The receptor for IgG on human normal and chronic myeloid leukemic granulocytes: functional and biochemical characterization

Receptor mediated endocytosis of fluorescein isothiocyanate-conjugated heat-aggregated IgG (Fl-HAIgG) via the receptor for IgG (Fc gamma R) was studied using granulocytes from normal donors and patients suffering from chronic myeloid leukemia (CML). Within 15 min of incubation at 37 degrees C, 75% of the normal granulocytes internalized the ligand, while only 13% of the CML granulocytes could internalize the ligand in the same time. This functional defect was seen in all the CML patients analyzed. To elucidate the reason for this defective endocytosis, the Fc gamma R was isolated from normal and leukemic granulocytes and biochemically characterized, by gel electrophoresis, high pressure liquid chromatography, and one- and two-dimensional peptide mapping. Our results show that the molecule from the two cell types is very similar. The defective endocytosis must therefore be due to events which occur after ligand-receptor binding.     

Decreased expression of Fc gamma RIII mRNA in leukemic granulocytes.

Morphologically mature granulocytes from patients with chronic myeloid leukemia show significant impairment in their ability to internalize aggregated IgG, a ligand that is rapidly phagocytosed by normal human granulocytes. With a view to understand the molecular basis of this defect, normal and leukemic granulocytes were examined for the steady-state levels of mRNA for Fc gamma RIII, a membrane-associated receptor that initially binds and traps the IgG-opsonized antigens. Northern blot analyses revealed that the level of the specific mRNA in CML granulocytes was between 0.08 and 0.69 times that seen in the normal granulocytes. This could be one of the contributory factors for the observed endocytic defect in the leukemic granulocytes.     

Plasma membrane proteins from human normal and chronic myeloid leukemic granulocytes: identification and partial characterization of the concanavalin A-binding and detergent resistant proteins

In this work granulocytes from normal human donors and patients suffering from chronic myeloid leukemia (CML) were externally labeled with 125Iodine, using the Iodogen method. 125Iodine labeled Concanavalin A binding proteins (CBP) and detergent-resistant proteins (DRP) were isolated from the cell lysates and characterized by one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D- and 2D-SDS-PAGE). Autoradiographs of the 2D-gels of DRP show seven proteins with Mr 118,000 (spot 1 a), Mr 112,000 (spot 1b), Mr 78,000-85,000 (spot 2), Mr 85,000 (spot 4), Mr 52,000 (spot 3, 3 a and 3 b). Of this set, spot 1 b, 2 and 4 are also present in the autoradiographs of 2D-gels of CBP and, hence, may be considered to be transmembrane components. Spot 4 is expressed more intensely in the normal granulocytes while spots 3 a and 3 b are mainly expressed on the leukemic granulocytes.     

Lysis of fresh leukemic blasts by interferon-activated human natural killer cells

In a comprehensive study of 30 leukemia patients, it was found that a measurable fraction of fresh leukemic blasts from 8 of 8 adult patients with chronic myelogenous leukemia (CML) in blast crisis and 10 of 11 pediatric patients with childhood acute lymphocytic leukemia (ALL) were efficiently lysed by human peripheral blood natural killer (NK) cells as measured in 4-hour chromium release assays. The observed lysis of these fresh, noncultured, neoplastic blasts was mediated by a population of interferon-augmentable, FcR-positive, non-adherent large granular lymphoid cells from normal donors, which were also able to kill the 'standard' NK target K562. It was of further interest that all 8 of the patients with blast crisis CML exhibited myeloid type morphology. Furthermore, neoplastic lymphoblasts from 9 of 10 patients with NK-susceptible childhood ALL lacked easily detectable B or T cell markers and were of 'null' cell type. In marked contrast to the lytic susceptibility of fresh leukemic blasts from patients with ALL and CML in blast crisis, fresh neoplastic granulocytes from 5 patients with chronic phase CML (2 of which eventually progressed to myeloid type blast crisis), as well as leukemic blasts from 8 patients with acute myeloid leukemias (AML, AMMoL, and AMoL) were resistant to lysis as mediated by human NK cells from normal donors. The clinical implications of these findings are discussed.     

Acid alpha-D-mannosidase of human leukocytes in the norm and during chronic myeloid leukemia

The activity and properties of acid alpha-mannosidase were studied in normal granulocytes and in two types of myeloid cells from patients with chronic myeloid leukemia. The activity of the enzyme in leukemic cells was 2-fold higher than that in normal granulocytes and in morphologically matured myeloid cells. Two latter types of cells did not differ in alpha-mannosidase activity. Kinetic properties, thermo- and pH stability of alpha-mannosidase from normal and leukemic cells were similar. alpha-mannosidase in leukemic and normal cells existed in two forms (A and B), which were easily separated on DEAE-cellulose column. These two forms differed in molecular mass (300 and 290 kD, respectively) and in the degree of sialylation. The quantitative ratios of A and B forms in normal and leukemic cells were different. In normal granulocytes and in mature cells from patients this ratio was 0.60 and 0.67, respectively. In leukemic cells the ratio was found to be 1.31. Thus, in leukemic cells form A of alpha-mannosidase predominanted, whereas in normal cells the predominance of form B was observed. It was suggested therefore that in leukemic cells the enhanced synthesis of alpha-mannosidase occurred in parallel with the accumulation of the B form. This accumulation was assumed as the cause of enhanced activity of the enzyme in immature leukemic cells.     

Influence of mature and immature myeloid cells on lymphocyte reactivity in chronic myelocytic leukemia

Summary Earlier studies have shown anergy in chronic myeloid leukemia (CML), and it is known that myeloid cells influence lymphocyte responses. Therefore, lymphocytes from CML patients who had received no cytostatics for 2 weeks were stimulated in 89 tests with PHA and ConA. In 39 control tests, normal lymphocytes were used.Lymphocytes from CML patients were significantly less (p<0.05) markedly stimulated than normal ones. Lymphocytes from CML patients with more than 10×10⁹ white blood cells (WBC) per liter blood were inhibited to a greater degree than those from patients with a normal WBC count.When normal lymphocytes were stimulated with PHA in the presence of mononuclear cells from the blood of CML patients (mostly leukemic myelocytes), their response was significantly (p<0.05) inhibited. Inhibition with leukemic myelocytes was significantly (p<0.05) greater than that with mature granulocytes from CML patients. The latter did not seem to have an inhibitory effect.We suggest that patients with manifest CML are anergic to some extent because leukemic myelocytes have a suppressor effect.Visiting scientist and Anna Villa Rusconi Fellow, on secondment from Institute of Medical Pathology, University of Ferrara, Italy     

Alteration of beta-hexosaminidase activity and isoenzymes in human leukemic cells

beta-Hexosaminidase (EC 3.2.1.20; Hex) activity and isoenzyme characteristics were analyzed in human normal and leukemic leukocytes. Unseparated CLL and CML cells had a specific activity that was lower, whereas ALL and AML blasts had a higher specific activity than normal lymphocytes and granulocytes. CLL B-cells had a lower specific activity compared with that in normal non-T-lymphocytes; CLL T-cells and normal T-cells had similar activity. Isoenzyme separation was performed by chromatofocusing on PBE-94 coupled with an automated enzyme assay. When using a single linear pH elution gradient, normal leukocytes and all leukemia cells contained two forms of isoenzyme (B and A). When a double pH elution gradient was performed, an extra distinct form of Hex (I) was recorded. Hex I was present in small amounts in normal granulocytes and PHA-stimulated normal lymphocytes; isoenzyme I was found in high amounts in all leukemias tested. The activity ratios I/B and I/A, as well as the I isoenzyme profile, may facilitate differentiation between normal and leukemic cells and between lymphoblastic and myeloblastic leukemias.     

Protein 1a: A major wheat germ agglutinin binding protein on the surface of human granulocytes associated with the cytoskeleton

Lectin-receptors on leukocyte and endothelial surfaces are becoming more important in the light of increasing evidence which implicates lectin-carbohydrate interactions in diverse physiological phenomena. This study reports the identification of a major 118 kDa granulocyte surface protein, (Protein 1a) which binds the lectin wheat germ agglutinin (WGA), and is distinctly different from reported WGA binding granulocyte membrane proteins. Protein 1a has been isolated from the Triton-soluble and Triton-insoluble lysates of normal individuals and patients with Chronic Myeloid Leukemia (CML) using a combination of differential solubilization, lectin affinity, ion exchange chromatography and HPLC. The protein from the detergent lysates of both normal and CML granulocytes has similar pI values, lectin affinities, and hydrophobicity. However, its solubility in Triton is different in the two cell types. In 71% of CML cases examined, Protein 1a exhibits decreased Triton solubility suggesting its increased association with the cytoskeleton (CSK). Stimulation of normal granulocytes with WGA leads to the translocation of the soluble form of Protein 1a to the Triton-insoluble fraction. This cytoskeletal recruitment of Protein 1a is sustained only under conditions of excess WGA and occupied receptor. The CSK disruptive agent dihydrocytochalasin B (H₂CB) releases the insoluble form of the receptor into the Triton-soluble fraction. Investigation of a CSK-involving process such as ligand internalization revealed that CML granulocytes exhibit slower kinetics of internalization of fluorescent WGA molecules. Since Protein 1a is a major WGA receptor on the granulocyte surface, its decreased Triton solubility in CML granulocytes suggests that this may be one of the factors contributing to the defective receptor-mediated endocytosis of WGA by CML cells, arising as a consequence of altered membrane-CSK interaction — a nodal point in the signal transduction cascade.     

Activity and function of hybrid ribonuclease in cells of acute and chronic myelogenous leukemia

The activity of hybrid ribonuclease (ribonuclease H) has been determined in mononuclear blood cells (lymphocytes plus monocytes) from 23 normal individuals and cells (pool of immature granulocytes, metamyelocytes and lymphocytes) from 35 untreated acute and chronic myelogenous leukemia cases. It was found that in 86% of the leukemic samples the activity of ribonuclease H was above two standard deviations from the mean activity level drawn for the group of normal samples along the 0-100% substrate hydrolysis scale. The activity of the enzyme in leukemic cells correlated linearly with the DNA-synthesizing activity of the cells in vitro and in the examined CML cases it paralleled the inverse relationship of the incorporation of tritiated thymidine into DNA to the size of the pool of immature granulocytes. In one CML patient who received chemotherapy with Myleran, the activity of ribonuclease H, high at the initiation of drug therapy, was reduced to a normal level at remission, but increased again at the stage of subsequent relapse. These findings indicate that the levels of ribonuclease H in leukemic cells reflect the proliferative activity of the population in the cases of untreated myelogenous leukemias.     

Human granulocyte-specific nuclear antigen(s). II. Detection of antigens in human proliferative syndromes

Antisera raised to dehistonized chromatin from isolated normal human granulocytes revealed the presence of chromatin-associated antigens specific for the human neutrophils that appear during late stages of myeloid cellular differentiation. Immunological specificity was demonstrated by C fixation, immunodiffusion, and immunocytochemical reactions. Chromatin prepared from both normal granulocytes and specimens of myeloid leukemia showed immunologic reactivity. Although the normal antigens were detected in a specimen of CML, the position of immunodiffusion precipitin lines was different from that obtained with normal granulocyte chromatin. In addition, chromatin prepared from the myeloid leukemic cell line HL-60 expressed only one of the three precipitin bands normally found in immunodiffusion. The immunocytochemical staining reaction was confined to the nucleus of mature neutrophils in normal peripheral blood smears. Greater than 90% of cells in peripheral blood specimens of CML showed positive immunocytochemical nuclear staining. In other types of leukaemia, the normal mature granulocyte reacted with antiserum, but the nonmyeloid leukemic cells in these specimens did not. The specificity of immunologic reactions described here suggests the usefulness of nuclear antigens as cell markers.     

Substrate-induced spectral changes in human normal and chronic myeloid leukemic granulocytes

Several drugs/chemicals were allowed to interact with the cytochrome P-450 dependent mixed function oxidase system in the postmitochrondrial supernatant fractions of Ficoll-Hypaque-separated granulocytes from human normal subjects and patients with chronic myeloid leukemia. The substrate-induced spectral changes were followed by recording the difference spectra. Compounds conventionally classified as type I and type II substrates, on addition to S1 fractions of both normal and leukemic granulocytes, caused spectral changes that were reverse to those reported for the rat liver microsomes. Aminopyrine, phenobarbital, and Tween 80 evoked a reverse type I spectral change with a peak at 420-430 nm and a trough at 380-400 nm, whereas aniline and pyridine induced a modified type I (a reverse type II) spectral change characterized by a peak at 408 nm and a trough at 421 nm. These changes were found to be quantitatively proportional to the amounts of substrate added. However, the magnitude of the peaks and troughs was considerably less in the S1 fraction of the leukemic granulocytes. Correspondingly, total heme content was significantly decreased in S1 fractions of CML granulocytes as compared to similar fractions of normal granulocytes.     

Activity of cyclic nucleotide phosphodiesterases in granulocytes of chronic myelogenous leukemia (CML). A preliminary report

Cyclic 3':5'-adenosinmonophosphate phosphodiesterase (cAMP-PDE), high KM value type isoenzyme, and cyclic 3':5'-guanosino-monophosphate phosphodiesterase (cGMP-PDE), high KM value type isoenzyme, were determined in granulocytes of patients with chronic myelogenous leukemia (CML) in the chronic phase of the disease. Granulocyte cAMP-PDE activity was similar in the general group of CML patients to that in normal granulocytes; the cGMP-PDE, however, was somewhat higher. By dividing the CML general group into the "low leukocyte count" subgroup including granulocytes of patients with WBC number ranging from 10,300 to 40,000 per microliter (mean 22,000 per microliter), and the "high leukocyte count" subgroup including patients with leukocyte count above 40,000 per microliter (mean 67,000) remarkable differences in the activities of cyclic nucleotide phosphodiesterases between these subgroups could be found: cAMP-PDE activity for the high leukocyte count subgroups was significantly higher than for that in normals, and in CML-low leukocyte count subgroup. On the other hand, cGMP-PDE activity in granulocytes of the high leukocyte count subgroup was found to be remarkably lower than that in normals, in the low leukocyte count subgroup and general CML group. In CML patients the ratio of cAMP-PDE activity to cGMP-PDE activity was always considerably higher than that in controls. The obtained results suggest CML granulocytes to differ from normal ones in respect to their control of intracellular cyclic nucleotide levels. This difference is related to the accumulation of CML granulocytes.     

Vesicular monoamine transporter 2 (VMAT2) expression in hematopoietic cells and in patients with systemic mastocytosis.

Uptake of monoamines into secretory granules is mediated by the vesicular monoamine transporters VMAT1 and VMAT2. In this study, we analyzed their expression in inflammatory and hematopoietic cells and in patients suffering from systemic mastocytosis (SM) and chronic myelogenous leukemia (CML). Normal human and monkey tissue specimens and tissues from patients suffering from SM and CML were analyzed by means of immunohistochemistry, radioactive in situ hybridization, real time RT-PCR, double fluorescence confocal laser scanning microscopy, and immunoelectron microscopy. In normal tissue specimens, VMAT2, but not VMAT1, was expressed in mast cells, megakaryocytes, thrombocytes, basophil granulocytes, and cutaneous Langerhans cells. Further hematopoietic and lymphoid cells showed no expression of VMATs. VMAT2 was expressed in all types of SM, as indicated by coexpression with the mast cell marker tryptase. In CML, VMAT2 expression was retained in neoplastic megakaryocytes and basophil granulocytes. In conclusion, the identification of VMAT2 in mast cells, megakaryocytes, thrombocytes, basophil granulocytes, and cutaneous Langerhans cells provides evidence that these cells possess molecular mechanisms for monoamine storage and handling. VMAT2 identifies normal and neoplastic mast cells, megakaryocytes, and basophil granulocytes and may therefore become a valuable tool for the diagnosis of mastocytosis and malignant systemic diseases involving megakaryocytes and basophil granulocytes.     

EFFECTS OF COLCHICINE, CYTOCHALASIN B, AND 2-DEOXYGLUCOSE ON THE TOPOGRAPHICAL ORGANIZATION OF SURFACE-BOUND CONCANAVALIN A IN NORMAL AND TRANSFORMED FIBROBLASTS

The distribution of surface-bound concanavalin A on the membranes of 3T3, and simian virus 40-transformed 3T3 cultured mouse fibroblasts was examined using a shadow-cast replica technique with a hemocyanin marker. When cells were prefixed in paraformaldehyde, the binding site distribution was always random on both cell types. On the other hand, labeling of transformed cells with concanavalin A (Con A) and hemocyanin at 37°C resulted in the organization of Con A binding sites (CABS) into clusters (primary organization) which were not present on the pseudopodia and other peripheral areas of the membrane (secondary organization). Treatment of transformed cells with colchicine, cytochalasin B, or 2-deoxyglucose did not alter the inherent random distribution of binding sites as determined by fixation before labeling. However, these drugs produced marked changes in the secondary (but not the primary) organization of CABS on transformed cells labeled at 37°C. Colchicine treatment resulted in the formation of a caplike aggregation of binding site clusters near the center of the cell, whereas cytochalasin B and 2-deoxyglucose led to the formation of patches of CABS over the entire membrane, eliminating the inward displacement of patches observed on untreated cells. The distribution of bound Con A on normal cells (3T3) at 37°C was always random, in both control and drug-treated preparations. Pretreatment of cells with Con A enhanced the effect of colchicine on cell morphology, but inhibited the morphological effects of cytochalasin B. The mechanisms that determine receptor movement and disposition are discussed.     

Control of normal differentiation of myeloid leukemic cells. XII. Isolation of normal myeloid colony-forming cells from bone marrow and the sequence of differentiation to mature granulocytes in normal and D+ myeloid leukemic cells

An enriched population of early myeloid cells has been obtained from normal mouse bone marrow by injection of mice with sodium caseinate and the removal of cells with C3 (EAC) rosettes by Ficoll-Hypaque density centrifugation. This enriched population had no EAC or Fc (EA) rosettes and contained 87% early myeloid cells stained for myeloperoxidase and/or AS-D-chloroacetate esterase, 7% cells in later stages (ring forms) of myeloid differentiation and 6% unstained cells, 2% of which were small lymphocytes. After seeding in agar with the macrophage and granulocyte inducer MGI, the enriched population showed a cloning efficiency of 14% when removed from the animal and of 24% after one day in mass culture. Both the enriched and the unfractionated bone marrow cells gave the same proportion of macrophage and granulocyte colonies. The normal early myeloid cells were induced to differentiate by MGI in mass culture in liquid medium to mature granulocytes and macrophages. The sequence of granulocyte differentiation was the formation of EA and EAC rosettes followed by the synthesis and secretion of lysozyme and morphological differentiation to mature cells. D⁺ myeloid leukemic cells with no EA or EAC rosettes had a similar morphology to normal early myeloid cells and showed the same sequence of differentiation. The induction of EA and EAC rosettes occurred at the same time in both the normal and D⁺ leukemic cells, but lysozyme synthesis and the formation of mature granulocytes was induced later in the leukemic than in the normal cells. The results indicate that selection for non-rosette-forming normal early myeloid cells also selected for myeloid colony forming cells, that these normal early myeloid cells can form colonies with differentiation to macrophages and granulocytes, that normal and D⁺ myeloid leukemic cells have a similar sequence of differentiation and that the normal cells had a greater sensitivity for the formation of mature cells by MGI.     

Signal transduction in monocytes and granulocytes measured by multiparameter flow cytometry.

The novel calcium indicator fura red and the oxidative burst indicator dihydrorhodamine (both excited at 488 nm) were used in combination with multiparameter flow cytometry to allow simultaneous kinetic measurements of calcium fluxes and oxidative bursts in monocytes and granulocytes. Using this method it was possible to obtain direct evidence for the following cell type- and stimulus-specific differences in signal transduction pathways: 1) n-formyl-methionyl-leucyl-phenylalanine (FMLP)/cytochalasin B-induced oxidative burst is several-fold higher in granulocytes than in monocytes although the calcium fluxes have similar amplitudes in the two cell types; 2) stimulus-induced calcium fluxes in granulocytes are mainly due to release from intracellular stores, whereas monocytes mobilize calcium mainly by influx from the medium; 3) the FMLP/cytochalasin B-induced calcium flux in monocytes is less sensitive to the G-protein inhibitor pertussis toxin than the flux in granulocytes; 4) in contrast to FMLP/cytochalasin B, the protein kinase C activator phorbol myristate acetate (PMA) induces an oxidative burst that is not preceded by a cytoplasmic calcium flux; 5) the PMA-induced oxidative burst can be triggered in monocytes and granulocytes that are depleted of intracellular calcium ions, whereas that induced by FMLP/cytochalasin B can not; 6) the G-protein inhibitor pertussis toxin blocks an early event in the signal transduction pathway of FMLP/cytochalasin B, as shown by inhibition of both calcium fluxes and oxidative burst; and 7) 100 nM of the protein kinase inhibitor staurosporine blocks the FMLP/cytochalasin B-induced respiratory burst by interfering with a step downstream to cytoplasmic calcium fluxes, whereas only 10-20 nM is necessary to block PMA-induced oxidative burst.     

Differences in the Membrane Skeleton Proteins of RBC of AMoL Patients

We report here the different components of erythrocyte membrane skeleton proteins between acute monocytic leukemic (AMoL) patients and normal people. The bands in the 2 region of ghost membrane from AMoL patients exhibited significant differences on SDS gel electrophoresis. Band 2.2 was found to be missing and a “new” band with molecular weight (MW) 161 000 appeared. Also band 4.9 was missing, and the amounts of spectrin, actin, and band 4.8 of AMoL patients were decreased markedly. No such alterations can be seen in normal individuals, even in acute myeloid leukemic (AML) and chronic myeloid leukemic (CML) patients     

Macrophage deformability and phagocytosis

The influence of several metabolic inhibitors and pharmacologic agents on macrophage deformation (induced by fluid shear stress) was examined in relationship to changes in ATP content and phagocytosis of latex beads. Two relatively specific inhibitors of glycolysis (iodoacetate [IA], and sodium fluoride [NaF]) and a sulfhydryl-binding agent (N-ethylmaleimide [NEM] markedly inhibited phagocytosis and reduced cell deformability. A microtubule-disrupting agent (vinblastine) and a highly specific inhibitor of glycolysis (2-deoxyglucose) markedly inhibited phagocytosis without influencing cell deformability. An organomercurial sulfhydryl binding agent p-chloromercuribenzene (PCMBS) and a microfilament-disrupting agent (cytochalasin B) inhibited phagocytosis and increased cell deformability. The effects of these agents on phagocytosis and cell deformability bore no consistent relationship to alterations in cellular content of ATP. The observation that 2-deoxyglucose, the most specific inhibitor of glycolysis examined, reduced ATP content to levels far lower (15 percent of control values) than those achieved by any other agent examined and inhibited phagocytosis without altering cell deformability, suggests that alterations in cell deformability induced by NaF, IA, NEM, PCMBS, and cytochalasin B are not due to inhibition of glycolysis per se, but instead result from direct or indirect effects of these agents on cell constituents, possibly contractile proteins, which are determinants of cell deformability. The finding that cytochalasin B, NEM, PCMBS, and IA interfere with phagocytosis and alter cell deformability, together with evidence that these agents interact with isolated actin and myosin, suggests that contractile proteins are important both in phagocytosis and as determinants of cell deformability. The observation that vinblastine, colchicines, and heavy water (D(2)O) did not alter cell deformability, even though vinblastine caused formation of intracellular crystals of microtubular protein, indicates that microtubules are not major determinants of cell deformability. The observations that beads adhered normally to surfaces of cytochalasin B- and of PCMBS-treated cells and that shear-stress induced deformation was increased whereas phagocytosis was markedly inhibited, suggest that deformation of cells around beads associated with ingestion depends on some form of cellular (contractile?) activity, whereas deformation of cells by fluid shear stress is a passive phenomenon.     

K562 chronic myeloid leukemia cells modify osteogenic differentiation and gene expression of bone marrow stromal cells

Bone marrow (BM) microenvironment plays an important role in normal and malignant hematopoiesis. As a consequence of interaction with the leukemic cells, the stromal cells of the bone marrow become deregulated in their normal function and gene expression. In our study, we found that mesenchymal stem cells (MSC) from BM of chronic myeloid leukemia (CML) patients have defective osteogenic differentiation and on interaction with K562 CML cells, the normal MSC showed reduced osteogenic differentiation. On interaction with K562 cells or its secreted factors, MSC acquired phenotypic abnormalities and secreted high levels of IL6 through NFκB activation. The MSC derived secreted factors provided a survival advantage to CML cells from imatinib induced apoptosis. Thus, a therapy targeting stromal cells in addition to leukemia cells might be more effective in eliminating CML cells.     

Effect of cytochalasin B on the oxidative metabolism of human peripheral blood granulocytes.

Pretreatment of human granulocytes with cytochalasin B before addition of opsonized zymosan particles resulted in strong inhibition of the oxygen consumption, the hydrogen peroxide production, and the hexose monophosphate shunt activity as compared to normal phagocytosing cells. In contrast, however, no effect of cytochalasin B was found on the generation of superoxide anions. These seemingly controversial results can be explained by the action of cytochalasin B on the cell membrane.