We have established an agonistic monoclonal antibody, UT12, that induces stimulatory signals comparable to those induced by lipopolysaccharide (LPS) through Toll-like receptor 4 and MD-2. UT12 activated nuclear factor B and induced the production of proinflammatory cytokines such as tumor necrosis factor alpha (TNF-␣) and interleukin-6 (IL-6) in peritoneal exudative cells. In addition, mice injected with UT12 rapidly fell into endotoxin shock concomitant with the augmentation of serum TNF-␣ and IL-6 levels, followed by death within 12 h. On the other hand, when the mice were pretreated with a sublethal dose of UT12, the mice survived the subsequent lethal LPS challenges, with significant suppression of serum TNF-␣ and IL-6, indicating that UT12 induced tolerance against LPS. This effect of UT12 was maintained for at least 9 days. In contrast, the tolerance induced by LPS continued for less than 3 days. These results illuminate a novel potential therapeutic strategy for endotoxin shock by the use of monoclonal antibodies against the Toll-like receptor 4/MD-2 complex.Lipopolysaccharide (LPS) is a glycolipid component of the gram-negative bacterial cell wall and induces various host responses, including the production of proinflammatory cytokines. When they are appropriately produced, these cytokines, such as tumor necrosis factor alpha (TNF-␣) and interleukin-6 (IL-6), activate host immunity to fight off bacteria. The excessive proinflammatory cytokines produced in response to large amounts of LPS, however, can provoke extreme systemic inflammation and often cause lethal endotoxin shock.Animals pretreated with a sublethal dose of LPS become tolerant to subsequent challenges with a lethal dose of LPS and display reduced mortality. This phenomenon is called LPS tolerance and is defined as the reduced capacity of the host or cultured macrophage/monocyte to respond to LPS following initial stimulation (6,26). It has also been reported that bacterial or fungal removal is improved during the tolerant state, despite attenuated cytokine production (14,20). Therefore, LPS tolerance is regarded as a reasonable response that simultaneously manages both the clearance of pathogens and host protection from excess inflammation.Here we report on the induction of long-term LPS tolerance realized by an agonistic monoclonal antibody (MAb) against the Toll-like receptor 4 (TLR4)/MD-2 complex. Mice pretreated with this MAb showed significant survival advantages compared with the survival of LPS-pretreated mice.
MATERIALS AND METHODSMice. C3H/HeN, C3H/HeJ, ddY, and SCID mice were from Japan SLC (Hamamatsu, Shizuoka, Japan). C57BL/6 mice were from Charles River Japan (Yokohama, Kanagawa, Japan). A TLR4-knockout mouse strain with the C57BL/6 background (12) was a kind gift from S. Akira (Osaka University, Osaka, Japan). All animals were maintained in the Center for Laboratory Animals at Saga Medical School and were treated in accordance with the regulations of the Scientists Center for Animal Welfare.Cell culture. All the cells were cult...