Different abilities of two distinct Fc gamma receptors on guinea pig polymorphonuclear leukocytes to trigger the arachidonic acid metabolic cascade

The nature of signals transmitted by two Fc gamma receptors (Fc gamma 2R for IgG2 and Fc gamma 1/gamma 2R for both IgG2 and IgG1) on guinea pig polymorphonuclear leukocytes was investigated. The specific binding of hen ovalbumin (OA)-complexed IgG1 antibody to Fc gamma 1/gamma 2R did not seem to trigger the release of [3H]arachidonic acid from the cells prelabeled with [3H]arachidonic acid. In contrast, marked release occurred on the binding of OA-complexed IgG2 antibody to the cells. This reaction was not inhibited, but rather enhanced, by the Fab' of a monoclonal antibody to Fc gamma 1/gamma 2R. Therefore, a signal for the activation of the arachidonic acid metabolic cascade was found to be transmitted by Fc gamma 2R, but scarcely by Fc gamma 1/gamma 2R.     

Effect of glycosylation inhibitors on binding properties of the Fc gamma receptors from guinea pig peritoneal macrophages.

Guinea pig peritoneal macrophages possess on their surfaces receptors for the Fc region of IgG immunoglobulins (Fc gamma R). The cells treated with the glycosylation inhibitors tunicamycin or monensin interacted with IgG with a higher affinity and showed a lower number of IgG-binding sites in comparison with control cells. This indicates that the interaction of IgG with the macrophage Fc gamma receptor depends on the degree of glycosylation of the cell surface glycoconjugates and that glycosylation of the macrophage Fc gamma receptor is important for the expression of the mature form of the receptor.     

Inhibition of anti-IgM and growth factor-induced proliferation of guinea pig B cells by one of two distinct Fc gamma receptors on the cells

Guinea pig B cells were found to proliferate when co-stimulated with F(ab')2 of rabbit anti-guinea pig IgM and human 12-kDa B cell growth factor (BCGF), though the proliferation did not occur with the replacement of the F(ab')2 by its parent IgG antibody. In addition, the intact antibody inhibited the proliferation induced by F(ab')2 of anti-IgM and BCGF. Because both two distinct types of FcR for IgG on the B cells, one specific for IgG2 (Fc gamma 2R) and the other for both IgG2 and IgG1 (Fc gamma 1/gamma 2R), can bind rabbit IgG, we determined whether they participate in the inhibition of the B cell proliferation by intact anti-guinea pig IgM antibody. Blocking Fc gamma 1/gamma 2R by F(ab')2 of anti-Fc gamma 1/gamma 2R mAb significantly reversed the inhibitory effect of intact anti-IgM antibody. F(ab')2 of anti-Fc gamma 2R mAb, however, was not effective. Furthermore, guinea pig IgG1 and IgG2 anti-rabbit IgG antibodies suppressed similarly the B cell proliferation induced by F(ab')2 of rabbit anti-IgM and BCGF. These results show that between these two types of Fc gamma R on B cells, Fc gamma 1/gamma 2R alone is involved in the regulation of anti-IgM and BCGF-induced B cell proliferation, and inhibits the response when cross-linked to the surface IgM.     

Structural differences among guinea pig Fc gamma 1/gamma 2 receptors on macrophages, polymorphonuclear cells, and lymphocytes.

Using the cDNA, D-3, coding for Fc gamma 1/gamma 2 receptor of guinea pig macrophages that binds IgG1 and IgG2 (Fc gamma 1/gamma 2R), we examined the cell distribution of this receptor by RNA blot analysis. The Fc gamma 1/gamma 2R mRNA was expressed in polymorphonuclear cells and B cells as well as in macrophages, but not at the detectable level in T cells. The cDNA amplified from RNA of polymorphonuclear cells in the polymerase chain reaction was the same as D-3. The cDNA of B cells was found to have about 140 bp cDNA segment inserted to the cytoplasmic tail of D-3. We found that the cDNA amplified from T cell RNA differed in signal peptide and extracellular domain sequence from cDNAs of other cell types. This cDNA does not seem to be amplified from the mRNAs of contaminating other cell types.     

Hemolysis of sheep erythrocytes with the cell membrane of liquid paraffin-induced guinea pig macrophages

As reported previously, the lysate of liquid paraffin-induced guinea pig peritoneal macrophages contains a hemolytic factor which is composed of two components: the soluble (S) and membrane-bound (M) components. To investigate the mechanism whereby the factor hemolysis sheep erythrocytes, an attempt was made to identify the S and M components. The fractionation of the cytosol of macrophages by DEAE-cellulose chromatography and the failure of the lysate from L-ascorbate-depleted macrophages to lyse erythrocytes demonstrated that the S component was L-ascorbate. In addition, L-ascorbate was found to be replaced by NADPH, a substrate of the membrane-bound NADPH oxidase, showing that L-ascorbate acts as a donor of active oxygen. When L-ascorbate was combined with the phospholipids isolated from the membrane fraction by extraction with chloroform-methanol and thin layer chromatography, it became able to lyse erythrocytes. The results so far obtained indicate that the hemolysis by the macrophage lysate is dependent on the formation of peroxidized phospholipids in the membrane fraction with certain active oxygen species produced either from L-ascorbate or by the NADPH oxidase.     

The NADPH oxidase-dependent hemolysis of sheep erythrocytes with the membrane fraction of guinea pig peritoneal macrophages

As previously reported, the membrane fraction of liquid paraffin-induced, guinea pig peritoneal macrophages exhibits an NADPH-dependent hemolytic activity toward sheep erythrocytes. This activity was inhibited with N-ethylmaleimide, superoxide dismutase, cytochrome c, catalase, desferrioxamine, mannitol, and benzoate. These inhibition profiles indicate that O2- generation by the NADPH oxidase, peroxidation of the membranous lipids with H2O2 or .OH secondarily formed from O2-, and hemolysis of sheep erythrocytes with the peroxides occur in this order in the hemolytic reaction. In fact, the lipid peroxides were found to be formed in the membrane fraction in the presence of Fe3+, subsequent to the O2- generation, and to act as a final hemolytic agent.     

Analysis of Fc receptors for IgG on guinea pig peritoneal macrophages by the use of a monoclonal antibody to one of the Fc receptors

The variety and properties of Fc receptors (FcR's) for homologous IgG on guinea pig peritoneal macrophages were investigated with the use of a mouse monoclonal antibody, VIA2 IgG1, prepared by fusion of splenic cells of a mouse immunized with guinea pig macrophages with a mouse myeloma cell line. VIA2 IgG1 completely inhibited the formation of macrophage rosettes with IgG1 antibody-sensitized erythrocytes, but not that with IgG2 antibody-sensitized erythrocytes. The Fab' of VIA2 IgG1 also completely inhibited the bindings of both monomeric and ovalbumin-bound IgG1 antibodies to macrophages. On the other hand, the Fab' did not affect the binding of monomeric IgG2 antibody to macrophages, although it partially inhibited that of ovalbumin-bound IgG2 antibody. These results show that at least two distinct types of FcR are present on guinea pig macrophages; one (FcR1,2) binds monomeric IgG1 antibody and also antigen-bound IgG1 and IgG2 antibodies, and the other (FcR2) binds monomeric and antigen-bound IgG2 antibodies alone, and also that VIA2 IgG1 binds specifically to FcR1,2. When FcR1,2 was isolated by affinity chromatography on F(ab')2 of VIA2 IgG1 coupled to Sepharose, it gave a main band with a molecular weight of 55,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which was indistinguishable from the main band isolated with the IgG1 immune complex. The number of FcR1,2 per macrophage cell was estimated to be 2 X 10(5) by measuring the binding of 125I-Fab' of VIA2 IgG1.     

Functional association of CD9 with the Fc gamma receptors in macrophages

CD9, a member of the tetraspan family of proteins, is highly expressed on macrophages. Although a clear function for the molecule has yet to be described, we have found that the anti-CD9 mAb activates mouse macrophages. The rat anti-CD9 mAb, KMC8.8, but not the F(ab')(2), induced tyrosine phosphorylation of proteins including syk and cbl and induced cell aggregation in the mouse macrophage cell line, J774, suggesting that co-cross-linking of CD9 and Fc gamma R was required for the signal. Co-cross-linking of CD9-Fc gamma R with KMC8.8 on macrophages from three different FcR-deficient mice, FcR gamma-chain(-/-), Fc gamma RIIB(-/-), and Fc gamma RIII(-/-), revealed that Fc gamma RIII is specific and crucial for syk phosphorylation. Although both KMC8.8 and the anti-Fc gamma RIIB/III mAb, 2.4G2, evoked similar phosphorylation patterns, only KMC8.8 induced cell aggregation. Additionally, KMC8.8 treatment led to reduce levels of TNF-alpha production and p42/44 extracellular signal-related kinase phosphorylation relative to 2.4G2 stimulation. Immunofluorescence staining showed that co-cross-linking of CD9-Fc gamma R with KMC8.8 induced filopodium extension before cell aggregation, which was followed by simultaneous colocalization of CD9, Fc gamma RIIB/III, Mac-1, ICAM-1, and F-actin at the cell-cell adhesion site. Moreover, KMC8.8 treatment of Fc gamma R-deficient macrophages revealed that the colocalization of CD9, Fc gamma RIII, Mac-1, and F-actin requires co-cross-linking of CD9-Fc gamma RIII, whereas co-cross-linking of CD9-Fc gamma RIIB induced the colocalization of only CD9 and Fc gamma RIIB. Our results demonstrate that co-cross-linking of CD9 and Fc gamma Rs activates macrophages; therefore, CD9 may collaborate with FcRs functioning in infection and inflammation on macrophages.     

Rab20 regulates phagosome maturation in RAW264 macrophages during Fc gamma receptor-mediated phagocytosis

Rab20, a member of the Rab GTPase family, is known to be involved in membrane trafficking, however its implication in FcγR-mediated phagocytosis is unclear. We examined the spatiotemporal localization of Rab20 during phagocytosis of IgG-opsonized erythrocytes (IgG-Es) in RAW264 macrophages. By the live-cell imaging of fluorescent protein-fused Rab20, it was shown that Rab20 was transiently associated with the phagosomal membranes. During the early stage of phagosome formation, Rab20 was not localized on the membranes of phagocytic cups, but was gradually recruited to the newly formed phagosomes. Although Rab20 was colocalized with Rab5 to some extent, the association of Rab20 with the phagosomes persisted even after the loss of Rab5 from the phagosomal membranes. Then, Rab20 was colocalized with Rab7 and Lamp1, late endosomal/lysosomal markers, on the internalized phagosomes. Moreover, our analysis of Rab20 mutant expression revealed that the maturation of phagosomes was significantly delayed in cells expressing the GDP-bound mutant Rab20-T19N. These data suggest that Rab20 is an important component of phagosome and regulates the phagosome maturation during FcγR-mediated phagocytosis.     

The IgG Fc contains distinct Fc receptor (FcR) binding sites: the leukocyte receptors Fc gamma RI and Fc gamma RIIa bind to a region in the Fc distinct from that recognized by neonatal FcR and protein A

The CH2-CH3 interface of the IgG Fc domain contains the binding sites for a number of Fc receptors including Staphylococcal protein A and the neonatal Fc receptor (FcRn). It has recently been proposed that the CH2-CH3 interface also contains the principal binding site for an isoform of the low affinity IgG Fc receptor II (Fc gamma RIIb). The Fc gamma RI and Fc gamma RII binding sites have previously been mapped to the lower hinge and the adjacent surface of the CH2 domain although contributions of the CH2-CH3 interface to binding have been suggested. This study addresses the question whether the CH2-CH3 interface plays a role in the interaction of IgG with Fc gamma RI and Fc gamma RIIa. We demonstrate that recombinant soluble murine Fc gamma RI and human Fc gamma RIIa did not compete with protein A and FcRn for binding to IgG, and that the CH2-CH3 interface therefore appears not to be involved in Fc gamma RI and Fc gamma RIIa binding. The importance of the lower hinge was confirmed by introducing mutations in the proposed binding site (LL234,235AA) which abrogated binding of recombinant soluble Fc gamma RIIa to human IgG1. We conclude that the lower hinge and the adjacent region of the CH2 domain of IgG Fc is critical for the interaction between Fc gamma RIIa and human IgG, whereas contributions of the CH2-CH3 interface appear to be insignificant.     

Human peritoneal macrophages possess two populations of IgG Fc receptors

To characterize the binding properties of the Fc receptors on human macrophages, the binding of radiolabeled human IgG1 to peritoneal macrophages was assessed. Cells were obtained at the time of diagnostic laparoscopy from women undergoing evaluation of infertility. Macrophages bound on the average more IgG1 monomer than monocytes but the avidity with which both types of cells bound IgG1 monomer was comparable. By contrast, macrophages bound much more IgG1 dimers than monocytes. Scatchard plots of the binding of dimer to monocytes were linear, but plots of binding to macrophages were markedly curvilinear. This curvilinearity was not an artifact of extensive ligand internalization or catabolism by cells, since 80% of binding was reversible and there was very little catabolism of ligand in the medium. Assuming that the observed curvilinearity was due to the presence of two independent subpopulations of receptors, an objective estimate for the number of receptors per cell and of the avidity with which each subpopulation bound IgG1 dimer was obtained using a previously described computer program (Scatfit). The analysis of the binding of dimer to macrophages from six donors suggested the presence of 42,000 +/- 33,000 high avidity receptors per cell which bind IgG1 dimer with a mean Ka of 2.7 X 10(9) M-1 and 218,000 +/- 127,000 low avidity receptors which bind the same ligand with a Ka of 1.1 X 10(7) M-1. ADCC of IgG antibody-coated sheep red blood cells mediated by macrophages was less readily inhibited by soluble IgG1 monomer than ADCC mediated by peripheral blood monocytes. This provides further evidence for the presence of low avidity receptors which bind monomeric IgG1 poorly and also suggests that these sites are functionally active in triggering antibody-dependent immune clearance.     

The structure and expression of the guinea pig Fc receptor for IgG1 and IgG2 (Fc gamma 1/gamma 2R).

A cDNA clone encoding the receptor for guinea pig immunoglobulin G was isolated from a guinea pig peritoneal macrophage cDNA library. The cloned cDNA encoded 271 amino acids containing an N-terminal signal sequence. The deduced amino acid sequence is most homologous to murine Fc gamma RII beta 2. The receptor protein could be expressed in COS-7 and L cells transfected with the cDNA, suggesting that the expression of this receptor does not require the co-expression of a second chain such as gamma chain of Fc epsilon RI or CD3 zeta chain. The transformant L cells showed the binding to both the guinea pig IgG1 and IgG2 antibodies complexed with antigen, indicating that the cDNA we cloned was the one for guinea pig Fc gamma 1/gamma 2R.     

Alveolar and peritoneal macrophages bear three distinct classes of Fc receptors for IgG

The FcR for IgG on the plasma membrane of cells of the mononuclear phagocyte system mediate a number of different biologic responses such as phagocytosis, pinocytosis, superoxide generation, and antibody-dependent cytotoxicity. In the interest of understanding the pathophysiology of these processes we have begun to characterize the FcR for IgG on two readily available sources of macrophages--the lung and the peritoneum--using antireceptor mAb. We find that all three of the distinct classes of FcR for IgG which have been described in man are present on both pulmonary and peritoneal macrophages. Most monocytes, we suggest, bear low numbers of Fc gamma RIII whereas a small subpopulation of monocytes expresses substantial numbers of Fc gamma RIII. Furthermore, we find that two different forms of Fc gamma RIII differ in their capacity to bind anti-Fc gamma RIII mab 3G8 in the presence of human IgG. Human IgG does not block the binding of mAb 3G8 to neutrophils, but it does block 3G8 binding to macrophages and large granular lymphocytes; this finding correlates with the expression of the two Fc gamma RIII genes, I and II, in man. Studies aimed at illuminating the molecular mechanisms of Fc gamma R-mediated processes in macrophages will require consideration of the receptors of all three classes.     

HIV-1 down-modulates gamma signaling chain of Fc gamma R in human macrophages: a possible mechanism for inhibition of phagocytosis

HIV-1 infection impairs a number of macrophage effector functions, thereby contributing to development of opportunistic infections and the pathogenesis of AIDS. FcgammaR-mediated phagocytosis by human monocyte-derived macrophages (MDM) is inhibited by HIV-1 infection in vitro, and the underlying mechanism was investigated in this study. Inhibition of phagocytosis directly correlated with the multiplicity of HIV-1 infection. Expression of surface FcgammaRs was unaffected by HIV-1 infection, suggesting that inhibition of phagocytosis occurred during or after receptor binding. HIV-1 infection of MDM markedly inhibited tyrosine phosphorylation of the cellular proteins, which occurs following engagement of FcgammaRs, suggesting a defect downstream of initial receptor activation. FcgammaR-mediated phagocytosis in HIV-infected MDM was associated with inhibition of phosphorylation of tyrosine kinases from two different families, Hck and Syk, defective formation of Syk complexes with other tyrosine-phosphorylated proteins, and inhibition of paxillin activation. Down-modulation of protein expression but not mRNA of the gamma signaling subunit of FcgammaR (a docking site for Syk) was observed in HIV-infected MDM. Infection of MDM with a construct of HIV-1 in which nef was replaced with the gene for the gamma signaling subunit augmented FcgammaR-mediated phagocytosis, suggesting that down-modulation of gamma-chain protein expression in HIV-infected MDM caused the defective FcgammaR-mediated signaling and impairment of phagocytosis. This study is the first to demonstrate a specific alteration in phagocytosis signal transduction pathway, which provides a mechanism for the observed impaired FcgammaR-mediated phagocytosis in HIV-infected macrophages and contributes to the understanding of how HIV-1 impairs cell-mediated immunity leading to HIV-1 disease progression.     

Further evidence for heterogeneity of Fc gamma-receptors on guinea pig splenic B and T lymphocytes: analysis using monoclonal antibodies to two distinct types of Fc gamma-receptor

In our previous paper, we reported that guinea pig splenic lymphocytes expressed two distinct Fc-receptors for homologous IgG (Fc gamma Rs), one monospecific for IgG2 (Fc gamma 2R) and the other bispecific for IgG1 and IgG2 (Fc gamma 1/gamma 2R), when analyzed by EA-rosette assay. These Fc gamma Rs on the cells were further studied by using two monoclonal antibodies toward the Fc gamma Rs on guinea pig peritoneal macrophages (anti-Fc gamma 1/gamma 2R and anti-Fc gamma 2R antibody). The anti-Fc gamma 1/gamma 2R antibody completely inhibited the rosette formation of splenic lymphocytes with IgG1-sensitized sheep erythrocytes [EA(IgG1)]. On the other hand, EA(IgG2)-rosette formation was inhibited partially by anti-Fc gamma 2R but not by anti-Fc gamma 1/gamma 2R antibody. Complete inhibition of the EA (IgG2)-rosette formation was achieved by simultaneous additions of both anti-Fc gamma 2R and anti-Fc gamma 1/gamma 2R antibodies. The binding of IgG2 antibody complexed with ovalbumin to the cells was partially inhibited by either anti-Fc gamma R antibody, and complete inhibition occurred in the presence of both the antibodies, indicating that two types of Fc gamma R, Fc gamma 1/gamma 2R, and Fc gamma 2R, are expressed on the cells. The determination of these Fc gamma Rs on B and T lymphocytes by two-color flow cytometry showed that about 52% of B lymphocytes expressed Fc gamma 1/gamma 2R alone and 32% of the cells expressed both the Fc gamma Rs. On the other hand, about 12% of T lymphocytes was found to express Fc gamma 2R alone and the cells expressing Fc gamma 1/gamma 2R were in the minority (3.8%). T lymphocytes expressing both the Fc gamma Rs were not detected. These results show that guinea pig B lymphocytes bear two types of Fc gamma Rs and are heterogeneous with regard to their Fc gamma Rs and that T lymphocytes express Fc gamma 2R mainly.     

The effect of 2-deoxyglucose on guinea pig polymorphonuclear leukocyte phagocytosis

The effects of 2-deoxyglucose (DOG), an inhibitor of glycolysis, on guinea pig polymorphonuclear leukocytes (PMN) obtained from peritoneal exudates was examined. ATP levels in PMN were reduced by 40% by one hour following an incubation with 2-deoxyglucose. When complement (C3) coated ¹⁴C-staphylococcus aureus, C3 coated lipopolysaccharide-paraffin oil droplets (LPSPO), ¹⁴C-pneumococcus opsonized with IgG, or albumin coated paraffin oil droplets opsonized with IgG were added to cell suspensions containing DOG, the phagocytizing rate was 1,310 ± 55 cpm/5 x 10⁶ cells/15 minutes, 6 ± 2 μg paraffin oil (PO)/10⁷ cells/minute, 2,250 ± 175 cpm/1 x 10⁶ cells/20 minutes or 0.037 ± 0.01 mg PO/10⁷ cells/minute compared to control values of 5,970 ± 275 cpm/5 x 10⁶ cells/15 minutes, 35 ± μg PO/10⁷ cells/15 minutes, 4,510 ± 200 cpm/1 x 10⁶ cells/20 minutes and 0.067 ± 0.01 mg PO/10⁷ cells/minute. In parallel studies the phagocytic index for latex was 0.74 ± 0.28 in DOG compared to control of 2.36 ± 1.13 and the phagocytic rate of albumin coated paraffin oil droplets was 0.029 ± 0.01 mg PO/10⁷ PMN/minute in DOG compared to control of 0.048 mg PO/10⁷ cells/minute. When ATP levels were maintained by the simultaneous addition of 5 mM glucose or pyruvate to media containing DOG, latex ingestion was improved to 1.15 ± 0.3 with glucose and 1.59 ± 0.64 with pyruvate and albumin coated particles to 0.045 ± 0.01 mg PO/10⁷ PMN/minute with pyruvate. There was no improvement in the uptake of either the C3 dependent particles or IgG coated Pneumococci in media containing DOG and glucose and/or pyruvate. Following the removal of DOG from the extracellular medium and the addition of pyruvate or glucose, phagocytosis of C3 dependent LPS-PO was restored to normal values. Neither the binding of C3 or IgG coated particles to the PMN nor the lateral movement of glycoprotein utilizing concanavalin A capping was affected by DOG. Thus, the presence of DOG in the PMN containing adequate amounts of ATP will selectively and reversibly inhibit those surface events required for phagocytosis of C3 and IgG bound particles but not latex particles or albumin particles which non-specifically bind to PMN.     

Down-regulation of Fc receptor expression in guinea pig peritoneal exudate macrophages by muramyl dipeptide or lipopolysaccharide

Expression of Fc receptors on the plasma membrane of guinea pig peritoneal exudate macrophages (PEM) was suppressed to almost one-half of that of the controls by long-term exposure to lipopolysaccharide (LPS) or muramyl dipeptide (MDP) in culture. The effect of the reagents was dose and time dependent, and as little as 0.5 ng/ml LPS or 5 ng/ml MDP was effective for the suppression. The expression of the Fc receptors decreased to 60 to 70% of the control level at 48 hr and to 45 to 50% at 72 hr after incubation of the cells in the presence of LPS or MDP. A Scatchard plot of the binding of 125I-soluble immune complexes (I.C.) to the cells revealed that the decrease in the binding of 125I-I.C. is due to a reduction in the number of Fc receptors on the cell membrane and not to a decreased affinity of the receptors. The membrane protein was radio-labeled with 125I, and the Fc receptors were purified by being bound to insoluble I.C. The specific binding of the 125I-labeled Fc receptors, from the LPS-treated macrophages, to the insoluble I.C. was almost one-half of that from the untreated control cells. SDS-PAGE analysis of the purified 125I-labeled Fc receptors revealed that the major peak of the m.w. 44,000 molecule in the LPS-treated cells was almost one-half of that of the control. Contrary to the effect of LPS or MDP, 72-hr incubation of macrophages with MIF-rich supernatant, cultured from lymph node cells, enhanced the expression of Fc receptors. Macrophages were treated with I.C. for 4 hr at 37 degrees C to remove the Fc receptors from the surface membrane. The reappearance of the receptors on the plasma membrane of the cells was significantly suppressed by LPS and MDP. The effect of LPS on the binding of five murine monoclonal antibodies (Ab) raised against PEM to the macrophage membrane and also that of 125I-wheat germ agglutinin (WGA) or 125I-insulin was studied. The monoclonal Ab were selected for their activity to induce superoxide anion generation in the macrophages, as do I.C., although the binding sites for the monoclonal Ab were not related to Fc receptors. The bindings of the five monoclonal Ab were not affected by exposure of the cells to LPS or MDP. Macrophages treated with the reagents bound as much 125I-insulin or WGA as did the untreated control cells.(ABSTRACT TRUNCATED AT 400 WORDS)