IVIG Down-Regulates LPS-Induced TNFα Production Via Inhibition of IκBα Activation: A Possible Mechanism of Action in the Treatment of Bacterial Infections.

Intravenous IgG (IVIG) preparations, originally developed as a substitution therapy for patients with low plasma IgG, are used in the treatment of various immune and nonimmune disorders including hemolytic uremic syndrome, necrotizing fasciitis, and idiopathic thrombocytopenic purpura (ITP); an autoimmune pro-inflammatory condition. However, the pleotropic effects of IVIG on Fcγ receptor-bearing immune cells are not fully understood. Bacterial lipopolyssacharide (LPS) is a principal pro-inflammatory signaling molecule recognized by the innate immune system. LPS binds to monocyte/macrophage Toll-like receptor 4 (TLR4) to activate transcription factors such as NF-κB/IκBα. In turn, NF-κB activation results in cytokine secretion such as tumor necrosis factor alpha (TNFα); a key pro-inflammatory cytokine that leads to monocyte apoptosis. Since IVIG reduces pro-inflammatory responses, we hypothesized that IVIG may down-regulate the LPS-induced pro-inflammatory response in monocytes. Using the human monocyte-like cell line THP-1 that expresses FcγRs and TLR4, we examined LPS-induced intracellular signaling after in vitro treatment with IVIG. Enzyme-linked immunosorbent assay (ELISA) on culture supernatants showed that 30 minute pre-treatment of THP-1 cells with IVIG (5 mg/mL final) downregulated subsequent LPS (200 ng/mL)-induced secretion of TNFα. Western blotting showed that IVIG increased Akt phosphorylation and resulted in phosphorylation of S6 ribosomal protein and Erk1/2 signaling molecules. The activation of S6 ribosomal protein was blocked by the PI3K inhibitor LY294002. More importantly, IVIG treatment inhibited LPS-induced IκBα activation; the likely reason for the decrease in LPS-induced TNFα secretion. In conclusion, IVIG down-regulates LPS-induced signal transduction and proinflammatory cytokine secretion, an action that is likely responsible for its usefulness in the treatment of bacterial infections and in other diseases where down-regulation of NF-κB is desirable.