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.     

Human Fc gamma RIII: cloning, expression, and identification of the chromosomal locus of two Fc receptors for IgG.

A cDNA clone encoding a human receptor for the Fc portion of IgG (Fc gamma R), Fc gamma RIII or CD16, was isolated from a human leukocyte library by a transient expression-immunoselection procedure. This cDNA (pGP5) encodes a 46-kDa phosphatidylinositol-linked cell surface protein with CD16 determinants and affinity for human IgG. The deduced protein sequence is most homologous to the murine receptor Fc gamma RII alpha, with slightly less homology to the human receptors Fc gamma RII and Fc epsilon RI. The cDNA hybridizes to a 2.2 kilobase mRNA in human leukocytes and a cloned human natural killer cell line. Fc gamma RIII is mapped to chromosome 1 by spot-blot analysis of sorted human chromosomes. Hybridization of Fc gamma RII and Fc gamma RIII probes to restriction digests of human genomic DNA separated by pulsed-field gel electrophoresis demonstrates physical linkage of the two genes within a maximum distance of 200 kilobases. The results identify a locus for at least two Fc gamma R genes on human chromosome 1.     

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.     

Mast cells cultured from the peripheral blood of normal donors and patients with mastocytosis originate from a CD34+/Fc epsilon RI- cell population

Mast cells may be cultured from human peripheral blood in the presence of recombinant human stem cell factor (rhSCF). The characteristics of the cells in peripheral blood that give rise to mast cells are unknown. Because mast cell precursors in human marrow are CD34+, human peripheral blood mononuclear cells from patients with mastocytosis and normal controls were sorted on the basis of CD34 expression and the positive and negative cell populations were cultured in rhSCF, recombinant human interleukin-3 (rhIL-3), or both for 6 weeks. Cell cultures were examined every 2 weeks for total and mast cell number and cell differential using Wright Giemsa and acid toluidine blue stains and antibodies to mast cell tryptase and chymase, cell-associated histamine, and expression of CD34, c-kit, Fc epsilon RI, and Fc gamma RII using flow cytometric analysis. The ultrastructural anatomy of mast cells was examined by electron microscopy. Peripheral blood CD34+ cells cultured in rhSCF with or without rhIL-3 gave rise to cell cultures consisting of greater than 80% mast cells by 6 weeks. CD34+ cells cultured in rhIL-3 alone did not give rise to mast cells, whereas rhIL- 3 plus rhSCF increased the final mast cell number eightfold when compared with cells cultured in rhSCF alone. Mast cells increased concomitantly with a decrease in large undifferentiated mononuclear cells. CD34- cells did not give rise to mast cells. Histamine content per cell at 6 weeks was approximately 5 pg. Electron microscopy of 4- week cultures showed immature mast cells containing predominantly tryptase-positive granules that were either homogeneous or contained lattice structures, partial scroll patterns, or central dense cores and mixtures of vesicles, fine granular material, and particles. The CD34+ population at day 0 expressed Kit (65%) and Fc gamma RII (95%), but not Fc epsilon RI, by fluorescence-activated cell sorter analysis. At 6 weeks, CD34+-derived mast cells exhibited Fc epsilon RI in addition to Kit and Fc gamma RII, and were negative for CD34 antigen. Patients with mastocytosis showed a higher number of mast cells per CD34+ cell cultured compared with normal controls. Thus, the mast cell precursor in human peripheral blood is CD34+/Fc epsilon RI- and gives rise to mast cells in the presence of rhSCF with or without rhIL-3, and the number of mast cells arising per CD34+ cell in culture is greater when the CD34+ cells are obtained from patients with mastocytosis compared with normal subjects.     

Fc gamma receptor II (CD32) on malignant B cells influences modulation induced by anti-CD19 monoclonal antibody

Antigenic modulation is one of many factors determining the effectiveness of monoclonal antibody (MoAb)-mediated therapy. To select the isotype of a CD19 MoAb most suitable for radioimmunotherapy of patients with B-cell malignancies, we studied the influence of MoAb isotype on modulation, after binding of the MoAb to different cell-line cells. The CD19-IgG1 MoAb was found to induce modulation of CD19 antigens on Daudi cell line cells more rapidly than did its IgG2a switch variant. We provide evidence that this difference in modulation rate is caused by the expression of Fc gamma receptor II (Fc gamma RII) on these cells. Experiments aimed at elucidating the mechanism of Fc gamma RII involvement in modulation induction by CD19-IgG1 showed that Fc gamma RII did not comodulate with CD19 MoAbs. However, cocrosslinking of CD19 and Fc gamma RII with CD19-IgG1 MoAb resulted in enhanced calcium mobilization in Daudi cells. This increased signal induction accompanies the enhanced capping and subsequent modulation of CD19 antigens. Because Fc gamma RII is expressed in varying densities on malignant B cells in all differentiation stages, our results have implications for the MoAb isotype most suitable for use in MoAb-based therapy of patients with B-cell malignancies.     

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.     

Retroviral WASP gene transfer into human hematopoietic stem cells reconstitutes the actin cytoskeleton in myeloid progeny cells differentiated in vitro

OBJECTIVE: Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency disorder characterized by recurrent infections, autoimmunity, microthrombocytopenia, and susceptibility to malignant tumors. Compared with the conventional treatment using allogeneic bone marrow transplantation, hematopoietic stem cell gene therapy might offer more specific and less toxic therapeutic options. METHODS: We investigated retroviral WAS protein (WASP) gene transfer to assess functional correction and potential toxicities in human CD34(+) cells from WAS patients and healthy individuals, respectively. RESULTS: WASP mRNA and protein levels were restored in CD14(+) cells derived from WASP-transduced hematopoietic stem cells. Functional reconstitution in WASP-transduced myeloid cells was documented by podosome formation and Fc gamma R-mediated phagocytosis. Importantly, overexpression of WASP in CD34(+) cells from healthy donors did not cause any discernible toxic effects. CONCLUSIONS: Our studies document the feasibility of WASP gene transfer into human CD34(+) cells and suggest that the phenotype of WASP-deficient myeloid cells can be restored upon retroviral gene transfer.     

Native human blood dendritic cells as potent effectors in antibody-dependent cellular cytotoxicity

Functional studies on native human dendritic cells (DCs) are hampered by technical difficulties in preparing fresh DCs. Recently, with the help of the monoclonal antibody M-DC8, we succeeded in isolating a major subpopulation of human blood DCs by a one-step immunomagnetic separation procedure. These cells strongly express Fc gamma RIII (CD16) and Fc gamma RII (CD32) and are quite efficient in the antigen-specific activation of naive T cells. Because some Fc gamma receptor-bearing cell types are known as effector cells in antibody-dependent cellular cytotoxicity (ADCC), we investigated whether M-DC8(+) DCs are capable of effectuating ADCC. In this report we show that freshly prepared M-DC8(+) DCs efficiently mediate tumor-directed ADCC and that both types of Fc gamma receptors as well as tumor necrosis factor alpha essentially contribute to the cytotoxic activity. The results provide evidence that, in addition to their pivotal role in primary T-cell activation, a subset of blood DCs displays efficient cytotoxicity in ADCC.     

The loss of Fc gamma RIIIb in paroxysmal nocturnal hemoglobinuria is functionally replaced by Fc gamma RII

Neutrophils from patients with paroxysmal nocturnal hemoglobinuria (PNH) show a deficiency for the glycosylphosphatidylinositol- (GPI) linked Fc gamma receptor IIIb (Fc gamma RIIIb, CD16). The functional consequences of this defect are not clear. Here, we examined Fc gamma RIIIb-deficient neutrophils for their activation via Fc gamma receptors. Hydrogen peroxide (H2O2) production and change of intracellular free calcium [Ca2+]i were used as parameters for cell activation. Fc gamma RII and Fc gamma RIIIb stimulation was reached by cross-linking using fragments of monoclonal antibodies or incubation with monoclonal IgG cryoglobulin complexes. In parallel to the deficiency of Fc gamma RIIIb expression, H2O2 production and [Ca2+]i influx were decreased after cross-linking of Fc gamma RIIIb in PNH neutrophils compared with that for normal neutrophils. Stimulation via Fc gamma RII was not affected. Cryoglobulin complexes previously shown to activate normal neutrophils predominantly via Fc gamma RIIIb stimulated PNH neutrophils at a level not significantly weaker than controls. But this activation was mediated only via Fc gamma RII as shown by blocking studies. The results suggest that the loss of GPI- anchored Fc gamma RIIIb is functionally replaced by Fc gamma RII during the immune complex stimulation of PNH neutrophils. Therefore, the equipment of neutrophils with pleomorphic Fc gamma receptors prevents an immunodeficiency in PNH.     

Fc receptors for IgG (Fc gamma Rs) on human monocytes and macrophages are not infectivity receptors for human immunodeficiency virus type 1 (HIV-1): studies using bispecific antibodies to target HIV-1 to various myeloid cell surface molecules, including the Fc gamma R.

Fc gamma Rs (Fc gamma RI, Fc gamma RII, and Fc gamma RIII) are highly expressed on human mononuclear phagocytes and function in the clearance of immune complexes and opsonized pathogens. We have examined the role of Fc gamma R in mediating antibody-dependent clearance of HIV-1 by human monocytes and monocyte-derived macrophages by using bispecific antibodies (BsAbs) to independently target the virus to Fc gamma RI, Fc gamma RII, or Fc gamma RIII. Virus production was markedly reduced in monocytes cultured with strain HIV-1IIIB opsonized with BsAbs that target the virus to either Fc gamma RI or Fc gamma RII compared to monocytes cultured with virus in the absence of BsAbs or in the presence of BsAbs that target the virus to non-Fc gamma R surface antigens (CD33 and HLA-A,B,C). These results were confirmed using the monotropic isolate HIV-1JRFL. Interaction of HIV-1JRFL with Fc gamma RI or Fc gamma RII on human monocytes and Fc gamma RI, Fc gamma RII, or Fc gamma RIII on monocyte-derived macrophages resulted in markedly reduced levels of virus production in these cultures. Moreover, HIV-1 infection of monocytes and monocyte-derived macrophages was completely blocked by anti-CD4 monoclonal antibodies, indicating that interaction with CD4 is required for infectivity even under conditions of antibody-mediated binding of HIV-1 to Fc gamma R. Thus, we propose that highly opsonized HIV-1 initiates high-affinity multivalent interactions with Fc gamma R that trigger endocytosis and intracellular degradation of the antibody-virus complex. At lower levels of antibody opsonization, there are two few interactions with Fc gamma R to initiate endocytosis and intracellular degradation of the antibody-virus complex, but there are enough interactions to stabilize the virus at the cell surface, allowing antibody-dependent enhancement of HIV-1 infection through high-affinity CD4 interactions. However, our results suggest that interaction of highly opsonized HIV-1 with Fc gamma Rs through BsAbs may reduce viral infectivity through Fc gamma R-mediated cytotoxic mechanisms and, therefore, that BsAbs offer promise as therapeutic reagents in HIV-1 infections.     

Expression of CD4 by human megakaryocytes.

The CD4 antigen, which serves as the receptor for human immunodeficiency virus type 1 (HIV-1) on T cells, has been detected on human megakaryocytes. Recent evidence of impaired thrombopoiesis in HIV-1-related thrombocytopenia suggested that these cells could be directly infected by the virus and prompted a search for a receptor on megakaryocytes of normal subjects that could permit entry of HIV-1. Bone marrow specimens from uninfected normal control subjects were centrifuged over Ficoll-Hypaque (1.077 g/ml) and analyzed by three-color analysis with a flow cytometer utilizing monoclonal antibodies against CD4 and a glycoprotein present on the surface of megakaryocytes and platelets (GPIIb/IIIa; CD41), as well as 7-aminoactinomycin D, a stain for DNA. Cells presumed to be megakaryocytes were identified by having a DNA content greater than tetraploid and staining brightly with anti-CD41. Approximately 0.4% of the nucleated cells of the marrow met these criteria. Twenty-five percent of these megakaryocytes stained as brightly as CD4+ T cells. Several clones of antibody recognizing different epitopes of the CD4 molecule gave similar results. Platelets were CD4-. Staining of megakaryocytes with anti-CD4 was confirmed by direct microscopic examination of Percoll-gradient-enriched megakaryocytes employing two-color (CD4-phycoerythrin and CD41-fluorescein) immunofluorescence analysis and phase-contrast microscopy. The proportion of double-labeled cells among 112 phase-contrast-identifiable megakaryocytes from five bone marrow specimens varied between 20% and 26% with a mean and SD of 22% +/- 2.5%. Thus some human megakaryocytes express CD4 on their surface that should be capable of binding the HIV-1 gp120 envelope protein. This could serve as a portal of entry for HIV-1.     

Response of human platelets to activating monoclonal antibodies: importance of Fc gamma RII (CD32) phenotype and level of expression.

Certain monoclonal antibodies (MoAbs) specific for platelet membrane glycoproteins are known to be capable of activating platelets, and it is generally thought that platelets from normal subjects are equally susceptible to stimulation by such MoAbs. We found that platelets from 20 normal donors varied significantly in their sensitivity to three IgG1 murine MoAbs specific for membrane glycoproteins CD9, GPIV (CD36), and the GPIIb/IIIa complex (CD41), respectively. The response of platelets to these MoAbs was blocked by prior addition of MoAb IV.3 specific for the Fc gamma RII receptor, indicating that activation was Fc receptor mediated. Platelets that responded poorly to these MoAbs failed to bind the MoAb 41H.16, specific for the "responder" form of Fc gamma RII, but platelets that responded well reacted with this MoAb. The average number of Fc gamma RII receptors on platelets from "responders" and "non-responders" was approximately the same. However, the number of Fc gamma RII receptors expressed influenced sensitivity of a subgroup of "responder" platelets to the anti-CD41 MoAb. These platelets were judged on the basis of MoAb binding studies to be heterozygous for the two alleles of Fc gamma RIIA. In contrast to their varying sensitivity to IgG1 MoAbs, members of the platelet panel responded equally well to 50H.19, an IgG2a MoAb specific for CD9, and these responses could not be blocked by MoAb IV.3 in the presence of plasma. This appears to be because of dual actions of 50H.19 on platelets: one FcR-dependent and the other complement-dependent. Our findings confirm previous reports that certain IgG1 MoAbs activate platelets through binding of their Fc domains to Fc gamma RII receptors and demonstrate that this response is influenced both by Fc gamma RII phenotype and (in the case of the anti-CD41 MoAb) by the number of Fc gamma RII receptors expressed. The failure of nonresponding platelets to bind detectable amounts of MoAb 41H.16, which is thought to recognize all Fc gamma RII receptors except for one allele of the Fc gamma RIIA gene, is consistent with the possibility that Fc gamma RIIA gene products, but not Fc gamma RIIB or Fc gamma RIIC gene products, are expressed on platelets.     

An alternative Fc gamma-receptor ligand: potential role in T-cell development.

Fetal pre-T cells express low-affinity receptors for IgG (Fc gamma R) at a developmental stage prior to the rearrangement and expression of immunoglobulin genes. The present studies investigated the possible functional significance of Fc gamma R on fetal pre-T cells. Between 13 and 17 days of fetal development a subpopulation of T-cell receptor-, Thy-1+ thymocytes express for gamma R. The same cells contain mRNA for several forms of Fc gamma R (Fc gamma RII beta 1, beta 2, and Fc gamma RIII). Concurrently, a Pgp-1-, Thy-1-, surface-immunoglobulin- fetal thymic cell binds recombinant soluble Fc gamma R. In principle this cell can interact with the pre-T cells through this counter-receptor. To test this possibility anti-Fc gamma RII/III antibody (2.4G2) was injected into pregnant mice and then into their offspring for 6 wk postpartum. The injected antibody induced a slight increase in the proportion of CD4 or CD8 single-positive, alpha/beta T cells in the thymus. However, in fetal thymic cultures in the presence of 2.4G2 or the recombinant soluble Fc gamma R there was an accelerated differentiation of thymocytes to single-positive, CD3-bright, heat-stable antigen-dull, alpha/beta T cells. These experiments show that Fc gamma Rs are present on pre-T cells during early fetal thymic development, and that a non-IgG ligand of the Fc gamma R is expressed concurrently on Thy- fetal thymocytes. Furthermore, the presumed interaction of Fc gamma R and the alternative ligand(s) influences T-cell development. IgG binding could be an adapted function of Fc gamma Rs, and, as shown for many members of the Ig super family, these receptors may have originally served as cell-cell recognition/interaction molecules required for hematopoietic development.     

Fyn tyrosine kinase associated with Fc epsilon RII/CD23: possible multiple roles in lymphocyte activation.

Expression of low-affinity Fc receptor for IgE (Fc epsilon RII), which is identical to the lymphocyte differentiation antigen CD23, is associated with activation of lymphoid cells. The mechanism of signal transduction through Fc epsilon RII/CD23 was dissected by transfection of cDNA coding for Fc epsilon RII to the YT human natural killer-like cell line, activation of which was easily detected by the induction of interleukin 2 receptor/p55(Tac). Cross-linking of Fc epsilon RII/CD23 with H107 anti-Fc epsilon RII monoclonal antibody markedly enhanced interleukin 2 receptor/p55 expression on the YT cells transfected with Fc epsilon RII cDNA (YTSER cells). Similar induction of interleukin 2 receptor/p55 by the cross-linking of Fc epsilon RII was observed on an Epstein-Barr virus-transformed B-cell line, 3B6, and fresh leukemic cells isolated from a patient with B-cell chronic lymphoblastic leukemia. Thus Fc epsilon RII/CD23 provides activation signals not only in YTSER cells but also in activated B cells. A possible involvement of protein-tyrosine kinase in the Fc epsilon RII-mediated signal transduction was studied. Fc epsilon RII was physically associated with a src family tyrosine kinase p59fyn and not with p56lck, which was also found in YT cells. Recently it was reported that p59fyn was associated with T-cell antigen receptor. Our results collectively suggest the multiple functions of p59fyn that may be implicated in Fc epsilon RII-mediated activation signal in YT cells.     

Phenotypic analysis of peripheral blood monocytes isolated from patients with rheumatoid arthritis.

The expression of CD14, Fc gamma receptor I (Fc gamma RI), Fc gamma RII, and HLA-DR on peripheral blood monocytes from patients with rheumatoid arthritis (RA) was studied to investigate their nature and their role in the pathogenesis of rheumatoid synovitis. Peripheral blood mononuclear cells obtained from 9 patients with active RA, 8 patients with RA in complete remission, and 14 healthy individuals, were stained with various monoclonal antibodies and analyzed on a fluorescence activated cell sorter. The expression of CD14 as well as Fc gamma RI and Fc gamma RII was upregulated on peripheral blood monocytes from patients with active RA, although the expression of HLA-DR was not increased. In addition, the expression of Fc gamma RI and Fc gamma RII on monocytes was still upregulated in patients with RA in complete remission, whereas the expression of CD14 on monocytes was normalized in these patients. These results indicate that peripheral blood monocytes in patients with active RA are already activated to express higher densities of CD14. In addition, our observation that CD14 density was increased on a subset of circulating blood monocytes in active RA, that HLA-DR was not significantly altered and that Fc gamma RI and Fc gamma RII were increased in both active and inactive RA is not compatible with the expected actions of interferon gamma. Finally, it is suggested that peripheral blood monocytes in patients with RA may have intrinsic abnormalities as evidenced by the enhanced expression of Fc gamma R, which is repeatedly observed regardless of the disease activity of RA.     

Tyrosine phosphorylation of phospholipase C-gamma 1 induced by cross-linking of the high-affinity or low-affinity Fc receptor for IgG in U937 cells.

The human monocytic cell line U937 possesses two classes of the IgG Fc receptor (Fc gamma R), a high-affinity 72-kDa Fc gamma R (Fc gamma RI) and a low-affinity 40-kDa Fc gamma R (Fc gamma RII). Cross-linking of either class of Fc gamma R in U937 cells elicits an increase in the concentration of free intracellular Ca2+. A rapid rise in the concentration of inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) and of several other inositol phosphates derived from Ins-1,4,5-P3 was observed after cross-linking of Fc gamma Rs in U937 cells. This result suggests that Ins-1,4,5-P3, generated by the action of phospholipase C (PLC), acts as a second messenger by which Fc gamma Rs mobilize intracellular Ca2+ in U937 cells. The mechanism by which the cross-linking of Fc gamma Rs triggers activation of PLC was studied. Cross-linking of Fc gamma RI or Fc gamma RII resulted in a rapid and transient phosphorylation of PLC-gamma 1 on tyrosine residues. It has previously been shown that phosphorylation of PLC-gamma 1 on tyrosine residues activates its enzymatic activity in cells. Prior incubation of U937 cells with a protein tyrosine kinase inhibitor, herbimycin A, prevented the tyrosine phosphorylation of PLC-gamma 1 and the hydrolysis of phosphatidylinositol 4,5-bisphosphate induced by the cross-linking of Fc gamma Rs. Thus, Fc gamma RI and Fc gamma RII appear to be functionally coupled to a nonreceptor tyrosine kinase that phosphorylates PLC-gamma 1 after receptor cross-linking, thereby causing activation of PLC-gamma 1.     

Neutrophils express the high affinity receptor for IgG (Fc gamma RI, CD64) after in vivo application of recombinant human granulocyte colony-stimulating factor.

Fc receptors are important effector molecules of neutrophilic granulocytes (polymorphonuclear neutrophils [PMN]), connecting phagocytic cells and the specific immune response. Neutrophils from healthy donors express the low-affinity receptors for IgG Fc gamma RII (CD32) and Fc gamma RIII (CD16), but not the high-affinity receptor Fc gamma RI (CD64). The latter has been found on neutrophils from patients with certain bacterial infections and can be induced in vitro after incubation with interferon-gamma. We show here that neutrophils strongly express Fc gamma RI after in vivo application of recombinant human granulocyte colony-stimulating factor (rhG-CSF). PMN from patients receiving rhG-CSF displayed higher cytotoxicity against Daudi lymphoma cells in vitro compared with control patients and with healthy donors. Fab fragments against Fc gamma RII (monoclonal antibody [MoAb] IV.3) inhibited neutrophil-mediated cytotoxicity of healthy donors but not of patients during rhG-CSF therapy. Therefore, expression of Fc receptors by PMN was investigated by flow cytometry and the mean fluorescence intensity (MFI) was compared. After staining with MoAb 32.2 against Fc gamma RL, the median MFI of neutrophils from G-CSF patients (median, 4.78; range, 2.40 to 8.50; n = 5) was significantly higher (P = .002 and P = .001, respectively) than the median MFI of patients not receiving G-CSF (median, 1.23; range, 1.01 to 1.58; n = 6) and the median MFI of healthy donors (median, 1.04; range, 0.67 to 1.12; n = 6). Fc gamma RI disappeared after the discontinuing of the G-CSF injections, but was reinduced during the next treatment cycle with rhG-CSF. The high expression of Fc gamma RI during rhG-CSF therapy correlated with enhanced cytotoxicity. In vitro incubation with rhG-CSF also enhances cytotoxicity, but only minor increments in Fc gamma RI expression were observed. Thus, during in vivo application of rhG-CSF neutrophils acquire an additional potent receptor for mediating tumor cell killing in vitro by induction of the high-affinity receptor for IgG (Fc gamma RI, CD64).     

Generation of natural killer cells from both Fc gamma RII/III+ and Fc gamma RII/III- murine fetal liver progenitors

In vitro culture of day-15.5 murine fetal liver (FL) cells in the presence of recombinant interleukin-2 (IL-2) results in the expansion of Fc gamma RII/III+ CD3-Ti-NK1.1+ cells displaying both natural killer (NK) and antibody-dependent cell cytotoxicity (ADCC) cytolytic activities. These FL-derived NK cells express Fc gamma RIII (CD16) in association with an Fc epsilon RI gamma homodimer on their surface. In contrast, in vitro expansion of FL cells in the absence of IL-2 generates noncytotoxic cells belonging to the myelomonocytic lineage (Mac1+Gr1+NK1.1-). Hence, IL-2 appears to be critical for the proliferation and differentiation of NK cells from FL progenitors. Experiments in which FL cells were fractionated by density gradient centrifugation before in vitro expansion showed that NK progenitors are contained within a cell population with a density of 1.04 < d < 1.08 g/mL. Cells with d > 1.08 g/mL (representing > or = 40% of FL cells) have no such NK progenitor activity. In addition, after intrathymic injection into Ly5 congenic host animals, day-15.5 CD4-CD8- FL cells mature into CD4+CD8+ thymocytes within 12 days. Interestingly, this T- cell progenitor activity is restricted to subpopulations of FL cells that also contain NK progenitors, but is absent in high-density (d > 1.08 g/mL) FL cells. Finally, fractionation of FL cells according to surface expression of Fc gamma RII/III complexes shows that NK (and T- lymphocyte) progenitors are found in both Fc gamma RII/III+ and Fc gamma RII/III-FL subpopulations.