A novel role for HMGB1 in TLR9-mediated inflammatory responses to CpG-DNA

CpG-DNA or its synthetic analog CpGODN activates innate immunity through Toll-like receptor 9 (TLR9). However, the mechanism of TLR9 activation by CpGDNA remains elusive. Here we have identified HMGB1 as a CpG-ODN-binding protein. HMGB1 interacts and preassociates with TLR9 in the endoplasmic reticulum-Golgi intermediate compartment (ERGIC), and hastens TLR9's redistribution to early endosomes in response to CpG.. ODN. CpG-ODN stimulates macrophages; and dendritic cells to secrete HMGB1; in turn, extracellular HMGB1 accelerates; the delivery of CpG-ODNs to its receptor., leading to a TLR9-dependent augmentation of IL-6, IL-12, and TNF alpha secretion.. Loss of HMGB1 leads to a defect in the IL-6, IL-12, TNFa, and iNOS response to CpG-ODN. However, lack of intracellular TLR9-associated HMGB1 can be compensated by extracellular HMGB1. Thus, the DNA-binding protein HMGB1 shuttles in and out of immune cells and regulates inflammatory responses to CpG-DNA.