The IgG Antibody Paradox in Insulin Resistance: Pathogenic and Therapeutic

Chronic low-grade inflammation and mitochondrial dysfunction are hallmarks of insulin resistance. However, the mechanisms by which the immune system can propagate systemic insulin resistance remains poorly understood. IgG antibodies are a critical component of immunity and display paradoxical properties. IgG can propagate inflammation by crosslinking Fc receptors activating innate immune cells, and conversely, when given intravenously at high doses (1–2 g/kg intravenous immunoglobulin), actively suppress inflammation. Here, we demonstrate that IgG can exert similar paradoxical properties on glucose metabolism. IgG can elicit insulin resistance, and conversely, when given at high doses, promote insulin sensitivity in a diabetic mouse model. IgG, through its Fc-mediated interactions, suppresses insulin-induced mitochondrial function as well as insulin signaling. Modulation of insulin-dependent mitochondrial respiration by serum or purified IgG highly correlates (R2 = 0.70) with the quantitative measurement of insulin sensitivity accessed by the modified insulin suppression test. Our studies indicate that IgG antibody glycosylation is critically important to these conflicting actions. In mice and humans, the progression of insulin resistance is associated with reduced IgG Fc region sialylation, and administration of asialylated IgG is sufficient to cause insulin resistance in IgG null mice. On the other hand, a single administration of high-dose IgG significantly improved insulin and glucose tolerance as well as plasma glucose levels lasting over 72 days post-administration. These results demonstrate new insights into the systemic nature of insulin resistance, a novel mechanism of the disease, and an innovative therapeutic strategy for treating type 2 diabetes.