TLR4-dependent activation of dendritic cells by an HMGB1-derived peptide adjuvant.

Rebecca Saenz, Diahnn Futalan, Lien Leutenez, Fien Eekhout, Jessie F Fecteau, Simeon Sundelius, Stig Sundqvist, Marie Larsson, Tomoko Hayashi, Boris Minev, Dennis Carson, Sadik Esener, Bradley Messmer, Davorka Messmer

Index: J. Transl. Med. 12 , 211, (2014)

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Abstract

High mobility group box protein 1 (HMGB1) acts as an endogenous danger molecule that is released from necrotic cells and activated macrophages. We have previously shown that peptide Hp91, whose sequence corresponds to an area within the B-Box domain of HMGB1, activates dendritic cells (DCs) and acts as an adjuvant in vivo. Here we investigated the underlying mechanisms of Hp91-mediated DC activation. Hp91-induced secretion of IL-6 was dependent on clathrin- and dynamin-driven endocytosis of Hp91 and mediated through a MyD88- and TLR4-dependent pathway involving p38 MAPK and NFκB. Endosomal TLR4 has been shown to activate the MyD88-independent interferon pathway. Hp91-induced activation of pIRF3 and IL-6 secretion was reduced in IFNαβR knockout DCs, suggesting an amplification loop via the IFNαβR. These findings elucidate the mechanisms by which Hp91 acts as immunostimulatory peptide and may serve as a guide for the future development of synthetic Th1-type peptide adjuvants for vaccines.