Human Basophilic Granulocytes Research Articles

Modulation of Allergic Reactions to Apple by Pesticide Residues

The question whether pesticides can modulate allergy relevant reactions is a controversial issue. In the allergist's office many food-allergic patients believe themselves to react particularly to 'chemically treated' food, especially fruits. Investigations on the influence of pesticides upon apple allergy should bring the problem closer to scientific understanding. Apples of the variety 'Golden Delicious' from 'biologic-dynamic' cultivation and the pesticides chlorpropham and thiram were studied in the experiments. Self-prepared apple protein extracts as well as the pesticides were examined in the in vitro mediator release test from human basophil granulocytes either alone or in combination (spiking experiments). The mediators histamine and leukotriene C4 were measured by high-performance liquid chromatography (HPLC). The possible binding of chlorpropham to the apple protein was examined using the enzyme allergosorbent test and immunoblotting with chlorpropham spiked apple allergen extracts. Chlorpropham but not thiram acted as a direct histamine liberator. Leukotriene C4 secretion was not induced by any pesticide. In the spiking experiments, when chlorpropham was added to apple extract, it showed a concentration dependent inhibition of histamine release compared to thiram, which had no effect. In an HPLC examination a binding of chlorpropham to apple protein up to 13% could be observed. In the enzyme allergosorbent test chlorpropham caused a reduced specific IgE antibody binding to the apple protein. In the immunoblot there was weakening by chlorpropham of the 18 kDa major allergen band (Mal d I). It is assumed that chlorpropham modulates the apple allergens leading to reduced antibody binding thereby decreasing allergenic potency.

Low-dose intragastric administration of Phaseolus vulgaris agglutinin (PHA) does not induce immunoglobulin E (IgE) production in Sprague-Dawley rats.

Native Phaseolus vulgaris agglutinin (PHA) poses a potential health threat, when ingested with improperly cooked red kidney beans. Since PHA triggers human basophilic granulocytes in culture to rapidly release considerable amounts of interleukin-(IL-)4 and IL-13, key cytokines for inducing immunoglobulin E (IgE) production, the question was addressed whether this lectin can evoke in vivo IgE production. IgE-low-responder (Sprague-Dawley) rats received PHA (6 mg/rat/day) intragastrically by gavage over a period of 10 days. Up to day 35, there was no IgE induction regardless of whether the animals were boostered subcutaneously with PHA or not, indicating that PHA cannot be regarded as a general IgE inducer in rats.

Role of Pseudomonas aeruginosa lipase in inflammatory mediator release from human inflammatory effector cells (platelets, granulocytes, and monocytes.

Previously, we have shown that Pseudomonas aeruginosa lipase and phospholipase C (PLC), two extracellular lipolytic enzymes, interact with each other during 12-hydroxyeicosatetraenoic acid (HETE) generation from human platelets. In this regard. the addition of purified P. aeruginosa lipase to PLC-containing crude P. aeruginosa culture supernatants enhances the generation of the chemotactically active 12-HETE from human platelets. Therefore, we analyzed the interaction of purified P. aeruginosa lipase and purified hemolytic P. aeruginosa PLC with regard to inflammatory mediator release from human platelets, neutrophilic and basophilic granulocytes, and monocytes. Purified P. aeruginosa PLC, but not purified lipase by itself, induced 12-HETE generation from human platelets, the generation of leukotriene B4 (LTB4) and oxygen metabolites, enzyme release from human neutrophils, and histamine release from basophils but diminished interleukin-8 (IL-8) release from human monocytes in a dose-dependent manner. The addition of purified lipase enhanced PLC-induced 12-HETE and LTB4 generation, did not influence enzyme, histamine, or IL-8 release, but diminished the PLC-induced chemiluminescent response. Similar results were obtained when the hemolytic PLC from Clostridium perfringens was used instead of P. aeruginosa PLC. For further comparison, we used the well-defined calcium ionophore A23187 and phorbol-12-myristate-13-acetate (PMA) as stimuli. Lipase enhanced calcium ionophore-induced LTB4 generation and beta-glucuronidase release but reduced calcium ionophore-induced and PMA-induced chemiluminescence. In parallel, we analyzed the role of lipase in a crude P. aeruginosa culture supernatant containing PLC and lipase. Lipase activity in the P. aeruginosa culture supernatant was inhibited by treatment with the lipase-specific inhibitor hexadecylsulfonyl fluoride, leaving the activity of PLC unaffected. The capacity of "lipase-inactivated culture supernatant" to induce 12-HETE and LTB4 generation was diminished by 50 to 100%. Our results suggest that the simultaneous secretion of lipase and PLC by P. aeruginosa residing in an infected host may result in severe pathological effects which cannot be explained by the sole action of the individual virulence factor on inflammatory effector cells.

Effects Of Staphylococcus Aureus Leukocidins On Inflammatory Mediator Release From Human Granulocytes

The secretion of the Panton-Valentine leukocidin (Luk-PV) but not of another leukocidin (Luk-R) from Staphylococcus aureus strains is correlated with severe pyodermic infections (dermonecrosis). The effects of both Luk-PV and Luk-R in amounts of 0-5000 ng on inflammatory mediator release from human leukocytes were studied. Luk-PV but not Luk-R induced a pronounced release of the vasodilator histamine from human basophilic granulocytes (up to 55% +/- 7%) and of enzymes (beta-glucuronidase, up to 45% +/- 10%; lysozyme, up to 35% +/- 7%), chemotactic components leukotriene B4 (42 +/- 8 ng/10(7) cells) and interleukin-8 (up to 33 +/- 5 ng/10(7) cells), and oxygen metabolites from human neutrophilic granulocytes. The results indicate that granulocytes play a central role in dermonecrosis; these in vitro data account for the histologic picture of Luk-PV infections, characterized by local vasodilation, infiltration of granulocytes, and a central necrotic area.

Purification of human basophils and mast cells by multistep separation technique and mAb to CDw17 and [formula omitted

Basophils and mast cells represent distinct cell lineages within the hemopoietic system. Based on the unique cell surface antigen profile of both cells, we have established methods which allow the reproducible purification to homogeneity (> 99%) of normal human basophil granulocytes from the peripheral blood and of mast cells from human dispersed tissues. Basophils ( n = 9) were purified by current counterflow elutriation followed by depletion of monocytes with CD14 mAb conjugated to magnetic beads, and subsequent cell sorting for CDw17 + cells. Basophil purity was 99.5 ± 0.4% (range 98.7–99.9%). Mast cells were obtained from lung ( n = 6), uterus ( n = 1), mastocytosis bone marrow ( n = 2), and human foreskin ( n = 2). Mast cells were purified by collagenase digestion followed by current counterflow elutriation and sorting with solCD117 c -kit mAb. Mast cell purity was 99.4 ± 0.7% (range: 97.5–99.9%). Purified cells were more than 90% viable and were able to release histamine on induction with IgE plus anti-IgE. Furthermore, the PCR technique could be applied on pure cells and confirmed expression of high affinity IgE receptor (FcεR1) α chain mRNA. Thus, by combining isolation techniques including elutriation, magnetic cell depletion and cell sorting with mAb, functionally intact normal human basophils and mast cells can be enriched to homogeneity.

Stimulation of human basophils results in homotypic aggregation. A response independent of degranulation.

For a better insight into the mechanisms determining the recruitment of human basophilic granulocytes from the circulation to sites of allergic reactions, we studied the homotypic aggregation of these cells. The aggregation was studied with > 95% pure basophil suspensions obtained from peripheral blood in a double-color flow cytometric analysis. Homotypic aggregation was induced by treatment of the basophils with anti-IgE, house dust mite allergen, the chemoattractant FMLP, PMA, or IL-3. The aggregation by anti-IgE was, in part, mediated by interactions with Fc gamma R-II as indicated by 43 +/- 15% inhibition after pretreatment with CD32 antibodies. The aggregation was mediated by beta 2-integrins, as was shown by inhibition of the response by CD18 antibodies. The aggregation induced by anti-IgE, allergen, and PMA displayed comparable kinetics (t1/2 max, 3 to 4 min), in contrast to the degranulation of basophils. FMLP induced the most rapid response (t1/2max, 1.6 min). Inhibition of protein kinase C by staurosporine resulted in a strong (> 90%) inhibition of the PMA-induced aggregation, whereas the FMLP-induced aggregation was more than doubled (from 11.7 +/- 1.9 to 24.4 +/- 1.9%). Staurosporine did not affect the extent of the anti-IgE-induced aggregation, but it induced a retardation of congruent to 10 min. In most experiments, no clear correlation was found between degranulation and aggregation of human basophils. Most strikingly, IL-3 did not induce degranulation but did induce aggregation. Thus, the homotypic aggregation response of human basophils is induced by intracellular signals not necessarily leading to degranulation. This might be important in the physiologic appearance of basophils at sites of allergic late-phase responses or inflammation.

Stimulus secretion coupling in human basophilic granulocytes

Clinical & Experimental AllergyVolume 23, Issue 6 p. 471-480 Stimulus secretion coupling in human basophilic granulocytes E. F. KNOL, E. F. KNOL Central Laboratory of the Netherlands Red Cross Blood Transfusion Service and Laboratory for Experimental and Clinical Immunology. University of Amsterdam. Amsterdam, The NetherlandsSearch for more papers by this authorA. J. VERHOEVEN, A. J. VERHOEVEN Central Laboratory of the Netherlands Red Cross Blood Transfusion Service and Laboratory for Experimental and Clinical Immunology. University of Amsterdam. Amsterdam, The NetherlandsSearch for more papers by this authorD. ROOS, D. ROOS Central Laboratory of the Netherlands Red Cross Blood Transfusion Service and Laboratory for Experimental and Clinical Immunology. University of Amsterdam. Amsterdam, The NetherlandsSearch for more papers by this author E. F. KNOL, E. F. KNOL Central Laboratory of the Netherlands Red Cross Blood Transfusion Service and Laboratory for Experimental and Clinical Immunology. University of Amsterdam. Amsterdam, The NetherlandsSearch for more papers by this authorA. J. VERHOEVEN, A. J. VERHOEVEN Central Laboratory of the Netherlands Red Cross Blood Transfusion Service and Laboratory for Experimental and Clinical Immunology. University of Amsterdam. Amsterdam, The NetherlandsSearch for more papers by this authorD. ROOS, D. ROOS Central Laboratory of the Netherlands Red Cross Blood Transfusion Service and Laboratory for Experimental and Clinical Immunology. University of Amsterdam. Amsterdam, The NetherlandsSearch for more papers by this author First published: June 1993 https://doi.org/10.1111/j.1365-2222.1993.tb03233.xCitations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume23, Issue6June 1993Pages 471-480 RelatedInformation

RANTES and related chemokines activate human basophil granulocytes through different G protein‐coupled receptors

Chemotactic cytokines related to interleukin-8 (IL-8; CXC-chemokines) or monocyte chemotactic protein-1 (MCP-1; CC-chemokines) have been shown to stimulate human basophils, and are considered important tissue-derived mediators of inflammation. We have studied the effects of four CC-chemokines and show that MCP-1, RANTES (regulated on activation, normal T expressed and secreted) and macrophage inflammatory protein-1 alpha (MIP-1 alpha) are potent basophil agonists inducing a rapid change of cytosolic free calcium ([Ca2+]i), the release of histamine and sulfido-leukotrienes, and chemotaxis. MCP-1 was the most potent stimulus of release, and the only chemokine that induced marked exocytosis in basophils without pretreatment with interleukin-3. RANTES was the strongest stimulus of chemotaxis, but only a moderate stimulus of release. MIP-1 alpha elicited relatively weak chemotaxis and release responses, but was effective at considerably lower concentrations than MCP-1 and RANTES. MIP-1 beta, by contrast, despite its high homology to MIP-1 alpha, was totally inactive. Normodense human eosinophils, tested for comparison, responded in a similar fashion to RANTES and MIP-1 alpha, but were unresponsive to MCP-1 and MIP-1 beta. All CC-chemokines except MIP-1 beta induced a similar rapid and transient rise of [Ca2+]i that was sensitive to pertussis toxin, indicating that they activate basophils via G-protein-coupled receptors. Cross-desensensitization experiments indicate that basophils bear different CC-chemokine receptors. Some interact selectively with MCP-1 or RANTES, while others are shared by RANTES and MIP-1 alpha.

Chronic myelogenous leukemia-derived basophilic granulocytes express a functional active receptor for the anaphylatoxin C3a.

The receptor for the inflammatory peptide C3a has scarcely been examined on human cells. This work demonstrates that human tumor-derived basophilic granulocytes express C3a receptors, and presents parts of the hitherto unknown C3a-signal transduction. When incubated with IL-3, these cells specifically liberated histamine on C3a stimulation. Independent from IL-3, 240,000 +/- 100,000 receptors per cell with a Kd of 5.6 +/- 0.9 nM were determined. [Ca2+]i increased from 120 +/- 35 nM to 300 +/- 80 nM after a C3a challenge, as measured by digital imaging fluorescence microscopy, and rested at its basal level in the presence of C3a-desArg, the immediate catabolic product of C3a in vivo. This [Ca2+]i increase could be completely desensitized homologously by C3a as well as inhibited by up to 75% by pertussis toxin. Thus, tumor-derived basophils are suitable for cloning of the human C3a receptor.

An improved method for the purification of basophilic granulocytes from human blood

Studies on human basophils are hampered by the low number of basophils in peripheral blood. Here we describe the purification of human basophilic granulocytes with immunomagnetic beads to improve an already established method of purification. A 70% pure basophil suspension was incubated with monoclonal antibodies (CD2, CD14, CD16 and CD19) recognizing the contaminating cells. After incubation with magnetic beads coated with goat anti-mouse IgG, the bead-cell rosettes were removed by a magnet. In this way, the basophil purity increased to 94%. The loss of basophils during the bead procedure was about 20%. The amount of histamine per basophil and the spontaneous release of histamine during subsequent incubation of the cells was not altered by the purification procedure. The kinetics and the dose response of histamine release after the addition of anti-IgE or FMLP was also unchanged. Binding of CD63 was not altered, indicating that the purification procedure did not result in activation of the basophils. This improved method for the purification of human basophils should permit the measurement of non-basophil-specific parameters, such as changes in intracellular free Ca 2+, without the problem of interference from contaminating cells.

Monitoring human basophil activation via CD63 monoclonal antibody 435

On activation of human basophilic granulocytes with anti-IgE or with the chemotactic peptide, formyl-methionyl-leucyl-phenylalanine, the expression of the CD63 antigen on the cell surface, detected by monoclonal antibody (MAb) 435, increased up to 100-fold. The kinetics of CD63 up regulation and histamine release were identical, and a strong correlation was found between percentage of MAb 435-binding basophils and extent of histamine release. Immunoelectronmicroscopy demonstrated that the epitope for MAb 435 in resting basophils is located on the basophilic granule membrane. After basophil activation, MAb 435 bound to the exterior of the plasma membrane. Experiments with various doses of anti-IgE demonstrated that the binding of MAb 435 to basophilic granulocytes follows an all-or-nothing-like response per cell. Basophils either do not bind the MAb at all, or they bind a maximal amount of the MAb. We also measured the up regulation of the CD11 CD18 leukocyte adhesion complex. Here, too, we noted an increase in cell-surface exposure of all subunits after activation. This increase was not as strong as increase found with MAb 435. Thus, MAb 435 is an interesting new tool for investigating the activation of human basophils, in addition to the measurement of mediator release. This MAb may be useful for the detection of basophil activation in vivo.

411 Charaterization of the role of Ca in the stimulation of human basophilic granulocytes

411 Charaterization of the role of Ca in the stimulation of human basophilic granulocytes

Blocking of passive sensitization of human mast cells and basophil granulocytes with IgE antibodies by a recombinant human epsilon-chain fragment of 76 amino acids.

The recombinant peptide corresponding to residues 301-376 at the junction of constant regions 2 and 3 of the human IgE epsilon chain blocked the in vivo passive sensitization of human skin mast cells and in vitro sensitization of human basophil granulocytes with human IgE antibodies. An injection of the recombinant peptide or E myeloma protein into normal skin sites 1 hr before sensitization with an allergic serum blocked passive sensitization. In this system, approximately 10-fold higher molar concentration of the recombinant peptide than E myeloma protein was required for 50% inhibition of Prausnitz-Küstner reactions. When the mononuclear cells of two normal individuals were preincubated with the recombinant peptide or E myeloma protein for 15 min before passive sensitization with the same allergic serum and the cells were challenged with an optimal concentration of an antigen, approximately 11- to 13-fold higher concentration of the recombinant peptide than E myeloma protein was required for 50% inhibition of antigen-induced histamine release. Further studies with several recombinant peptides indicated that amino acid resides 363-376 in the Fc epsilon-chain fragment are not essential for binding of the peptide to Fc epsilon-chain receptor I.

Interleukin 3 activates human blood basophils via high-affinity binding sites.

Pure populations of human basophilic granulocytes were obtained from chronic myeloid leukemia (CML) blood by negative selection using a mixture of monoclonal antibodies and complement. 125I-radiolabeled recombinant human interleukin 3 (rhIL-3) bound to purified basophils in a specific manner. Quantitative binding studies and Scatchard plot analyses performed on samples from two donors revealed the presence of a single class of high-affinity IL-3 binding sites (500 and 2100 sites per cell; dissociation constant at equilibrium, 230 and 160 pmol/liter, respectively). Purified CML basophils maintained in suspension in the presence of rhIL-3 (100 units/ml) incorporated up to 12 times more [3H]thymidine than basophils in control cultures. Furthermore, after preincubation in vitro with rhIL-3 (100 units/ml) for 30 min, normal blood basophils released 2- to 3-fold more histamine than basophils pretreated with control medium when exposed to various concentrations of an anti-IgE antibody. Together, these results show that rhIL-3 binds to a specific receptor on blood basophils and is a regulator of basophil function.

Induction of histamine release from rat mast cells and human basophilic granulocytes by clinical Escherichia coli isolates and relation to hemolysin production and adhesin expression

We investigated the role of 27 disease-relevant Escherichia coli strains isolated from humans in the induction of histamine release from rat peritoneal mast cells and human basophilic granulocytes. Our data indicated that only the hemolysin-positive (HLY+) bacteria and the hemolysin-positive culture supernatants induced histamine release. For the latter, the hemolysin activity determined the degree of histamine secretion. Incubation of the target cells with washed HLY+ bacteria revealed a different secretory response. For the rat mast cells, histamine release paralleled expression of hemolysin activity, with the exception of strain S98 (O75:K5:H- HLY+), which induced less histamine, although its hemolysin activity was relatively high. No correlation between histamine secretion and hemolysin activity was observed when human basophils were stimulated with the HLY+ bacteria. Large amounts of histamine were still released, even when the hemolysin activity declined to zero. Our results support the potent role of the E. coli hemolysin as a pathogenicity factor in bacterial infection.

Unique Features of Human Basophilic Granulocytes Developed in in vitro Culture

Human basophilic granulocytes were obtained in suspension culture of mononuclear cells from umbilical cord blood. Precursors of basophils in the cord blood are nonadherent cells and bear neither surface Ig nor T cell marker. Cultured basophils contain chondroitin-4-sulfate proteoglycan, 1.74 micrograms histamine per 10(6) cells in average, and bear 120,000-380,000 IgE receptors per cell. The IgE receptor molecule has a molecular weight of approximately 64,000 daltons. Human, rat and mouse IgE bind to the receptors with comparable high affinity and passively sensitize the cells for mediator release. Challenge of sensitized basophils with anti-IgE resulted in stimulation of phospholipid methylation, 45Ca uptake, release of both histamine and free arachidonic acid, and enhancement of phosphatidylinositol (PI) turnover. Evidence was obtained that the activation of membrane-associated proteolytic enzyme and methyltransferases is involved in subsequent IgE-mediated biochemical cascades such as PI turnover, Ca2+ uptake and mediator release.

Morphologic and immunologic characterization of human basophils developed in cultures of cord blood mononuclear cells.

Selective growth of human basophilic granulocytes was obtained in suspension cultures of mononuclear cells from umbilical cord blood. Approximately 50 to 80% of nonadherent cells recovered from 2- to 3-wk-old cultures contained metachromatic granules, and these cells were identified as human basophilic granulocytes by electron microscopy. Histamine content of cultured human basophils was comparable to that in peripheral blood basophils. Cultured basophils bear 2.7 to 3.7 X 10(5) IgE receptors per cell that bind both human IgE and rodent IgE with comparable affinity. Average equilibrium constants of the receptors for human IgE and mouse IgE were 2.56 +/- 0.88 X 10(9) M-1 and 1.85 +/- 0.86 X 10(9) M-1, respectively. The cell-surface component of the IgE receptors on cultured basophils has a m.w. of 64,000. Cultured basophils could be passively sensitized with human IgE and mouse IgE monoclonal antibody, and sensitized basophils released characteristic cytoplasmic granules and both histamine and arachidonate upon challenge with either anti-human IgE or antigen. Incubation of cultured basophils with ionophore A23187 or F-Met-Leu-Phe resulted in histamine release. However, compound 48/80 failed to induce histamine release from the cells.

Biochemical analysis of initial triggering events of IgE-mediated histamine release from human lung mast cells.

Mast cells were isolated from human lung tissues by counter current centrifugation elutriation, followed by flotation through Percoll gradients. Purified human mast cells released histamine upon challenge with anti-IgE. An optimal concentration of anti-IgE for maximum histamine release from human lung mast cells was comparable to that required for histamine release from normal human basophil granulocytes. Human lung mast cells could be passively sensitized with mouse monoclonal IgE antibody for antigen-induced histamine release. Bridging of cell-bound IgE molecules on human mast cells by anti-IgE or its F(ab')2 fragments induced phospholipid methylation and an increase in intracellular cyclic AMP (cAMP). Incorporation of [3H]methyl groups into phospholipid reached a maximum at 30 sec after challenge with anti-IgE, whereas intracellular cAMP reached a maximum at 1 min. Both values declined to base line levels within 2 to 3 min. These biochemical events were followed by Ca2+ influx and histamine release. Ca2+ uptake and histamine release reached maximum at 2 to 3 min and 5 to 8 min, respectively. Neither phospholipid methylation nor initial rise in cAMP was inhibited by indomethacin, which indicates that these biochemical events are not the result of prostaglandin synthesis. However, inhibition of phospholipid methylation by inhibitors of S-adenosyl-L-methionine-mediated methylation, such as 3-deazaadenosine and S-isobutyryl 3-deazaadenosine, inhibited not only phospholipid methylation but also cAMP rise and subsequent Ca2+ uptake and histamine release. The results indicate that phospholipid methylation induced by bridging of IgE receptors on human mast cells is essential for Ca2+ influx and histamine release.

Anaphylatoxin-induced histamine release with human leukocytes: studies of C3a leukocyte binding and histamine release.

Purified human C3a and synthetic COOH-terminal peptides of C3a, i.e., a pentapeptide, Leu-Gly-Leu-Ala-Arg (5R), and an octapeptide, Ala-Ala-Ala-Leu-Gly-Leu-Ala-Arg (8R) induced histamine release from human basophil granulocytes. On a molar basis, 5R was one-tenth and 8R was one-fifth as active as C3a in causing histamine release. It was found that 125I-C3a binds to whole leukocytes, interacting with both mononuclear cells and neutrophils and the binding was inhibited by preincubation of cells with unlabeled C3a, but not by C5a. 5R and 8R also inhibited the binding of 125I-C3a to the cells. However, on a molar basis, 2,000 times more 8R or 6,000 times more 5R is required for 50% inhibition of 125I-C3a binding as compared with native C3a. Autoradiography of cells using 125I-C3a and 125I-C5a showed preferential binding of 125I-C3a to eosinophils and basophils, whereas 125I-C5a binds primarily to neutrophils and eosinophils and to a lesser extent to basophils. The preferential binding of C3a and C5a to different cell types may herald significance related to their physiological functions.

Demonstration of Fcγ Receptors on Human Basophil Granulocytes

Abstract Fcγ receptors were detected on human basophil granulocytes. The mononuclear cell fraction of human peripheral blood was incubated with heat-aggregated human IgG (HGG) followed by 125I-anti-HGG. Autoradiography of the cells showed that the majority of basophil granulocytes gave a significant number of grains. Basophils were not labeled by preincubation of the same cells with monomeric HGG followed by 125I-anti-HGG. However, the binding of aggregated HGG to basophils was inhibited by the presence of a high concentration of monomeric HGG or its Fc fragment but not by the Fab fragment. Evidence was obtained that Fcγ receptors are distinct from IgE receptors on the same cells: i) Saturation of basophils with IgE did not affect the binding of aggregated HGG to the cells. ii) Preincubation with and the presence of aggregated HGG failed to affect the binding of 125I-IgE to basophils, or to block passive sensitization of the cells with IgE antibodies. iii) The Fcγ receptors did not co-cap with IgE receptors. Aggregated HGG failed to induce histamine release from basophils even in the presence of D2O. It was also found that the presence of aggregated HGG on basophils did not modulate IgE-mediated histamine release from the cells.