30: Anti-IL-37 antibody abrogates the protection in IL-37 transgenic mice to LPS-induced septic shock

Abstract

IL-37 is a fundamental inhibitor of innate immunity by reducing systemic and local inflammation. For example, mice transgenic for the IL-37 precursor (IL-37tg) are protected against LPS-induced septic shock. We have observed that processing of the IL-37 precursor by caspase-1 is required for its anti-inflammatory function in vitro and that IL-37 is secreted into the extracellular space. In the present study, we intended to neutralize secreted IL-37 in transfected macrophage cells and in IL-37tg mice in order to determine the functional role of extracellular IL-37. RAW macrophages expressing IL-37 (RAW-IL-37) and mock transfected cells were preincubated with goat anti-human IL-37-IgG (R&D Systems) or control IgG for 4 h and then stimulated with 100 ng/ml LPS for 18 h. Supernatants were analyzed for IL-6. As expected, compared to mock transfected cells, RAW-IL-37 cells did not produce significant IL-6 after LPS stimulation. Pretreatment with anti-IL-37 did not affect the IL-6 response in RAW-IL-37 or control cells. Next, we pretreated IL-37tg and wild type C57/Bl6 mice with 200 μg of the anti-IL-37-IgG or control IgG 2 h prior to injecting 100 μg of LPS. After 4 and 24 h serum was prepared for IL-6 levels. Pretreatment with the anti-IL-37-IgG did not modulate the LPS response of wildtype C57/Bl6 mice. In contrast, there was a 2.5-fold increase of serum IL-6 after LPS administration in IL-37tg mice that had received anti-IL-37-IgG compared to control IgG. Thus neutralizing endogenous IL-37 in IL37tg mice abrogates the protective effect of IL-37 in a model of septic shock. We therefore conclude that LPS induces the release of biologically active IL-37 from IL-37tg mice in vivo and that IL-37 binds to membrane receptors resulting in a suppression of LPS-inducible genes. In contrast, intracellular IL-37, which is not targeted by anti-IL-37-IgG, has major impact upon LPS stimulation in transfected cells.