Characterization of expression, cytokine regulation, and effector function of the high affinity IgG receptor Fc gamma RI (CD64) expressed on human blood dendritic cells.

The mechanisms responsible for efficient sequestration of Ag by cells of the dendritic cell (DC) lineage remain incompletely characterized. One pathway, internalization of Ag-IgG complexes via CD32 (the type II IgG FcR, Fc gamma RII) enhances Ag presentation 100-fold over noncomplexed Ag. Blood leukocytes differentially express two additional IgG FcR, Fc gamma RI (CD64) and Fc gamma RIII (CD16), which may also participate in leukocyte functions such as phagocytosis, Ab-dependent cellular cytotoxicity (ADCC), release of oxygen intermediates, and enhancement of Ag presentation.

Intracluster restriction of Fc receptor gamma-chain tyrosine phosphorylation subverted by a protein-tyrosine phosphatase inhibitor.

This study shows that aggregation of U937 cell high affinity IgG Fc receptor (Fc gamma RI) results in the transient tyrosine phosphorylation of Fc gamma RI gamma-chain but not the phosphorylation of gamma-chains associated with nonaggregated IgA Fc receptors (Fc alpha R) on the same cells. Thus, normally, tyrosine phosphorylation of gamma-chains is limited to FcR in aggregates. In contrast, aggregation of Fc gamma RI in the presence of vanadate induced the sustained tyrosine phosphorylation of Fc gamma RI gamma-chains and the rapid and extensive phosphorylation of nonaggregated Fc alpha R gamma-chains and low affinity IgG Fc receptors (Fc gamma RII).

Construction and characterization of a humanized anti-gamma-Ig receptor type I (Fc gamma RI) monoclonal antibody.

The murine mAb 22 (M22) binds to the human high affinity receptor for the Fc portion of IgG (Fc gamma RI). This mAb recognizes an epitope on Fc gamma RI that is distinct from the natural ligand (Fc) binding site, and, therefore, can bind to Fc gamma RI in the presence of saturating levels of IgG found in vivo. Fc gamma RI is expressed only on cytotoxic effector cells and it acts as an efficient mediator (trigger molecule) of effector functions.

A novel role for IgG-Fc. Transductional potentiation for human high affinity Fc gamma receptor (Fc gamma RI) signaling.

Human type 1 Fc gamma receptors (Fc gamma RI) bind with high affinity (Kd = approximately 10(-9) M) Fc regions of monomeric IgG1 and IgG3. As demonstrated in this report, interaction of IgG-Fc with the ligand binding site on Fc gamma RI alters its capacity for aggregation-dependent signaling. This Fc-dependence was demonstrated in normal monocytes and U937-10.

Association of IgA-Fc receptors (Fc alpha R) with Fc epsilon RI gamma 2 subunits in U937 cells. Aggregation induces the tyrosine phosphorylation of gamma 2.

We investigated the possibility that IgA-binding chains of Fc alpha R on monocytic cells are physically associated with gamma 2 subunits of Fc epsilon RI (Fc epsilon RI gamma 2 or gamma 2). Fc alpha R was precipitated from lysates of IFN gamma-treated U937 cells, subclone 10.6, and probed by immunoblotting with Ab against human gamma 2.

Induction of intracellular Ca2+ mobilization and cytotoxicity by hybrid mouse monoclonal antibodies. Fc gamma RII regulation of Fc gamma RI-triggered functions or signaling?

We studied the interaction of bispecific mouse mAb with human IgG Fc receptors, and assessed their ability to activate the monocytic cell line U937. Binding of monomeric hybrid anti-HuIgA1/HRP mAb to the high-affinity IgG receptor, Fc gamma RI, on U937 cells was only observed when mAb with one or more mIgG2a H chains (hybrid mIgG1-2a, mIgG2a-2b, and mIgG2a-2a) were used. These Fc gamma RI-bound hybrid mAb were capable of enhancing the internal free cytosolic Ca2+ concentration ([Ca2+]i) in U937 cells only when bound mIgG were cross-linked using F(ab')2 fragments of goat anti-mIg antibody.

Functional comparison of the inductions of NADPH oxidase activity and Fc gamma RI in IFN gamma-treated U937 cells.

The capacity to generate superoxide anion (O2-) can be induced in U937 cells by various agents known to cause myeloid cell differentiation. Other reported differentiation events include diminished cell proliferation and the induction by gamma-interferon (IFN gamma) of Fc receptors for immunoglobulin G1 (Fc gamma RI). In this study, we differentiated U937 cells and high Fc gamma RI-expression mutants of U937 cells by treating them with IFN gamma.

Transient activation of the NADPH oxidase through Fc gamma RI. Oxidase deactivation precedes internalization of cross-linked receptors.

It is well known that Fc gamma R mediate the rapid release of agents of inflammation and, in addition, play an important role in the uptake of stimulatory antibody complexes. Activation of the FcR for human IgG1 (Fc gamma RI) on human monocytic cells triggers a transient activation of the NADPH oxidase. In this study, we tested the possibility that transience of the NADPH oxidase activation might have been the result of rapid internalization of cross-linked Fc gamma RI.

Cross-linking of the high affinity Fc receptor for human immunoglobulin G1 triggers transient activation of NADPH oxidase activity. Continuous oxidase activation requires continuous de novo receptor cross-linking.

Cross-linking of the high affinity Fc receptor for human immunoglobulin G1 (Fc gamma RI) on U937 cells triggered superoxide anion (O-2) release. This was accomplished by the binding of an Fc gamma RI-specific monoclonal antibody, mAb 32, followed by cross-linking of the mAb on the cell with anti-mouse IgG F(ab')2 by Fc gamma RI-specific mAbs 32 and 22 used as an equimolar mixture or by Fc gamma RI-specific mAb 197 (a murine IgG2a and thus a multivalent ligand for Fc gamma RI) alone. At subsaturating concentrations of the Fc gamma RI-cross-linking ligands, O2- generation was continuous over relatively long intervals.

Transmembrane signaling: an ion-flux-independent model for signal transduction by complexed Fc receptors.

Fluxes of Na+/K+ that precede effector functions in stimulated phagocytes are thought to play a role in signal transduction. To examine this hypothesis, phagocytosis, phagosomal acidification, and superoxide anion generation (O2-) were stimulated in media in which the Na+ was replaced with K+ or choline+. Counts of particles internalized and assessment of acidification of the phagosomes by acridine orange staining indicated that Na+/K+ fluxes were not necessary for phagocytosis or phagosomal acidification in J774.

Quantitative studies of the mutagenesis of Toxoplasma gondii.

The induction of mutants resistant to 5-fluorodeoxyuridine (FUDR) was used to measure the efficiency of various physical and chemical mutagens on extracellular and intracellular Toxoplasma gondii. The frequency of resistant mutant was measured by plaque assay in human fibroblast cultures in the presence and absence of FUDR. When considered as a function of lethality, the most efficient mutagenesis was obtained with nitrosoguanidine treatment of extracellular parasites and with ethylmethane sulfonate treatment of actively growing intracellular parasites.

The biochemical basis for resistance to adenine arabinoside in a mutant of Toxoplasma gondii.

We have previously reported the isolation and preliminary characterization of a mutant of Toxoplasma gondii that was resistant to adenine arabinoside. Fiftyfold higher concentrations of adenine arabinoside were required to inhibit the growth of the resistant parasite in human fibroblast cultures. To determine the enzymic basis for resistance, we measured the kinases and deaminases that act on adenosine or deoxyadenosine.

[Coronary heart disease risk factors in white-collar and manual workers at a large Munich industrial firm (author's transl)].

1477 employees of a large industrial firm in Munich (868 males and 609 females, aged 40-59) were examined for coronary heart diseases risk factors. Among males, hypercholesterolemia predominates with a distribution of over 40%. Every fifth male has high blood pressure or is a heavy cigarette smoker.

Specific labeling of intracellular Toxoplasma gondii with uracil.

Radioactive uracil was not significantly incorporated into the nucleic acids of human fibroblast cells. Infection of these cells with Toxoplasma gondii resulted in an exponential increase in the rate of uracil incorporation that paralleled the exponential growth of the parasite. One day after infection the rate of uracil incorporation was increased 100-fold.

Arabinosyl nucleosides inhibit Toxoplasma gondii and allow the selection of resistant mutants.

Adenine arabinoside, which inhibits the synthesis of DNA by intracellular Toxoplasma gondii, is more inhibitory to the parasite than it is to cultured human fibroblast host cells. A single-step mutant of T. gondii that is 50-fold more resistant to adenine arabinoside was isolated after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine.