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 demy elinating encephalomyelitis (ADEM) have shown that intravenous immunoglobul ins (IVIg) are of therapeutic benefit in central nervous system (CNS) infla mmatory diseases. Studies in experimental autoimmune encephalomyelitis (EAE ) have suggested these effects are mediated by modulation of the cytokine n etwork 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) product ion in a dose-dependent manner in microglia stimulated with IFN gamma. The increase was only marginal in LPS-treated cells, and no effect was seen in untreated microglia or after stimulation with TNF alpha or PMA. This enhanc ement of NO production depended on the Fc portion of IVIg and could be abro gated by the pharmacological inhibition of Syk and phosphatidylinositol 3-k inase, two enzymes involved in the signalling cascade of Fc receptors. TNF alpha secretion was dose-dependently stimulated by IVIg in both untreated m icroglia and after stimulation with LPS or IFN gamma. Again, this effect wa s mediated through the Fc portion. Finally, we showed that Fc receptor-medi ated phagocytosis was inhibited by IVIg, presumably by blockade of the Fc r eceptor. These different effects may protect oligodendrocytes from antibody mediated phagocytosis and on the other hand could terminate the immune rea ction by induction of apoptosis in infiltrating T cells via NO and TNF alph a. We propose that IVIg, in addition to known effects on the peripheral imm une system, may also modulate the local immune reaction in CNS inflammatory disease. (C) 2001 Elsevier Science B.V. All rights reserved.