unlike Fc gamma RIII on neutrophils, is not a phosphatidylinositol-linked protein.

The low affinity IgG Fc receptor, Fc gamma RIII, expressed on circulating neutrophils, natural killer (NK) cells, and tissue macrophages, is involved in effector functions such as cytotoxicity and immune complex clearance by these cells. While Fc gamma RIII is reported to be a phosphatidylinositol (PI)-linked, rather than peptide-linked, protein on neutrophils and NK cells, its membrane linkage in macrophages has not been studied. We examined the sensitivity of Fc gamma RIII to cleavage by PI-specific phospholipase C (PI-PLC) in cultured monocytes and alveolar tissue macrophages and report that this receptor is not PI-linked on these cells. We also observed normal levels of Fc gamma RIII on cultured monocytes of a patient with paroxysmal nocturnal hemoglobinuria, a disease in which PI-linked proteins are deficient. The results suggest that Fc gamma RIII occurs solely in a transmembrane form in cells of the monocyte/macrophage lineage. In addition, we studied Fc gamma RIII on a cloned NK cell line and found it to be resistant to the effects of PI-PLC under conditions that cleaved Fc gamma RIII on neutrophils. Taken together, our results provide evidence for a distinct form of Fc gamma RIII that differs from the neutrophil receptor in its structure and, possibly, in its function.

Antigens, Differentiation↗
PubMed1989

Monocyte Fc gamma receptor recognition of cell-bound and aggregated IgG.

Monocyte and macrophage Fc gamma receptors are important components in the recognition of IgG-coated cells and IgG-containing immune complexes. Two proteins have been identified on human peripheral blood monocytes that can function as Fc gamma receptors, Fc gamma RI (70 Kd) and Fc gamma RII (40 Kd). We studied the role of Fc gamma RI and Fc gamma RII on human monocytes by examining their binding of IgG-sensitized cells (human IgG anti-D-coated RBCs and rabbit IgG-sensitized sheep RBCs) and their binding of human trimeric IgG. To examine the function of monocyte Fc gamma RII, we used an anti-Fc gamma RII monoclonal antibody (MoAb) that competes for the Fc gamma RII ligand binding site. Preincubation of monocytes with saturating concentrations of anti-Fc gamma RII MoAb did not alter the recognition of IgG (anti-D)-sensitized human RBCs by monocytes. Furthermore, ligand-binding studies demonstrated that anti-Fc gamma RII antibody altered neither the number nor the affinity of monocyte-binding sites for human IgG trimer. Anti-Fc gamma RII inhibited monocyte binding of rabbit IgG-sensitized sheep RBCs, but only at low ionic strength or temperature when increased numbers of monocyte Fc gamma RII were expressed. At low ionic strength and 4 degrees C, anti-Fc gamma RII also partially inhibited monocyte binding of human trimeric IgG. Thus, monocyte Fc gamma RII does not appear to recognize IgG-sensitized RBCs or trimeric IgG at physiologic temperatures and ionic strength. The data suggest that Fc gamma RI is the primary Fc gamma receptor on monocytes involved in the binding of IgG (anti-D)-sensitized erythrocytes and low mol wt complexes of IgG.

Animals↗
PubMed1989

Modulation of Fc gamma receptors on the human macrophage cell line U-937.

Macrophage receptors for the Fc portion of IgG play an important role in host defense, inflammation, and the pathophysiology of autoimmune disorders. We studied one important function of Fc gamma receptors--the ability to bind IgG ligand. Direct binding experiments analyzed by nonlinear regression were consistent with monomeric and trimeric IgG binding to a single class of receptors. Indirect binding experiments were also consistent with this interpretation and revealed that both IgG ligands completely inhibited the binding of the other. In addition, we used an anti-Fc gamma RII monoclonal antibody known to compete for the Fc gamma RII ligand binding site and known to inhibit IgG trimer binding to other cells. At concentrations of antibody which saturated all Fc gamma RII sites, no inhibition of IgG trimer binding to U-937 was observed. This was evident despite the observation that the numbers of Fc gamma RI and Fc gamma RII, determined by equilibrium binding of monomeric IgG and anti-Fc gamma RII antibody, respectively, were similar on U-937. Monoclonal antibodies were used to compare the expression and modulation of Fc gamma receptor proteins with their ability to bind monomeric and trimeric IgG ligands. Dexamethasone and gamma-interferon regulated U-937 Fc gamma RI protein expression and IgG ligand binding to a similar degree. In contrast, the expression of Fc gamma RII was not altered by dexamethasone. Interferon-gamma primarily stimulated Fc gamma RI, as determined both by reactivity with monoclonal antibody (227 +/- 26%) and by monomeric IgG ligand binding (350 +/- 151%). In addition, dexamethasone inhibited by 33% the gamma-interferon effect on Fc gamma RI protein and by 56% the effect on Fc gamma RI binding of monomeric IgG. Preincubation of U-937 with anti-Fc gamma RII antibody did not alter the effect of dexamethasone or gamma-interferon on IgG trimer binding. These data indicate that on U-937 cells Fc gamma RII does not function in the recognition of small molecular weight immune complexes and that Fc gamma RI is the Fc gamma receptor responsible for the binding of both monomeric and trimeric human IgG. Furthermore, Fc gamma RI is the major Fc gamma receptor on U-937 that is modulated by both gamma-interferon and glucocorticoids.

Antibodies, Monoclonal↗
PubMed1989

Modulation of human mononuclear phagocyte Fc gamma RII mRNA and protein.

Human monocytes and macrophages express three different classes of cell surface receptors for the Fc portion of IgG, Fc gamma RI (CD64), Gc gamma RII (CD32), and Fc gamma RIII (CD16). We utilized a cDNA probe for Fc gamma RII to examine the modulation of Fc gamma RII mRNA by dexamethasone, a synthetic glucocorticoid, and interferon-gamma. We also determined the changes in the expression of both Fc gamma RI and Fc gamma RII protein following treatment with these agents by flow cytometry. In studies performed with the monocyte-like cell line. U937, Northern blot analysis revealed that cells treated with interferon-gamma showed a 2.5-fold increase in Fc gamma RII mRNA levels that was maximal at 14 hr and declined to 1.4-fold over baseline by 48 hr of incubation. Treatment of U937 cells with dexamethasone did not significantly change the level of Fc gamma RII transcripts, but was able to inhibit by up to 50% the increase seen following interferon-gamma treatment. The expression of Fc gamma RII protein on U937 cells was increased 56-72% after 16-24 hr of interferon-gamma treatment, but was only 18% over baseline after 48 hr of incubation. Treatment with dexamethasone caused a small, but significant, decrease in Fc gamma RII protein, and inhibited by 20-60% the induction of Fc gamma RII by interferon-gamma. The modulation by dexamethasone and interferon-gamma of Fc gamma RI protein expression on U937 cells was markedly different from that of Fc gamma RII in both magnitude and kinetics. Interferon-gamma treatment increased Fc gamma RI expression by 240% at 16 hr, and Fc gamma RI remained elevated through 48 hr. Treatment with dexamethasone decreased Fc gamma RI expression by 39%, and also inhibited by 40% the increase induced by interferon-gamma. In contrast to the findings with U937 cells, dexamethasone and/or interferon-gamma treatment had no significant effect on Fc gamma RII mRNA levels or protein expression in monocytes. However, interferon-gamma treatment increased Fc gamma RI expression on monocytes, and this increase was further augmented by treatment with dexamethasone. These data indicate that the modulation of Fc gamma RII on U937 cells is at least in part due to changes in steady state levels of Fc gamma RII mRNA. The difference between the magnitude of the changes in Fc gamma RII mRNA and protein suggests that some translational or post-translational control is involved in regulating the expression of Fc gamma RII.(ABSTRACT TRUNCATED AT 400 WORDS)

Antibodies, Monoclonal↗
PubMed1989

Fc gamma receptor recognition of IgG ligand by human monocytes and macrophages.

We examined the binding characteristics of human monocytes and macrophages with the IgG ligands, human monomeric IgG and a small human IgG aggregate, trimeric IgG. Our purpose was to utilize fresh monocytes, in vitro cultured monocytes, and alveolar macrophages in direct and indirect binding experiments. Freshly isolated monocytes expressed only a single binding site for IgG monomer and IgG trimer. In contrast, in vitro cultured monocytes, gamma-interferon-treated monocytes, and freshly isolated alveolar macrophages expressed a single binding site for IgG monomer and, in addition, a high and low affinity binding site for IgG trimer. The high affinity binding site for IgG trimer (Kd approximately equal to 1 nM) appeared identical to the binding site for IgG monomer. The low affinity binding site for IgG trimer (Kd = 50 to 250 nM) appeared to be due to Fc gamma RII, because antibody to Fc gamma RII inhibited its expression. Since Fc gamma RII, in contrast to Fc gamma RI, does not bind monomeric IgG, the data suggest that this low affinity receptor for trimeric IgG, Fc gamma RII, can bind low molecular weight circulating immune complexes at concentrations 10- to 100-fold lower than Fc gamma RI. Thus, these studies suggest that at 37 degrees C, macrophage Fc gamma RII may play a functional role in the recognition of small molecular weight immune complexes.

Antigens, Differentiation↗
PubMed1988

Modulation of the human monocyte binding site for monomeric immunoglobulin G by activated Hageman factor.

Macrophage Fc gamma receptors play a significant role in inflammation and host defense. One monocyte/macrophage Fc gamma receptor, Fc gamma RI, the binding site for monomeric IgG, appears to be especially responsive to modulatory signals by hormones and mediators. Since Factor XIIa is generated during inflammation, we studied the effect of XIIa on Fc gamma RI. Factor XIIa, in a concentration-dependent manner (0.01-0.19 microM), reduced the number of monocyte binding sites for monomeric IgG up to 80% without altering the affinity of binding. Its precursor, Factor XII, and the low molecular weight fragment of XIIa, lacking most of the heavy chain region, did not reduce the expression of Fc gamma RI. Neither corn trypsin inhibitor (36 microM) nor diisopropylfluorophosphate (3.6 mM) diminished the effect of Factor XIIa on Fc gamma RI, although each completely inhibited the coagulant and amidolytic activity contained on the light chain of Factor XIIa. Protein synthesis was not a requirement for this effect of Factor XIIa, nor was internalization of Fc gamma RI necessary. In contrast to similar concentrations of IgG, Factor XIIa failed to displace significantly monomeric IgG from the monocyte surface, suggesting that Factor XIIa does not directly compete for Fc gamma RI. The data suggest that the heavy chain of XIIa, which contains domains that may have cell hormone activity, also contains a domain that regulates Fc gamma RI on monocytes. In addition to other hormones and mediators, Factor XIIa may serve a regulatory function in modulating Fc gamma receptor expression during inflammation.

Binding Sites↗
PubMed1987

Effect of danazol in immune thrombocytopenic purpura.

Danazol and vinblastine are effective in many patients with chronic immune thrombocytopenic purpura (ITP). To evaluate the mechanism of action of these drugs, we studied six consecutive patients with chronic ITP treated with danazol and one treated with vinblastine. All the patients responded clinically without a notable change in the level of platelet-associated IgG. Instead, the clinical response to therapy was associated with a decrease in the number of monocyte binding sites for monomeric IgG (Fc receptors). In one patient, clinical relapse was associated with a spontaneous 2.7-fold increase in the number of monocyte Fc (IgG) receptors, without a change in the level of platelet-associated immunoglobulin. A decrease in the number of monocyte Fc (IgG) receptors following vinblastine infusion was associated with a clinical remission. We conclude that the clinical course of ITP may be influenced by the expression of monocyte or macrophage Fc (IgG) receptors. Danazol and vinblastine may mediate their clinical effect, at least in part, by influencing the number of available Fc (IgG) receptors on phagocytic cells.

Adolescent↗
PubMed1986

Increased monocyte Fc(IgG) receptor expression in sarcoidosis.

Since the macrophage Fc(IgG) receptor appears to be modulated by inflammatory stimuli, we measured the binding of monomeric IgG to monocytes and alveolar macrophages from patients with pulmonary sarcoidosis. Equilibrium binding studies were performed, and the number and affinity of Fc(IgG) receptors were calculated from Scatchard plots of the data. Monocytes from patients with sarcoidosis had nearly twice the number of binding sites for monomeric IgG as did the monocytes from normals. In contrast to the findings with monocytes, alveolar macrophages from patients with sarcoidosis did not have a greater number of monomeric IgG binding sites than did normal alveolar macrophages. These findings are consistent with those on the activation of circulating monocytes in sarcoidosis. That the number of Fc(IgG) receptors on sarcoid alveolar macrophages was not greater than that on normal alveolar macrophages suggests that Fc(IgG) receptor activity on alveolar macrophages does not reflect the activated state of sarcoidosis.

Adult↗
PubMed1986

The binding of monomeric IgG to human blood monocytes and alveolar macrophages.

Macrophage receptor sites for IgG are important in the immune clearance of particles both from the blood and lung. We studied the number, affinity, and density of binding sites for monomeric IgG on human blood monocytes and alveolar macrophages. Monocytes and alveolar macrophages had a similar affinity for monomeric IgG at 37 degrees and 4 degrees C. The half-time for dissociation of the IgG-receptor complex was also similar for both cells. However, alveolar macrophages expressed approximately 5-fold more IgG binding sites than monocytes at both 37 degrees and 4 degrees C. Nevertheless, when cell surface area was estimated, these cells expressed a similar density of IgG binding sites (monocytes = 110 +/- 14.8 IgG binding sites/square micron; pulmonary macrophages = 138 +/- 46.9 IgG binding sites/square micron; p greater than 0.50). Gamma interferon increased the number and density of monocyte binding sites for monomeric IgG by 162 +/- 89%. Furthermore, patients with sarcoidosis, a disorder in which gamma interferon is spontaneously elaborated, expressed a similar increase in the number of IgG binding sites per monocyte, from 24,968 +/- 1,361 for normal subjects to 44,860 +/- 6,652 for patients with sarcoidosis. However, alveolar macrophages from 5 patients with sarcoidosis expressed a normal number of IgG binding sites. These data suggest that there is no major alteration in the Fc(IgG) receptor as monocytes differentiate into alveolar macrophages. Both gamma interferon treatment and sarcoidosis are associated with enhanced expression of the Fc(IgG) receptor on monocytes.

Binding Sites↗