IVIg-mediated inhibition of antigen presentation: predominant role of naturally occurring cationic IgG

Intravenous immunoglobulin mediates anti-inflammatory effects in peripheral blood mononuclear cells by inducing autophagy

Autophagy plays an important role in the regulation of autoimmune and autoinflammatory responses of the immune cells. Defective autophagy process is associated with various autoimmune and inflammatory diseases. Moreover, in many of these diseases, the therapeutic use of normal immunoglobulin G or intravenous immunoglobulin (IVIG), a pooled normal IgG preparation, is well documented. Therefore, we explored if IVIG immunotherapy exerts therapeutic benefits via induction of autophagy in the immune cells. Here we show that IVIG induces autophagy in peripheral blood mononuclear cells (PBMCs). Further dissection of this process revealed that IVIG-induced autophagy is restricted to inflammatory cells like monocytes, dendritic cells, and M1 macrophages but not in cells associated with Th2 immune response like M2 macrophages. IVIG induces autophagy by activating AMP-dependent protein kinase, beclin-1, class III phosphoinositide 3-kinase and p38 mitogen-activated protein kinase and by inhibiting mammalian target of rapamycin. Mechanistically, IVIG-induced autophagy is F(ab')₂-dependent but sialylation independent, and requires endocytosis of IgG by innate cells. Inhibition of autophagy compromised the ability of IVIG to suppress the inflammatory cytokines in innate immune cells. Moreover, IVIG therapy in inflammatory myopathies such as dermatomyositis, antisynthetase syndrome and immune-mediated necrotizing myopathy induced autophagy in PBMCs and reduced inflammatory cytokines in the circulation, thus validating the translational importance of these results. Our data provide insight on how circulating normal immunoglobulins maintain immune homeostasis and explain in part the mechanism by which IVIG therapy benefits patients with autoimmune and inflammatory diseases.

Targeted Therapies for Autoimmune Bullous Diseases: Current Status

Autoimmune bullous skin disorders are rare but meaningful chronic inflammatory diseases, many of which had a poor or devastating prognosis prior to the advent of immunosuppressive drugs such as systemic corticosteroids, which down-regulate the immune pathogenesis in these disorders. Glucocorticoids and adjuvant immunosuppressive drugs have been of major benefit for the fast control of most of these disorders, but their long-term use is limited by major side effects such as blood cytopenia, osteoporosis, diabetes mellitus, hypertension, and gastrointestinal ulcers. In recent years, major efforts were made to identify key elements in the pathogenesis of autoimmune bullous disorders, leading to the identification of their autoantigens, which are mainly located in desmosomes (pemphigus) and the basement membrane zone (pemphigoids). In the majority of cases, immunoglobulin G, and to a lesser extent, immunoglobulin A autoantibodies directed against distinct cutaneous adhesion molecules are directly responsible for the loss of cell-cell and cell-basement membrane adhesion, which is clinically related to the formation of blisters and/or erosions of the skin and mucous membranes. We describe and discuss novel therapeutic strategies that directly interfere with the production and regulation of pathogenic autoantibodies (rituximab), their catabolism (intravenous immunoglobulins), and their presence in the circulation and extravascular tissues such as the skin (immunoadsorption), leading to a significant amelioration of disease. Moreover, we show that these novel therapies have pleiotropic effects on various proinflammatory cells and cytokines. Recent studies in bullous pemphigoid suggest that targeting of immunoglobulin E autoantibodies (omalizumab) may be also beneficial. In summary, the introduction of targeted therapies in pemphigus and pemphigoid holds major promise because of the high efficacy and fewer side effects compared with conventional global immunosuppressive therapy.

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.

Fragments of truth: T-cell targets of polyclonal immunoglobulins in autoimmune diseases

The expanding therapeutic use of high-dose intravenous immunoglobulin (IVIg) in autoimmune diseases has raised important practical and conceptual issues over the last few years. These have prompted a number of research efforts aimed at characterizing aspects of the mechanism of action of current IVIg preparations, which might lead to the development of standardized, more cost-effective agents. Although polyclonal IgG in these preparations are mostly thought to act via direct interference with disease-specific, pathogenic autoantibodies, evidence from clinical and experimental work points to the involvement of crucial checkpoints upstream of self-reactive B-cell activation and autoantibody production. Reviewed herein are the results of the most recent studies documenting the crucial role of regulatory T cells (Treg) in the immunomodulatory activity of IVIg, and the molecular mechanisms mediating the effect of specific IgG fragments and glycoforms on Treg activity and the ensuing downregulation of T-cell effector responses of different sign and magnitude. Further progress in this area of translational research may lead to the development of innovative strategies aimed at restoring tolerance in autoimmune diseases.

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.