Human intravenous immunoglobulin (IVIG) preparations degranulate human neutrophils in vitro

Abrogation of neutrophil inflammatory pathways and potential reduction of neutrophil-related factors in COVID-19 by intravenous immunoglobulin

Pathogenesis of lung injury in COVID-19 is not completely understood, leaving gaps in understanding how current treatments modulate the course of COVID-19. Neutrophil numbers and activation state in circulation have been found to correlate with COVID-19 severity, and neutrophil extracellular traps (NETs) have been found in the lung parenchyma of patients with acute respiratory distress syndrome (ARDS) in COVID-19. Targeting the pro-inflammatory functions of neutrophils may diminish lung injury in COVID-19 and ARDS. Neutrophils were isolated from peripheral blood of healthy donors, treated ex vivo with dexamethasone, tocilizumab and intravenous immunoglobulin (IVIG) and NET formation, oxidative burst, and phagocytosis were assessed. Plasma from critically ill COVID-19 patients before and after clinical treatment with IVIG and from healthy donors was assessed for neutrophil activation-related proteins. While dexamethasone and tocilizumab did not affect PMA- and nigericin-induced NET production ex vivo, IVIG induced a dose-dependent abrogation of NET production in both activation models. IVIG also reduced PMA-elicited reactive oxygen species production, but did not alter phagocytosis. COVID-19 patients were found to have elevated levels of cell-free DNA, neutrophil elastase and IL-8 as compared to healthy controls. Levels of both cell-free DNA and neutrophil elastase were lower 5 days after 4 days of daily treatment with IVIG. The lack of impact of dexamethasone or tocilizumab on these neutrophil functions suggests that these therapeutic agents may not act through suppression of neutrophil functions, indicating that the door might still be open for the addition of a neutrophil modulator to the COVID-19 therapeutic repertoire.

Administration of intravenous immunoglobulin in the treatment of COVID-19: A review of available evidence

Since December 31, 2019, unknown causes of pneumonia have been reported in Wuhan, China. This special pneumonia associated with a novel coronavirus was named 2019-nCoV by the World Health Organization (WHO) in January 2020. From the beginning of this infectious disease, clinicians and researchers have been endeavoring to discover an effective and suitable treatment for affected patients. To date, there is no definitive and specific treatments for coronavirus disease-19 (COVID-19) infection while drugs introduced are still in the clinical trial phase. Intravenous immune globulin (IVIG) is a biological product prepared from the serum and an optional treatment for patients with antibody deficiencies. In many countries, much attention has been paid to the use of IVIG in the treatment of patients with COVID-19. Due to the therapeutic importance of IVIG in virus infections, in the current study, we reviewed the possible effect of IVIG in viral infections and potential evidence of IVIG therapy in patients with COVID-19 virus.

Common variable immunodeficiency patients display elevated plasma levels of granulocyte activation markers elastase and myeloperoxidase

Common variable immunodeficiency disorders (CVIDs) represent a group of primary immunodeficiency diseases characterized by hypogammaglobulinemia and dysfunctional immune response to invading pathogens. Previous studies have indicated that CVID is associated with microbial translocation and systemic myeloid cell activation.

The goal of this study was to determine whether patients with CVID display elevated systemic levels of markers of granulocyte activation and whether the levels are further influenced by intravenous immunoglobulin (IVIg) infusions. The plasma levels of granulocyte activation markers elastase and myeloperoxidase were determined using enzyme-linked immunosorbent assay (ELISA) in 46 CVID patients and 44 healthy controls. All CVID patients were in a stable state with no apparent acute infection. In addition, granulocyte activation markers’ plasma levels in 24 CVID patients were determined prior to and 1 h following IVIg administration. Neutrophil elastase and myeloperoxidase plasma levels were significantly higher in CVID patients than in healthy controls. Systemic elastase levels were further increased following IVIg administration. In vitro stimulation of 13 CVID patients’ whole blood using IVIg in a therapeutically relevant dose for 2 h resulted in a significant increase in plasma elastase levels compared to unstimulated blood. The data presented here indicate that CVID is associated with chronic granulocytic activation which is further exacerbated by administering IVIg. Increased myeloperoxidase and elastase levels may contribute to associated comorbidities in CVID patients.

Pharmaceutical immunoglobulins reduce neutrophil extracellular trap formation and ameliorate the development of MPO-ANCA-associated vasculitis

Objectives: Intravenous immunoglobulin (IVIG) therapy is effective against some autoimmune diseases. We examined the effects of pharmaceutical immunoglobulins on the development of MPO-ANCA-associated vasculitis (MPO-AAV).Methods: Peripheral blood neutrophils were pretreated with 5 mg/ml sulfo-immunoglobulins (IVIG-S) and then exposed to 100 nM phorbol myristate acetate (PMA). Thereafter, neutrophil extracellular traps (NETs) were detected by flow cytometry. Next, Wistar-Kyoto rats were given oral administration of 10 mg/kg/day propylthiouracil for 28 days and intraperitoneal (i.p.) injection of 1 μg PMA on days 0 and 7. These rats were divided into two groups: Group 1 with i.p. injection of 400 mg/kg IVIG-S on days 8-12 and Group 2 with vehicle similarly. ANCA titers were chronologically determined by indirect immunofluorescence. On day 28, all rats were killed to examine NET formation in the peritoneum and the development of AAV.Results: IVIG-S significantly inhibited NET formation induced by PMA in vitro. NET amounts in the peritoneum in Group 1 were significantly smaller than in Group 2, and ANCA titers in Group 1 were significantly lower than in Group 2. The degree of pulmonary hemorrhage in Group 1 was also smaller than in Group 2.Conclusion: IVIG-S reduce NET formation and ameliorate the development of MPO-AAV.

Engineered hexavalent Fc proteins with enhanced Fc-gamma receptor avidity provide insights into immune-complex interactions

Autoantibody-mediated diseases are currently treated with intravenous immunoglobulin, which is thought to act in part via blockade of Fc gamma receptors, thereby inhibiting autoantibody effector functions and subsequent pathology. We aimed to develop recombinant molecules with enhanced Fc receptor avidity and thus increased potency over intravenous immunoglobulin. Here we describe the molecular engineering of human Fc hexamers and explore their therapeutic and safety profiles. We show Fc hexamers were more potent than IVIG in phagocytosis blockade and disease models. However, in human whole-blood safety assays incubation with IgG1 isotype Fc hexamers resulted in cytokine release, platelet and complement activation, whereas the IgG4 version did not. We used a statistically designed mutagenesis approach to identify the key Fc residues involved in these processes. Cytokine release was found to be dependent on neutrophil FcγRIIIb interactions with L234 and A327 in the Fc. Therefore, Fc hexamers provide unique insights into Fc receptor biology.

Tania Rowley et al. present multivalent Fc molecules with enhanced avidity for Fc gamma receptors in order to improve the treatment of autoantibody-mediated human diseases. They found several key amino acids involved in Fc receptor binding interactions.

Intravenous immunoglobulin replacement treatment reduces in vivo elastase secretion in patients with common variable immune disorders

BACKGROUND

Intravenous immunoglobulin (IVIg) treatment partially replaces antibody defects and modulates innate and adaptive immune cells in patients with primary antibody deficiencies.

MATERIALS AND METHODS

This study was focused on the evaluation of the effects of in vivo IVIg administration on neutrophils from patients with common variable immune disorders (CVID). We examined polymorphonuclear neutrophil (PMN) phagocytosis, PMN oxidative burst, release of neutrophil elastase, serum level of interleukin-8 and PMN expression of CXCR1, CD11c and CD66b.

RESULTS

CVID patients on chronic IVIg treatment had reduced elastase release, but normal expression of CXCR1, CD66b and CD11c receptors on PMN, normal phagocytic ability and normal secretion of interleukin-8. We found that IVIg infusions rapidly reduced the serum level of interleukin-8, the expression of its receptor, CXCR1, and the release of neutrophil elastase, suggesting that IVIg exert a dampening effect on neutrophil activity. In contrast, IVIg infusions did not alter neutrophil phagocytosis or the expression of the other receptors analysed.

DISCUSSION

These findings add further information regarding the anti-inflammatory role of immunoglobulins and suggest additional benefits in keeping with recent attempts to use new therapies targeting neutrophil inflammation.

Dimeric IgG complexes from IVIg are incapable of inducing in vitro neutrophil degranulation or complement activation

Purpose

Intravenous immunoglobulin (IVIg) products contain various amounts of dimeric IgG complexes. Current insights into the possible biological activities of these dimers remain controversial, and both immunemodulating and immune-activating effects have been reported. Here, we analyzed the putative immune-activating effects of dimers isolated from IVIg.

Methods

Dimers isolated from IVIg were purified by high-performance size-exclusion chromatography (HP-SEC) and tested for the ability to induce neutrophil degranulation in vitro.

Results

Dimers isolated from IVIg were found to be incapable of inducing in vitro neutrophil degranulation or complement activation, even at concentrations exceeding those expected to be reached upon administration in patients. These results depend on the removal of artefactual activation by using 0.1 micron filtration and the use of poloxamer to prevent adsorption of IgG onto the solid phase.

Conclusions

The data suggest dimeric IgG found in IVIg may bind to Fc-receptors without causing activation.

Armed for destruction: formation, function and trafficking of neutrophil granules

Neutrophils respond nearly instantly to infection, rapidly deploying a potent enzymatic and chemical arsenal immediately upon entering an infected site. This capacity for rapid and potent responses is endowed by stores of antimicrobial proteins contained in readily mobilizable granules. These granules contain the proteins necessary to mediate the recruitment, chemotaxis, antimicrobial function and NET formation of neutrophils. Four granule types exist, and are sequentially deployed as neutrophils enter infected sites. Secretory vesicles are released first, enabling recruitment of neutrophils out of the blood. Next, specific and gelatinase granules are released to enable neutrophil migration and begin the formation of an antimicrobial environment. Finally, azurophilic granules release potent antimicrobial proteins at the site of infection and into phagosomes. The step-wise mobilization of these granules is regulated by calcium signaling, while specific trafficking regulators and membrane fusion complexes ensure the delivery of granules to the correct subcellular site. In this review, we describe neutrophil granules from their formation through to their deployment at the site of infection, focusing on recent developments in our understanding of the signaling pathways and vesicular trafficking mechanisms which mediate neutrophil degranulation.

Effect of intravenous immunoglobulin administration on erythrocyte and leucocyte parameters

BACKGROUND

Intravenous immunoglobulins (IVIG) are an attractive therapeutic tool for therapy of toxic epidermal necrolysis and severe forms of certain autoimmune diseases, including dermatomyositis, autoimmune blistering diseases, systemic vasculitis and lupus erythematodes.

OBJECTIVES

Prompted by a case of IVIG-associated haemolytic anaemia, the effects of IVIG administrations on haematological parameters in patients with dermatological conditions were investigated.

METHODS

Erythrocyte and leucocyte parameters were retrospectively analysed in 16 patients who had received IVIG at doses from 1 to 3 g/kg bodyweight (n = 35 cycles). The influence of IVIG on leucocyte survival was determined in vitro.

RESULTS

Decreased absolute erythrocyte numbers, haemoglobin and haematocrit levels and a case of haemolytic anaemia were linked to transfusion of high-, but not low-dose IVIG. In contrast, leucopenia post-IVIG occurred in the vast majority of the recipients, unrelated to the administered IVIG amounts. In vitro investigations revealed a dose-dependent impairment of cell survival by IVIG in the neutrophil and monocyte, but not in the lymphocyte subpopulations. In several IVIG preparations, substantial amounts of blood group anti-A/anti-B antibodies were detected which could have accounted for the observed changes in the haematological parameters in our study cohort.

CONCLUSIONS

IVIG products should be administered strictly according to indications. Commercially available IVIG products can contain blood group-specific antibodies that may induce haemolysis in some recipients. Monitoring of blood counts during applied IVIG therapy, especially when high doses are administered, is recommended.

The effect of Intravenous Immunoglobulin (IVIG) on \textit{ex vivo} activation of human leukocytes

INTRODUCTION

Intravenous immunoglobulin (IVIG) has been widely used to treat various conditions, including inflammatory and autoimmune diseases. IVIG has been shown to have a direct influence on neutrophils, eosinophils and lymphocytes. However, many aspects IVIG's effect on neutrophils activation still remain unknown.

OBJECTIVE

To evaluate the effect of IVIG on PMA-induced activation of neutrophils, with and without priming with TNF-α, in a series of in vitro experiments performed on whole blood.

RESULTS

Our data coincided with well-known literature indicating that the effect of phorbol 12-myristate 13-acetate (PMA) on human leukocytes includes activation of neutrophils, monocytes and eosinophils, increase of chemiluminescence (CL) and induction of netosis, resulting in assembly of traps. In presence of IVIG (10 mg/mL), CL was reduced by 25% in response to PMA compared to PMA-induced leukocyte activation without IVIG. Decreasing IVIG concentration to 1 mg/mL and below did not inhibit PMA-induced activation of CL.PMA-induced activation after TNF-α priming resulted in approximately 50% increase of amplitude of CL response to PMA. Moreover, maximum CL was reached by minute 5, which was more rapid than in the absence of TNF-α-priming (in this case maximum CL was reached by minute 15).The IVIG concentrations did not affect morphological changes of leukocytes after sequential addition of TNF-α and PMA. IVIG had no effect on leukocyte content and on PMA-induced CL of primed leukocytes.Addition of IVIG under TNF-α priming significantly increased the number of traps in the smears in response to PMA activation. Of note, such an increase in the number of traps was depended on the IVIG concentration in plasma.

CONCLUSION

In conclusion, we suggest that IVIG is able to reduce the degradation of traps under priming with TNF-α. Moreover, IVIG might switch the activation of primed leukocytes to netosis.

Intravenous immunoglobulin replacement treatment does not alter polymorphonuclear leukocytes function and surface receptors expression in patients with common variable immunodeficiency

The study of the expression of CD16, CD11b and Siglec 9 receptors and the oxidative burst provides insights on polymorphonuclear leukocytes (PMN) functionality in common variable immunodeficiency (CVID) and on the possible effects of intravenous immunoglobulin (IVIg) infusion. We evaluated in vivo before and soon after IVIg administration the CD16, CD11b and Siglec 9 expression on unstimulated and Escherichia coli-stimulated PMN and the oxidative burst induced by Escherichia coli and PMA. The E. coli stimulation up-regulated CD16 and Siglec 9 expression and it induced a strong CD11b up-regulation at baseline and soon after IVIg. The oxidative burst overlapped that observed in healthy donors when induced by Escherichia coli while it increased when induced by PMA. Soon after IVIg infusion, the oxidative burst decreased only when induced by PMA. Our results showed that the IVIg infusion in vivo had a minimal effect on CVID's PMN.

Matrix metalloproteinases as input and output signals for post-myocardial infarction remodeling

Despite current optimal therapeutic regimens, approximately one in four patients diagnosed with myocardial infarction (MI) will go on to develop congestive heart failure, and heart failure has a high five-year mortality rate of 50%. Elucidating mechanisms whereby heart failure develops post-MI, therefore, is highly needed. Matrix metalloproteinases (MMPs) are key enzymes involved in post-MI remodeling of the left ventricle (LV). While MMPs process cytokine and extracellular matrix (ECM) substrates to regulate the inflammatory and fibrotic components of the wound healing response to MI, MMPs also serve as upstream signaling initiators with direct actions on cell signaling cascades. In this review, we summarize the current literature regarding MMP roles in post-MI LV remodeling. We also identify the current knowledge gaps and provide templates for experiments to fill these gaps. A more complete understanding of MMP roles, particularly with regards to upstream signaling roles, may provide new strategies to limit adverse LV remodeling.

Prevention of immunoglobulin G immobilization eliminates artifactual stimulation of dendritic cell maturation by intravenous immunoglobulin in vitro

Intravenous immunoglobulin (IVIg), a therapeutic preparation containing pooled human immunoglobulin (Ig) G, has been suggested to inhibit differentiation and maturation of dendritic cells (DCs); however, controversies exist on this issue. We aimed to reinvestigate the effects of IVIg on human DC maturation and cytokine production, and to determine whether an artifactual determinant is involved in the observed effects. Human monocyte-derived DCs or freshly isolated blood myeloid DCs were cultured in the presence of IVIg in vitro, and the expression of maturation markers CD80, CD86, CD83, and Human Leukocyte Antigen-DR were determined by flow cytometry, whereas production of interleukin (IL)-12 and IL-10 was measured by enzyme-linked immunosorbent assay, and T-cell stimulatory capacity was determined in cocultures with allogeneic CD4(+) T cells. Interestingly, we observed that IVIg did not inhibit, but instead stimulated, spontaneous maturation and T-cell stimulatory ability of human DCs, while leaving lipopolysaccharide-induced DC maturation and cytokine production unaffected. Strikingly, prevention of IVIg binding to culture plate surface, or blocking of the activating Fcγ receptor IIa on DC, abrogated the stimulatory effect of IVIg on costimulatory molecule expression and on T-cell stimulatory capacity of DCs, suggesting that IVIg activates DCs on IgG adsorption to the plastic surface. This study warrants for careful study design when performing cell culture studies with IVIg to prevent artifactual effects, and shows that IVIg does not modulate directly costimulatory molecule expression, cytokine production, or allogeneic T-cell stimulatory capacity of human DCs.

A novel splice variant of FcγRIIa: a risk factor for anaphylaxis in patients with hypogammaglobulinemia

BACKGROUND

Our index case was a patient with common variable immunodeficiency (CVID). She had anaphylactoid reactions on administration of intravenous immunoglobulin (IVIg) associated with the presence of IgG antibodies against IgA.

OBJECTIVE

We sought to determine the role of Fcγ receptor (FcγR) IIa in IVIg-induced anaphylactoid reactions.

METHODS

Neutrophils and PBMCs were isolated from healthy subjects and IVIg-treated patients. FcγRIIa mRNA and DNA were analyzed by using real-time PCR and sequencing. IgG-mediated elastase release and intracellular Ca(2+) mobilization were determined in neutrophils and transfected cell lines, respectively.

RESULTS

A novel splice variant of FcγRIIa containing an expressed cryptic exon 6* (FcγRIIa(exon6∗)) was identified in our index patient. This exon is normally spliced out of all FcγRII isoforms, except the inhibitory FcγRIIb1. Compared with healthy control subjects, the heterozygous FCGR2A(c.742+871A>G) mutation was more frequent in patients with CVID (n = 53, P < .013). Expression in patients with CVID was associated with anaphylaxis on IVIg infusion (P = .002). On screening of additional IVIg-treated patient cohorts, we identified 6 FCGR2A(c.742+871A>G) allele-positive patients with Kawasaki disease (n = 208) and 1 patient with idiopathic thrombocytopenia (n = 93). None had adverse reactions to IVIg. Moreover, FcγRIIa(exon6∗) was also demonstrated in asymptomatic family members. Functional studies in primary cells and transfected murine cells demonstrated enhanced cellular activation by FcγRIIa(exon6∗) compared with its native form, as shown by increased elastase release and intracellular calcium mobilization.

CONCLUSION

A novel splice variant, FcγRIIa(exon6∗), was characterized as a low-frequency allele, coding for a gain-of-function receptor for IgG. In the presence of immune complexes, FcγRIIa(exon6∗) can contribute to anaphylaxis in patients with CVID.

A differential concentration-dependent effect of IVIg on neutrophil functions: relevance for anti-microbial and anti-inflammatory mechanisms

BACKGROUND

Polymorphonuclear neutrophils (PMN) play a key role in host defences against invading microorganisms but can also potentiate detrimental inflammatory reactions in case of excessive or misdirected responses. Intravenous immunoglobulins (IVIg) are used to treat patients with immune deficiencies and, at higher doses, in autoimmune, allergic and systemic inflammatory disorders.

METHODOLOGY/PRINCIPAL FINDINGS

We used flow cytometry to examine the effects of IVIg on PMN functions and survival, using whole-blood conditions in order to avoid artifacts due to isolation procedures. IVIg at low concentrations induced PMN activation, as reflected by decreased L-selectin and increased CD11b expression at the PMN surface, oxidative burst enhancement, and prolonged cell survival. In contrast, IVIg at higher concentrations inhibited LPS-induced CD11b degranulation and oxidative burst priming, and counteracted LPS-induced PMN lifespan prolongation.

CONCLUSIONS/SIGNIFICANCE

IVIg appears to have differential, concentration-dependent effects on PMN, possibly supporting the use of IVIg as either an anti-microbial or an anti-inflammatory agent.

Hypothesis: hemolytic transfusion reactions represent an alternative type of anaphylaxis

Classical anaphylaxis is the most severe, and potentially fatal, type of allergic reaction, manifested by hypotension, bronchoconstriction, and vascular permeability. Similarly, a hemolytic transfusion reaction (HTR) is the most feared consequence of blood transfusion. Evidence for the existence of an alternative, IgG-mediated pathway of anaphylaxis may be relevant for explaining the pathophysiology of IgG-mediated-HTRs. The purpose of this review is to summarize the evidence for this alternative pathway of anaphylaxis and to present the hypothesis that an IgG-mediated HTR is one example of this type of anaphylaxis.

Intravenous immunoglobulin (IVIG) treatment for modulation of immune activation in human immunodeficiency virus type 1 infected therapy-naive individuals

We evaluated the ability of intravenous immunoglobulin (IVIG) to diminish immune hyperactivation, which is considered a major cause of CD4+ T cell loss during chronic HIV-1 infection and whether this affected CD4+ T cell counts and plasma HIV-1 RNA (pVL). Therefore, we treated six chronically HIV-1-infected, antiretroviral-therapy-naive patients with IVIG (0.4 g/kg) at weeks 0 and 4, with a follow-up of 12 weeks after the second dosage during which pVL, T cell numbers, and T cell activation were measured. At baseline median CD4+ T cell counts were 300 (range 200-460) x 10(6)/liter and median pVL was 5.0 (range 3.2-5.2) log10 copies/ml. IgG plasma levels peaked during the first days after administration. We observed a decrease in the percentage of activated (CD38+ HLA-DR+) CD4+ and CD8+ T cells [3.5% (range 1-7%) and 5% (1-10%), respectively (p = 0.027)], but no effect on the fraction of proliferating CD4+ or CD8+ T cells as measured by Ki67 expression. CD4+ T cell counts were significantly increased on day 4 (median +55 cells, range 0-150, p = 0.043). pVL was significantly increased on day 1 after IVIG infusion (median +0.13 log10, range 0.01-0.55, p = 0.028). All these parameters returned to baseline levels within 1 week after infusion. In conclusion, administration of IVIG caused a temporary decrease in T cell activation and an increase in CD4+ T cell counts, despite an increase in pVL. Our results support the hypothesis that T cell activation, rather than direct HIV-1 infection, mediates the loss of CD4+ T cells and suggest that immunomodulating therapy in HIV-1 infection could indeed be effective.

Antibody therapy (IVIG): evaluation of the use of genomics and proteomics for the study of immunomodulation therapeutics

BACKGROUND AND OBJECTIVES

Intravenous immunoglobulin (IVIG) is used for an increasingly diverse number of therapeutic applications as an immunomodulation drug. Although it has demonstrated therapeutic effectiveness, the mechanism of action of IVIG in these disorders is poorly understood; this lack of understanding complicates rational clinical application and reimbursement for 'off-label' use.

MATERIALS AND METHODS

Selected literature on the clinical use of IVIG as an immunomodulation drug is reviewed. We present a brief description of DNA microarray and protein microarray technology and the application of such technologies to the study of immune system cells. The several studies on the application of DNA microarray technology to study gene expression in response to IVIG are presented.

RESULTS

There is increasing data on the use of DNA microarray and protein microarray technology to study gene expression in immune system cells including T cells, B cells, macrophages, and leucocytes. There is less information on the effect of IVIG on gene expression in immune system cells. However, there is sufficient information available to suggest that this is a practical approach with the caveat that such work will require careful experimental design and clear definition of the normal population.

CONCLUSIONS

DNA and protein microarray assays can be used to (i) provide rational indications for the clinical use of IVIG, (ii) provide for specific analysis of raw material and end product IVIG in screening for content related to immunomodulation, and (iii) accelerate the development of next generation products which would be more focused and/or targeted therapeutics.

Intravenous immunoglobulins and haematopoietic growth factors in the prevention and treatment of neonatal sepsis: ground reality or glorified myths?

Neonatal sepsis is a significant cause of morbidity and mortality in the neonatal intensive care unit. The epidemiology of neonatal infections is complex; however, they are in large part secondary to developmentally immature host defence mechanisms. These immunodeficiencies, which are exaggerated in premature and sick neonates, include quantitative and qualitative deficits in phagocytes, complement components, cytokines and immunoglobulins. Therapies that modulate or augment host defences may attenuate the virulence of neonatal infections. In this paper, we have reviewed immunotherapies that modulate the immune system of the neonate, including intravenous immunoglobulins and myeloid haematopoietic growth factors. Future studies should focus on investigating other abnormalities of neonatal host defence and/or combined immunotherapy approaches in an attempt to circumvent the immaturity of host defence and potentially reduce both the incidence and severity of neonatal sepsis.

Intravenous immunoglobulins contain naturally occurring antibodies that mimic antineutrophil cytoplasmic antibodies and activate neutrophils in a TNFα-dependent and Fc-receptor–independent way

Intravenous immunoglobulin (IVIg) preparations are increasingly used for therapy of several neuroimmunologic diseases. IVIg therapy is considered safe, although serious side effects like aseptic meningitis, cerebral vasospasm, or ischemic encephalopathy have been reported. These side effects are frequently associated with neutrophilic pleocytosis in the cerebrospinal fluid (CSF), suggesting a neutrophil-mediated mechanism. To elucidate the potential role of neutrophil activation, we analyzed IVIg preparations from 5 different commercial sources for the presence of antineutrophil cytoplasmic antibody (ANCA)–like immunoglobulins against ethanol-fixed peripheral-blood neutrophils, purified human antigens, and a panel of human and nonhuman tissues. All IVIg batches tested (n = 13) contained atypical ANCAs (IgG titer up to 1:2048, IgA up to 1:512). Moreover, all preparations were capable of inducing hydrogen peroxide production in TNFα-primed human neutrophils, with a significant correlation (P < .005) between atypical ANCA titers in IVIg preparations and neutrophil activation. Fc-mediated binding and activation was ruled out by the use of IVIg-F(ab′)2 fragments. Our findings strongly suggest that in vivo activation of TNFα-primed neutrophils by atypical ANCAs of IVIg may contribute to the side effects of IVIg therapy and for the first time demonstrate that the activation of neutrophil granulocytes by IVIg occurs in an Fc receptor (FcR)–independent, hence antigen-dependent, way.

Neutrophil responsiveness to IgG, as determined by fixed ratios of mRNA levels for activating and inhibitory FcγRII (CD32), is stable over time and unaffected by cytokines

We tested the hypothesis that the ratio between the activating and inhibitory Fcγ receptor type II (FcγRII) in neutrophils determines their responsiveness to immune complexes. We measured mRNA levels of FcγRII isoforms and observed differences in the ratio of FcγRIIa to FcγRIIb2 mRNA in granulocytes of 50 white and 10 black healthy volunteers, and found 4 discrete groups of ratios (ie, 4:1; 3:1, 2:1, or 1:1). The response to either dimeric IgG or aggregated IgG (aIgG) was assessed. Up-regulation of CD11b on the surface as well as the elastase release was significantly more pronounced in neutrophils with a high FcγRIIa/FcγRIIb2 mRNA ratio of 4:1 compared with a 2:1 or 1:1 ratio. Individual ratios as well as the functional responsiveness of neutrophils were constant over time, as was tested over 12 months. Neutrophil stimulation with various agents in vitro did not alter the FcγRIIa/FcγRIIb2 mRNA ratio in the neutrophils of these donors, in clear contrast to the findings in their mononuclear cells. We found a strong association between the 2B.4 haplotype of the FCGR2B promoter with increased transcriptional activity in individuals with 1:1 ratios and the more common low-expression 2B.1 haplotype in individuals with FcγRIIa/FcγRIIb2 mRNA ratios of 2:1, 3:1, or 4:1.

Gene expression profiling of the effects of intravenous immunoglobulin in human whole blood

Intravenous immunoglobulin (IVIG) is involved in many complex mechanisms that act in synergy including expression and function of Fc receptors, complement activation, the cytokine network, interaction with the anti-idiotypic network and modulation of B and T cell activation. To gain insight into the early effects of IVIG on this broad range of activities at the gene level we performed DNA microarray analysis. Human whole blood was incubated in vitro for 4 h followed by extraction of RNA which was hybridized to a chip containing 8793 genes. About 75 upregulated genes and 21 downregulated genes were identified using a cut off for the false discovery rate of 5%. These genes are associated with a wide range of cellular immune functions in line with the broad mechanism of action of IVIG. A striking upregulation of a series of genes coding for chemokines was measured. This finding was confirmed at the protein level as pharmacologically relevant concentrations of CXCL9 and CXCL10 were measured in serum. Interestingly, IVIG shows a partial overlap of its gene expression program with lipopolysaccharide. Our data suggests multiple hypotheses regarding the pharmacology of IVIG that must be validated by complementary studies.

Characterization of immunoglobulin G fragments in liquid intravenous immunoglobulin products

BACKGROUND

Intravenous immunoglobulin (IVIG) products formulated as a liquid instead of a powder have become commercially available. Preferably, such liquid products should not alter after storage outside the refrigerator. Therefore, a thorough characterization of immunoglobulin G (IgG) fragmentation at various storage temperatures is required.

STUDY DESIGN AND METHODS

Storage experiments with liquid IVIG products from five manufacturers were performed at 4, 25, and 37 degrees C and IgG fragments were analyzed.

RESULTS

Storage of liquid IVIG products at 4 degrees C resulted in negligible alterations, whereas an increase of IgG fragments was observed after prolonged storage at elevated temperatures. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis of five liquid IVIG products revealed three IgG fragments (12, 26, and 54 kDa) in all products. Fragments of similar molecular mass were produced upon incubations of IgG with blood-derived proteases. N-terminal amino acid sequencing revealed the cleavage site of these fragments, suggesting human neutrophil elastase to cause the 12-kDa fragment. The presence of elastase in liquid IVIG was confirmed by enzyme-linked immunosorbent assay. The origin of the 26- and 54-kDa fragments, both with an aspartic acid residue at the cleavage site, could not be determined unambiguously.

CONCLUSION

IgG fragmentation in liquid IVIG is negligible when stored in the refrigerator. Only after prolonged storage at elevated temperature does proteolytic degradation of IgG become apparent.

Intravenous immunoglobulin preparations promote apoptosis in lipopolysaccharide-stimulated neutrophils via an oxygen-dependent pathway in vitro

Since prolonged survival of activated neutrophils has an autotoxic potential, neutrophil apoptosis plays an important role in the rapid resolution of inflammation. Intravenous immunoglobulin (IVIG) preparations, which are beneficial therapeutic agents for the treatment of autoimmune diseases and systemic inflammatory diseases, have been reported to induce apoptosis of lymphocytes and endothelial cells in vitro. In the present study, we investigated whether IVIG may induce apoptosis of neutrophils cultured in vitro. After neutrophils prestimulated with or without lipopolysaccharide (LPS) were cultured in the presence or absence of IVIG, the number of apoptotic cells, intracellular H2O2 and GSH were measured by a flow cytometer. IVIG induced apoptosis of LPS-stimulated neutrophils dose dependently, but not in unstimulated neutrophils. Although anti-Fas monoclonal antibodies (mAbs) had no effect on the IVIG-induced apoptosis in the LPS-stimulated neutrophils, anti-Fc gamma receptor (Fc gammaR) II- and III-blocking mAbs significantly inhibited the IVIG-induced apoptosis. IVIG increased the production of intracellular H2O2, while it decreased the production of GSH, in the LPS-stimulated neutrophils. Furthermore, a specific NADPH oxidase inhibitor and anti-oxidants inhibited the IVIG-induced neutrophil apoptosis. Therefore, these findings indicate that IVIG preparations induce apoptosis of LPS-stimulated neutrophils and suggest that the IVIG-induced apoptosis may be mediated by an oxygen-dependent pathway via Fc gammaRII and III.

gamma-Globulin-induced modulation with necrotic-like morphology of peripheral blood neutrophils

To determine the effect of intravenous immunoglobulin-administration on neutrophil function, we obtained neutrophils from patients with an acute phase of Kawasaki disease. In vitro IgG-induced modulation of neutrophils into Annexin-V-positive and propidium iodide-negative cells was observed in 20 of 28 patients in the presence of more than 300 microg/ml IgG and showed necrosis-like changes in morphologic features. However, we could not find any patients showing promotion of the sub-G1 cell fraction on DNA content analysis. The modulatory effect of in vitro IgG was not observed in neutrophils from healthy volunteers and was significantly correlated with the antifebrile effect of in vivo IgG.

Neutropenia following IVIG therapy in pediatric patients with immune-mediated thrombocytopenia

It has been observed that some children with immune-mediated thrombocytopenia (ITP) who are treated with intravenous immunoglobulin (IVIG) experience a decline in their absolute neutrophil count (ANC). The aim of this study was to investigate the incidence of neutropenia following IVIG therapy in a large cohort of children with ITP. This retrospective comparative cohort study determined the incidence of neutropenia in 104 patients (110 treatment courses) admitted for ITP to the Children's Hospital of Philadelphia from January 2000 to October 2003. Post-treatment ANCs were compared between patients who received IVIG and patients who received anti-D immunoglobulin. The incidence of neutropenia in each group was analyzed using the Fisher exact test. Pretreatment ANCs were not significantly different between the two treatment groups (P = 0.72). Neutropenia (ANC < 1,500/microL), developed during 18 of 64 (28%) treatment courses with IVIG, compared with 0 of 46 (0%) treatment courses with anti-D immunoglobulin (P < 0.001). This study suggests that IVIG may cause neutropenia commonly in children with ITP. While this is likely to be a transient condition, its recognition may affect clinical decisions such as the need for a bone marrow examination.

Intravenous immunoglobulin g attenuates pulmonary hypertension but induces local neutrophil influx in meconium aspiration in piglets

BACKGROUND

Pulmonary hypertension and inflammation are well-identified pathogenetic features in meconium aspiration syndrome of newborns, but current approaches to their treatment or prevention are still often unsatisfactory.

OBJECTIVES

To investigate the possible protective effects of human intravenous immunoglobulin G (IVIG) on the hypertensive and inflammatory lung injury in severe neonatal meconium aspiration.

METHODS

Eleven newborn (10-12 days old) ventilated and catheterized piglets that received an intratracheal bolus (3 ml/kg) of a 65-mg/ml mixture of human meconium were studied for 6 h. IVIG was infused in 5 piglets 30 min before meconium administration, and 6 piglets served as controls and received the vehicle only.

RESULTS

Meconium instillation induced a biphasic pulmonary hypertensive response, which was significantly diminished by IVIG pretreatment. Similarly, IVIG improved the oxygenation of the piglets, but the intrapulmonary shunt fraction or systemic hemodynamic parameters did not differ between the study groups, except of a minor decrease in the mean arterial blood pressure caused by IVIG. The blood leukocyte count was comparable in the 2 groups. The lung tissue ultrastructural and histological changes, number of apoptotic cells and phospholipase A2 activity were similar in the 2 groups. The amount of neutrophil accumulation, assessed by myeloperoxidase activity, was however significantly increased in macroscopically damaged lung tissue after IVIG administration.

CONCLUSIONS

Our results thus indicate that IVIG treatment of newborns with severe meconium aspiration significantly diminishes the pulmonary hypertensive response and improves oxygenation, but the effects do not extend to protection of lung cellular injury.

Suppressive effect of intravenous immunoglobulin on peripheral blood neutrophil count in patients with idiopathic thrombocytopenic purpura

PURPOSE

To determine the effect of intravenous immunoglobulin (IVIG) on neutrophil count, the authors studied patients with idiopathic thrombocytopenic purpura (ITP).

PATIENTS AND METHODS

Thirty-one of 40 patients with ITP were treated with an IVIG regimen (400 mg/kg/daily for 5 days), while the other 9 were observed without any medications. Peripheral samples were examined during the clinical course.

RESULTS

The absolute neutrophil count in 22 patients with no fever as a side effect decreased significantly by day 2 after the start of IVIG, but in most patients it began to increase soon after the last IVIG. There was also a significant difference between the decreased level of the absolute neutrophil count in patients with and without IVIG. However, re-administration of IVIG within 2 weeks did not significantly suppress the neutrophil count. In contrast, the neutrophil count increased in every patient with a fever as a side effect of IVIG.

CONCLUSIONS

IVIG induced a decrease in peripheral blood neutrophil count in patients with ITP.

Monomeric IgG in Intravenous Ig Preparations Is a Functional Antagonist of FcγRII and FcγRIIIb

Intravenous Ig preparations (IVIg), originally developed as a substitution therapy for patients with low plasma IgG, are nowadays frequently used in the treatment of various immune diseases. However, the mechanism of action of IVIg in these diseases remains elusive and is often referred to as "immunomodulatory." We hypothesized that monomeric IgG may act as a low-affinity FcgammaR antagonist and sought experimental evidence for this hypothesis. Human neutrophils as well FcgammaRIIa-transfected IIA1.6 cells were used as FcgammaR-positive cells and aggregated IgG (aIgG) or stable dimeric IgG as FcgammaR-specific agonists for these cells. We found that monomeric IgG purified from IVIg at concentrations similar to that of IgG in plasma, diminished the binding of stable dimeric IgG to FcgammaRIIa transfectants, reduced aIgG-induced influx of Ca(2+) ions into the cytosol of neutrophils, and attenuated the aIgG-induced release of elastase. Notably, monomeric IgG by itself did not elicit these responses, nor did it affect these processes in response to fMLP. Absorption of IgG from normal plasma revealed that plasma IgG exerted similar effects as monomeric IgG in IVIg. In addition, adding monomeric IgG to blood of healthy volunteers showed a dose-dependent decrease of aIgG-induced elastase release. Finally, we observed decreased aIgG-induced polymorphonuclear neutrophil responses in two hypogammaglobulinemic patients upon treatment with IVIg. We conclude that monomeric IgG at physiological levels acts as a low-affinity FcgammaR antagonist. Moreover, FcgammaR antagonism constitutes an immunomodulatory effect of IVIg.

Can polyclonal intravenous immunoglobulin limit cytokine mediated cerebral damage and chronic lung disease in preterm infants?

Recent evidence suggests that inflammatory cytokines may play an important role in cerebral and pulmonary injury, especially in preterm infants. Immunomodulatory agents may help to limit such injury by reducing inflammation. Immunoglobulin has multiple anti-inflammatory properties and can modulate the inflammatory cytokine response. New evidence is required to test the hypotheses that prophylaxis or treatment with intravenous immunoglobulin may limit such inflammatory damage.

Proteolytic enzyme levels are increased during granulocyte colony-stimulating factor-induced hematopoietic stem cell mobilization in human donors but do not predict the number of mobilized stem cells

Previous studies from our laboratory indicate that functional, mature neutrophils are essential for interleukin-8 (IL-8)-induced stem cell mobilization. To study a possible role of neutrophils in granulocyte colony-stimulating factor (G-CSF) induced hematopoietic mobilization, we assessed the number of circulating CD34+ cells in healthy allogeneic stem cell donors on days 3, 4, and 5 of mobilization for comparison with the number of peripheral blood neutrophils and the plasma levels of IL-8, Flt3 ligand (FL), matrix metalloproteinase-9 (MMP-9), and human neutrophil elastase (HNE). Thirty-seven of 45 donors required 1 day of apheresis to obtain 5 x 10(6) CD34+/kg recipient body weight (high responders), the remaining 8 donors required 1 extra day of apheresis on day 6 (low responders). On day 5, CD34+ numbers in the blood were significantly highe in high responders (116 x 10(3) +/- 10.4/ml) than in low responders (54.1 x 10(3) +/- 10.3, p < 0.001). In all donors, MMP-9 and HNE levels were increased compared to nonmobilized individuals, but in high responders, plasma MMP-9 levels on days 3-5 of mobilization were substantially higher than in low responders (p < or = 0.02 for MMP-9 and p = 0.89, p = 0.05 and p = 0.52 for HNE on days 3, 4, and 5, respectively). These results are in accordance with the hypothesis that neutrophils play a role in G-CSF-induced mobilization through the release of proteases such as MMP-9 and elastase. No change in plasma levels of IL-8 or Flt3 ligand was observed, suggesting that these cytokines do not play a role in stem cell mobilization. However, because stem cell numbers could not be predicted by proteolytic enzyme levels and/or neutrophil numbers, other undefined factors may be more important.

Antineutrophil cytoplasmic antibodies induce human monocytes to produce oxygen radicals in vitro

OBJECTIVE

Antineutrophil cytoplasmic antibodies (ANCA) are believed to play a pathogenetic role in necrotizing small-vessel vasculitis. While the involvement of neutrophils in this disease has been extensively studied in vitro, we undertook to analyze thoroughly the contribution of monocytes to tissue destruction in systemic vasculitis.

METHODS

Monocytes obtained from normal human individuals were stimulated by ANCA isolated from patients with active vasculitis. The formation of oxygen radicals was measured by a fluorometric assay using 2',7'-dichlorofluorescin diacetate.

RESULTS

ANCA induced monocytes to produce oxygen radicals, resulting in a mean 43% increase (range 21-84%) in oxygen radical formation compared with normal IgG. The formation of reactive oxygen species was time and concentration dependent and was also induced by ANCA F(ab')2 fragments. Normal nonspecific IgG or their corresponding F(ab')2 fragments induced no release or very little release of oxygen radicals. Preincubation of monocytes with the Fcy receptor type II-blocking monoclonal antibody IV.3 before addition of ANCA greatly reduced formation of oxygen radicals. Using ligand affinity chromatography with proteinase 3 (PR3) and myeloperoxidase (MPO), ANCA were further purified by depletion of patient IgG. The stimulation of monocytes with these pure PR3- and MPO-ANCA confirmed that cellular activation was specifically induced by ANCA.

CONCLUSION

These results show that ANCA induce the formation of reactive oxygen species in human monocytes. These findings support the notion that ANCA specifically activate monocytes by several mechanisms to participate in the inflammatory process of ANCA-associated vasculitis.

Different proteolytic mechanisms involved in Fc gamma RIIIb shedding from human neutrophils

The Fc gamma receptor type IIIb (CD16) is highly expressed on human neutrophils and is found in a soluble form in plasma and in other body fluids. Upon activation of neutrophils in vitro, Fc gamma RIIIb is shed from the cell surface by proteolytic cleavage. We have now investigated the effect of metalloproteinase inhibitors and a serine proteinase inhibitor on the shedding of Fc gamma RIIIb induced by phorbol 12-myristate 13-acetate (PMA) or cytochalasin B (cyto B) + N-formyl-methionyl-leucyl-phenylalanine (fMLP). Metalloproteinase inhibitors blocked to a large extent PMA-induced, but not cyto B + fMLP-induced shedding of Fc gamma RIIIb. Inhibition of members of the ADAM (a disintegrin and metalloproteinase) family appeared most efficient. In contrast, the serine protease inhibitor N-methoxysuccinyl-alanine-alanine-proline-valine-chloromethylketone (MeOsuc-AAPV-CMK) largely blocked cyto B + fMLP-induced, but not PMA-induced shedding of Fc gamma RIIIb. Metalloproteinase inhibitors in combination with the serine proteinase inhibitor resulted in full inhibition of Fc gamma RIIIb shedding induced by either PMA or cyto B + fMLP. The shedding of Fc gamma RIIIb that accompanied apoptosis was inhibited by 60% in the presence of inhibitors of metalloproteinases but was insensitive to inhibition of serine proteinases. These results show that distinct types of proteolytic enzyme are involved in the stimulus-induced shedding of Fc gamma RIIIb from human neutrophils and suggest that these proteinases may become differentially activated under various physiological or pathological conditions.

Intravenous immunoglobulin preparations induce mild activation of neutrophils in vivo via triggering of macrophages--studies in a rat model

Despite widespread use in various immune disorders, the in vivo mechanisms of action of intravenous immunoglobulin (IVIG) preparations are not well known. We previously reported that human neutrophils degranulate after incubation with IVIG in vitro as a result of interaction with FcgammaRII. The purpose of this study was to determine whether IVIG might stimulate neutrophils in vivo. Anaesthetized rats received a bolus intravenous injection of IVIG preparations, containing either high (aged IVIG) or low (fresh IVIG) amounts or IgG dimers at a dose of 250 mg/kg. Administration of aged IVIG induced neutrophil activation in vivo, whereas no effect was observed after infusion of fresh IVIG. Histological examination of lung tissue demonstrated mild influx of neutrophils into the pulmonary tissue after aged IVIG administration, though gross damage did not occur. Macrophage-depleted rats no longer showed activation of neutrophils after infusion of aged IVIG, suggesting that neutrophils become activated via an indirect macrophage dependent way. We conclude that IVIG induces a mild activation of neutrophils in vivo via triggering of macrophages depending on the amount of IgG dimers. For this reason, IVIG preparations with a high content of dimers may not always be as harmless as generally believed and may be responsible for some of the side-effects observed during IVIG infusions.

Polyclonal immunoglobulins (IVIg) modulate nitric oxide production and microglial functions in vitro via Fc receptors

Controlled trials in multiple sclerosis (MS) and case reports in acute demyelinating encephalomyelitis (ADEM) have shown that intravenous immunoglobulins (IVIg) are of therapeutic benefit in central nervous system (CNS) inflammatory diseases. Studies in experimental autoimmune encephalomyelitis (EAE) have suggested these effects are mediated by modulation of the cytokine network and T cell responses. However, there are no data on the influence of IVIg on the local immune reaction in the CNS, the site of inflammation in EAE. We have therefore studied the effect of IVIg on cultured rat microglia, the main immune cell in the CNS. IVIg increased nitric oxide (NO) production in a dose-dependent manner in microglia stimulated with IFNgamma. The increase was only marginal in LPS-treated cells, and no effect was seen in untreated microglia or after stimulation with TNFalpha or PMA. This enhancement of NO production depended on the Fc portion of IVIg and could be abrogated by the pharmacological inhibition of Syk and phosphatidylinositol 3-kinase, two enzymes involved in the signalling cascade of Fc receptors. TNFalpha secretion was dose-dependently stimulated by IVIg in both untreated microglia and after stimulation with LPS or IFNgamma. Again, this effect was mediated through the Fc portion. Finally, we showed that Fc receptor-mediated phagocytosis was inhibited by IVIg, presumably by blockade of the Fc receptor. These different effects may protect oligodendrocytes from antibody mediated phagocytosis and on the other hand could terminate the immune reaction by induction of apoptosis in infiltrating T cells via NO and TNFalpha. We propose that IVIg, in addition to known effects on the peripheral immune system, may also modulate the local immune reaction in CNS inflammatory disease.

Vasoactive side effects of intravenous immunoglobulin preparations in a rat model and their treatment with recombinant platelet-activating factor acetylhydrolase

Previously, we observed in a rat model that intravenous administration of intramuscular immunoglobulin preparations induced a long-lasting hypotension, which appeared to be associated with the presence of IgG polymers and dimers in the preparations, but unrelated to complement activation. We found evidence that this hypotensive response is mediated by platelet-activating factor (PAF) produced by macrophages. In this study, we compared the vasoactive effects of 16 intravenous immunoglobulin (IVIG) products from 10 different manufacturers, in anesthetized rats. Eight of the IVIG preparations showed no hypotensive effects (less than 15% decrease), whereas the other 8 had relatively strong effects (15%-50% decrease). The hypotensive effects correlated with the IgG dimer content of the preparations. Pretreatment of the rats with recombinant PAF acetylhydrolase completely prevented the hypotensive reaction on IVIG infusion, and administration after the onset of hypotension resulted in normalization of the blood pressure. We also observed PAF production on in vitro incubation of human neutrophils with IVIG, which could be blocked by anti-Fcγ receptor antibodies. This indicates that induction of PAF generation may also occur in a human system. Our findings support the hypothesis that the clinical side effects of IVIG in patients may be caused by macrophage and neutrophil activation through interaction of IgG dimers with Fcγ receptors. Because phagocyte activation may also lead to the release of other inflammatory mediators, recombinant PAF acetylhydrolase (rPAF-AH) provides a useful tool to determine whether PAF plays a role in the clinical side effects of IVIG. If so, rPAF-AH can be used for the treatment of those adverse reactions.

Activation of human granulocytes by intravenous immunoglobulin preparations is mediated by FcgammaRII and FcgammaRIII receptors

Previous studies from our laboratory have shown that i.v. Ig (IVIG) exposure triggers superoxide anion (O2) generation by and increases bactericidal capacity of human blood granulocytes. However, the molecular interactions between IVIG and granulocytes have not been evaluated before. The objective of this study was to investigate the role of FcgammaRII and FcgammaRIII receptors in the immunomodulatory effects of IVIG concentrates on granulocytes. We found that four different IVIG preparations (concentration range, 1-10 mg/mL) shared the ability to stimulate O2- release in vitro by granulocytes in a dose-dependent manner. Dimers fractionated from IVIG were significantly more potent in inducing activity of the respiratory burst than were monomers. MAb (concentration range, 0.1-10 microg/mL) specific for FcgammaRII and FcgammaRIII receptors inhibited the IVIG-induced O2- release, with a more profound inhibitory effect observed with anti-FcgammaRIII. These findings suggest the involvement of Fcgamma receptors in triggering O2- release by granulocytes exposed to IVIG. We also report that IVIG added to granulocyte suspensions elicited a rapid and vigorous increase in the concentration of cytosolic free calcium, a finding suggesting direct activation and not priming of granulocytes by IVIG through FcgammaRII and FcgammaRIII receptors. The in vitro effects described here might occur in patients treated with IVIG and may, in part, be responsible for inflammatory reactions evoked by infused Ig concentrates as well as the immunomodulatory effect of Ig in patients with autoimmune and inflammatory diseases.

Actin polymerization induces shedding of FcgammaRIIIb (CD16) from human neutrophils

FcgammaRIIIb (CD16) is a glycosyl phosphatidylinositol (GPI)-anchored low-affinity IgG receptor, exclusively expressed on human neutrophils. FcgammaRIIIb associates with complement receptor 3 (CR3, Mac-1, CD11b/CD18), which may indirectly link FcgammaRIIIb to the actin cytoskeleton. Upon neutrophil activation, apoptosis, or chemotaxis, FcgammaRIIIb is shed from the cell surface. In all of these events, actin rearrangements play an important role. To establish a role for the actin cytoskeleton in the control of FcgammaRIIIb shedding, we treated human neutrophils with jasplakinolide, an actin-polymerizing peptide. We show that enhanced actin polymerization induces time- and dose-dependent shedding of FcgammaRIIIb. This effect was not restricted to FcgammaRIIIb, because the cell surface expression of CD43, CD44, and L-selectin was also downregulated after induction of actin polymerization. This actin-dependent pathway is staurosporine sensitive but does not appear to involve activation of PKC or CR3. These data show that the actin cytoskeleton can regulate protein ectodomain shedding from human neutrophils.