Immunomodulation of autoimmune diseases by high-dose intravenous immunoglobulins

Low-dose intravenous immunoglobulin (IVIg) in different immune-mediated conditions

IVIg has been used for a long time as a replacement therapy for primary and secondary immunodeficiencies. Beside this supplementary role, when used at higher doses (i.e., 2 g/kg/monthly) it exerts an immunomodulatory role able to control multiple autoimmune and systemic inflammatory diseases. Several mechanisms of action have been described and hypothesized, nonetheless a synergistic action on the different component of the immune response seems to be crucial. The other side of the coin are the costs which showed an increase during the years due to the production of highly purified preparations which limit side reactions. This renders the product not easily accessible especially for low-income countries. Moreover, it is based on plasma donations that experienced a significant shrinkage after the COVID-19 pandemic and the consequences are still impactful. Due to the above-mentioned problems different authors tried to find out if a lower dosage of IVIg (< 2 g/kg/monthly) might exert an immunoregulatory role. In this review we aimed to summarize the current literature about a possible beneficial effect of a lower dosage of IVIg in multiple conditions that would help to treat a vast majority of patients. Even though in some cases (e.g., Kawasaki disease and immune thrombocytopenia) results are promising, for other conditions more research is needed.

High-dose IgG therapy mitigates bile duct-targeted inflammation and obstruction in a mouse model of biliary atresia

BACKGROUND

A proposed etiology of biliary atresia (BA) entails a virus-induced, progressive immune-mediated injury of the biliary system. Intravenous Ig (IVIg) has demonstrated clinical benefit in several inflammatory diseases. The aim of this study was to determine the therapeutic effects of high-dose IgG treatment in the rhesus rotavirus (RRV)-induced mouse model of BA.

METHODS

Newborn mice were infected with RRV, and jaundiced mice were given high-dose IgG or albumin control. Survival, histology, direct bilirubin, liver immune cell subsets, and cytokine production were analyzed.

RESULTS

There was no difference in overall survival between RRV-infected groups, however high-dose IgG resulted in decreased bilirubin, bile duct inflammation, and increased extrahepatic bile duct patency. High-dose IgG decreased vascular cell adhesion molecule-1, resulting in limited migration of immune cells to portal tracts. High-dose IgG significantly decreased CD4(+) T cell production of interleukin (IL)-2, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α and CD8(+) T cell production of IFN-γ, as well as increased levels of regulatory T cells.

CONCLUSION

High-dose IgG therapy in murine BA dramatically decreased Th1 cell-mediated inflammation and biliary obstruction. This study lends support for consideration of IVIg clinical trials in infants with BA, to diminish the progressive intrahepatic bile duct injury.

Immunomodulation of human B cells following treatment with intravenous immunoglobulins involves increased phosphorylation of extracellular signal-regulated kinases 1 and 2

In the treatment of autoimmune diseases, intravenous Igs (IVIg) are assumed to modulate immune cells through the binding of surface receptors. IVIg act upon definite human B cell populations to modulate Ig repertoire, and such modulation might proceed through intracellular signaling. However, the heterogeneity of human B cell populations complicates investigations of the intracellular pathways involved in IVIg-induced B cell modulation. The aim of this study was to establish a model allowing the screening of IVIg signal transduction in human B cell lines and to attempt transposing observations made in cell lines to normal human B lymphocytes. Nine human B cell lines were treated with IVIg with the goal of selecting the most suitable model for human B lymphocytes. The IgG(+) DB cell line, whose response was similar to that of human B lymphocytes, showed reduced IVIg modulation following addition of PD98059, an inhibitor of extracellular signal-regulated protein kinase 1/2 (ERK1/2). The IVIg-induced ERK1/2 phosphorylation was indeed proportional to the dosage of monomeric IVIg used when tested on DB cells as well as Pfeiffer cells, another IgG(+) cell line. In addition, two other intermediates, Grb2-associated binder 1 (Gab1) and Akt, showed increased phosphorylation in IVIg-treated DB cells. IVIg induction of ERK1/2 phosphorylation was finally observed in peripheral human B lymphocytes, specifically within the IgG(+) B cell population. In conclusion, IVIg immunomodulation of human B cells can thus be linked to intracellular transduction pathways involving the phosphorylation of ERK1/2, which in combination with Gab1 and Akt, may be related to B cell antigen receptor signaling.

Intravenous immunoglobulins induce the in vitro differentiation of human B lymphocytes and the secretion of IgG

The therapeutic effects of intravenous immunoglobulins (IVIGs) in several autoimmune diseases are characterized by a decrease in pathologic autoantibody levels. Although little direct evidence has been reported in humans, the large repertoire of natural immunoglobulin G (IgG) antibodies in IVIGs is expected to be involved in the regulation of autoreactive B lymphocytes. In normal adult mice, IVIGs have been reported to modulate immature B cells as well as peripheral B lymphocytes through V-region connections. Studies with human serum also indicated that anti-idiotypic antibodies, present in IVIG preparations, could recognize both natural and pathologic autoantibodies. We have used an in vitro culture system to characterize the direct effect of IVIGs on human B lymphocytes. This in vitro culture system involves CD40 activation of B lymphocytes by its ligand CD154 in the presence of cytokines. In this system, addition of IVIGs decreased by 50% to 80% the expansion of B lymphocytes. This reduced expansion was due to a decrease in the proliferation rate. In addition, a portion of B lymphocytes was differentiated into IgG-secreting cells in the presence of IVIGs and the secreted IgGs were reactive with antigens such as nucleoprotamine, dsDNA, tetanus toxin, and human IgG F(ab')(2) fragments. These observations indicate that IVIGs can have direct effects on B lymphocytes and suggest that such IVIG regulation of B lymphocytes could be involved in the therapeutic effects of IVIGs in autoimmune diseases.