Sialylation-independent mechanism involved in the amelioration of murine immune thrombocytopenia using intravenous gammaglobulin

Production of α2,6-sialylated IgG1 in CHO cells

The presence of α2,6-sialic acids on the Fc N-glycan provides anti-inflammatory properties to the IgGs through a mechanism that remains unclear. Fc-sialylated IgGs are rare in humans as well as in industrial host cell lines such as Chinese hamster ovary (CHO) cells. Facilitated access to well-characterized α2,6-sialylated IgGs would help elucidate the mechanism of this intriguing IgG's effector function. This study presents a method for the efficient Fc glycan α2,6-sialylation of a wild-type and a F243A IgG1 mutant by transient co-expression with the human α2,6-sialyltransferase 1 (ST6) and β1,4-galactosyltransferase 1 (GT) in CHO cells. Overexpression of ST6 alone only had a moderate effect on the glycoprofiles, whereas GT alone greatly enhanced Fc-galactosylation, but not sialylation. Overexpression of both GT and ST6 was necessary to obtain a glycoprofile dominated by α2,6-sialylated glycans in both antibodies. The wild-type was composed of the G2FS(6)1 glycan (38%) with remaining unsialylated glycans, while the mutant glycoprofile was essentially composed of G2FS(6)1 (25%), G2FS(3,6)2 (16%) and G2FS(6,6)2 (37%). The α2,6-linked sialic acids represented over 85% of all sialic acids in both antibodies. We discuss how the limited sialylation level in the wild-type IgG1 expressed alone or with GT results from the glycan interaction with Fc's amino acid residues or from intrinsic galactosyl- and sialyl-transferases substrate specificities.

Efficacy of Intravenous Immunoglobulin in Neurological Diseases

Owing to its anti-inflammatory efficacy in various autoimmune disease conditions, intravenous immunoglobulin (IVIG)-pooled IgG obtained from the plasma of several thousands individuals-has been used for nearly three decades and is proving to be efficient in a growing number of neurological diseases. IVIG therapy has been firmly established for the treatment of Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, and multifocal motor neuropathy, either as first-line therapy or adjunctive treatment. IVIG is also recommended as rescue therapy in patients with worsening myasthenia gravis and is beneficial as a second-line therapy for dermatomyositis and stiff-person syndrome. Subcutaneous rather than intravenous administration of IgG is gaining momentum because of its effectiveness in patients with primary immunodeficiency and the ease with which it can be administered independently from hospital-based infusions. The demand for IVIG therapy is growing, resulting in rising costs and supply shortages. Strategies to replace IVIG with recombinant products have been developed based on proposed mechanisms that confer the anti-inflammatory activity of IVIG, but their efficacy has not been tested in clinical trials. This review covers new developments in the immunobiology and clinical applications of IVIG in neurological diseases.

Rapid and improved characterization of therapeutic antibodies and antibody related products using IdeS digestion and subunit analysis

Antibody subunits LC, Fd and Fc/2, generated by IdeS digestion has been applied in analytical methodologies to characterize antibody quality attributes such as glycosylation, oxidation, deamidation, and identity.

Enhanced sialylation of a human chimeric IgG1 variant produced in human and rodent cell lines

Glycosylation of the IgG-Fc is essential for optimal binding and activation of Fcγ receptors and the C1q component of complement. However, it has been reported that the effector functions are down-regulated when the Fc glycans terminate in sialic acid residues and that sialylated IgG mediates anti-inflammatory effects of intravenous immunoglobulin (IVIG). Although recombinant IgG is hypo-sialylated, Fc sialylation is shown to be markedly increased when a mouse/human chimeric IgG3 Phe243Ala (F243A) variant is expressed in Chinese hamster ovary (CHO)-K1 cells. Here we investigate whether sialylation is increased in IgG1 F243A when expressed in CHO-K1, mouse myeloma J558L and human embryonic kidney (HEK) 293. Although the sialylation level was 2-5% for IgG1 wild type (WT), it was increased to 31%, 10% and 33% for the variant from CHO-K1, J558L and HEK293 cells, respectively. Interestingly, an increased addition of bisecting GlcNAc and α(1-3)-galactose residues to the Fc glycan was observed for HEK293-derived and J558L-derived IgG1 F243A, respectively. Fucosylation of HEK293-derived IgG1 F243A was maintained despite increased bisecting GlcNAc content. Although sialic acid and bisecting GlcNAc residues are reported to have an opposing effect on antibody-dependent cellular cytotoxicity (ADCC), IgG1 F243A showed 7 times lower ADCC activities than IgG1 WT, irrespective of bisecting GlcNAc residue. Thus, highly sialylated, human cell-derived IgG1 F243A with lowered ADCC activity may be of interest for the development of therapeutic antibodies with anti-inflammatory properties as an alternative to IVIG.

Pathways Responsible for Human Autoantibody and Therapeutic Intravenous IgG Activity in Humanized Mice

Immunoglobulin G (IgG) antibodies are major drivers of autoimmune pathology, but they are also used in the form of intravenous IgG (IVIg) therapy to suppress autoantibody activity. To identify the pathways underlying human autoantibody and IVIg activity, we established a humanized mouse model of an autoantibody-dependent autoimmune disease responding to treatment with IVIg preparations. We show that the human IgG subclass strongly impacts autoantibody activity and that the Fc-receptor genotype of the human donor immune system further modulates autoantibody activity. Human mononuclear phagocytes were responsible for autoantibody activity, and IVIg therapy was able to suppress disease pathology in an Fc-fragment-dependent manner. While highly sialylated IgG glycovariants were essential for IVIg activity, it was independent of the Fc-receptor genotype and did not result in a general block of activating or the neonatal Fc-receptor. These findings may help in the development of strategies to block autoantibody and enhance therapeutic IVIg activity in humans.

Induction of Regulatory T Cells by Intravenous Immunoglobulin: A Bridge between Adaptive and Innate Immunity

Intravenous immunoglobulin (IVIg) is a polyclonal immunoglobulin G preparation with potent immunomodulatory properties. The mode of action of IVIg has been investigated in multiple disease states, with various mechanisms described to account for its benefits. Recent data indicate that IVIg increases both the number and the suppressive capacity of regulatory T cells, a subpopulation of T cells that are essential for immune homeostasis. IVIg alters dendritic cell function, cytokine and chemokine networks, and T lymphocytes, leading to development of regulatory T cells. The ability of IVIg to influence Treg induction has been shown both in animal models and in human diseases. In this review, we discuss data on the potential mechanisms contributing to the interaction between IVIg and the regulatory T-cell compartment.

Mechanisms of immune regulation by IVIG

PURPOSE OF REVIEW

In the past few years there have been many advances in our understanding of the mechanisms by which intravenous immune globulin (IVIG) modulates immune function in autoimmune disorders.

RECENT FINDINGS

Previous investigations have focused on the Fc domain of the IgG molecule, and the role of the FcγRIIB receptor and the sialylated Fc domain that have been show to mediate the anti-inflammatory effects in certain murine models of autoantibody-mediated diseases. More recent findings have implicated the F(ab')₂ domain in IVIG-induced immune modulation in T-cell-mediated autoimmune disease models in which upregulation of T-regulatory cells and downregulation of the Th17 pathways are important components of this mechanism. The prostaglandin E pathway may be playing a role in the IVIG-induced changes in the T-regulatory pathway.

SUMMARY

Many of the mechanisms proposed for the immune-modulating effects of IVIG demonstrate the complexity of immune effector functions in disease processes. Although controversy exists on the role of the FcγRIIB receptor and the importance of the sialylated Fc domain in human autoimmune disorders, probably no one single mechanism is responsible for the effects of IVIG in autoimmune and inflammatory diseases. The potential role of the prostaglandin E pathway may offer alternative treatments.

Contributions of T lymphocyte abnormalities to therapeutic outcomes in newly diagnosed patients with immune thrombocytopenia

T cell abnormalities have been reported to play an important role in pathogenesis of immune thrombocytopenia (ITP) besides specific autoantibodies towards platelet. The aim of this study was to explore the clinical importance of T lymphocyte subsets in adult patients with newly diagnosed ITP before and after first-line treatment. Elderly ITP patients were also studied and we tried to analyze the relationships between these items and therapeutic outcomes. The patients were treated with intravenous immunoglobulin (IVIG) plus corticosteroids and therapeutic responses were evaluated. As a result, compared with the controls, absolute lymphocyte counts in ITP patients decreased significantly before treatment. After treatment, lymphocyte counts restored to control level regardless of their treatment outcomes. In addition, we observed increased IgG and CD19+ cell expression and decreased CD4+/CD8+ cell ratio in both whole ITP group and elderly group before treatment. After treatment, the increased IgG and CD19+ cell expression could be reduced in both respond and non-respond group regardless of patient age, while CD4+/CD8+ cell ratio could not be corrected in non-respond ITP patients. In non-respond ITP patients, increased CD8+ cell expression was noticed and could not be corrected by first-line treatment. Furthermore, even lower NK cell expression was found in non-respond elderly patients after treatment when compared with that in controls. Our findings suggest that ITP patients usually had less numbers of peripheral lymphocytes and patients with higher levels of CD8+ cells or lower levels of CD4+/CD8+ cell ratio were less likely to respond to first-line treatment. Lower levels of NK cells made therapies in elderly ITP patients even more difficult.

Intravenous IgG (IVIG) and subcutaneous IgG (SCIG) preparations have comparable inhibitory effect on T cell activation, which is not dependent on IgG sialylation, monocytes or B cells

IVIG modulates T cell activation in vitro and inflammatory-autoimmune conditions in vivo. Sialylation of IgG, Fc receptor interactions, modulation of monocyte/macrophage/B cell functions have been implicated in IVIG effects. Subcutaneous IgG (SCIG) therapy is increasingly used for IgG replacement but whether these preparations share the effects of IVIG on T cell modulation is not documented. We compared the potency of SCIG-Hizentra™ (20% IgG preparation) with IVIG-Privigen® (10% IgG) for T cell inhibition, and assessed the involvement of IgG sialylation, monocytes and B cells in this process. Human PBMCs or sorted cells were cultured 3-7 days, and T cells were stimulated with immobilized anti-CD3 mAb or Candida antigen. Thymidine incorporation into DNA was quantitated and cytokines assayed by ELISA/Luminex® assay. IVIG and SCIG both dose-dependently (1-20mg/ml) inhibited (up to >80%) T cell proliferation to anti-CD3 mAb. Response to Candida albicans was comparably inhibited by IVIG and SCIG by 50-80% at 10mg/ml with inhibition even at 3mg/ml (P<0.05). These effects were not affected by depletion of sialic acid containing IgG using neuraminidase treatment or lectin affinity chromatography. With anti-CD3 or Candida stimulation, IL-1β, IL-2, IL-5, IL-6, IL-13, GMCSF, TNF-α, interferon-γ (with anti-CD3) and IL-17 (with Candida) levels were suppressed by IVIG or SCIG, with no effect on IL-4, IL-10, IL-12, IL-15 or TGFβ. Monocytes or B cells were not required for IgG-induced suppression of proliferation, in fact depletion of monocytes potentiated the IgG-induced inhibition. Reconstitution with monocytes restored the original inhibitory effect. These data show that IVIG (Privigen®) and SCIG (Hizentra™) have comparable inhibitory effects on T cell activation, which do not require sialylation of IgG. Inhibition is independent of monocytes or B cells. There is a potent suppression of multiple effector cytokines. Like IVIG, SCIG therapy is expected to show immunomodulatory activity.

Protection in antibody- and T cell-mediated autoimmune diseases by antiinflammatory IgG Fcs requires type II FcRs

The antiinflammatory activity of intravenous immunoglobulin (IVIG) is dependent on the presence of sialic acid in the core IgG fragment crystallizable domain (Fc) glycan, resulting in increased conformational flexibility of the CH2 domain with corresponding modulation of Fc receptor (FcR) binding specificity from type I to type II receptors. Sialylated IgG Fc (sFc) increases the activation threshold of innate effector cells to immune complexes by stimulating the up-regulation of the inhibitory receptor FcγRIIB. We have found that the structural alterations induced by sialylation can be mimicked by specific amino acid modifications to the CH2 domain. An IgG Fc variant with a point mutation at position 241 (F→A) exhibits antiinflammatory activity even in the absence of sialylation. F241A and sFc protect mice from arthritis in the K/BxN-induced model and, in the T cell-mediated experimental autoimmune encephalomyelitis (EAE) mouse model, suppress disease by specifically activating regulatory T cells (Treg cells). Protection by these antiinflammatory Fcs in both antibody- and T cell-mediated autoimmune diseases required type II FcRs and the induction of IL-33. These results further clarify the mechanism of action of IVIG in both antibody- and T cell-mediated inflammatory diseases and demonstrate that Fc variants that mimic the structural alterations induced by sialylation, such as F241A, can be promising therapeutic candidates for the treatment of various autoimmune disorders.

Differences in Anti-Inflammatory Actions of Intravenous Immunoglobulin between Mice and Men: More than Meets the Eye

Intravenous immunoglobulin (IVIg) is a therapeutic preparation of polyspecific human IgGs purified from plasma pooled from thousands of individuals. When administered at a high dose, IVIg inhibits inflammation and has proven efficacy in the treatment of various autoimmune and systemic inflammatory diseases. Importantly, IVIg therapy can ameliorate both auto-antibody-mediated and T-cell mediated immune pathologies. In the last few decades, extensive research in murine disease models has resulted in the elucidation of two novel anti-inflammatory mechanisms-of-action of IVIg: induction of FcγRIIB expression by sialylated Fc, and stimulation of regulatory T cells. Whereas controversial findings in mice studies have recently inspired intense scientific debate regarding the validity of the sialylated Fc-FcγRIIB model, the most fundamental question is whether these anti-inflammatory mechanisms of IVIg are operational in humans treated with IVIg. In this review, we examine the evidence for the involvement of these anti-inflammatory mechanisms in the therapeutic effects of IVIg in humans. We demonstrate that although several elements of both immune-modulatory pathways of IVIg are activated in humans, incorrect extrapolations from mice to men have been made on the molecular and cellular components involved in these cascades that warrant for critical re-evaluation of these anti-inflammatory mechanisms of IVIg in humans.

Developing the IVIG biomimetic, hexa-Fc, for drug and vaccine applications

The remarkable clinical success of Fc-fusion proteins has driven intense investigation for even more potent replacements. Using quality-by-design (QbD) approaches, we generated hexameric-Fc (hexa-Fc), a ~20 nm oligomeric Fc-based scaffold that we here show binds low-affinity inhibitory receptors (FcRL5, FcγRIIb, and DC-SIGN) with high avidity and specificity, whilst eliminating significant clinical limitations of monomeric Fc-fusions for vaccine and/or cancer therapies, in particular their poor ability to activate complement. Mass spectroscopy of hexa-Fc reveals high-mannose, low-sialic acid content, suggesting that interactions with these receptors are influenced by the mannose-containing Fc. Molecular dynamics (MD) simulations provides insight into the mechanisms of hexa-Fc interaction with these receptors and reveals an unexpected orientation of high-mannose glycans on the human Fc that provides greater accessibility to potential binding partners. Finally, we show that this biosynthetic nanoparticle can be engineered to enhance interactions with the human neonatal Fc receptor (FcRn) without loss of the oligomeric structure, a crucial modification for these molecules in therapy and/or vaccine strategies where a long plasma half-life is critical.

7th International Immunoglobulin Conference: Mechanisms of action

Although intravenous immunoglobulin (IVIg) is widely used for replacement therapy in immunodeficiencies and to treat autoimmune and inflammatory diseases, its mechanisms of action are not fully understood. Examination of immunoglobulin (Ig) receptors, including the Fc-gamma receptors (FCγRs) and the neonatal Fc receptor, have revealed genetic variations that are linked to autoimmune diseases and to the efficacy of IVIg treatment. However, the beneficial effect of IVIg encompasses multiple mechanisms of action. One of these is scavenging of activated complement fragments, such as C3a, C5a, C3b and C4b, by infused Ig molecules. This interaction prevents binding of complement fragments to their receptors on target cells, thus attenuating the immune damage. Additionally, anti-inflammatory effects may be facilitated by IgA via specific receptors and/or complement scavenging. Glycosylation of both the Fc- and Fab-fragments has also been implicated in the anti-inflammatory action of IVIg. Although there is evidence to support a role for sialylated IgG glycovariants in mediating the effect of IVIg, evidence from animal models of inflammatory disease suggest that sialylation may not be a critical factor. However, an increase in IgG glycosylation has been observed following IVIg treatment in Guillain-Barré syndrome patients, and this has been associated with improved clinical outcomes.

Controlled tetra-Fc sialylation of IVIg results in a drug candidate with consistent enhanced anti-inflammatory activity

Despite the beneficial therapeutic effects of intravenous immunoglobulin (IVIg) in inflammatory diseases, consistent therapeutic efficacy and potency remain major limitations for patients and physicians using IVIg. These limitations have stimulated a desire to generate therapeutic alternatives that could leverage the broad mechanisms of action of IVIg while improving therapeutic consistency and potency. The identification of the important anti-inflammatory role of fragment crystallizable domain (Fc) sialylation has presented an opportunity to develop more potent Ig therapies. However, translating this concept to potent anti-inflammatory therapeutics has been hampered by the difficulty of generating suitable sialylated products for clinical use. Therefore, we set out to develop the first, to our knowledge, robust and scalable process for generating a well-qualified sialylated IVIg drug candidate with maximum Fc sialylation devoid of unwanted alterations to the IVIg mixture. Here, we describe a controlled enzymatic, scalable process to produce a tetra-Fc-sialylated (s4-IVIg) IVIg drug candidate and its qualification across a wide panel of analytic assays, including physicochemical, pharmacokinetic, biodistribution, and in vivo animal models of inflammation. Our in vivo characterization of this drug candidate revealed consistent, enhanced anti-inflammatory activity up to 10-fold higher than IVIg across different animal models. To our knowledge, this candidate represents the first s4-IVIg suitable for clinical use; it is also a valuable therapeutic alternative with more consistent and potent anti-inflammatory activity.

Immunomodulation by IVIg and the Role of Fc-Gamma Receptors: Classic Mechanisms of Action after all?

Intravenous IgG (IVIg) contains polyclonal immunoglobulin G (IgG) from thousands of donors. It is administered at a low dose at regular intervals as antibody replacement therapy and at a higher dose as immunomodulatory treatment in various auto-immune or auto-inflammatory diseases. The working mechanism of immunomodulation is not well understood. Many different explanations have been given. During the last decade, we have focused on classical antibody binding via the Fc-domain of the IgG molecules to the common IgG receptors, i.e. the Fcγ receptors (FcγRs). Variation in the genes encoding human FcγRs determines function as well as expression among immune cells. As described here, NK cells and myeloid cells, including macrophages, can express different FcγR variants, depending on the individual's genotype, copy number variation (CNV), and promoter polymorphisms. B-cells seem to only express the single inhibitory receptor. Although these inhibitory FcγRIIb receptors are also expressed by monocytes, macrophages, and only rarely by NK cells or neutrophils, their presence is unlikely to explain the immunomodulatory capacity of IVIg, nor does the sialylation of IgG. Direct IVIg effects at the level of the activating FcγRs, including the more recently described FcγRIIc, deserve renewed attention to describe IVIg-related immunomodulation.

Inhibition of FcγR-mediated phagocytosis by IVIg is independent of IgG-Fc sialylation and FcγRIIb in human macrophages

Phagocytosis of IgG-opsonized blood cells by human macrophages is inhibited by intravenous immunoglobulins. This inhibition is independent of IgG-Fc sialylation but improves with IgG preparations that bind FcγRs more avidly.

Rapid and reversible responses to IVIG in autoimmune neuromuscular diseases suggest mechanisms of action involving competition with functionally important autoantibodies

Intravenous immunoglobulin (IVIG) is widely used in autoimmune neuromuscular diseases whose pathogenesis is undefined. Many different effects of IVIG have been demonstrated in vitro, but few studies actually identify the mechanism(s) most important in vivo. Doses and treatment intervals are generally chosen empirically. Recent studies in Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy show that some effects of IVIG are readily reversible and highly dependent on the serum IgG level. This suggests that in some autoantibody-mediated neuromuscular diseases, IVIG directly competes with autoantibodies that reversibly interfere with nerve conduction. Mechanisms of action of IVIG which most likely involve direct competition with autoantibodies include: neutralization of autoantibodies by anti-idiotypes, inhibition of complement deposition, and increasing catabolism of pathologic antibodies by saturating FcRn. Indirect immunomodulatory effects are not as likely to involve competition and may not have the same reversibility and dose-dependency. Pharmacodynamic analyses should be informative regarding most relevant mechanism(s) of action of IVIG as well as the role of autoantibodies in the immunopathogenesis of each disease. Better understanding of the role of autoantibodies and of the target(s) of IVIG could lead to more efficient use of this therapy and better patient outcomes.

Optimal attenuation of experimental autoimmune encephalomyelitis by intravenous immunoglobulin requires an intact interleukin-11 receptor

Background

Intravenous immunoglobulin (IVIg) has been used to treat a variety of autoimmune disorders including multiple sclerosis (MS); however its mechanism of action remains elusive. Recent work has shown that interleukin-11 (IL-11) mRNAs are upregulated by IVIg in MS patient T cells. Both IVIg and IL-11 have been shown to ameliorate experimental autoimmune encephalomyelitis (EAE), an animal model of MS. The objective of this study was to determine whether the protective effects of IVIg in EAE occur through an IL-11 and IL-11 receptor (IL-11R)-dependent mechanism.

Methods

We measured IL-11 in the circulation of mice and IL-11 mRNA expression in various organs after IVIg treatment. We then followed with EAE studies to test the efficacy of IVIg in wild-type (WT) mice and in mice deficient for the IL-11 receptor (IL-11Rα^−/−). Furthermore, we evaluated myelin-specific Th1 and Th17 responses and assessed spinal cord inflammation and demyelination in WT and IL-11Rα^−/− mice, with and without IVIg treatment. We also examined the direct effects of mouse recombinant IL-11 on the production of IL-17 by lymph node mononuclear cells.

Results

IVIg treatment induced a dramatic surge (>1000-fold increase) in the levels of IL-11 in the circulation and a prominent increase of IL-11 mRNA expression in the liver. Furthermore, we found that IL-11Rα^−/− mice, unlike WT mice, although initially protected, were resistant to full protection by IVIg during EAE and developed disease with a similar incidence and severity as control-treated IL-11Rα^−/− mice, despite initially showing protection. We observed that Th17 cytokine production by myelin-reactive T cells in the draining lymph nodes was unaffected by IVIg in IL-11Rα^−/− mice, yet was downregulated in WT mice. Finally, IL-11 was shown to directly inhibit IL-17 production of lymph node cells in culture.

Conclusion

These results implicate IL-11 as an important immune effector of IVIg in the prevention of Th17-mediated autoimmune inflammation during EAE.

Intravenous immunoglobulin-induced IL-33 is insufficient to mediate basophil expansion in autoimmune patients

Intravenous immunoglobulin (IVIg) is used in the therapy of various autoimmune and inflammatory diseases. Recent studies in experimental models propose that anti-inflammatory effects of IVIg are mainly mediated by α2,6-sialylated Fc fragments. These reports further suggest that α2,6-sialylated Fc fragments interact with DC-SIGN⁺ cells to release IL-33 that subsequently expands IL-4-producing basophils. However, translational insights on these observations are lacking. Here we show that IVIg therapy in rheumatic patients leads to significant raise in plasma IL-33. However, IL-33 was not contributed by human DC-SIGN⁺ dendritic cells and splenocytes. As IL-33 has been shown to expand basophils, we analyzed the proportion of circulating basophils in these patients following IVIg therapy. In contrast to mice data, IVIg therapy led to basophil expansion only in two patients who also showed increased plasma levels of IL-33. Importantly, the fold-changes in IL-33 and basophils were not correlated and we could hardly detect IL-4 in the plasma following IVIg therapy. Thus, our results indicate that IVIg-induced IL-33 is insufficient to mediate basophil expansion in autoimmune patients. Hence, IL-33 and basophil-mediated anti-inflammatory mechanism proposed for IVIg might not be pertinent in humans.

Therapeutic effect of IVIG on inflammatory arthritis in mice is dependent on the Fc portion and independent of sialylation or basophils

High-dose i.v. Ig (IVIG) is used to treat various autoimmune and inflammatory diseases; however, the mechanism of action remains unclear. Based on the K/BxN serum transfer arthritis model in mice, IVIG suppression of inflammation has been attributed to a mechanism involving basophils and the binding of highly sialylated IgG Fc to DC-SIGN-expressing myeloid cells. The requirement for sialylation was examined in the collagen Ab-induced arthritis (CAbIA) and K/BxN serum transfer arthritis models in mice. High-dose IVIG (1-2 g/kg body weight) suppressed inflammatory arthritis when given prophylactically. The same doses were also effective in the CAbIA model when given subsequent to disease induction. In this therapeutic CAbIA model, the anti-inflammatory effect of IVIG was dependent on IgG Fc but not F(ab')2 fragments. Removal of sialic acid residues by neuraminidase had no impact on the anti-inflammatory activity of IVIG or Fc fragments. Treatment of mice with basophil-depleting mAbs did not abrogate the suppression of either CAbIA or K/BxN arthritis by IVIG. Our data confirm the therapeutic benefit of IVIG and IgG Fc in Ab-induced arthritis but fail to support the significance of sialylation and basophil involvement in the mechanism of action of IVIG therapy.

Enhanced Anti-Diabetogenic Effect of Intravenous Immune Globulin Modified by Ferrous Ion Exposure

The aim of this study was to investigate the immunomodulatory capacity of native and Fe(II)-exposed intravenous immune globulin (IVIg) in multiple low dose streptozotocin-induced diabetes and to delineate the mechanisms of their influence on immune cell functions. Optimal doses (200–600mg/kg) of IVIg prevented the development of hyperglycemia, glycosuria and attenuated mononuclear cell infiltration in pancreatic islets. Fe(II) exposure of IVIg decreased their optimal therapeutic dose to 100mg/kg which significantly decreased the serum levels of proinflammatory cytokines compared to the same dose of native IVIg. This was accompanied by lower numbers of TNF-α, IFN-γ and IL-17 producing CD4+ T cells and increased frequencies of CD4+IL-10+ and CD4+IL-4+ T cells in the pancreatic lymph nodes and islets on day 16 after diabetes induction. Ferrous ion-exposed IVIg enhanced the bias towards Th2 response while the regulatory Foxp3+ T cells were not affected.

Sweet and sour: the role of glycosylation for the anti-inflammatory activity of immunoglobulin G

The importance of immunoglobulin G (IgG) molecules for providing long-term sterile immunity as well as their major contribution to tissue inflammation during autoimmune diseases is generally accepted. In a similar manner, studies over the last years have elucidated many details of the molecular and cellular pathways underlying this protective activity in vivo, emphasizing the role of cellular recognizing the constant antibody fragment. In contrast, the active anti-inflammatory activity of IgG, despite being known and actually identified in human autoimmune patients more than 30 years ago, is much less defined. Recent evidence from several independent model systems suggests that IgG glycosylation is critical for the immunomodulatory activity of IgG and that both monomeric IgG as well as IgG immune complexes can diminish Fc receptor and complement dependent inflammatory processes. Moreover, there is increasing evidence that IgG molecules also modulate B and T cell responses, which may suggest that IgG is centrally involved in the establishment and maintenance of immune homeostasis.

Lack of galactosylation enhances the pathogenic activity of IgG1 but Not IgG2a anti-erythrocyte autoantibodies

IgG bears asparagine-linked oligosaccharide side chains in the Fc region. Variations in their extent of galactosylation and sialylation could modulate IgG Fc-dependent effector functions, and hence Ab activity. However, it has not yet been clarified whether the pathogenic potential of IgG autoantibodies is consistently enhanced by the absence of galactose residues per se or the lack of terminal sialylation, which is dependent on galactosylation. Moreover, it remains to be defined whether the increased pathogenicity of agalactosylated IgG is related to activation of the complement pathway by mannose-binding lectin, as suggested by in vitro studies. Using a murine model of autoimmune hemolytic anemia, we defined the contribution of galactosylation or sialylation to the pathogenic activity of IgG1 and IgG2a anti-erythrocyte class-switch variants of 34-3C monoclonal autoantibody. We generated their degalactosylated or highly sialylated glycovariants and compared their pathogenic effects with those of highly galactosylated or desialylated counterparts. Our results demonstrated that lack of galactosylation, but not sialylation, enhanced the pathogenic activity of 34-3C IgG1, but not IgG2a autoantibodies. Moreover, analysis of in vivo complement activation and of the pathogenic activity in mice deficient in C3 or IgG FcRs excluded the implication of mannose-binding lectin-mediated complement activation in the enhanced pathogenic effect of agalactosylated IgG1 anti-erythrocyte autoantibodies.

Mechanisms and potential therapeutic targets in allergic inflammation: recent insights

Deeper insight into pathogenetic pathways and into the biological effects of immunomodulatory agents will help to optimize or adopt therapeutic strategies for atopic disorders. In this article, we highlight selected findings of potential therapeutic relevance that emerged from recent mechanistic studies with focus on molecular and cellular aspects of allergic inflammation. Furthermore, the often complex mechanisms of action of pleiotropic immunomodulatory agents, such as glucocorticoids, vitamin D, or intravenous immunoglobulin (IVIG), are discussed, as their dissection might reveal targets for novel therapeutics or lead to a more rational use of these compounds. Besides reporting novel evidence, this article points to areas of current debate or uncertainty and aims at stimulating scientific discussion and experimental work.

Intravenous immunoglobulin expands regulatory T cells via induction of cyclooxygenase-2-dependent prostaglandin E2 in human dendritic cells

CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) play a critical role in the maintenance of immune tolerance. Intravenous immunoglobulin (IVIg), a therapeutic preparation of normal pooled human IgG, expands Tregs in various experimental models and in patients. However, the cellular and molecular mechanisms by which IVIg expands Tregs are relatively unknown. As Treg expansion in the periphery requires signaling by antigen-presenting cells such as dendritic cells (DCs) and IVIg has been demonstrated to modulate DC functions, we hypothesized that IVIg induces distinct signaling events in DCs that subsequently mediate Treg expansion. We demonstrate that IVIg expands Tregs via induction of cyclooxygenase (COX)-2-dependent prostaglandin E2 (PGE2) in human DCs. However, costimulatory molecules of DCs such as programmed death ligands, OX40 ligand, and inducible T-cell costimulator ligands were not implicated. Inhibition of PGE2 synthesis by COX-2 inhibitors prevented IVIg-mediated Treg expansion in vitro and significantly diminished IVIg-mediated Treg expansion in vivo and protection from disease in experimental autoimmune encephalomyelitis model. IVIg-mediated COX-2 expression, PGE2 production, and Treg expansion were mediated in part via interaction of IVIg and F(ab')2 fragments of IVIg with DC-specific intercellular adhesion molecule-3-grabbing nonintegrin. Our results thus uncover novel cellular and molecular mechanism by which IVIg expands Tregs.

Cationized IVIg as a potential substitute to IVIg for the treatment of experimental immune thrombocytopenia

In this study, we evaluated the possibility of using cationized IVIg (cIVIg) instead of IVIg as a more effective therapy for the treatment of experimental immune thrombocytopenia in mice. The pharmacokinetics (PK) and biodistribution of cIVIg and IVIg in mice were compared. cIVIg displayed a shorter plasma half-life and an increased organ uptake in both the spleen and liver compared to IVIg, suggesting that cIVIg could be more potent than IVIg to prevent platelet clearance in a mouse model of thrombocytopenia. However, although the biodistribution of cIVIg in the spleen and liver was improved, its ability to prevent platelet clearance in mice remained similar to that of IVIg. Altogether, our data demonstrate the possibility of using chemical cationization of IVIg preparations to increase organ uptake, and also highlight the challenges of developing effective substitutes to IVIg.

Intravenous immunoglobulin therapy: how does IgG modulate the immune system?

Intravenous immunoglobulin (IVIG) preparations comprise pooled IgG antibodies from the serum of thousands of donors and were initially used as an IgG replacement therapy in immunocompromised patients. Since the discovery, more than 30 years ago, that IVIG therapy can ameliorate immune thrombocytopenia, the use of IVIG preparations has been extended to a wide range of autoimmune and inflammatory diseases. Despite the broad efficacy of IVIG therapy, its modes of action remain unclear. In this Review, we cover the recent insights into the molecular and cellular pathways that are involved in IVIG-mediated immunosuppression, with a particular focus on IVIG as a therapy for IgG-dependent autoimmune diseases.

Analysis and functional consequences of increased Fab-sialylation of intravenous immunoglobulin (IVIG) after lectin fractionation

It has been proposed that the anti-inflammatory effects of intravenous immunoglobulin (IVIG) might be due to the small fraction of Fc-sialylated IgG. In this study we biochemically and functionally characterized sialic acid-enriched IgG obtained by Sambucus nigra agglutinin (SNA) lectin fractionation. Two main IgG fractions isolated by elution with lactose (E1) or acidified lactose (E2) were analyzed for total IgG, F(ab’)₂ and Fc-specific sialic acid content, their pattern of specific antibodies and anti-inflammatory potential in a human in vitro inflammation system based on LPS- or PHA-stimulated whole blood. HPLC and LC-MS testing revealed an increase of sialylated IgG in E1 and more substantially in the E2 fraction. Significantly, the increased amount of sialic acid residues was primarily found in the Fab region whereas only a minor increase was observed in the Fc region. This indicates preferential binding of the Fab sialic acid to SNA. ELISA analyses of a representative range of pathogen and auto-antigens indicated a skewed antibody pattern of the sialylated IVIG fractions. Finally, the E2 fraction exerted a more profound anti-inflammatory effect compared to E1 or IVIG, evidenced by reduced CD54 expression on monocytes and reduced secretion of MCP-1 (CCL2); again these effects were Fab- but not Fc-dependent. Our results show that SNA fractionation of IVIG yields a minor fraction (approx. 10%) of highly sialylated IgG, wherein the sialic acid is mainly found in the Fab region. The tested anti-inflammatory activity was associated with Fab not Fc sialylation.