Inhibition of monocyte and polymorphonuclear granulocyte immune phagocytosis by monoclonal antibodies specific for Fc gamma RI, II and III

Anti-dengue virus nonstructural protein 1 antibodies contribute to platelet phagocytosis by macrophages

Thrombocytopenia is an important clinical manifestation of dengue disease. The hypotheses concerning the pathogenesis of thrombocytopenia include decreased production and increased destruction or consumption of platelets. We previously suggested a mechanism of molecular mimicry in which antibodies (Abs) directed against dengue virus (DENV) nonstructural protein 1 (NS1) cross-react with platelets. Furthermore, several lines of evidence show activation of endothelial cells (ECs) and macrophages are related to dengue disease severity. Previous studies also suggested that Ab-opsonised platelets facilitate the engulfment of platelets by macrophages. Here we show that TNF-α-activated ECs upregulate adhesion molecule expression to enhance the binding of platelets and macrophages and lead to anti-DENV NS1 Ab-mediated platelet phagocytosis. We further demonstrate that the interaction between macrophages and TNF-α-activated ECs requires binding of FcγR with the Fc region of platelet-bound anti-DENV NS1 Abs. Importantly, the binding of anti-DENV NS1 Abs to platelets did not interfere with platelet adhesion to ECs. The adhesion molecules ICAM-1 and β3 integrin expressed on ECs as well as the FcγR expressed on macrophages were critical in anti-DENV NS1 Ab-mediated platelet phagocytosis on activated ECs. Moreover, anti-DENV NS1 Abs dramatically enhanced platelet engulfment by macrophages in a murine model of DENV infection. Our study provides evidence for a novel role for anti-DENV NS1 Abs in the pathogenesis of thrombocytopenia in dengue disease by enhancing platelet phagocytosis by macrophages.

Low expression of FCGRIIB in macrophages of immune thrombocytopenia-affected individuals

Immune thrombocytopenia (ITP) is an autoimmune disorder described as autoantibody-mediated platelet deterioration. Platelets with affiliated IgG are targeted for exploitation by Fc receptor-mediated phagocytic cellular material within the reticuloendothelial system. The objective of this research is to investigate the relationship between the appearance of FC gamma receptors (FCGR) IIB and IIIA on macrophages and clinicopathological characteristics in ITP patients. FCGRIIB and FCGRIIIA were recognized by immunohistochemistry staining of 62 samples, including regular (n = 20) and ITP (n = 42) samples. Subsequently, the relationship of FC gamma expression levels to ITP progression and clinicopathological characteristics was statistically reviewed. Furthermore, the relationship between Helicobacter pylori (HP) infection and FC gamma expression was analyzed. IHC staining with the coordinated spleen tissue trial samples showed that expression of FCGRIIB on macrophages of ITP patients was tremendously reduced in comparison to the healthy control group. However, no variance was discovered between the two groups with respect to FCGRIIIA expression. There was no substantial correlation among FCGRIIB and FCGRIIIA expression and patient age and gender. Significant differences were found between HP infection and decreased expression of FCGRIIB, while there was no difference with the expression of FCGRIIIA. Lower expression of FCGRIIB is likely involved in the etiology of ITP. HP infection is correlated with decreased expression of FCGRIIB. A rise in FCGRIIB may serve as a therapeutic target for human ITP treatment or possibly as a biomarker for ITP analysis.

Genetic variation of the HNA-3a encoding gene

BACKGROUND

Antibodies against the human neutrophil alloantigen-3a (HNA-3a) play an important role in transfusion-related acute lung injury. The HNA-3a and -3b alloantigens result from a single-nucleotide exchange in the choline transporter-like protein 2 gene (CTL2). We sought for additional polymorphisms that might impair antibody binding to or genotyping of the HNA-3a or -3b antigens.

STUDY DESIGN AND METHODS

CTL2-specific complementary DNA (cDNA) fragments were generated from 67 unrelated blood donors followed by DNA sequencing. Polymerase chain reaction with sequence-specific primers (PCR-SSP) was used to test a higher number of donors for relevant new single-nucleotide polymorphisms (SNPs). The granulocyte agglutination test recommended for HNA-3a antibody detection was performed to check HNA-3a antibody binding to the products of the CTL-2 gene variants.

RESULTS

Two new missense mutations were demonstrated in the CTL2 cDNA: a 537C>T* exchange leading to a Leu153Phe amino acid substitution and 988C>T variation predicting Thr301Met change. The inherited 537T variant is located in HNA-3a allele results impaired granulocyte agglutination by four of 14 antibodies tested while 988T remains nearly unaffected.

CONCLUSIONS

The Leu153Phe exchange next to the HNA-3a/b defining amino acid position can impede the binding of HNA-3a alloantibodies. The HNA-3a genotyping by PCR-SSP might produce misleading results in HNA-3ab heterozygous individuals with the additional CTL2-537T variation of the HNA-3a antigen. These findings must account for the development of new screening assays.

A robust, high-throughput assay to determine the phagocytic activity of clinical antibody samples

Phagocytosis can be induced via the engagement of Fcγ receptors by antibody-opsonized material. Furthermore, the efficiency of antibody-induced effector functions has been shown to be dramatically modulated by changes in antibody glycosylation. Because infection can modulate antibody glycans, which in turn modulate antibody functions, assays capable of determining the induction of effector functions rather than neutralization or titer provide a valuable opportunity to more fully characterize the quality of the adaptive immune response. Here we describe a robust and high-throughput flow cytometric assay to define the phagocytic activity of antigen-specific antibodies from clinical samples. This assay employs a monocytic cell line that expresses numerous Fc receptors: including inhibitory and activating, and high and low affinity receptors--allowing complex phenotypes to be studied. We demonstrate the adaptability of this high-throughput, flow-based assay to measure antigen-specific antibody-mediated phagocytosis against an array of viruses, including influenza, HIV, and dengue. The phagocytosis assay format further allows for simultaneous analysis of cytokine release, as well as determination of the role of specific Fcγ-receptor subtypes, making it a highly useful system for parsing differences in the ability of clinical and vaccine induced antibody samples to recruit this critical effector function.

Binding of rituximab, trastuzumab, cetuximab, or mAb T101 to cancer cells promotes trogocytosis mediated by THP-1 cells and monocytes

More than 20 years ago clinical investigations in the immunotherapy of cancer revealed that infusion of certain immunotherapeutic mAbs directed to tumor cells induced loss of targeted epitopes. This phenomenon, called antigenic modulation, can compromise mAb-based therapies. Recently we reported that rituximab (RTX) treatment of chronic lymphocytic leukemia patients induced substantial loss of targeted CD20 on B cells found in the circulation after RTX infusion; this "shaving" of RTX-CD20 complexes from B cells is also promoted in vitro by THP-1 monocytes and by PBMC in a reaction mediated by Fcgamma receptors. The mechanism responsible for shaving appears to be trogocytosis, a process in which receptors on effector cells remove and internalize cognate ligands and cell membrane fragments from target cells. We now report that three therapeutic mAbs approved by the U.S. Food and Drug Administration for the treatment of cancer, RTX, cetuximab, and trastuzumab, as well as mAb T101, which has been shown to induce antigenic modulation in the clinic, promote trogocytosis in vitro upon binding to their respective target cells. Trogocytosis of the mAb-opsonized cells is mediated by THP-1 monocytes and by primary monocytes isolated from PBMC. In view of these results, it is likely that these mAbs and possibly other anticancer mAbs now used in the clinic may promote trogocytic removal of the therapeutic mAbs and their cognate Ags from tumor cells in vivo. Our findings may have important implications with respect to the use of mAbs in cancer immunotherapy.

Copy number of FCGR3B, which is associated with systemic lupus erythematosus, correlates with protein expression and immune complex uptake

Copy number (CN) variation (CNV) has been shown to be common in regions of the genome coding for immune-related genes, and thus impacts upon polygenic autoimmunity. Low CN of FCGR3B has recently been associated with systemic lupus erythematosus (SLE). FcgammaRIIIb is a glycosylphosphatidylinositol-linked, low affinity receptor for IgG found predominantly on human neutrophils. We present novel data demonstrating that both in a family with FcgammaRIIIb-deficiency and in the normal population, FCGR3B CNV correlates with protein expression, with neutrophil uptake of and adherence to immune complexes, and with soluble serum FcgammaRIIIb. Reduced FcgammaRIIIb expression is thus likely to contribute to the impaired clearance of immune complexes, which is a feature of SLE, explaining the association between low FCGR3B CNV and SLE that we have confirmed in a Caucasian population. In contrast, antineutrophil cytoplasmic antibody-associated systemic vasculitis (AASV), a disease not associated with immune complex deposition, is associated with high FCGR3B CN. Thus, we define a role for FCGR3B CNV in immune complex clearance, a function that may explain why low FCGR3B CNV is associated with SLE, but not AASV. This is the first report of an association between disease-related gene CNV and variation in protein expression and function that may contribute to autoimmune disease susceptibility.

Neutrophils interact with adenovirus vectors via Fc receptors and complement receptor 1

Neutrophils are effectors of the innate immune response to adenovirus vectors. Following the systemic administration of Cy2-labeled AdLuc in mice, flow cytometry and PCR analysis of liver leukocytes revealed that 25% of recruited neutrophils interacted with adenovirus vectors. In vitro, flow cytometry of human neutrophils incubated with Cy2-labeled AdLuc also demonstrated a significant interaction with adenovirus vectors. Fluorescence and electron microscopy confirmed vector internalization by neutrophils. The AdLuc-neutrophil interaction reduced vector transduction efficiency by more than 50% in coincubation assays in epithelium-derived cells. Adenovirus vector uptake by neutrophils occurred independently of coxsackievirus adenovirus receptor (CAR) and capsid RGD motifs, since neutrophils do not express CAR and uptake of the RGD-deleted vector AdL.PB* was similar to that of AdLuc. Furthermore, both AdLuc and AdL.PB* activated neutrophils and induced similar degrees of L-selectin shedding. Neutrophil uptake of AdLuc was dependent on the presence of complement and antibodies, since the interaction between AdLuc and neutrophils was significantly reduced when they were incubated in immunoglobulin G-depleted or heat-inactivated human serum. Blocking of complement receptor 1 (CD35) but not complement receptor 3 (CD11b/CD18) significantly reduced neutrophil uptake of AdLuc. Blocking of Fc gammaRI (CD64), Fc gammaRII (CD32), and Fc gammaRIII (CD16) individually or together also reduced neutrophil uptake of AdLuc, although less than blocking of CD35 alone. Combined CR1 and Fc receptor blockade synergistically inhibited neutrophil-AdLuc interactions close to baseline. These results demonstrate opsonin-dependent adenovirus vector interactions with neutrophils and their corresponding receptors.

Mechanisms of Intravenous Immunoglobulin Action in Immune Thrombocytopenic Purpura

The use of high-dose intravenous gamma immunoglobulin (IVIG) for the treatment of immune thrombocytopenic purpura (ITP) was first reported more than two decades ago. After the therapeutic benefit of IVIG was established in ITP, it was then successfully used to treat many other autoimmune diseases. Although a complete definition of the mechanism of IVIG action is still lacking, extensive research suggests that IVIG may achieve its therapeutic effects through multiple mechanisms. IVIG exerts immunomodulatory effects that may include antiidiotypic neutralization of antiplatelet antibodies, stimulation of Fcgamma receptor IIB expression, and inhibition of Fcgamma receptor-mediated platelet destruction. Recent work suggests that a large fraction of the benefit provided by IVIG may be the result of competitive inhibition of neonatal Fc receptor (FcRn) and IVIG-induced acceleration of antiplatelet antibody elimination. This review provides an overview and critical discussion of mechanisms that may be responsible of IVIG effects in ITP.

CD64 (Fcgamma receptor I) cell surface expression on maturing neutrophils from preterm and term newborn infants

BACKGROUND

The expression of CD64 (FcgammaRI) is increased from an almost negligible to a marked level on neutrophils in patients with bacterial infections. CD64 expression on neutrophils might therefore be a potential candidate for the diagnosis of bacterial infections in infants.

AIM

This study was performed to monitor changes of neutrophil expression of CD64 during the postpartum period to further evaluate the usefulness of this analysis. The possible influence on the expression of this receptor by other factors was also investigated, including respiratory distress syndrome (RDS) and preterm rupture of the membranes (PROM).

METHODS

Cell surface expression of CD64 on neutrophils from preterm and term newborn infants and healthy adults was analysed by flow cytometry. The expression of the other Fcgamma receptors, CD32 and CD16, and the complement receptors CD11b/CD18 and CD35 was also analysed for comparison.

RESULTS

Neutrophils from preterm newborn infants showed a moderately increased level of CD64 expression that, during their first month of life, was reduced to the level observed on neutrophils from term newborn infants and adults. In contrast, the level of neutrophil expression of CD32 and CD16 was significantly lower in preterm than term newborn infants and adults. Neutrophils from all groups indicated similar levels of CD11b expression, but the expression on neutrophils from newborn infants increased after birth.

CONCLUSION

Our results showed that neutrophil expression of CD64 is moderately increased in preterm newborn infants at birth. It seems not to be influenced by RDS, PROM or other factors related to preterm birth but by bacterial infection.

Role of Fcgamma receptors in the pathogenesis and treatment of idiopathic thrombocytopenic purpura

Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease characterized by autoantibody-mediated platelet destruction. Platelets with associated IgG are targeted for destruction by phagocytic cells bearing Fc receptors in the reticuloendothelial system. While there are a variety of therapeutics available for this incompletely understood disease, one of the treatments of choice is infusion of intravenous immunoglobulin (IVIG). This review will discuss the pathophysiology of ITP with an emphasis on the role of Fcgamma receptors in both the pathogenesis and treatment of the disease by IVIG. Other prominent theories of the mechanisms of action of IVIG, including the role of anti-idiotype antibodies, will also be addressed.

Mechanism of action of IVIG and anti-D in ITP

Infusion of large amounts of intravenous immunoglobulin (IVIG) or polyclonal anti-D can reverse thrombocytopenia in patients with idiopathic thrombocytopenic purpura within hours of the administration of these products. It has been suggested that the effects of IVIG appear to far outlast several half-lives of the product. Several mechanisms have been proposed to explain both the acute and long term effects of IVIG. These will be discussed in this review.

Mechanism of action of IVIG in ITP

IVIG is prepared from large pools of plasma from healthy donors and the IgG is present predominantly in monomeric form. It was first reported in 1981 by Dr. Paul Imbach that high doses of IVIG promote fast recovery of ITP in children. Despite extensive clinical use in a variety of autoimmune and inflammatory states, the mechanism of action of IVIG remains as yet incompletely understood. Several theories have been proposed to explain how administration of IVIG to individuals with ITP increases the platelet count. Following is an overview of some of the major theories.

Differential role of neutrophil Fcgamma receptor IIIB (CD16) in phagocytosis, bacterial killing, and responses to immune complexes

OBJECTIVE

To determine the roles played by the neutrophil Fcgamma receptor type II (FcgammaRII) (CD32) and FcgammaRIIIb (CD16) in phagocytosis, bacterial killing, and activation by immune complexes (ICs) and to test the hypothesis that inhibition of pathologic effector neutrophil function is possible without compromising host defense.

METHODS

Receptor function was probed by enzymic removal of FcgammaRIIIb from the cell surface and by use of Fab/F(ab')(2) fragments of monoclonal antibodies to block receptor-ligand binding. Cells were challenged with (a) serum-opsonized Staphylococcus aureus, (b) serum- and IgG-opsonized latex particles, and (c) synthetic soluble and insoluble ICs to mimic bacterial and inflammatory stimuli.

RESULTS

Phosphatidylinositol-phospholipase C treatment removed >97% of surface FcgammaRIIIb from neutrophils previously treated with tumor necrosis factor alpha to mobilize intracellular stores of receptor. This treatment profoundly inhibited activation of primed neutrophils by soluble ICs of the type found in diseased rheumatoid joints, but had no effect on phagocytosis and killing of serum-opsonized S aureus.

CONCLUSION

FcgammaRIIIb plays a major role in the secretion of toxic products in response to ICs, but little or no role in the phagocytosis and killing of serum-opsonized bacteria. The selective suppression of effector neutrophil function is therefore possible. FcgammaRIIIb, or its intracellular signaling pathway, is a potential therapeutic target in inflammatory diseases such as rheumatoid arthritis, because disruption of its function should decrease inflammatory tissue damage, but not jeopardize host protection against infection.

Fcgamma receptor-mediated immune phagocytosis depends on the class of FcgammaR and on the immunoglobulin-coated target cell

BACKGROUND AND OBJECTIVES

Three human Fcgamma receptors (FcgammaR) are known to mediate immune phagocytosis. A variety of different phagocytic assays have been described, but their comparability is complicated by the use of different effector cells and different antibody-coated target cells. The aim of this study was to determine the influence of these variable components on the FcgammaR-mediated phagocytosis.

MATERIALS AND METHODS

We sensitized human red blood cells (RBC) with polyclonal human anti-D (huaD), or with human monoclonal anti-D of the isotypes IgG1 (huIgG1) or IgG3 (huIgG3). Sheep RBC coated with rabbit immunoglobulin (RBC-RAS) were also used. Monocytes or polymorphonuclear neutrophils (PMN) were incubated with different FcgammaR-specific antibodies or their F(ab')2 fragments to determine the contribution of the different FcgammaRs on these effector cells in the phagocytic process of different antibody-coated target cells.

RESULTS

huaD-RBC and huIgG1-RBC were preferentially ingested via the FcgammaRI on monocytes and, to a minor extent, also by the FcgammaRII. PMN ingested these target cells only after induction of the FcgammaRI by interferon-gamma (IFN-gamma). huIgG3-RBC extensively formed rosettes with monocytes but were seldom ingested. RAS-RBC phagocytosis was induced primarily via the FcgammaRI on monocytes and was mediated by the FcgammaRII on PMN.

CONCLUSION

When performing phagocytosis assays with different effector and target cells, one has to take into account that phagocytosis is mediated by different FcgammaR, making comparability of these assays more difficult.

Involvement of pp125FAK and p60SRC in the signaling through Fc gamma RII-Fc gamma RIII in murine macrophages

Cross-linking the FcgammaRs can activate a wide variety of biological responses in macrophages. Receptor stimulation induces activation of protein tyrosine kinase cascades that result in phagocytosis, a process known to involve cytoskeletal rearrangements. Therefore, an involvement of non-receptor tyrosine kinases such as pp125FAK, in FcgammaR signaling is likely. Using the murine macrophage cell line J774, we demonstrate that FcgammaRII-RIII cross-linking induces a time- and dose-dependent increase in tyrosine phosphorylation of the focal adhesion kinase pp125FAK that correlates with an increase in its catalytic activity. Interestingly enough, pp125FAK activation results in its association both to the FcgammaRII-III and to p60Src. The results presented here define a novel-signaling pathway likely to be important in low affinity FcgammaRII-III mediated phagocytosis.

High incidence of maternal HLA A, B and C antibodies associated with a mild course of haemolytic disease of the newborn. Group for the Study of Protective Maternal HLA Antibodies in the Clinical Course of HDN

Mild courses of haemolytic disease of the foetus or newborn (HDN) due to Rh (D) blood group antibodies are associated with and may therefore be ameliorated by maternal antibodies reacting with human leucocyte antigens (HLA) of the child, an observation drawn from our own earlier data (Neppert J, Kissel K. Lancet 1992;339:1481). This study (i) corroborates this association; (ii) reveals shortcomings in the published data; and (iii) examines the characteristics of HDN cases when these shortcomings have been rectified. Samples from 51 women with antibodies against their child's blood group antigens of the Rh system were analysed for HLA A, B, C and DR antibodies during parturition. The mothers were divided into two groups, either severe or mild, dependent upon the clinical course of the HDN, and the incidence of HLA antibody production was determined for each group. HLA A, B, C and/or DR antibodies were detected in 85.2% of those women whose children had a mild course of HDN prenatally or perinatally (n=27). This is statistically greater than the incidence of 50.0% (Fisher's exact test: p=0.014) found in the group of women whose children had a severe HDN either pre- or perinatally (n=24) and is greater than the 35% (n=20; p=0.0001) found in women without Rh or other irregular antibodies. HLA DR antibodies were detected in three cases. The findings support our hypothesis that maternal anti HLA A, B and C antibodies may protect against a potential severe HDN. We therefore assume that those women will benefit who have already had a child with a severe HDN and in whom HLA antibodies were not previously detected, if HLA antibody production is provoked by subcutaneously inoculating with the father's leucocytes before or at the beginning of the new pregnancy.

Neutrophils from term and preterm newborn infants express the high affinity Fcgamma-receptor I (CD64) during bacterial infections

The high affinity Fcgamma-receptor I (FcgammaRI, CD64) is normally expressed only to a very low extent by neutrophils. During bacterial infections, however, neutrophils from adult patients significantly increase their expression of FcgammaRI. Stimulation through FcgammaRI is a highly effective way to improve various aspects of neutrophil function, including phagocytosis. In our study the expression of FcgammaRI on neutrophils from preterm (n = 9) and term (n = 3) newborn infants, children (n = 14), and adults (n = 6) during the early phase of an acute bacterial infection was investigated. Our results showed that neutrophils from newborn infants with bacterial infection expressed FcgammaRI to a significantly higher extent than both noninfected preterm (p < 0.001) and term (p < 0.001) newborn infants and that neutrophils from preterm neonates expressed FcgammaRI to the same extent as neutrophils from term neonates and older infants, children, and adults. No difference in the neutrophil cell surface expression of FcgammaRI during bacterial infections was found among newborn infants, children, and adults. Expression of FcgammaRI probably represents an important mechanism to improve neutrophil phagocytosis as well as other aspects of neutrophil function during bacterial infections, especially in preterm infants. Our study indicates that measurement of cell surface expression of FcgammaRI on neutrophils could be a useful indicator of severe bacterial infections in preterm and term neonates, as well as in older children and adults.

Monoclonal Lym-1 Antibody-Dependent Cytolysis by Neutrophils Exposed to Granulocyte-Macrophage Colony-Stimulating Factor: Intervention of FcγRII (CD32), CD11b-CD18 Integrins, and CD66b Glycoproteins

Murine monoclonal antibody (MoAb) Lym-1 is an IgG2a able to bind HLA-DR variants on malignant B cells and suitable for serotherapeutic approaches in B-lymphoma patients. We have previously shown that Lym-1 can synergize with granulocyte-macrophage colony-stimulating factor (GM-CSF) to trigger neutrophil cytolysis towards Raji cells used as a model of B-lymphoma targets. Here we provide evidence for the intervention of certain neutrophil receptors or surface molecules in this model of cell-mediated lysis. The lysis was completely inhibited by the anti-FcγRII MoAb IV.3 and unaffected by the anti-FcγRIII MoAb 3G8. This suggests that neutrophil cytolysis involves FcγRII without cooperation of this receptor with FcγRIII. Moreover, the lysis was inhibited by an anti-CD18 MoAb (MEM48) and by a MoAb specific for carcinoembryonic antigen (CEA)-like and glycophosphatidyl inositol (GPI)-linked glycoproteins (CD66b). Using an immunofluorescence staining procedure, cross-linking of CD66b induced the redistribution of CD11b on neutrophils with distinct areas of CD11b clustering via a process susceptible of inhibition by D-mannose. This is consistent with the ability of CD11b-CD18 and CD66b to undergo lectin-like physical interactions on the neutrophil surface. Such a type of interaction is presumably instrumental for neutrophil cytolytic activity in that the lysis was inhibited by D-mannose and enhanced by the MoAb VIM-12, which mimics the cooperation between CD11b and GPI-anchored molecules by specifically interacting with CD11b lectin-like sites. Therefore, the present results prove the absolute requirement for FcγRII in neutrophil GM-CSF/Lym-1–mediated cytolysis and, on the other hand, define the crucial role of CD66b and CD11b/CD18 in the expression of the cell lytic potential.

FMLP- and TNF-stimulated monoclonal Lym-1 antibody-dependent lysis of B lymphoblastoid tumour targets by neutrophils

Human neutrophils, incubated with Cr51-labelled B lymphoblastoid Raji cells in the presence of the anti-target monoclonal antibody (mAb) Lym-1 plus formyl-methionyl-leucyl-phenylalanine (FMLP) or tumour necrosis factor alpha (TNF-alpha), were found to induce significant C51 release, i.e. significant cytolysis. The lytic process was inhibited by mAb IV.3, specific for the Fcgamma receptor (FcgammaR) type II. The mAb 3G8, which reacts with FcgammaR type III, was ineffective. Moreover, the lysis was inhibited by the anti-CD18 mAb MEM-48. These data suggest that FMLP/Lym-1 as well as TNF-alpha/Lym-1 cytolytic systems strictly require FcgammaRII and CD18 integrins. As the lysis induced by TNF-alpha/Lym-1 was prevented by pertussis toxin (PT), PT-sensitive G-proteins are likely to intervene in post-FcgammaRII signal transduction. Both the FMLP- and the TNF-alpha-dependent systems were also found to be equally susceptible to inhibition by various inhibitors of kinases (genistein, staurosporin, 1-(5-isoquinolinnylsulphonyl)-2-methylpiperazine and wortmannin). On the contrary, an inhibitor of protein kinase C (bis-indolyl-maleimide, BIM) was effective only in the FMLP/Lym-1 cytolytic system. Therefore, it appears that signals delivered by FMLP or TNF-alpha, BIM-sensitive and insensitive respectively, converge and synergize with those from G-protein-coupled FcgammaRII and, probably, CD18-integrins to promote the expression of the neutrophil cytolytic potential.

A microscopic study of Fc gamma RIII-mediated respiratory burst in neutrophils

We investigated the relationship between the respiratory burst in neutrophils and the membrane distribution of the IgG receptor, Fc gamma RIII. Fc gamma RIII receptors were labeled with a fluoresceinated antibody that does not block binding of immune complexes. The respiratory burst was detected using covalently bound rosamine stain previously described for flow cytometric applications. This method allows visualization of intracellular oxidant production in fixed cells using attenuated illumination with a laser. Strong cytosolic oxidation of rosamine was observed only in those cells that displayed prominent receptor endocytosis upon interaction with insoluble immune complexes. Soluble immune complexes or insoluble complexes in the presence of cytochalasin B did not stimulate endocytosis of Fc gamma RIII and induced no rosamine oxidation. Extracellular superoxide production measured by the cytochrome c test did not correlate with intracellular rosamine oxidation: it was maximal in cytochalasin-treated cells and did not require any visible receptor rearrangement. Our results demonstrate the utility of the rosamine stain as an intracellular marker of the oxidative burst, support the role of Fc gamma RIII in neutrophil activation and emphasize the compartmental regulation of the oxidative burst.