Lymphotoxin b Receptor Activation on Macrophages Induces Cross-Tolerance to TLR4 and TLR9 Ligands

Our previous studies indicated that lymphotoxin b receptor (LTbR) activation controls and downregulates inflammatory reactions. In this study, we report that LTbR activation on primary mouse macrophages results in induction of tripartite motif containing (TRIM) 30a, which negatively regulates NF-kB activation induced by TLR signaling. LTbR activation results in a downregulation of proinflammatory cytokine and mediator expression upon TLR restimulation, demonstrating that LTbR signaling is involved in the induction of TLR cross-tolerance. Specific knockdown experiments using TRIM30a-specific small interfering RNA abolished the LTbR-dependent induction of TRIM30a and LTbR-mediated TLR cross-tolerance. Concordantly, LTbR activation on bone marrow-derived macrophages induced cross-tolerance to TLR4 and TLR9 ligands in vitro. Furthermore , we have generated cell type-specific LTbR-deficient mice with ablation of LTbR expression on macrophages/neutrophils (LTbR flox/flox 3 LysM-Cre). In bone marrow-derived macrophages derived from these mice LTbR-induced cross-tolerance to TLR4 and TLR9 ligands was impaired. Additionally, mice with a conditional ablation of LTbR expression on macrophages (LTbR flox/flox 3 LysM-Cre) are resistant to LTbR-induced TLR4 tolerance in vivo. Collectively, our data indicate that LTbR activation on macrophages by T cell-derived lymphotoxin a 1 b 2 controls proinflammatory responses by activation of a TRIM30a-controlled, counterregulatory signaling pathway to protect against exacerbating inflammatory reactions. I nflammation is a complex pathophysiological condition initially mediated primarily by innate immune cells in response to infection and/or tissue damage (1, 2). Innate immune cells detect and respond to danger signals such as pathogens and/or tissue damage by activating their TLRs on their cell surface. However, chronic and repeated stimulation through TLRs renders immune cells hyporesponsive to subsequent stimulation, a phenomenon known as TLR tolerance (3). The activation of innate immune cells triggers a robust but essential inflammatory response that needs to be tightly regulated (4, 5). Uncontrolled in-flammatory reactions lead to extensive tissue damage and the manifestation of pathophysioplogical conditions such as chronic inflammation, sepsis, and autoimmune disease (6). Membrane-anchored lymphotoxin (LT)a 1 b 2 and LIGHT, both members of the TNF superfamily, are functional ligands for the LTb receptor (LTbR). Both ligands are expressed only on activated lym-phocytes, NK cells, and a subset of follicular B cells, whereas the LTbR is primarily expressed on epithelial and stromal cells and cells of the myeloid lineage (7, 8). So far, most studies have focused on the critical role of LTbR signaling in the development and maintenance of secondary lymphoid organ integrity (9–11) and the control of dendritic cell-mediated immune …