IVIg‐mediated amelioration of ITP in mice is dependent on sialic acid and SIGNR1

Abstract

Intravenous immunoglobulin G (IVIg) therapy is widely used to treat autoimmune and inflammatory diseases. Recent evidence suggests that in mice, splenic resident cells might be important for the anti-inflammatory activity of IVIg in a model of serum transfer arthritis. Splenectomized human immunothrombocytopenia (ITP) patients, however, still respond to IVIg therapy. To investigate whether the requirement of the spleen is essential for mouse ITP, we used a passive model of induced ITP and demonstrated that IVIg activity was functional in splenectomized animals. Further analysis showed that the IVIgmediated amelioration of platelet phagocytosis was fully dependent on terminal sialic acid residues in the IVIg preparation and could be blocked with a specific ICAM3 grabbing nonintegrin-related 1 (SIGNR1) specific antibody. These results suggest that, similar to the human system, a spleen-independent but sialic acid-and SIGNR1-dependent pathway is responsible for IVIg-mediated suppression of autoantibody-dependent platelet depletion in mice.Supporting Information available online IntroductionIntravenous immunoglobulin G (IVIg) has been used for more than 30 years to treat autoimmune diseases such as immunothrombocytopenia (ITP), Guillain-Barre Syndrome, Kawasaki's disease, and chronic inflammatory demyelinating polyneuropathy (CIDP) [1, 2]. A variety of mechanisms depending either on the IgG variable (Fab fragment) or the constant crystallizable fragment (Fc fragment) have been suggested to be responsible for the anti-inflammatory activity of this IgG preparation [1, 2]. Data from human patients and mouse models of ITP, rheumaCorrespondence: Dr. Falk Nimmerjahn e-mail: fnimmerj@biologie.uni-erlangen.de toid arthritis, and nephrotoxic nephritis indicate that the IgG Fc fragment is important for IVIg activity in these autoimmune diseases in vivo [3][4][5][6][7]. Furthermore, the anti-inflammatory activity of IVIg was abrogated in mice deficient in the inhibitory Fcγ-receptor IIB (FcγRIIB) in a variety of model systems [3,5,[7][8][9][10][11][12][13][14]. A plausible explanation for the role of FcγRIIB was afforded by studies in mice and human patients with CIDP, which showed that FcγRIIB becomes upregulated on innate immune effector cells thereby raising the threshold for cell activation by immune complexes [3,5,7,15]. Further studies revealed that the sugar moiety attached to the IgG Fc fragment and especially terminal sialic acid residues in the Fc-linked but not the Fab-linked sugar moiety of serum IgG are essential for the anti-inflammatory activity [6,[11][12][13]16]. Removal of terminal sialic acid residues strongly impaired the suppressive activity of IVIg or the isolated Fc fragment, whereas enrichment for 2,6-linked sialic acid residues in the Fc-domain or in vitro hypersialylated IgG enhanced the antiinflammatory activity [6,12,13]. Of note, mouse and human antibodies rich in terminal sialic acid residues have a decreased affinity for classical FcγRs and were shown to gain the capacity to bind to mouse SIGNR1 ...

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

“…This theory was substantiated in a mouse model of arthritis that showed similar levels of anti-inflammatory activity when using 1 g/kg IVIg and 0.1 g/kg sialic acid-enriched IVIg, therefore indicating a 10-fold enhancement with the addition of terminal sialic acids (23,24). Additional results supporting this theory were subsequently reported in other independent studies and other animal models (25,26). It was further shown that the anti-inflammatory activity of sialylation can be recapitulated using a sialylated Fc fragment derived from IVIg or an IgG1 recombinant antibody (after in vitro sialylation of the Fc) at a 30-fold lower dose than IVIg (24,27).…”

“…in a variety of independent in vivo models (23)(24)(25)(26)(27) have opened the door to the development of new anti-inflammatory therapeutics.…”

“…For example, studies using desialylated IVIg in immune thrombocytopenic purpura (ITP) models (28) and Sambucus nigra agglutinin (SNA) -enriched IVIg in arthritis models (29) have shown that sialylation does not enhance IVIg activity or that it may even be dispensable for its therapeutic effects. On the contrary, more comprehensive studies performed by several independent laboratories testing desialylated or hypersialylated IVIg across different animal models under preventive and therapeutic treatment modalities have shown that sialylation is critical for the anti-inflammatory activity of IVIg (24)(25)(26)(27)30). Furthermore, T cell-independent vaccinations resulted in the generation of hypersialylated immunomodulatory antibodies that were able to modulate other immune responses, establishing a broad relevance of these sialylated IgG glycoforms as modulators of immune responses (31).…”

Intravenous Gammaglobulin Inhibits Encephalitogenic Potential of Pathogenic T Cells and Interferes with their Trafficking to the Central Nervous System, Implicating Sphingosine-1 Phosphate Receptor 1–Mammalian Target of Rapamycin Axis

“…FcgRIIB is dispensable for IVIg-mediated reciprocal modulation of effector and regulatory CD4 subsets Anti-inflammatory effect of IVIg in several animal models of Ab-mediated pathology is attributed to the inhibitory Fc receptor FcgRIIB (22,23 (Fig. 3A, 3B).…”

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

“…Its antiinflammatory activity has been shown to result from the presence of a specific glycan, the α2,6-sialylated, complex biantennary structure present on the C H 2 domain of the fragment crystallizable domain (Fc) and found in a small proportion of heterogeneous antibody preparations in IVIG (4). Sialylation of the Fc glycan on the C H 2 domain results in IgGs that can engage type II Fc receptors (FcRs) such as specific ICAM-3 grabbing non-integrin-related 1 (SIGN-R1), dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN), and CD23 (5)(6)(7)(8), while reducing their binding affinity to type I FcRs (9)(10)(11). Studies in mouse models of serum-induced arthritis, antibody-dependent ITP, nephrotoxic nephritis, and autoimmune blistering diseases confirmed the antiinflammatory activity of the sialylated Fc, whether from IVIG or generated from recombinantly expressed IgG1 (5,9,12,13).…”